SMD0603

ZXLD1370 DIODES | Alldatasheet

Document overview

Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
PDF pages: 33

Technical content

Features

0.5% typical output current accuracy
6 to 60V operating voltage range
LED driver supports Buck, Boost and Buck-boost
configurations
Wide dynamic range dimming o 20:1 DC dimming o 1000:1 dimming range at 500Hz
Up to 1MHz switching
High temperature control of LED current using T ADJ Typical Application Circuit Buck-boost diagram utilizing thermistor and Tadj

Document number: DS32165 Rev. 2 - 2 2 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Pin Descriptions Pin Name Pin Type‡ Description ADJ 1 I Adjust input (for dc output current control) Connect to REF to set 100% output current. Drive with dc voltage (125mV<VADJ< 2.5V) to adjust output current from 10% to 200% of set value. The ADJ pin has an internal clamp that limits the internal node to less than 3V. This provides some failsafe should they get overdriven REF 2 O Internal 1.25V reference voltage output TADJ 3 I Temperature Adjust input for LED thermal current control Connect thermistor/resistor network to this pin to reduce output current above a preset temperature threshold. Connect to REF to disable thermal compensation function. (See section on thermal control.) SHP 4 I/O Shaping capacitor for feedback control loop Connect 100pF ±20% capacitor from this pin to ground to provide loop compensation STATUS 5 O Operation status output (analog output) Pin is at 4.5V (nominal) during normal operation. Pin switches to a lower voltage to indicate specific operation warnings or fault conditions. (See section on STATUS output.) Status pin voltage is low during shutdown mode SGND 6 P Signal ground (Connect to 0V) PGND 7 P Power ground - Connect to 0V and pin 8 to maximize copper area N/C 8 - Not Connected internally – recommend connection to pin 7, (PGND), to maximize PCB copper for thermal dissipation N/C 9 Not Connected internally – recommend connection pin 10 (GATE) to permit wide copper trace to gate of MOSFET GATE 10 O Gate drive output to extern al NMOS transistor – connect to pin 9 VAUX 11 P Auxiliary positive supply to internal switch gate driver Connect to VIN, or auxiliary supply from 6V to 15V supply to reduce internal power dissipation (Refer to application section for more details) Decouple to ground with capacitor close to device (refer to Applications section) VIN 12 P Input supply to device (6V to 60V) Decouple to ground with capacitor close to device (refer to Applications section) ISM 13 I Current monitor input. Connect current sense resistor between this pin and VIN The nominal voltage across the resistor is 225mV FLAG 14 O Flag open drain output Pin is high impedance during normal operation Pin switches low to indicate a fault, or warning condition PWM 15 I Digital PWM output current control Pin driven either by open Drain or push-pull 3.3V or 5V logic levels. Drive with frequency higher than 100Hz to gate output ‘on’ and ‘off’ during dimming control The device enters standby mode when PWM pin is driven with logic low level for more than 15ms nominal (Refer to application section for more details) GI 16 I Gain setting input Used to set the device in Buck mode or Boost, Buck-boost modes Connect to ADJ in Buck mode operation For Boost and Buck-boost modes, connect to resistive divider from ADJ to SGND. This defines the ratio of switch current to LED current (see application section). The GI pin has an internal clamp that limits the internal node to less than 3V. This provides some failsafe should they get overdriven EP PAD P Exposed paddle. Connect to 0V plane for electrical and thermal management Notes: ‡. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin.

Document number: DS32165 Rev. 2 - 2 3 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated) Symbol Parameter Rating Unit VIN Input supply voltage relative to GND -0.3 to 65 V VAUX Auxiliary supply voltage relative to GND -0.3 to 65 V VISM Current monitor input relative to GND -0.3 to 65 V VSENSE Current monitor sense voltage (V IN-VISM) -0.3 to 5 V VGATE Gate driver output voltage -0.3 to 20 V IGATE Gate driver continuous output current 18 mA VFLAG Flag output voltage -0.3 to 40 V VPWM, VADJ, VTADJ, VGI, VPWM Other input pins -0.3 to 5.5 V TJ Maximum junction temperature 150 °C TST Storage temperature -55 to 150 °C These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability. Recommended Operating Conditions Symbol Parameter Performance/Comment Min Max Unit VIN Input supply voltage range Normal operation 8 60 V Functional (Note 1) 6.3 VAUX Auxiliary supply voltage range (Note 2) Normal operation 8 60 V Functional 6.3 VISM Current sense monitor input range 6.3 60 V VSENSE Differential input voltage VVIN-VISM, with 0 ≤ VADJ ≤ 2.5 0 450 mV VADJ External dc control voltage applied to ADJ pin to adjust output current DC brightness control mode from 10% to 200% 0.125 2.5 V IREF Reference external load current REF sourcing current 1 mA fmax Recommended switching frequency range (Note 3) 300 1000 kHz VTADJ Temperature adjustment (TADJ) input voltage range 0 VREF V fPWM Recommended PWM dimming frequency range (Note 4) To achieve 1000:1 resolution 100 500 Hz To achieve 500:1 resolution 100 1000 Hz tPWMH/L PWM pulse width in dimming mode PWM input high or low 0.002 10 ms VPWMH PWM pin high level input voltage 2 5.5 V VPWML PWM pin low level input voltage 0 0.4 V TJ Operating Junction Temperature Range -40 125 °C GI Gain setting ratio for boost and buck-boost modes Ratio= VGI/VADJ 0.20 0.50 Notes: 1. The functional range of V IN is the voltage range over which the device will function. Output current and device parameters may deviate from their normal values for V IN and VAUX voltages between 6V and 8V, depending upon load and conditions. 2. V AUX can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a voltage should not be applied to V AUX in the absence of a voltage at VIN. 3. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency are not tested in production. 4. This gives maximum resolution at the expense of accuracy. To ensure accuracy the following equation should be used: 2*Resolution *fPWM < fSWH

Document number: DS32165 Rev. 2 - 2 4 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Electrical Characteristics (Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.) Symbol Parameter Conditions Min Typ Max Units Supply and reference parameters VUV- Under-Voltage detection threshold Normal operation to switch disabled VIN or VAUX falling 5.2 5.6 6.3 V VUV+ Under-Voltage detection threshold Switch disabled to normal operation VIN or VAUX rising 5.5 6 6.5 V IQ-IN Quiescent current into V IN PWM pin floating. Output not switching 1.5 3 mA IQ-AUX Quiescent current into V AUX 150 300 µA ISB-IN Standby current into V IN. PWM pin grounded for more than 15ms 90 150 µA ISB-AUX Standby current into V AUX. 0.7 10 µA VREF Internal reference voltage No load 1.237 1.25 1.263 V ΔVREF Change in reference voltage with output current Sourcing 1mA -5 mV Sinking 100 µA 5 VREF_LINE Reference voltage line regulation VIN = VAUX , 6.5V<VIN = <60V -60 -90 dB VREF-TC Reference temperature coefficient +/-50 ppm/°C DC-DC converter parameters VADJ ‡ External dc control voltage applied to ADJ pin to adjust output current DC brightness control mode 10% to 200% 0.125 1.25 2.5 V IADJ ADJ input current VADJ ≤ 2.5V VADJ = 5.0V† 100 nA µA VGI ‡ GI Voltage threshold for boost and buck- boost modes selection VADJ = 1.25V 0.8 V IGI GI input current VGI ≤ 2.5V VGI = 5.0V† 100 nA µA IPWM PWM input current VPWM = 5.5V 36 100 µA tPWMoff PWM pulse width (to enter shutdown state) PWM input low 10 15 25 ms TSDH Thermal shutdown upper threshold (GATE output forced low) Temperature rising. 150 ºC TSDL Thermal shutdown lower threshold (GATE output re-enabled) Temperature falling. 125 ºC High-Side Current Monitor (Pin ISM) IISM Input Current Measured into ISM pin and VISM = 12V 11 20 µA VSENSE_acc Accuracy of nominal VSENSE threshold voltage VADJ = 1.25V ±0.25 ±2 % VSENSE-OC Over-current sense threshold voltage 300 350 375 mV Notes: † The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This provides some failsafe should those pins get overdriven .

Document number: DS32165 Rev. 2 - 2 5 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Electrical Characteristics (Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.) Symbol Parameter Conditions Min Typ Max Units Output Parameters VFLAGL FLAG pin low level output voltage Output sinking 1mA 0.5 V IFLAGOFF FLAG pin open-drain leakage current VFLAG=40V 1 µA VSTATUS STATUS Flag no-load output voltage (Note 5) Normal operation 4.2 4.5 4.8 V Out of regulation (VSHP out of range) (Note 6) 3.3 3.6 3.9 VIN under-voltage (VIN < 5.6V) 3.3 3.6 3.9 Switch stalled (tON or tOFF> 100µs) 3.3 3.6 3.9 Over-temperature (TJ > 125°C) 1.5 1.8 2.1 Excess sense resistor current (VSENSE > 0.32V) 0.6 0.9 1.2 RSTATUS Output impedance of STATUS output Normal operation 10 k Ω Driver output (PIN GATE) VGATEH High level output voltage No load Sourcing 1mA (Note 7) 10 11 V VGATEL Low level output voltage Sinking 1mA, (Note 8) 0.5 V VGATECL High level GATE CLAMP voltage VIN = VAU X= VISM = 18V IGATE = 1mA 12.8 15 V IGATE Dynamic peak current available during rise or fall of output voltage Charging or discharging gate of external switch with QG = 10nC and 400kHz ±300 mA tSTALL Time to assert ‘STALL’ flag and warning on STATUS output (Note 9) GATE low or high 100 170 µs LED Thermal control circuit (TADJ) parameters VTADJH Upper threshold voltage Onset of output current reduction (VTADJ falling) 560 625 690 mV VTADJL Lower threshold voltage Output current reduced to <10% of set value (VTADJ falling) 380 440 500 mV ITADJ TADJ pin Input current VTADJ = 1.25V 1 µA Notes: 5. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g. ‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. The voltage levels on the STATUS output assume the Internal regulator to be in regulation and VADJ<=VREF. A reduction of the voltage on the STATUS pin will occur when the voltage on VIN is near the minimum value of 6V. 6. Flag is asserted if VSHP<2.5V or VSHP>3.5V 7. GATE is switched to the supply voltage VAUX for low values of VAUX (i.e. between 6V and approximately 12V). For VAUX>12V, GATE is clamped internally to prevent it exceeding 15V. 8. GATE is switched to PGND by an NMOS transistor 9. If t ON exceeds tSTALL, the device will force GATE low to turn off the external switch and then initiate a restart cycle. During this phase, ADJ is grounded internally and the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be repeated automatically until the operating conditions are such that normal operation can be sustained. If tOFF exceeds tSTALL, the switch will remain off until normal operation is possible.

Document number: DS32165 Rev. 2 - 2 6 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Typical Characteristics – Buck Mode – RS = 150mΩ – L = 33µH - ILED = 1.5A 1.430 1.440 1.450 1.460 1.470 1.480 1.490 1.500 Input Voltage (V) Figure 1: Load Current vs. Input Voltage & Number of LED1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs LED Current (A) 100 200 300 400 500 600 700 800 900 1000 Input Voltage (V) Figure 2: Frequency vs. Input Voltage & Number of LED

1 LED 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LE Ds 13 LEDs 15 LEDs

T = 2 5 ° C V = V A AUX IN Switching Frequency (kHz) 60% 65% 70% 75% 80% 85% 90% 95% 100% Input Voltage (V) Figure 3: Efficiency vs. Input & Number of LED Efficiency

Document number: DS32165 Rev. 2 - 2 7 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Typical Characteristics – Buck Mode – Rs = 300mΩ - L = 47µH - ILED = 750mA 0.715 0.720 0.725 0.730 0.735 0.740 Input Voltage (V) Figure 4: I vs. Input & Number of LEDLED

2 LEDs 3 LEDs 5 LEDs 7 LEDs 9 LEDs 11 LEDs 13 LEDs 15 LEDs

LED Current (A) T = 2 5 ° C V = V A AUX IN 100 200 300 400 500 600 700 800 900 1000 Input Voltage (V) Figure 5: Frequency ZXLD1370 - Buck Mode - L47 Hμ Switching Frequency (kHz) T = 25°C V = V A AUX IN 60% 65% 70% 75% 80% 85% 90% 95% 100% Input Voltage (V) Figure 6: Efficiency vs. Input Voltage & Number of LED T = 2 5 ° C V = V A AUX IN Efficiency

Document number: DS32165 Rev. 2 - 2 8 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Typical Characteristics – Boost mode – ILED = 350mA – RS = 150mΩ – GIRATIO = 0.23 0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 Input Voltage (V) Figure 7: I vs. Input Voltage & Number of LEDLED

3 LEDs 4 LEDs 6 LEDs 8 LEDs 10 LEDs 12 LEDs 14 LEDs 16 LEDs

LED Current (A) T = 2 5 ° C V = V A AUX IN 100 150 200 250 300 350 400 450 500 Input Voltage (V) Figure 8: Frequency vs. Input Voltage & Number of LED Switching Frequency (kHz) T = 2 5 ° C V = V A AUX IN Boosted voltage across LEDs approaching VIN 60% 65% 70% 75% 80% 85% 90% 95% 100% Input Voltage (V) Figure 9: Efficiency vs. Input Voltage & Number of LED T = 2 5 ° C V = V A AUX IN

Document number: DS32165 Rev. 2 - 2 9 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Typical Characteristics – Buck-Boost mode – RS=150mΩ - ILED = 350mA - GIRATIO = 0.23 0.330 0.335 0.340 0.345 0.350 0.355 0.360 0.365 0.370 6.5 8 9.5 1 1 12.5 14 15.5 17 Input Voltage (V) Figure 10: LED Current vs. Input Voltage & Number of LED

3 LEDs 4 LEDs 5 LEDs 6 LEDs 7 LEDs 8 LEDs

LED Current (A) 100 200 300 400 500 600 700 800 6.5 8 9.5 11 12.5 14 15.5 17 Input Voltage (V) Figure 11: Switching Frequency vs. Input Voltage & Number of LED Switching Frequency (kHz) 60% 65% 70% 75% 80% 85% 90% 95% 100% 6 . 5 8 9 . 5 1 1 1 2 . 51 41 5 . 51 7 Input Voltage (V) Figure 12: Efficiency vs. Input Voltage & Number of LED

Document number: DS32165 Rev. 2 - 2 12 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated

Application Information

A basic ZXLD1370 application circuit is shown in Figure 13 and 15. External component selection is driven by the characteristics of the load and the input supply, since this will determine the kind of topology being used for the system. Component selection starts with the current setting procedure, the inductor/frequency setting and the MOSFET selection. Finally after selecting the freewheeling diode and the output capac itor (if needed), the application section will cover the PWM dimming and thermal feedback. Setting the output current The first choice when defining the output current is whether the devic e is operating with the load in series with the sense resistor (buck mode) or whether the load is not in series with the sense resistor (boost and buck-boost modes). The output current setting depends on the choi ce of the sense resistor Rs, the volt age on the ADJ pin and the voltage on the GI pin, according to the device working mode. The sense resistor Rs sets the coil current IRS. The ADJ pin may be connected directly to the internal 1.25V reference (V REF) to define the nominal 100% LED current. The ADJ pin can also be overdriven with an external dc voltage bet ween 125mV and 2.5V to adjust the LED current proportionally between 10% and 200% of the nominal value. ADJ and GI are high impedance inputs within their normal operat ing voltage ranges. An internal 2.6V clamp protects the device against excessive input voltage and limits the maximu m output current to approx imately 4% above the maximum current set by VADJ if the maximum input voltage is exceeded. Below are provided the details of the LED current calculation bot h when the load in series with the sense resistor (buck mode) and when the load is not in series with the sense resistor (boost and buck-boost modes). In Buck mode, GI is connected to ADJ giving the ratio of average LED current (I LED) to average sense resistor/coil current (IRS). REF ADJ S RsLED V V R mV 225I I = = If the ADJ and GI pins are connected to V REF directly, this becomes: S RsLED R mV 225II = = Therefore: LED s I mV 225R = RS ISMVIN REF ADJ GI SGND Figure 17: Buck configuration In Boost and Buck-boost mode GI is connected to ADJ through a voltage divider. With VADJ equal to V REF, the ratio defined by the resistor divider at the GI pin determines the ratio of average LED current (ILED) to average sense resistor/coil current (IRS). Rs

2 GI 1 GI

LED I) R (R RIV VI +== Where REF ADJ S Rs V V R mV 225I = When the ADJ pin is connected to V REF directly, this becomes: S Rs R mV 225I = RS ISMVIN REF ADJ GI SGND RGI2 RGI1 Figure 18: Boost and Buck-boost connection

Document number: DS32165 Rev. 2 - 2 13 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Therefore: LED2 GI 1 GI 1 GI s I mV 225 ) R (R RR += Note that the average LED current for a boost or buck-boost converter is alwa ys less than the average sense resistor current. For the ZXLD1370, the recommended potential divider ratio is given by: 50 . 0) R R ( R2 . 0

1 GI ≤+≤

It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current. In general the design procedure to follow is: - Define input conditi ons in terms of VIN and IIN - Set output conditions in terms of LED current and the number of LEDs - Define controller topology – Buck, Boost or Buck-boost Calculate the maximum duty-cycle as: Buck mode MIN IN LEDs MAX V VD = Boost mode LEDS MIN INLEDS MAX V V VD −= Buck-boost mode MIN INLEDS LEDS MAX V V VD += Set the appropriate GI ratio according to the circuit duty and the max switch current admissible cycle limitations MAX GI D 1) R (R R V V − ≤+= - Set RGI1 as: Ω≤≤Ω k 200 R k 101 GI - Calculate RGI2 as: 1 GI MAX MAX

2 GI R xD 1

DR −≈ - Calculate the sense resistor as: LED2 GI 1 GI 1 GI s I mV 225 ) R (R RR += If the potential divider ratio is greater than 0.64, the device detects that buck-mode operation is desired and the output current will deviate from the desired value. For example, as in the typical application circuit, in order to get ILED= 350mA with IRS=1.5A the ratio has to be set as:

Document number: DS32165 Rev. 2 - 2 14 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated 23 . 0) R (R R V V I I LED ≈+= = Setting RGI1= 33kΩ it results Ω = −= k 110 ) 1V V( R R GI ADJ

1 GI 2 GI

This will result in: Ω =+= m 150I mV 225 ) R (R RR LED2 GI 1 GI 1 GI s Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors Table 1 GI ratio RGI1 RG2 0.2 30k Ω 120k Ω 0.25 33k Ω 100k Ω 0.3 39k Ω 91k Ω 0.35 30kΩ 56k Ω 0.4 100kΩ 150k Ω 0.45 51k Ω 62k Ω 0.5 30k Ω 30k Ω INDUCTOR/FREQUENCY SELECTION Recommended inductor values for the ZXLD1370 are in the range 22 μH to 100 μH. The chosen coil should have a saturation current higher than the peak sensed current a nd a continuous current rating above the required mean sensed current by at least 50%. The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended limits over the supply voltage and load current range. The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz – 400kHz in most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs or the input voltage increases. The graphs below can be used to select a recommended inductor to maintain the ZXLD1370 switching frequency within a predetermined range when used in different topologies. Buck inductor selection: Figure 19: 1.5A Buck mode inductor selection for target frequency of 400 kHz ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor Target Switching frequency - 400kHz 0 1 02 03 04 05 06 0 15Number of LEDs Supply Voltage (V) L=10uH L=22uH L=33uH L=47uH

Document number: DS32165 Rev. 2 - 2 18 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor Target Switching frequency > 500kHz 0 1 02 03 04 05 06 0 15Number of LEDs Supply Voltage (V) L=22uH L=33uH L=47uH Figure 26: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz Suitable coils for use with the ZXLD1370 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range manufactured by NIC components. The following websites may be useful in finding suitable components www.coilcraft.com www.niccomp.com www.wuerth-elektronik.de MOSFET Selection The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node. The current rating is recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the resistive and switching power losses. switchingresistive P P P+ = Resistive power losses The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance. Calculate the current for the different topologies as follows: Buck mode LEDMAXMAXMOSFET I x DI =− Boost / Buck-boost mode LED MAX MAX MAXMOSFET I xD 1 DI −=− The approximate RMS current in the MOSFET will be: Buck mode D II LEDRMSMOSFET =− Boost / Buck-boost mode LEDRMSMOSFET I xD 1 DI −=−

Document number: DS32165 Rev. 2 - 2 19 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated The resistive power dissipation of the MOSFET is: ON DS RMSMOSFETresistive R xI P −−= Switching power losses Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using a first order rough approximation, the switching power dissipation of the MOSFET is: GATE LOADswIN RSS switching I I x f x V x CP = where CRSS is the MOSFET's reverse-transfer capacitance (a data sheet parameter), fSW is the switching frequency, IGATE is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold. Matching the MOSFET with the controller is primarily based on th e rise and fall time of the gate voltage. The best rise/fall time in the application is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit inductance, switching frequency, etc. How fast a MOSFET can be turned on and off is related to how fast the gate capacitance of the MOSFET can be charged and discharged. The relationship between C (and the relative total gate charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as: I Qg I C dVdt =⋅= where dt = turn-on/turn-off time dV = gate voltage C = gate capacitance = Qg/V I = drive current – constant current source (for the given voltage value) Here the constant current source” I ” usually is approximated with the peak drive current at a given driver input voltage. Example 1) Using the DMN6068 MOSFET (V DS(MAX) = 60V, ID(MAX) = 8.5A): Æ QG = 10.3nC at VGS = 10V ZXLD1370 IPEAK = I GATE = 300mA ns 35mA 300 nC 3 . 10 I Q dt PEAK g = = = Assuming that cumulatively the rise ti me and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt Æ f = 1/ t PERIOD = 1.43MHz This frequency is well above the max frequency the device can handle, therefore the DNM 6068 can be used with the ZXLD1370 in the whole spectrum of frequencies recommended for the device (from 300kHz to 1MHz). Example 2) Using the ZXMN6A09K (VDS(MAX) = 60V, ID(MAX) = 12.2A): Æ QG = 29nC at VGS = 10V ZXLD1370 IPEAK = 300mA ns 97mA 300 nC 29 I Q dt PEAK g = = = Assuming that cumulatively the rise ti me and fall time can account for a maximum of 10% of the period, the maximum frequency allowed in this condition is: tPERIOD = 20*dt Æ f = 1/ t PERIOD = 515kHz This frequency is within the recommended frequency range the device can handle, ther efore the ZXMN6A09K is recommended to be used with the ZXLD1370 for frequencies from 300kHz to 500kHz). The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC.

Document number: DS32165 Rev. 2 - 2 20 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Junction temperature estimation Finally, the ZXLD1370 junction temperature can be estimated using the following equations: Total supply current of ZXLD1370: IQTOT ≈ IQ + f • QG Where I Q = total quiescent current IQ-IN + IQ-AUX Power consumed by ZXLD1370 PIC = VIN • (IQ + f • Qg) Or in case of separate voltage supply, with VAUX < 15V PIC = VIN • IQ-IN + Vaux • (IQ-AUX + f • Qg) TJ = T A + PIC • RTH(JA)= TA + PIC • (RTH(JC)+ RTH(CA)) Where the total quiescent current IQ TOT consists of the static supply current (IQ) and the current required to charge and discharge the gate of the power MOSFET. Moreover the part of thermal resistance between case and ambient depends on the PCB characteristics. DIODE SELECTION For maximum efficiency and performance, the rectifier (D1) sh ould be a fast low capacitance Schottky diode* with low reverse leakage at the maximum operating voltage and temper ature. The Schottky diode also provides better efficiency than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time. It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on the Drain of the external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the Drain of the external MOSFET, including supply ripple, does not exceed the specified maximum value. *A suitable Schottky diode would be PDS3100 (Diodes Inc). OUTPUT CAPACITOR An output capacitor may be required to limit interferen ce or for specific EMC purposes. For boost and buck-boost regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first switching subinterval. An output capaci tor in a buck topology will simply reduce the LED current ripple below the inductor current ripple. In other words, this capacitor changes the curr ent waveform through the LED(s) from a triangular ramp to a more sinusoidal version without altering the mean current value. In all cases, the output capacitor is c hosen to provide a desired current ripple of the LED current (usually recommended to be less than 40% of the average LED current). Buck: PP LEDLEDSW PP L OUTPUT I x r x f x 8 IC Δ Boost and Buck-boost PP LEDLEDSW PP LED OUTPUT I x r x f I x DC where:

ΔIL is the ripple of the inductor current, usually ± 20% of the average sensed current
ΔILED is the ripple of the LED current, it should be <40% of the LEDs average current
f sw is the switching frequency (From graphs and calculator)
r LED is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the datasheet of the LED manufacturer). The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. The minimum RMS current for the output capacitor is calculated as follows:

Document number: DS32165 Rev. 2 - 2 21 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Buck II PP LED RMSCOUTPUT − = Boost and Buck-boost MAX MAX LEDRMSCOUTPUT D 1 DII −=− Ceramic capacitors with X7R dielectric are the best choice du e to their high ripple current rating, long lifetime, and performance over the voltage and temperature ranges. INPUT CAPACITOR The input capacitor can be calculated knowing the input voltage ripple ΔVIN-PP as follows: Buck PP INSW LED IN V x f I x ) D 1 ( x DC −= Use D = 0.5 as worst case Boost PP INSW PP L IN V x f x 8 IC Δ Buck-boost PP INSW LED IN V x f I x DC −Δ= Use D = D MAX as worst case The minimum RMS current for the output capacitor is calculated as follows: Buck ) D 1 ( Dx x I ILEDRMS CIN −=− use D=0.5 as worst case Boost II PP L RMSCIN − = Buck-boost ) D 1 ( Dx I ILEDRMS CIN −=− Use D=D MAX as worst case PWM OUTPUT CURRENT CONTROL & DIMMING The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with up to 1000:1 resolution; however higher dimming frequencies ca n be used – at the expense of dimming dynamic range and accuracy. Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is better than 1% for PWM from 5% to 100%. This is shown in the graph below:

Document number: DS32165 Rev. 2 - 2 23 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the PWM pin to turn the controller on and off. This will produce an average output current pr oportional to the duty cycle of the control signal. During PWM operation, the device remains powered up and only the output switch is gated by the control signal. The PWM signal can achieve very high LED current resolution. In fact, dimming down from 100% to 0, a minimum pulse width of 2µs can be achieved resulting in very high accuracy. While the maximum recommended pulse is for the PWM signal is10ms. PWM < 10 ms 2µs Gate < 10 ms 2µs Figure 31:PWM dimming minimum and maximum pulse The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In t he shutdown state, most of the circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status p in will go down to GND while the FLAG and REF pins will stay at their nominal values. Fig 32: Stand-by state from PWM signal

Document number: DS32165 Rev. 2 - 2 24 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated TADJ pin - Thermal control of LED current The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on the TADJ pin to 625mV at the required te mperature threshold. This will give 100% LED current below the threshold temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the value of Rth and/or the thermistor to suit the requirements of the chosen LED. The Thermal Control feature can be disabled by connecting TADJ to REF. Here is a simple procedure to design the thermal feedback circuit: 1) Select the temperature threshold T threshold at which the current must start to decrease 2) Select the Thermistor TH 1 (both resistive value at 25˚C and beta) 3) Select the value of the resistor R th as Rth = TH at Tthreshold Figure 33: Thermal feedback network For example, 1) Temperature threshold T threshold = 70˚C 2) TH1 = 10k Ω at 25˚C and beta= 3500 Æ TH = 3.3kΩ @ 70˚C 3) R th = TH at Tthreshold = 3.3kΩ Over-Temperature Shutdown The ZXLD1370 incorporates an over-temperature shutdown ci rcuit to protect against damage caused by excessive die temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125°C nominal and the output is disabled when die temperature exceeds 150°C nomi nal. Normal operation resumes when the device cools back down to 125°C.

Document number: DS32165 Rev. 2 - 2 25 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated FLAG/STATUS Outputs The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output, which is normally off, but switches low to indicate that a warning, or fault condition exists. STATUS is a DAC output, which i s normally high (4.5V), but switches to a lower voltage to indicate the nature of the warning/fault. Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table: Table 2 Warning/Fault condition Severity (Note 9) Monitored parameters FLAG Nominal STATUS voltage Normal operation H 4.5 Supply under-voltage 1 VAUX<5.6V L 4.5 2 VIN<5.6V L 3.6 Output current out of regulation (Note 10) 2 VSHP outside normal voltage range L 3.6 Driver stalled with switch ‘on’, or ‘off’ (Note 11) 2 tON, or tOFF>100µs L 3.6 Device temperature above maximum recommended operating value 3 TJ>125°C L 1.8 Sense resistor current IRS above specified maximum 4 VSENSE>0.32V L 0.9 Notes: 9. Severity 1 denotes lowest severity. 10. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be a ble to maintain regulation. 11. This warning will be indicated if the gate pin stays at the same level for greater than 100us (e.g. the output transistor cannot pass enough current to reach the upper switching threshold). VREF FLAG VOLTAGESTATUS VOLTAGE Normal Operations SEVERITY 4.5V 3.6V 2.7V 1.8V 0.9V VAUX UVLO - VIN UVLO - STALL - OUT of REG Over Temperature Over Current 0 1 2 3 4 Fig 34: Status levels In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g. ‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. If V ADJ>1.7V, V SENSE may be greater than the excess coil current thre shold in normal operation and an error will be reported. Hence, STATUS and FLAG are only guaranteed for VADJ<=VREF.

Document number: DS32165 Rev. 2 - 2 26 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Diagnostic signals should be ignored during the device start – up for 100 μs. The device start up sequence will be initiated both during the first power on of the device or after the PWM signal is kept low for more than 15ms, initiating the standby state of the device. In particular, during the first 100 μs the diagnostic is signaling an over-current then an out-of-regulation status. These two events are due to the charging of the inductor and are not true fault conditions. VREF Ov er Cur rent 225m V/ R1 FLAGSTATUSCoil current Out of r egul at i on 100us Fig 35: Diagnostic during Start-up Boosting VAUX supply voltage in Boost and Buck-Boost mode When the input voltage is lower than 8V, the gate voltage will also be lower 8V. This means that depending on the characteristics of the external MOSFET , the gate voltage may not be enough to fully enhance the power MOSFET. This boosting technique is particularly important when the output MOSFET is operating at full current, since the boost circuit allows the gate voltage to be higher than 12V. This guarantees that the MOSFET is full y enhanced reducing both the power dissipation and the risk of thermal runaway of the MOSFET it self. An extra diode D2 and decoupling capacitor C3 can be used, as shown below in figure 36, to generate a boosted voltage at V AUX when the input supply voltage at V IN is below 8V. This enables the device to operate with full output current when V IN is at the minimum value of 6V. In the case of a low voltage threshold MOSFET, the bootstrap circuit is generally not required. Fig 36: Bootstrap circuit for Boost and Buck-boost low voltage operations The resistor R2 can be used to limit the current in the bootstrap circuit in order to reduce the impact of the circuit itself on the LED accuracy. The impact on the LED current is usually a decrease of maximum 5% compared to the nominal current value set by the sense resistor. The Zener diode D3 is used to limit the voltage on the VAUX pin to less than 60V. Due to the increased number of components and the loss of current accuracy, the bootstrap circuit is recommended only when the system has to operate continuous ly in conditions of low input voltage (between 6 and 8V) and high load current. Other circumstances such as low input volt age at low load current, or transient low in put voltage at high current should be evaluated keeping account of the external MOSFET power dissipation. Over-voltage Protection

Document number: DS32165 Rev. 2 - 2 28 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more than 5mm from the SHP pin. Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of 2.2uF, X7R, 100V (C3 and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of 1uF, X7R, 100V each (C2, C8), as well as a further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9). VIN and VAUX pins can be short-circuited when the device is used in buck mode, or can be driven from a separate supply. APPLICATION EXAMPLES Example 1: 2.8A Buck LED driver In this application example, the ZXLD1370 is connected as a buck LED driver. The schematic and parts list are shown below. The LED driver is able to deliver 2.8A of LED current with an input voltage range of 8V to 24V. In order to achieve high efficiency at high LED current, a Super Barrier Rectifier (SBR) with a low forward voltage is used as the free wheeling rectifier. This LED driver is suitable for applications which require high LED current such as LED projector, automatic LED lighting etc. Figure 39: Application circuit: 2.8A Buck LED driver Table 3: Bill of Material Ref No. Value Part No. Manufacturer U1 60V LED driver ZXLD1370 Diodes Inc Q1 60V MOSFET ZXMN6A09K Diodes Inc D1 45V 10A SBR SBR10U45SP5 Diodes Inc L1 33uH 4.2A 744770933 Wurth Electronik C1 100pF 50V SMD 0805/0603 Generic C2 1uF 50V X7R SMD1206 Generic C3 C4 C5 4.7uF 50V X7R SMD1210 Generic R1 R2 R3 300mΩ 1% SMD1206 Generic R4 400m Ω 1% SMD1206 Generic R5 0Ω SMD 0805/0603 Generic

Document number: DS32165 Rev. 2 - 2 29 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated Typical Performance Efficiency vs Input Voltage 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 10 12 14 16 18 20 22 24 Input Voltage (V) Efficiency (%)

1 LED

2 LED

Figure 40: Efficiency LED Current vs Input Voltage 500 1000 1500 2000 2500 3000 10 12 14 16 18 20 22 24 Input Voltage (V) LED Current (mA) Figure 41: Line regulation Example 2: 400mA Boost LED driver In this application example, the ZXLD1 370 is connected as a boost LED driver. The schematic and parts list are shown below. The LED driver is able to deliver 400mA of LED current into 12 high-brightness LEDs with an input voltage range of 16V to 32V. The overall high efficiency of 92%+ makes it ideal for app lications such as solar LED street lighting and general LED illuminations. Figure 42: Application circuit - 400mA Boost LED driver

Document number: DS32165 Rev. 2 - 2 32 of 33 www.diodes.com May 2010 © Diodes Incorporated A Product Line of Diodes Incorporated

Ordering Information

Device Packaging Status Part Marking Reel Quantity Tape Width Reel Size ZXLD1370EST16TC TSSOP-16 EP Active ZXLD1370 2500 16mm 13” Package Thermal Data Thermal Resistance Package Unit Junction-to-Case, θJC TSSOP-16 EP 23 °C/W Package Thermal Data TSSOP-16 EP

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Summary

60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER DS32165 Rev. 2 - 2

Description

The ZXLD1370 is an LED driver controller IC for driving external MOSFETs to drive high current LEDs. It is a multi topology controller enabling it to efficiently control the current through series connected LEDs. The multi-topology enables it to operate in buck, boost and buck-boost configurations. The 60V capability coupled with its multi-topology capability enables it to be used in a wide range of applications and drive in excess of 15 LEDs in series.

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