RT2910A RICHTEK | Alldatasheet
Document overview
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Technical content
Features
HV Switch Driver ► Adjustable Output Clamp Voltage ► Over-Current Protection ► Wide Operation Range : 5V to 60V ► Reverse Input Protection to −60V ► Adjustable Fault Timer ► Support N-MOSFET Inverting PWM Converter ► 12.5V to 0.5V Output ► Integrate High-Side P-MOSFET ► 300kHz to 800kHz Switching Frequency ► Current-Mode PWM Control ► Internal Soft-Start ► Power Ok Indicator
Applications
Ga-N MOSFET Bias Positive to Negative Conversion Industrial and Telecom Power Supplies Distributed Power System Simplified Application Circuit RT2910A RT NFB VIN GND VIN LX CS COMP FDLY VL SFB NVOUTVB PGND VREF5VDET POK ENHV TMR FB GATE OUT VOUT VHV SNS VHV
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017
Ordering Information
QW : WQFN-24L 5x5 (W-Type) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT2910A GQW YMDNN RT2910AGQW : Product Number YMDNN : Date Code Pin Configuration (TOP VIEW) NFB CS PGND SFB VL ENHV TMR GND VIN VB FB OUT RT COMP 5VDET FDLY LX LX SNS VHV VIN VREF GATE POK GND 8 9 10 11 23 22 21 20 WQFN 5x5 24L
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com Functional Pin Description Pin No. Pin Name Pin Function 1 NFB Feedback voltage input. The feedback for inverting output threshold is 0.6V for PWM inverting converter. 2 SFB Secondary feedback voltage input. For adjusting POK threshold of Inverting. NVOUT for PWM inverting converter. 3 PGND Negative rail for driver and negative current sense input. Connected to GND. 4 CS Positive current sense input for PWM inverting converter. 5, 6 LX Switch node for PWM inverting converter. 7, 8 VIN Power supply input for inverting PWM controller for PWM inverting converter. 9 VB Voltage level keeper. Connect a 0.1F ceramic capacitor to VIN. 10 FB Voltage regulation feedback input for HV switch driver. 11 OUT Output voltage sense input for HV switch driver. 12 GATE N-MOSFET gate drive output for HV switch driver. 13 SNS HVIN current sense input for HV switch driver. 14 VHV Positive supply voltage input for HV switch driver. 15 ENHV Enable control input for HV switch driver. 16 TMR Fault timer setting for HV switch driver . Connect a 22nF at least ceramic capacitor to GND. There is a 3ms sense blanking time after POK pull high. 17, 25 (Exposed Pad) GND Ground. The exposed PAD must be soldered to a large PCB and connected to GND for maximum power dissipation. 18 VL Low dropout regulator output for PWM inverting converter. Connect a ceramic capacitor from VL to GND. The capacitor value range from 0.47F to 1F.
19 POK
Logic output. Active high when SFB voltage is lower than its threshold and FDLY is higher than 1.25V. This pin can be used as HV swap controller enable control for PWM inverting converter.
20 FDLY
Delay set input for PWM inverting converter. There is an internal 10A from VL after VTMR higher than 0.6V threshold. POK is low during FDLY charge time. Connect a ceramic capacitor to GND for setting Fault delay time. 21 5VDET VIN detection set input. For PWM Inverting Converter. 22 COMP Compensation node for error amplifier for PWM inverting converter. 23 RT Oscillator frequency setting for PWM inverting converter. Connect a resistor to GND for adjusting switching frequency from 300kHz to 800kHz. 24 VREF 1.25V reference output. Bypass only with a 0.1F ceramic capacitor from VREF to GND for PWM inverting converter.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 Functional Block Diagram VIN CS 100mV 0.6V PGND NFB SFB Reference OC COMP VB LXLDOVL RT 10µA VL 1.25V FDLY POK VREF GND Control Circuitry 0.6V 1.4V VHV - 1.25V TMR FBCurrent Limit OUT GATESNSVHV ENHV CP_EN Fault 1µA - 1V 5VDET - 0.6V TMR Operation HV Power-Switch The HV power switch embedded an over -voltage protection regulator that drives an external N-MOSFET only as the pass transistor. It can operate within a wide supply voltage range from 5V to 6 0V. The internal charge pump turns on the N-MOSFET to supply current to the loads with very little power loss. This improves the efficiency and increases the available supply voltage level to the load circuitry. Normally, the pass transistor is fully on, p owering the loads with very little voltage drop. When the supply voltage surges too high, the Voltage Amplifier (VA) controls the Gate of the N- MOSFET and regulates the voltage at the OUT pin to a level that is set by the external resistive divider from the OUT pin to ground and the internal 1.25V reference. If the over -voltage/current is detected, a current source starts charging up the capacitor connected at the TMR pin to ground .The pass transistor stays on until the TMR pin reaches 1.4 5V, at which point the GATE pin pulls low turning off the N-MOSFET. The potential at the TMR pin starts decreasing as soon as the over-voltage condition disappears. As the voltage at the TMR pin reaches 0.5V, the GATE pin begins to rise and turn on the MOSFET again. The RT2910A senses an over -current condition by monitoring the voltage across a sense resistor placed between the VHV and SNS pins. An active current limit circuit controls the GATE pin to limit the sense voltage
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com to 50mV. A current is generated to start charging up the TMR pin when over current condition is detected. The MOSFET is turned off when it reaches 1.45V. PWM Inverting Converter PWM inverting converter can act a current mode non - synchronous Buck -Boost converter to generated negative outpu t voltage, embedded an internal P - MOSFET. The UVLO (under-voltage lockout) function ensures PWM converter operates correctly with minimum VIN voltage. The VB regulator provides (VIN 5V) voltage for circuit powered directly by VIN. Connect a resistor from the RT pin to GND to set PWM switching frequency between 300 kHz to 800 kHz. Current limit comparator compares the CS pin voltage with 100mV reference voltage. Connect resistor between inductor and PGND to set peak inductor current limit threshold. 5VDET pin is VIN detection. After soft-start beginning, if 5VDET pin above 1V and SFB pin less 0.6V POK will pull high. If HV-Switch Over-current/Over-voltage is triggered, the TMR pin will be charge. When VTMR above 0.6V. POK will pull low immediately to turn off GATE. At the same time, a 10A current source is charging the FDLY capacitor. When the FDLY pin is a above 1.25V, POK will pull high to turn on GATE again. The PWM converter also provides Over Temperature Protection (OTP).
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 Absolute Maximum Ratings (Note 1) Power Dissipation, PD @ TA = 25°C Package Thermal Resistance (Note 2) ESD Susceptibility (Note 3) Recommended Operating Conditions (Note 4)
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com
Electrical Characteristics
(VIN = VENHV = 5V, RRT = 300k, CREF = 0.1F , VHV = 12V, TJ = 40°C to 125°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Hot Swap Regulator with Over-Voltage Protection VHV Supply Current IVHV VENHV = 0V -- 7 25 A VENHV = 5V (VGATE VOUT) -- 2.3 5 mA GATE Output High Voltage (Note 5) VGATE 8V < VHV < 80V (VGATE VOUT) 10 12 16 V GATE Pull-Up Current IGATE_UP VGATE = 12V 15 40 60 VGATE = VHV = 48V 30 70 120 GATE Pull-Down Current IGATE_DN Over voltage, VFB = 1.4V, VGATE = 12V 45 80 150 mA Over current, VHV VSNS = 120mV, VGATE = 12V 1 3 4 Shutdown mode, VENHV = 0V, VGATE = 12V 45 80 150 Output FB Voltage VFB VGATE = 12V, VOUT = 12V 1.18 1.25 1.32 V FB Input Current IFB VFB = 1.25V -- 0.3 1 A Over Current Threshold VSNS VHV VSNS VHV = 12V 40 50 58 mV VHV = 48V 38 48 56 SNS Input Current ISNS VSNS = VHV = 12V to 48V -- 120 -- A OUT Pin Input Current IOUT VSNS = VHV = 12V -- 200 500 A VOUT = VHV = 12V, VENHV = 0V -- 0.5 2 mA ENHV Input Voltage VENHV_H VHV = 12V to 48V 3 -- -- V VENHV_L VHV = 12V to 48V -- -- 0.5 ENHV Input Current IENHV VENHV = 3V -- 0.4 -- A TMR Current ITMR_SO Sourcing, VTMR = 1V, VFB = 1.5V or VSNS = 60mV 20 25 30 A ITMR_SI Sinking, VTMR = 1V, VFB = 1V or VSNS = 0V 2.5 3.5 5 A Inverting PWM Converter VIN Supply Voltage Range VIN 4 -- 7 V VIN Supply Current IVIN VNFB = 0.6V, V IN > VUVLO, VCOMP = 0V -- 0.75 1.5 mA UVLO Threshold VUVLO VIN rising -- 3.6 3.9 V VIN falling 3.2 3.5 -- NFB Threshold VNFB No load 0.585 0.6 0.615 V NFB Input Current INFB VNFB = 0.6V -- 0.1 -- A
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 Parameter Symbol Test Conditions Min Typ Max Unit SFB Threshold VSFB SFB rising 0.585 0.6 0.615 V Current Limit Threshold VCS 90 100 110 mV Inverting Output Voltage Range NVOUT 12.5 -- 0.5 V TMR Fault Detection TMR Threshold VTMR_FT POK pull low, FDLY source 10A CURRENT -- 0.6 -- V TMR Sense Blank Time VTMR_BLK TMR blank sensing after POK High -- 3 -- ms FDLY FDLY Threshold VFDLY Rising edge -- 1.25 -- V FDLY Output Current IFDLY -- 10 -- A Reference & LDO VREF Output Voltage VREF IREF = 50A 1.225 1.25 1.275 V VL Output Voltage VVL VIN = 5V, IVL = 0A 3.85 4.25 4.65 V VL Load Regulation VVL_Load VIN = 5V, 0 < IVL < 2mA -- 20 60 mV Oscillator Oscillator Frequency fSW RRT = 300k 400 500 600 kHz Maximum Duty DMAX 300kHz to 800kHz -- 85 -- % 5VDET 5VDET Threshold V5VDET Falling edge, hys = 50mV 0.92 1 1.08 V RDS(ON) & Thermal Shutdown Internal P-MOSFET On-Resistance RDS(ON) VIN = 5V, ILX = 10mA -- 80 120 m Thermal Shutdown Temperature TSD -- 150 -- °C Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. JA is measured under natural convection (still air) at TA = 25C with the component mounted on a high effective-thermal- conductivity four-layer test board on a JEDEC 51-7 thermal measurement standard. JC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. GATE to OUT voltage is internally generated and clamped. External driving at GATE pin is forbidden because it may damage the device. Note 6. All currents into device pins are positive, all currents out of device pins are negative. All voltages are referenced to GND unless otherwise specified.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com Typical Application Circuit 820µF RT2910A RT NFB VIN 20μF 7, 8 15200k 30m 10μH 47μF x 4 112k 13.7k GND 17, 25 (Exposed Pad) 4.5V to 7V LX 5, 6 CS 4 CDBB540-G 112k 13k COMP22 FDLY20 4.7μF VL18 0.47μF 2.2pF SFB 2 0.1μF NVOUT 0.1μF VB9 3.3nF 200k PGND 3 VREF 24 5VDET21 POK 19 10k ENHV 15 TMR16 91k FB 10 GATE OUT 11 VHV14 SNS13 10µF 22nF 12V to 48V Output VIN IPB027N10N3 2N700233k 10k IPB027N10N3 CMSH5-20 2.2nF 6.8M -5V@1A -10V@0.5A
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 Typical Operating Characteristics VIN = 5.5V , NVOUT = -5V , INVOUT = 0A Inverting Power On from VIN Time (5ms/Div) NVOUT (5V/Div) 5VDET (1V/Div) POK (4V/Div) PH (7V/Div) VIN = 5.5V , NVOUT = -5V , INVOUT = 1A Inverting Power On from VIN Time (2ms/Div) NVOUT (5V/Div) 5VDET (1V/Div) POK (4V/Div) PH (7V/Div) VIN = 5.5V , NVOUT = -5V , INVOUT = 0.1A Inverting Power Off from VIN Time (10ms/Div) NVOUT (5V/Div) 5VDET (1V/Div) POK (4V/Div) PH (7V/Div) VIN = 5.5V , NVOUT = -5V , INVOUT = 1A Inverting Power Off from VIN Time (10ms/Div) NVOUT (5V/Div) 5VDET (1V/Div) POK (4V/Div) PH (7V/Div) VIN = 5.5V , NVOUT = 5V , INVOUT = 0.1A to 1A Inverting Load Transient Time (5ms/Div) NVOUT (100mV/Div) INVOUT (1A/Div) PH (7V/Div) VHV = 55V , IOUT = 0A HV Switch Turn On from ENHV Time (1ms/Div) NVOUT (2V/Div) GATE TO GND (0V/Div) OUT TO GND (30V/Div) ENHV (5V/Div)
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com VHV = 55V , IOUT = 10A HV Switch Turn On from ENHV Time (1ms/Div) NVOUT (2V/Div) OUT TO GND (30V/Div) GATE TO GND (30V/Div) ENHV (5V/Div) VHV = 55V , IOUT = 0A , INVOUT = 1A HV Switch Turn Off from ENHV Time (500s/Div) NVOUT (5V/Div) GATE TO GND (50V/Div) OUT TO GND (50V/Div) ENHV (5V/Div) VHV = 55V , IOUT = 10A , INVOUT = 1A HV Switch Turn Off from ENHV Time (500s/Div) NVOUT (5V/Div) GATE TO GND (50V/Div) OUT TO GND (50V/Div) ENHV (5V/Div) VHV = 55V , IOUT = 5A TO 10A , INVOUT = 1A HV Switch OCP Time (500s/Div) NVOUT (5V/Div) OUT TO GND (30V/Div) IIN (10A/Div) ENHV (5V/Div) VHV = 65V , IOUT = 0A , INVOUT = 1A HV Switch OVP Time (5ms/Div) NVOUT (5V/Div) OUT TO GND (50V/Div) GATE TO OUT (50V/Div) ENHV (5V/Div) Efficiency vs. Output Current Output Current (A) Efficiency (%) VIN = 5.5V , NVOUT = 5V
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 NVOUT vs. Output Voltage 5.009 5.010 5.011 5.012 5.013 5.014 5.015 5.016 5.017 5.018 5.019 Output Current (A) NVOUT (V) VIN = 5.5V , NVOUT = 5V Quiescent Current vs. Ambient Temperature 550 600 650 700 750 800 850 900 950 4 5 6 7 8 Input Voltage (V) Quiescent Current (μA) VIN = 5.5V , NVOUT = 5V TA = 40°C TA = 25°C TA = 105°C NVOUT VS. Ambient Temperature 5.005 5.010 5.015 5.020 5.025 5.030 5.035 -50 -25 0 25 50 75 100 125 Ambient Temperature (°C) NVOUT (V) VIN = 5.5V , NVOUT = 5V, TA = 40°C to 105°C IOUT = 0A IOUT = 0.5A
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com
Application Information
The RT2910A is a PWM inverting converter integrates HV power switch driver . Features of the inverting converters include programmable constant switching frequency, current mode topology with slope compensation in case of sub-harmonic at over 50% duty cycle operation , internal linear regulator , and internal 0.6V NFB reference with soft-start control allows output voltage to be precisely regulated at adjustable output voltage .Protection features include adjustable current limit and over-temperature protection. The HV power switch is suited for hot swap applications as an over -voltage protection regulator with programmable current limit threshold equals 50mV that drives an external N-MOSFET as the pass transistor. It features a TMR function for over-voltage protection and over-current protection to avoid N-Channel MOSFET damaged. It operates from a wide supply voltage range of 5V to 60V. The internal charge pump circuit is included to turn on the N-Channel MOSFET to supply curr ent to the loads with very little power loss. HV Power Switch Driver Over-Voltage Protection The RT2910A is equipped with over-voltage protection (OVP) function. When the voltage at FB pin exceeds a threshold of approximate 1.25V, the MOSFET is turned off. The MOSFET can be turned on again once the voltage at FB pin drops below 1.25V During this period, the N-MOSFET is still on, and continues to supply current to the load. This allows uninterrupted operation during short over -voltage transient events. When the voltage regulation loop is engaged for longer than the time-out period, set by the timer capacitor connected from the TMR pin to ground, the GATE pin is pulled low to turn off the MOSFET . This prevents the N-MOSFET from being damaged during a long period of over-voltage. The OVP voltage can be set by the following equation: VOUT_OVP = 1.25 x (1 + R3 / R4) Where, R3 and R4 are the voltage divider from VOUT to GND with the divider ce nter node connected to FB pin. Over-Current Protection The RT2910A features an adjustable current limit that protects against short circuits or excessive load current. During an over-current event, the GATE pin is regulated to limit the current sense voltage between the VHV and SNS pins to 50mV. The current limit is set by the following equation: ILIM = 50mV/RSNS An over -current fault occurs when the current limit circuitry has been engaged for longer than the time-out delay set by the TMR pin timer capacitor. The GATE pin is then immediately pulled low to GND turning off the MOSFET. Fault Timer The RT2910A includes an adjustable fault timer pin. Connecting a capacitor from the TMR pin to ground sets the delay timer period before the MOSFET is turned off. The same capacitor also sets the cool off period before the MOSFET is allowed to turn back on after the fault condition has disappeared. The TMR pin should be tied to ground if this feature is not used. Once a fault condition, either over -voltage or over - current event, is detected, a current source charges up the TMR capacitor. The timer charge up current is fixed around 25A. When the voltage at the TMR pin, reaches the 0.6V threshold, 1. POK pin is pulled low. 2. The ENHV pin is pulled low. 3. The VGATE_OUT is pulled low. 4. CFDLY start to charge , when VTMR drop to 0.2V. 5. POK pin is pulled high again. The fault sequence is as Figure 1.
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. DS2910A-00 August 2017 www.richtek.com During an over -current (OC) event the MOSFET wi ll regulate the output current delivered to the load and the output voltage will collapse to whatever voltage is needed to sustain the OC threshold current. According to the timing determined by the capacitor connected at the TMR pin, the circuit will turn the load on and off periodically until the over -current event ends. While regulating the load current, the MOSFET will dissipate power and heat up. Unlike an O V event, the output voltage and the MOSFET’s drain -source voltage may not be easily predicted. If the output is shorted the voltage may collapse nearly to zero, placing the entire input voltage across the MOSFET. Further, this type of event is likely to continue for long periods. If the output voltage during the OC event is not easily determined, use zero for VOUT. For the rare OC event that is short compared to the TMR timing, examine the MOSFET’s safe operating area (SOA) graph, using (VHV – VOUT) for MOSFET drain to source voltage and your I OC_THRESHOLD for drain current, to determine if the over-current event will cause MOSFET damage. If the OC event lasts more than one TMR cycle then the MOSFET will turn on and o ff, dissipating power each time it is on and cooling down when it is off. In this case, use one of the longer timed areas of the SOA graph (perhaps the DC area) but adjust the IOC_THRESHOLD value by the 12% duty cycle of the MOSFET on periods to determine if the MOSFET will work. For ther mal management, the MOSFET dissipation dur ing long over-current events is : PDMOSFET(OC) = DC x (VHV – VOUT) x IOC_THRESHOLD where DC is the duty cycle of current regulation, typically about 12%. Parallel MOSFETs Select a single MOSFET for most applications. If the RDS(ON) target is very low and difficult to achieve at the necessary voltage rating, multiple devices may be used in parallel. Parallel devices can decrease the voltage drop in normal operation and reduce dissipation. However, SOA requirements must generally be met by a single device. In OV and OC conditions, GATE will decrease until the programmed output voltage or current is maintained. In that state, the MOSFET with the lowest threshold will carry more current than other parallel MOS FETs with higher thresholds, perhaps dramatically more. It’s generally best to assume that one device will be subjected to the entire SOA stress. Application Design Example Using the typical applications circuit as a design example wit h the following spec ifications: Automotive Application VHV = 48V to 55V DC with transients up to 80V. Output Voltage : VOUT <60V Current Limit (ILIM) : 10A Over-voltage Duration : 5ms Output Over-voltage Protection Setting : Set the OVP threshold at 58V, choose R4 as 2k and calculate R3 according to the following equation: VOUT_OVP = 1.25 x (1 + R3 / R4) Select R3 as a standard 1% value of 91k and calculate the resulting threshold as : VOUT_OVP = 1.25 x (1 + 91K / 2K) = 58.125V Calculate the sense resistor, R SNS, according to the following formula : RSNS = (VSNS / ILIM) = (50m / 10A) = 5m Calculate the power dissipation of RSNS to avoid overheating the sense resistor : PD(RSNS) = 1.2 x (ILIM)2 x RSNS = 1.2 x (10)2 x 5m = 0.6W Select a 1W sense resistor consider a parallel combination of lower-wattage resistors. Over-voltage/Over-current Timer Setting : Calculate the value of fault timing capacitor (C TMR) using the typical TMR pull -up current and TMR latch threshold with the following formula : CTMR = (tLATCH x ITMR_UP) / VTMR = (5ms x 25A) / 1.45 = 0.086F Select the standard value of 0.1 F and calculate the resulting fault timing : TLatch = (CTMR x VTMR) / ITMR_UP = (0.1 x 1.45) / 25= 5.8ms. During an over-voltage or over-current event, GATE will
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 regulate the output voltage or current while CTMR charges. When the voltage on the timing capacitor (VTMR) reaches the fault threshold (V TMR_F, 1.4 5V typical) GATE will turn off the external MOSFET soon. In the event of a long fault, GATE will turn on an d off repeatedly. The on and off timings (t GATE_ON and tGATE_OFF) are controlled by the TMR charge and discharge currents (I TMR_UP and I TMR_DN) and the voltage difference between the TMR latch and unlatch thresholds (VTMR_L - VTMR_UL) : tGATE_ON = [CTMR x (VTMR_L VTMR_UL) / ITMR_UP] tGATE_ON = [0.1F x (1.45V 0.4V) / 25A] = 4.2ms tGATE_OFF = [CTMR x (VTMR_L VTMR_UL) / ITMR_DN] tGATE_OFF = [0.1F x (1.45V 0.4V) / 3.5A] = 30ms Choose the MOSFET Select the MOSFET VDS rating, allowing for your maximum input voltage and transients. Then select an operating R DS(ON) to meet any voltage drop specifications and your on-state dissipation allowance. Finally, its package must be able to handle that dissipation and control its operating temperature. Most manufacturers list a maximum R DS(ON) at 25°C and provide a typical characteristics curve from which values at other temperatures can be estimated. You can also use the below equation to estimate maximum RDS(ON) from the 25°C specification : RDS(ON)_MAX = TJ(MAX) 25°C) x 0.5% / 1°C Given the 48V minimum input and the 10A output current, the RDS(ON) must be very low to avoid dropping a large percentage of the input voltage. To limit the drop to 1% of 48V (48mV) requires an 4.8m maximum. The package needs to dissipate about (10A) 2 x 4.8m = 0.48W into a hot automotive ambient temperature. Something like the IR Rectifier IRFS4310PbF, with its VD-S at 100V rating, 5.6m RDS(ON) (typ.) can be to parallel in order to reduce thermal on MOSFET . D2PAK package should be more than adequate. PWM Inverting Converter Internal Soft-start The RT2910A feature a “digital soft-start” that is preset and requires no external capacitor. Upon startup, the NFB threshold decrements from the reference voltage 0.6V in 128 steps, and each step is 18 clock cycle. So soft-start time can be calculated as below TSS = (128 x 18) / FS Where FS is PWM switching frequency. Soft-start is implemented: 1. When exiting under-voltage lockout. 2. When V5VDET is above 1V. 3. When exiting OTP . Once POK is high, soft-stare is canceled and NFB reference pulled to 0.6V immediately. Internal Regulator The RT291 0A incorporates an internal low -dropout regulator (LDO). This LDO has a 4.25V output and provides PWM converter internal circuit power request. The internal LDO has under -voltage lockout circuit which monitors the voltage of VL. The under -voltage lockout threshold is typical 3.6V. For best performance, it is recommended to connect VL to VIN when the input supply is less than 4.5V and connect a 0.47F capacitor to GND to compensate loop and decoupling. UVLO (Under-Voltage Lockout) The RT2910A have an internal under-voltage lockout circuit that monitors the voltage of VIN. If VIN falls below the UVLO threshold (Typ. 3.5V) the control logic turn s off the internal P -MOSFET. The other internal circuits are still powered and operating. When VIN higher than UVLO fall ing threshold plus 100mV , the RT2910A resumes operation from a start-up condition (soft-start). Oscillator Frequency The RT291 0A is a current mode constant switching frequency converter and i t provides the RT pin for switching fre quency setting. User can set switching frequency by resistor (RTON) connected from the RT pin to GND. The switching frequency calculation is shown as below : FS = 1 / [(R // RTON) x C + 0.2294s] Where R is inverting resistor: R = 325k C = 11.4pF
Copyright © 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. www.richtek.com DS2910A-00 August 2017 Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.250 0.350 0.010 0.014 D 4.950 5.050 0.195 0.199 D2 3.100 3.400 0.122 0.134 E 4.950 5.050 0.195 0.199 E2 3.100 3.400 0.122 0.134 e 0.650 0.026 L 0.350 0.450 0.014 0.018 W-Type 24L QFN 5x5 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.