T8322AD TMT | Alldatasheet

Document overview

  • Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
  • PDF pages: 10

Technical content

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 1 Publication Date: Sep. 2014 to change products or specifications without notice. Revision:C PWM Control 1500mA Step-Down Converter

FEATURES

  • Wide Input Voltage Range: 4.5V to 30V
  • LED Output Current Up to 1500mA
  • Soft-start
  • Single pin on/off and brightness control using DC voltage or PWM
  • High efficiency (up to 97%)
  • Up to 1MHz switching frequency
  • Typical 5% output current accurac y
  • SOP-8 Lead-free Package

Applications

  • LED/Display Back Light Driver
  • Lightings
  • Portable Communication Devices
  • Handheld Electronics GENERAL DESCRIPTION The T8322AD is a continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The device operates from an input supply between 4.5V and 30V and provides an externally adjustable output current of up to 1500mA. Depending upon supply voltage and external components, this can provide up to 24 watts of output power. The T8322AD includes the output switch and a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. The T8322AD is available in SOP-8 Lead-free package. PART NUMBER EXAMPLES PART NO. PACKAGE T8322AD SOP-8

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 2 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C PIN ARRANGEMENT(Top view) PIN DESCRIPTION Symbol SOP-8 Description LX 3,4 Drain of NDMOS switch GND 5.6 Ground EN 1 Enable control signal, H: Active, L: Power Dow n ADJ 2 ADJ Multi-function Dimming and brightness control pin: Leave floating for normal operation.(V ADJ =V REF =1.25V giving nominal average output current I OUTnom = 0.1/RS) Drive with DC voltage(0.25V < V ADJ <1.25V) to adjust output current from 0% to 100% of I OUTnom TTL PWM Dimmering input MAX ADJ frequency 20KHz. ISENSE 8 Connect resistor Rs from this pin to VIN to define nominal average output current I OUTnom =0.1/Rs VIN 7 Input voltage (4.5V to 30V). Decouple to ground with 47uF or higher X7R ceramic capacitor close to device.

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 3 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C ABSOLUTE MAXIMUM RATINGS Parameter Symbol Value Unit Voltage on input pin relative to GND VIN -0.3 to +4 0 V ISENSE pin Voltage -5 to +0.3 V EN pin ＆ADJ pin Voltage -0.3 to +6 V Operating junction Temperature Rang T j -40 to 150 ℃ Operating Temperature Rang TA -40 to 105 ℃ Maximum Soldering Temperature (at lead, 10sec) T LEAD 300 ℃ Storage Temperature Rang TS -65 to +150 ℃ Power Dissipation, PD @ TA=25℃ SOP-8 0.8 W Package Thermal Resistance, JAθ SOP-8 50 /W℃

Electrical Characteristics

(TA=-40 to 85 ℃ unless otherwise noted. Typical values are at TA=25 ℃, VDD=24V) Symbol Description Conditions Min. Typ. Max. Unit VIN Input voltage 4.5 - 30 V U VLO Under Voltage lock out 3.6 V V IRU Internal regulator start-up threshold VIN rising 3.65 V V IRD Internal regulator shutdown V IN falling 3.55 V IQOff Quiescent supply current with output off CDI/EN pin grounded 170 uA IQOn Quiescent supply current with output switching CDI/EN pin floating fsw= 250kHz 1.8 5 mA ISENSE Mean current sense threshold voltage (Defines LED current setting accuracy) Measured on I SENSE pin with respect to V IN , VADJ = 2.5V 95 100 105 mV ISENTH Sense threshold hysteresis ±15 % System current hysteresis IOUT =0.5 A～1.5A ±25 % ISENSE ISENSE pin input current V SENSE = V IN -0.1 10 uA VΔ REF / TΔ Temperature coefficient of VREF 50 ppm/ K V EN Internal Supply Voltage 5 V V IH EN CDI Input Voltage High V EN =0V-5V 2 V V IL EN CDI Input Voltage Low V EN =0V-5V 0.8 V V DT Slow start Vadj=1.25V 300 μμ μμS ILXM Continuous LX switch current TA=2 5℃ 1.5 A R LX LX Switch ‘On’ resistance V IN 12V @I LX =1.5A SOP -8 0.3 0.35 Ω

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 4 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C ILXI LX switch leakage current 5 uA TTP Thermal Shutdown Protect 160 ℃ V REF Internal reference voltage Measured on ADJ pin with pin floating 1.25 V V ADJ DC brightness control 0%-100% 0.25 1.25 V V ADJ OFF Output Current OFF voltage 0.2 V FADJ MAX ADJ frequency 20 KHZ D ADJ Duty cycle range of PWM signal applied to ADJ pin during low frequency PWM dimming mode PWM frequenc ＞ 10Hz PWM amplitude = V REF Measured on CDI /EN pin 0.001 1 Brightness control range 1000:1 D ADJ Duty cycle range of PWM signal applied to ADJ pin during high frequency PWM dimming mode PWM frequency< 20KHz PWM amplitude = VREF 0.2 1 Brightness control range Measured on ADJ pin 5:1 fLX Operating frequency EN&ADJ pin floating, L=33uH(0.093ohm) I OUT =1.5A @V LED =3.6V Driving 1LED

280 KHz

TONmin Minimum switch ‘ON’ time LX switch ‘ON’ 240 ns TOFFmin Minimum switch ‘OFF’ time LX switch ‘OFF’ 200 ns TPWminR Recommended minimum switch ‘ON’ time LX switch 'ON' or ‘OFF’ 800 ns fLXmax Recommended maximum operating frequency 1 MHz D LX Recommended duty cycle range of output switch at fLXmax 0.2 0.9 TPD Internal comparator propagation delay 50 ns Notes : Parameters are not tested at production. Parameters are guaranteed by design, characterization and process control.Block Diagram Operating temperature 2 5℃ and adequate cooling conditions, the temperature, the higher the maximum current decreasing

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 5 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C Block Diagram

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 6 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C Functional Description The device, in conjunction with the coil (L1) and current sense resistor (RS), forms a selfoscillating continuous-mode buck converter. Device operation Operation can be best understood by assuming that the EN pin of the device is unconnected and the voltage on this pin (V EN ) appears directly at the (+) input of the comparato r。 When input voltage V IN is first applied, the initial current in L1 and RS is zero and there is no output from the current sense circuit. Under this condition, the (-) input to the comparator is at ground and its output is high. This turns MN on and switches the LX pin low, causing current to flow from V IN to ground, via RS, L1 and the LED(s). The current rises at a rate determined by V IN and L1 to produce a voltage ramp (V SENSE ) across RS. The supply referred voltage V SENSE is forced across internal resistor R1 by the current sense circuit and produces a proportional current in internal resistors R2 and R3. This produces a ground referred rising voltage at the (-) input of the comparator .When MN is off, the current in L1 continues to flow via D1 and the LED(s) back to V IN . The current decays at a rate determined by the LED(s) and diode forward voltages to produce a falling voltage at the input of the comparator. Switching thresholds Define an average VSENSE switching threshold of 100mV (measured on the ISENSE pin with respect to VIN). The average output current IOUTnom is then defined by this voltage and RS according to: IOUTnom = 100mV/RS Nominal ripple current is ±15mV/RS Output shutdown The output of the low pass filter drives the shutdown circuit. When the input voltage to this circuit falls below the threshold, the internal regulator and the output switch are turned off. The voltage reference remains powered during shutdown to provide the bias current for the shutdown circuit. Quiescent supply current during shutdown is nominally 35uA and switch leakage is below 5uA.

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 7 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C Applications Information Setting nominal average output current with external resistor R S The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (R S) connected between V IN and I SENSE and is given by: IOUTnom = 0.1/R S [for RS ≥ 0.066 ohm] The table below gives values of nominal average output current for several preferred values of current setting resistor (R S) in the typical application circuit : RS (ohm) 0.067 0.125 0.2 0.285 Nominal average output current (mA) 1500 800 500 350 The above values assume that the EN pin is floating. Note: that RS = 0.125 ohm is the minimum allowed value of sense resistor under these conditions to maintain switch current below the specified maximum value. Shutdown mode Taking the EN pin to a voltage below 0.5V for more than approximately 100us, will turn off the output and supply current will fall to a low standby level of 35uA nominal.

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 8 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C Capacitor selection A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the input supply. A minimum value of 47uF is acceptable if the input source is close to the device, but higher values will improve performance at lower input voltages, especially when the source impedance is high. In order to avoid high frequency noise influence and improve circuit stability, it is recommended to shunt a value of 0.22uF Capacitor. The input capacitor should be placed as close as possible to the IC. For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should not be used. Inductor selection Recommended inductor values for the T8322AD are in the range 33uH to 100uH. Higher values of inductance are recommended at higher supply voltages in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as close to the device as possible with low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher than the peak output current and a continuous current rating above the required mean output current. The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the specified limits over the supply voltage and load current range. LX switch on time : t on = L ∆I / (V IN – V LED - Iavg (R S+r L+R LX )) , note: t onmin > 240ns LX switch off time : t off = L ∆I / (V LED + V D + Iavg (R S+r L)) , note: t offmin > 200ns Where: “L” is the coil inductance (H) ∆I” is the coil peak-peak ripple current (A) {Internally set to 0.3 x I avg } “rL” is the coil resistance (ohm) S” is the current sense resistance “I avg ” is the required LED current (A) “V IN ” is the supply voltage (V) “V LED ” is the total LED forward voltage (V) “R LX ” is the switch resistance (ohm) {=0.3 ohm nominal} “V D ” is the diode forward voltage at the required load current (V)

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 9 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C TYPICAL APPLICATION CIRCUITS * note : When outputs the big current, the noise are big, this and the system environment and PCB layout have the influential, may defer to the actual need to increase the capacitor filtration noise.

TEC Htm Preliminary T8322AD TM Technology, Inc. reserves the right P. 10 Publication Date: Sep . 2014 to change products or specifications without notice. Revision:C PACKAGE DIMENSIONS 8-LEAD SOP A 1 A B B 1 CC 1 C 2 D E F H T h e rm a l P a d * J K Dimension in mm Dimension in inch C2 0 - 0.15 0.000 - 0.006 J 2.23 REF 0.088 REF K 2.97 REF 0.117 REF H 0~8° 0~8° *Note : The thermal pad on the IC’s bottom has to be mounted on the copper foil. To eliminate the noise influence, the thermal pad is suggested to be connected to GND on PCB. In addition, desired thermal conductivity will be improved, if a heat-conducting copper foil on PCB is soldered with thermal pad. The thermal pad enhances the power dissipation. As a result, a large amount of current can be sunk safely in one package.