® RT9625A Dual-Channel Synchronous Rectified MOSFET Driver General Description Features The RT9625A is a high frequency, synchronous rectified, two phase MOSFET driver designed for normal MOSFET driving applications and high performance CPU VR driving capabilities. z Drive Four N-MOSFETs for Two-Phase PWM Control z Shoot Through Protection Embedded Bootstrap Diode Support High Switching Frequency Fast Output Rising Time Tri-State PWM Input for Output Shutdown Enable Control Small 16-Lead WQFN Package RoHS Compliant and Halogen Free The RT9625A can be supplied from 4.5V to 13.2V. The applicable power stage VIN range is from 5V to 23V. The RT9625A also builds in internal power switches to replace external bootstrap diodes. z z z z z z z The RT9625A can support switching frequency efficiently up to 500kHz. The RT9625A has the UGATE and LGATE driving circuits for synchronous rectified DC/DC converter applications. The shoot through protection mechanism is designed to prevent shoot through between high side and low side power MOSFETs. The RT9625A has tri-state PWM input with shutdown and EN shutdown functions, which can force driver to output low UGATE and LGATE signals. The RT9625 comes in a small footprint with WQFN-16L 4x4 package. Applications z Core Voltage Supplies for Desktop, Motherboard CPU z High Frequency Low Profile DC/DC Converters High Current Low Voltage DC/DC Converters Core Voltage Supplies for GFX Card z z Marking Information 06 : Product Code YMDNN : Date Code 06 YM DNN Simplified Application Circuit VIN 12V VCC RT9625A L1 PWM1 PWM2 Chip Enable PWM1 PWM2 EN1 EN2 PHASE1 VOUT L2 PHASE2 GND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT9625A Ordering Information Pin Configurations RT9625A Note : Richtek products are : 1 GND 2 PWM2 3 GND 15 14 13 12 VCC 11 LGATE1 10 PHASE1 9 UGATE1 GND 17 Suitable for use in SnPb or Pb-free soldering processes. 5 6 7 POR 4 8 BOOT1 EN2 PWM1 RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` 16 EN1 ` BOOT2 LGATE2 Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free) PHASE2 Package Type QW : WQFN-16L 4x4 (W-Type) UGATE2 (TOP VIEW) WQFN-16L 4x4 Function Pin Description Pin No. Pin Name 1 BOOT2 8 BOOT1 2, 13 (Exposed Pad) GND Pin Function Bootstrap Power Pins for Channel 2 and Channel 1. This pin powers the high side MOSFET driver. Connect this pin to the junction of the bootstrap capacitor and the cathode of the bootstrap diode. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 3 PWM2 6 PWM1 4 EN2 5 EN1 Chip Enable. When this pin is low, both UGATEx and LGATEx are driven to low. 7 POR Power On Reset Signal. 9 UGATE1 16 UGATE2 High Side Gate Drive Outputs for channel 1 and channel 2. Connect this pin to Gate of high side power MOSFET. 10 PHASE1 15 PHASE2 11 LGATE1 14 LGATE2 Low Side Gate Drive Output for Channel 1 and Channel 2. This pin drives the Gate of low side MOSFET. 12 VCC Supply Input. VCC supplies current for Channel 1 and Channel 2 gate drivers. PWM Signal Input. Connect this pin to the PWM output of the controller. Switch Nodes of High Side Driver 1 and Driver 2. Connect this pin to the high side MOSFET Source together with the low side MOSFET Drain and the inductor. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS9625A-03 June 2013 RT9625A Function Block Diagram VCC POR Bootstrap Control POR Enable Detect EN1 BOOT1 Internal VDD Tri-State Detect PWM1 Shoot-Through Protection UGATE1 Turn Off Detection PHASE1 VCC Shoot-Through Protection LGATE1 GND VCC1 Bootstrap Control Enable Detect EN2 Internal VDD PWM2 Tri-State Detect BOOT2 Shoot-Through Protection UGATE2 Turn Off Detection PHASE2 VCC Shoot-Through Protection LGATE2 GND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT9625A Operation POR (Power On Reset) Bootstrap Control POR block detects the voltages at VCC pin. When the VCC pin voltage is higher than POR rising threshold, POR pin output voltage (POR output) is high. POR output is low when VCC is not higher than POR rising threshold. When the POR pin voltage is high, UGATEx and LGATEx can be controlled by PWMx input voltage. If the POR pin voltage is low, both UGATEx and LGATEx will be pulled to low. Bootstrap control block controls the integrated bootstrap switch. When LGATEx is high (low side MOSFET is turned on), the bootstrap switch is turned on to charge the bootstrap capacitor connected to BOOTx pin. When LGATEx is low (low side MOSFET is turned off), the bootstrap switch is turned off to disconnect VCC pin and BOOTx pin. Turn-Off Detection Enable Detect When ENx pin input voltage is higher/lower than EN rising threshold, MOSFET driver is enabled/disabled. When the ENx input and POR output are high, UGATEx and LGATEx can be controlled by PWMx input voltage. When ENx input is low, both UGATEx and LGATEx are pulled to low. Turn-off detection block detects whether high side MOSFET is turned off by monitoring PHASEx pin voltage. To avoid shoot through between high side and low side MOSFETs, low side MOSFET can be turned on only after high side MOSFET is effectively turned off. Shoot-Through Protection Tri-State Detect When both POR block output and ENx pin voltages are high, UGATEx and LGATEx can be controlled by PWMx input. There are three PWMx input modes, which are high, low, and shutdown state. If PWMx input is within the shutdown window, both UGATEx and LGATEx output are low. When PWMx input is higher than its rising threshold, UGATEx is high and LGATEx is low. When PWMx input is lower than its falling threshold, UGATEx is low and LGATEx is high. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Shoot-through protection block implements the dead time when both high side and low side MOSFETs are turned off. With shoot-through protection block, high side and low side MOSFET are never turned on simultaneously. Thus, shoot through between high side and low side MOSFETs is prevented. is a registered trademark of Richtek Technology Corporation. DS9625A-03 June 2013 RT9625A Absolute Maximum Ratings z z z z z z z z z z z z z (Note 1) Supply Voltage, VCC -------------------------------------------------------------------------------- −0.3V to 15V BOOTx to PHASEx ---------------------------------------------------------------------------------- −0.3V to 15V PHASEx to GND DC -------------------------------------------------------------------------------------------------------- −0.3V to 30V < 20ns --------------------------------------------------------------------------------------------------- −10V to 35V LGATEx to GND DC -------------------------------------------------------------------------------------------------------- −0.3V to (VCC + 0.3V) < 20ns --------------------------------------------------------------------------------------------------- −2V to (VCC + 0.3V) UGATEx to GND DC -------------------------------------------------------------------------------------------------------- (VPHASE − 0.3V) to (VBOOT + 0.3V) < 20ns --------------------------------------------------------------------------------------------------- (VPHASE − 2V) to (VBOOT + 0.3V) ENx, PWMx to GND --------------------------------------------------------------------------------- −0.3V to 7V POR to GND ------------------------------------------------------------------------------------------- −0.3V to 5V Power Dissipation, PD @ TA = 25°C WQFN-16L 4x4 --------------------------------------------------------------------------------------- 1.852W Package Thermal Resistance (Note 2) WQFN-16L 4x4, θJA ---------------------------------------------------------------------------------- 54°C/W WQFN-16L 4x4, θJC --------------------------------------------------------------------------------- 7°C/W Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------- 260°C Junction Temperature -------------------------------------------------------------------------------- 150°C Storage Temperature Range ----------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Model) ------------------------------------------------------------------------- 2kV Recommended Operating Conditions z z z z (Note 4) Supply Voltage, VCC -------------------------------------------------------------------------------- 4.5V to 13.2V Input Voltage, (VIN + VCC) ------------------------------------------------------------------------- < 35V Junction Temperature Range ----------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ----------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 12V, TA = 25°C unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 4.5 -- 13.2 V Power Supply Voltage VCC Power Supply Current IVCC VBOOTx = 12V, PWMx Floating -- 180 -- μA POR Rising Threshold VPOR_r VCC Rising -- 4 4.4 V POR Falling Threshold VPOR_f VCC Falling 3 3.5 -- V POR Pin High Voltage VPOR_H -- 3.5 4 V POR Pin Low Voltage VPOR_L -- -- 0.5 V Power On Reset (POR) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT9625A Parameter Symbol Test Conditions Min Typ Max Unit EN Input ENx Rising Threshold VENH -- 1.3 1.6 V ENx Falling Threshold VENL 0.7 1 -- V PWM Input Maximum Input Current IPWM VPWMx = 0V or 5V -- 160 -- μA PWMx Floating Voltage VPWM_fl PWMx = Open -- 1.8 -- V PWMx Rising Threshold VPWM_rth 2.3 2.8 3.2 V PWMx Falling Threshold VPWM_fth 0.7 1.1 1.4 V Timing UGATEx Rising Time tUGATEr 3nF load -- 25 -- ns UGATEx Falling Time tUGATEf 3nF load -- 12 -- ns LGATEx Rising Time tLGATEr 3nF load -- 24 -- ns LGATEx Falling Time tLGATEf 3nF load -- 10 -- ns tUGATEpdh VBOOTx − VPHASEx = 12V See Timing Diagram -- 60 -- -- 22 -- -- 30 -- -- 8 -- Propagation Delay tUGATEpdl tLGATEpdh tLGATEpdl See Timing Diagram ns ns Output UGATEx Drive Source RUGATEsr VBOOT − VPHASE = 12V, ISource = 100mA -- 1.7 -- Ω UGATEx Drive Sink RUGATEsk VBOOT − VPHASE = 12V, ISink = 100mA -- 1.4 -- Ω LGATEx Drive Source RLGATEsr I Source = 100mA -- 1.6 -- Ω LGATEx Drive Sink RLGATEsk I Sink = 100mA -- 1.1 -- Ω 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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC 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. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS9625A-03 June 2013 RT9625A Typical Application Circuit RT9625A R1 2.2 12V 12 VCC2 C1 1µF BOOT1 8 UGATE1 7 5 Chip Enable 4 POR EN1 PHASE1 LGATE1 PWM1 3 PWM2 PWM2 2, 13, 17 (Exposed Pad) GND UGATE2 R3 2.2 VIN 12V C2 270µF x 2 Q1 L1 10 R4 0 11 EN2 PWM1 C3 1µF 9 BOOT2 1 6 R2 1 16 R6 1 C6 1µF R7 2.2 Q2 C4 3.3nF VIN Q3 L2 PHASE2 15 LGATE2 14 VOUT C5 820µF x 3 R5 2.2 R8 0 R9 2.2 Q4 C7 3.3nF Timing Diagram PWMx LGATEx tLGATEpdl 90% tUGATEpdl 1.5V 1.5V 1.5V 90% 1.5V UGATEx tUGATEpdh Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 tLGATEpdh is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 ® RT9625A Typical Operating Characteristics Drive Enable Drive Disable UGATE (50V/Div) UGATE (50V/Div) PHASE (20V/Div) PHASE (20V/Div) LGATE (20V/Div) LGATE (20V/Div) EN (10V/Div) EN (10V/Div) VIN = 12V, No Load VIN = 12V, No Load Time (1μs/Div) Time (1μs/Div) PWM Rising Edge PWM Falling Edge PWM (10V/Div) PWM (10V/Div) UGATE (20V/Div) UGATE (20V/Div) LGATE (10V/Div) LGATE (10V/Div) PHASE (10V/Div) PHASE (10V/Div) Time (20ns/Div) Time (20ns/Div) Dead Time Dead Time UGATE UGATE PHASE PHASE LGATE LGATE (5V/Div) (5V/Div) Full Load Full Load Time (20ns/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 Time (20ns/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 8 ® RT9625A Dead Time Dead Time UGATE UGATE PHASE PHASE LGATE (5V/Div) LGATE (5V/Div) No Load Time (20ns/Div) No Load Time (20ns/Div) Short Pulse UGATE LGATE PHASE (5V/Div) UGATE − PHASE No Load Time (20ns/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT9625A Application Information The RT9625A is a high frequency, two-channel synchronous rectified MOSFET driver containing Richtek's advanced MOSFET driver technologies. The RT9625A is designed to be able to adapt from normal MOSFET driving applications to high performance CPU VR driving capabilities. Supply Voltage and Power On Reset The RT9625A can be utilized under both VCC = 5V or VCC = 12V applications which may happen in different fields of electronics application circuits. In terms of efficiency, higher VCC equals higher driving voltage of UGATEx/ LGATEx which may result in higher switching loss and lower conduction loss of power MOSFETs. The choice of VCC = 12V or VCC = 5V can be a tradeoff to optimize system efficiency. The RT9625A controls both high side and low side NMOSFETs of two half-bridge power according to two external input PWMx control signals. It has Power On Reset (POR) function which held UGATEx and LGATEx low before the VCC voltage rises to higher than rising threshold voltage. When VCC exceeds the POR threshold voltage, the voltage at the POR pin will be pulled high. Enable and Disable The RT9625A includes an ENx pin for sequence control. When the ENx pin rises above the VENH trip point, the RT9625A begins a new initialization and follows the PWMx command to control the UGATEx and LGATEx. When the ENx pin falls below the VENL trip point, the RT9625A shuts down and keeps UGATEx and LGATEx low. Tri-state PWM Input After the initialization, the PWMx signal takes the control. The rising PWMx signal first forces the LGATEx signal to turn low then UGATEx signal is allowed to go high just after a non-overlapping time to avoid shoot through current. The falling of PWMx signal first forces UGATEx to go low. When UGATEx and PHASEx signal reach a predetermined low level, LGATEx signal is allowed to turn high. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 The PWMx signal is acted as “ High” if the signal is above the rising threshold and acted as “ Low” if the signal is below the falling threshold. When PWM signal level enters and remains within the shutdown window, the output drivers are disabled and both MOSFET gates are pulled and held low. If the PWMx signal is left floating, the pin will be kept around 1.8V by the internal divider and provide the PWMx controller with a recognizable level. Bootstrap Power Switch The RT9625A builds in internal bootstrap power switches to replace external bootstrap diode, and this can facilitate PCB design and reduce total BOM cost of the system. Hence, no external bootstrap diode is required in real applications. Non-overlap Control To prevent the overlap of the gate drivers during the UGATEx pull low and the LGATEx pull high, the non-overlap circuit monitors the voltages at the PHASEx node and high side gate drive (UGATEx − PHASEx). When the PWMx input signal goes low, UGATEx begins to pull low (after propagation delay). Before LGATEx is pulled high, the non-overlap protection circuit ensures that the monitored voltages have gone below 1.1V. Once the monitored voltages fall below 1.1V, LGATEx begins to turn high. By waiting for the voltages of the PHASEx pin and high side gate driver to fall below 1.1V, the non-overlap protection circuit ensures that UGATEx is low before LGATEx pulls high. Also to prevent the overlap of the gate drivers during LGATEx pull low and UGATEx pull high, the non-overlap circuit monitors the LGATEx voltage. When LGATEx goes below 1.1V, UGATEx goes high after propagation delay. Driving Power MOSFETs The DC input impedance of the power MOSFET is extremely high. When Vgs1 or Vgs2 is at 12V or 5V, the gate draws the current only for few nano-amperes. Thus once the gate has been driven up to “ ON” level, the current could be negligible. is a registered trademark of Richtek Technology Corporation. DS9625A-03 June 2013 RT9625A However, the capacitance at the gate to source terminal should be considered. It requires relatively large currents to drive the gate up and down 12V (or 5V) rapidly. It is also required to switch drain current on and off with the required speed. The required gate drive currents are calculated as follows. d1 s1 VPHASEx VIN L VOUT Cgd2 Igs1 Igd1 Ig1 g1 d2 D2 Igs2 Cgs2 dt = Cgs1 x 12 (2) tr2 low side is turned on. From Figure 1, the body diode “ D2” will be turned on before high side MOSFETs turn on. dV 12 = Cgd1 dt tr1 (3) Before the low side MOSFET is turned on, the Cgd2 have been charged to VIN. Thus, as Cgd2 reverses its polarity and g2 is charged up to 12V, the required current is Ig2 Igd2 g2 dVg2 Before driving the gate of the high side MOSFET up to 12V, the low side MOSFET has to be off; and the high side MOSFET will be turned off before the Igd1 = Cgd1 Cgs1 Cgd1 Igs2 = Cgs1 Igd2 = Cgd2 s2 VIN + 12 dV = Cgd2 dt tr2 (4) GND Vg1 VPHASEx +12V t Vg2 It is helpful to calculate these currents in a typical case. Assume a synchronous rectified Buck converter, input voltage VIN = 12V, Vgs1 = 12V, Vgs2 = 12V.The high side MOSFET is PHB83N03LT whose C iss = 1660pF, Crss = 380pF, and tr = 14ns. The low side MOSFET is PHB95N03LT whose Ciss = 2200pF, Crss = 500pF and tr = 30ns, from the equation (1) and (2) we can obtain 12V Igs1 = 1660 x 10-12 x 12 14 x 10 t Figure 1. Equivalent Circuit and Waveforms (VCC = 12V) In Figure 1, the current Ig1 and Ig2 are required to move the gate up to 12V. The operation consists of charging Cgd1, Cgd2 , Cgs1 and Cgs2. Cgs1 and Cgs2 are the capacitors from gate to source of the high side and the low side power MOSFETs, respectively. In general data sheets, the Cgs1 and C gs2 are referred as “ Ciss” which are the input capacitors. Cgd1 and Cgd2 are the capacitors from gate to drain of the high side and the low side power MOSFETs, respectively and referred to the data sheets as “ Crss” the reverse transfer capacitance. For example, tr1 and tr2 are the rising time of the high side and the low side power MOSFETs respectively, the required current Igs1 and Igs2, are shown as below : dVg1 Cgs1 x 12 (1) Igs1 = Cgs1 = dt tr1 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 Igs2 = -9 2200 x 10-12 x 12 30 x 10-9 = 1.428 = 0.88 (5) (A) (A) (6) from equation. (3) and (4) Igd1 = Igd2 = 380 x 10-12 x 12 14 x 10-9 = 0.326 (A) 500 x 10-12 x (12+12 ) -9 (7) = 0.4 (A) (8) 30 x 10 the total current required from the gate driving source can be calculated as following equations. Ig1 = Igs1 + Igd1 = (1.428 + 0.326 ) = 1.754 (A) Ig2 = Igs2 + Igd2 = ( 0.88 + 0.4 ) = 1.28 (A) (9) (10) By a similar calculation, we can also get the sink current required from the turned off MOSFET. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT9625A Select the Bootstrap Capacitor Figure 2 shows part of the bootstrap circuit of the RT9625A. The VCB (the voltage difference between BOOTx and PHASEx on RT9625A) provides a voltage to the gate of the high side power MOSFET. This supply needs to be ensured that the MOSFET can be driven. For this, the capacitance CBOOT has to be selected properly. It is determined by the following constraints. CBOOT 1µF 10 12V 1µF VCC 12V BOOTx UGATEx 2N7002 RT9625A POR Chip Enable PWMx CU 3nF POR PHASEx ENx PWNx VIN 2N7002 20 LGATEx GND CL 3nF BOOTx UGATEx PHASEx CBOOT Figure 3. Power Dissipation Test Circuit + VCB - VCC LGATEx Figure 4 shows the power dissipation of the RT9625A as a function of frequency and load capacitance when VCC = 12V. The value of CU and CL are the same and the frequency is varied from 100kHz to 1MHz. GND Power Dissipation vs. Frequency 1000 Figure 2. Part of Bootstrap Circuit of RT9625A Power Dissipation (mW) In practice, a low value capacitor CBOOT will lead to the over charging that could damage the IC. Therefore, to minimize the risk of overcharging and to reduce the ripple on VCB, the bootstrap capacitor should not be smaller than 0.1μF, and the larger the better. In general design, using 1μF can provide better performance. At least one low-ESR capacitor should be used to provide good local de-coupling. It is recommended to adopt a ceramic or tantalum capacitor. 900 800 CU = CL = 3nF 700 600 CU = CL = 2nF 500 400 300 200 CU = CL = 1nF 100 VCC = 12V 0 0 Power Dissipation To prevent driving the IC beyond the maximum recommended operating junction temperature of 125°C, it is necessary to calculate the power dissipation appropriately. This dissipation is a function of switching frequency and total gate charge of the selected MOSFET. Figure 3 shows the power dissipation test circuit. CL and C U are the UGATEx and LGATEx load capacitors, respectively. The bootstrap capacitor value is 1μF. 200 400 600 800 1000 Frequency (kHz) Figure 4. Power Dissipation vs. Frequency The operating junction temperature can be calculated from the power dissipation curves (Figure 4). Assume VCC = 12V, operating frequency is 200kHz and CU = CL = 1nF which emulate the input capacitances of the high side and low side power MOSFETs. From Figure 4, the power dissipation is 100mW. Thus, for example, with the SOP8 package, the package thermal resistance θJA is 120°C/ W. The operating junction temperature is then calculated as : TJ = (120°C/W x 100mW) + 25°C = 37°C (11) where the ambient temperature is 25°C. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS9625A-03 June 2013 RT9625A Thermal Considerations Layout Consideration For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : Figure 6 shows the schematic circuit of a synchronous buck converter to implement the RT9625A. The converter operates from 5V to 12V of input Voltage. PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WQFN-16L 4x4 packages, the thermal resistance, θJA, is 54°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : For the PCB layout, it should be very careful. The power circuit section is the most critical one. If not configured properly, it will generate a large amount of EMI. The location of QUGx, QLGx, Lx should be very close. Next, the trace from UGATEx, and LGATEx should also be short to decrease the noise of the driver output signals. PHASEx signals from the junction of the power MOSFET, carrying the large gate drive current pulses, should be as heavy as the gate drive trace. The bypass capacitor CVCC should be connected to GND directly. Furthermore, the bootstrap capacitors (CBOOTx) should always be placed as close to the pins of the IC as possible. VIN 12V LIN 12V + PD(MAX) = (125°C - 25°C) / (54°C/W) = 1.852W for WQFN-16L 4x4 package CIN The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 5 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. QUGx Lx CIN2 RVCC CBOOTx VOUT BOOTx VCC RT9625A UGATEx + PHB83N03LT PHASEx COUT QLGx CVCC PHB95N03LT LGATEx PWMx ENx PWMx ENx GND Maximum Power Dissipation (W) 2.0 Four-Layer PCB 1.8 Figure 6. Synchronous Buck Converter Circuit 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 5. Derating Curve of Maximum Power Dissipation Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS9625A-03 June 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT9625A Outline Dimension D SEE DETAIL A D2 L 1 E E2 e b A A1 1 1 2 2 DETAIL A Pin #1 ID and Tie Bar Mark Options A3 Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol 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 0.380 0.010 0.015 D 3.950 4.050 0.156 0.159 D2 2.000 2.450 0.079 0.096 E 3.950 4.050 0.156 0.159 E2 2.000 2.450 0.079 0.096 e L 0.650 0.500 0.026 0.600 0.020 0.024 W-Type 16L QFN 4x4 Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. 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. www.richtek.com 14 DS9625A-03 June 2013