RT9602 Dual Channel Synchronous-Rectified Buck MOSFET Driver General Description Features The RT9602 is a dual power channel MOSFET driver specifically designed to drive four power N-Channel MOSFETs in a synchronous-rectified buck converter topology. These drivers combined with RT9237/A and RT9241A/B series of Multi-Phase Buck PWM controllers provide a complete core voltage regulator solution for advanced microprocessors. l The RT9602 can provide flexible gate driving for both high side and low side drivers. This gives more flexibility of MOSFET selection. l l l l l l l Applications l The output drivers in the RT9602 have the capability to drive a 3000pF load with a 40nS propagation delay and 80nS transition time. This device implements bootstrapping on the upper gates with only a single external capacitor required for each power channel. This reduces implementation complexity and allows the use of higher performance, cost effective, N-Channel MOSFETs. Adaptive shoot-through protect-ion is integrated to prevent both MOSFETs from conducting simultaneously. The RT9602 can detect high side MOSFET drain-to-source electrical short at power on and pull the 12V power by low side MOS and cause power supply to go into over current shutdown to prevent damage of CPU. Drives Four N-Channel MOSFETs Adaptive Shoot-Through Protection Internal Bootstrap Devices Small 14-Lead SOIC Package 5V to 12V Gate-Drive Voltages for Optimal Efficiency Tri-State Input for Bridge Shutdown Supply Under-Voltage Protection Power ON Over-Voltage Protection l l Core Voltage Supplies for Intel Pentium 4 and AMD AthlonTM Microprocessors High Frequency Low Profile DC-DC Converters High Current Low Voltage DC-DC Converters Pin Configurations (TOP VIEW) PWM1 PWM2 GND LGATE1 PVCC PGND LGATE2 2 3 4 5 6 7 14 13 12 11 10 9 8 VCC PHASE1 UGATE1 BOOT1 BOOT2 UGATE2 PHASE2 SOP-14 Ordering Information RT9602 Package Type S : SOP-14 Operating Temperature Range C : Commercial Standard P : Pb Free with Commercial Standard DS9602-03 March 2004 www.richtek.com 1 www.richtek.com 2 12V 2.4K 18K +5V 3K 66pF 15K 3 VID2 2.4K VID0 VID4 VDD VID3 PGOOD 19 20 0.1uF 10 9 ISN2 ISP2 GND PWM2 RT9241A/B SS DVD 8 ADJ 16 11 15 13 17 VID2 PWM1 18 4 ISP1 VID1 5 12 VID0 ISN1 6 COMP 7 FB 14 VSEN 2 VID3 VID1 1 VID4 1uF 3K 3K 3K 3K +5V PGOOD 10K 12V VCORE 1.2uH x1500uF 2uH 1000uF x1500uF 2uH 1000uF PHB95N03LT 7 8 9 4 13 12 1uF 1uF PHB83N03LT 1uF PHB95N03LT PHB83N03LT 1uF PVCC 14 VCC 5 PGND GND PWM2 Optional BOOT2 10 LGATE2 PHASE2 UGATE2 LGATE1 RT9602 6 3 2 PHASE1 PWM1 1 UGATE1 11 BOOT1 Optional 1uF 100 12V RT9602 Typical Application Circuit DS9602-03 March 2004 RT9602 Functional Pin Description Pin No. Pin Name Pin Function 1 PWM1 Channel 1 PWM Input 2 PWM2 Channel 2 PWM Input 3 GND Ground Pin 4 LGATE1 Lower Gate Drive of Channel 1 5 PVCC Upper and Lower Gate Driver Power Rail 6 PGND Lower Gate Driver Ground Pin 7 LGATE2 Lower Gate Drive of Channel 2 8 PHASE2 9 UGATE2 Upper Gate Drive of Channel 2 10 BOOT2 Floating Bootstrap Supply Pin of Channel 2 11 BOOT1 Floating Bootstrap Supply Pin of Channel 1 12 UGATE1 Upper Gate Drive of Channel 1 13 PHASE1 14 VCC Connect this pin to phase point of channel 2. Phase point is the connection point of high side MOSFET source and low side MOSFET drain Connect this pin to phase point of channel 1. Phase point is the connection point of high side MOSFET source and low side MOSFET drain Control Logic Power Supply DS9602-03 March 2004 www.richtek.com 3 RT9602 Function Block Diagram VCC PVCC BOOT1 Internal 5V Shoot-Through Protection UGATE1 PHASE1 40K PWM1 Power-On OVP 40K PVCC Shoot-Through Protection Internal 5V Control Logic LGATE1 PGND PGND BOOT2 PVCC Shoot-Through Protection UGATE2 40K PHASE2 PWM2 40K Power-On OVP PVCC Shoot-Through Protection GND LGATE2 PGND Absolute Maximum Ratings Supply Voltage (VCC) -------------------------------------------------------------------------------- 15V l Supply Voltage (PVCC) ------------------------------------------------------------------------------ VCC + 0.3V l BOOT Voltage (VBOOT -VPHASE) --------------------------------------------------------------------- 15V l Input Voltage (VPWM) --------------------------------------------------------------------------------- GND - 0.3V to 7V l UGATE -------------------------------------------------------------------------------------------------- V - 0.3V to VBOOT + 0.3V PHASE l LGATE --------------------------------------------------------------------------------------------------- GND - 0.3V to V + 0.3V PVCC l Package Thermal Resistance SOP-14, JA ---------------------------------------------------------------------------- 127.67 C /W l Ambient Temperature -------------------------------------------------------------------------------- 0 C to 70 C l Junction Temperature -------------------------------------------------------------------------------- 0 C to 125 C l Storage Temperature Range ------------------------------------------------------------------------ -40 C to 150 C l Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------- 260C l ESD Level (Note) - HBM ----------------------------------------------------------------------------------------------------- 2kV - MM ------------------------------------------------------------------------------------------------------- 200V l www.richtek.com 4 DS9602-03 March 2004 RT9602 Electrical Characteristics Parameter Symbol Test Conditions Min Typ Max Units VCC Supply Current Bias Supply Current IVCC fPWM = 250kHz, V PVCC = 12V, CBOOT = 0.1F, RPHASE = 20 -- 5.5 8 mA Power Supply Current IPVCC fPWM = 250kHz, VPVCC = 12V, CBOOT = 0.1F, RPHASE = 20 -- 5.5 10 mA VCC Rising Threshold 8.6 9.9 10.7 V Hysteresis 0.6 1.35 -- V Power-On Reset PWM Input Maximum Input Current VPWM = 0 or 5V 80 127 150 A PWM Floating Voltage Vcc = 12V 1.1 2.1 3.7 V PWM Rising Threshold 3.3 3.7 4.3 V PWM Falling Threshold 1.0 1.26 1.5 V UGATE Rise Time VPVCC = VVCC = 12V, 3nF load -- 30 -- ns LGATE Rise Time VPVCC = VVCC = 12V, 3nF load -- 30 -- ns UGATE Fall Time VPVCC = VVCC = 12V, 3nF load -- 40 -- ns LGATE Fall Time VPVCC = VVCC = 12V, 3nF load -- 30 -- ns UGATE Turn-Off Propagation Delay VVCC = VPVCC = 12V, 3nF load -- 60 -- ns LGATE Turn-Off Propagation Delay VVCC = VPVCC = 12V, 3nF load -- 45 -- ns 1.26 -- 3.7 V Shutdown Window Output Upper Drive Source RUGATE VVCC = 12V, VPVCC = 12V -- 1.75 3.0 Upper Drive Sink RUGATE VVCC = 12V, VPVCC = 12V -- 2.8 5.0 Lower Drive Source RLGATE VVCC = 12V, VPVCC = 12V -- 1.9 3.0 Lower Drive Sink RLGATE VVCC = VPVCC = 12V -- 1.6 3.0 Note: Devices are ESD sensitive, especially for PHASE and LGATE pins. Handling precaution recommended. The human body model is a 100pF capacitor discharged through a 1.5kW resistor into each pin. DS9602-03 March 2004 www.richtek.com 5 RT9602 Application Information The RT9602 has power on protection function which held UGATE and LGATE low before VCC up cross the rising threshold voltage. After the initialization, the PWM signal takes the control. The rising PWM signal first forces the LGATE signal turns low then UGATE signal is allowed to go high just after a non-overlapping time to avoid shootthrough current. The falling of PWM signal first forces UGATE to go low. When UGATE and PHASE signal reach a predetermined low level, LGATE signal is allowed to turn high. The non-overlapping function is also presented between UGATE and LGATE signal transient. The PWM signal is recognized as high if above rising threshold and as low if below falling threshold. Any signal level in this window is considered as tri-state, which causes turn-off of both high side and low-side MOSFET. When PWM input is floating (not connected), internal divider will pull the PWM to 1.9V to give the controller a recognizable level. The maximum sink/source capability of internal PWM reference is 60A. The PVCC pin provides flexibility of both high side and low side MOSFET gate drive voltages. If 8V, for example, is applied to PVCC, then high side MOSFET gate drive is 8V to 1.5V (approximately, internal diode plus series resistance voltage drop). The low side gate drive voltage is exactly 8V. The RT9602 implements a power on over-voltage protection function. If the PHASE voltage exceeds 1.5V at power on, the LGATE would be turn on to pull the PHASE low until the PHASE voltage goes below 1.5V. Such function can protect the CPU from damage by some short condition happened before power on, which is sometimes encountered in the M/B manufacturing line. Driving power MOSFETs The DC input impedance of the power MOSFET is extremely high. When Vgs at 12V (or 5V), the gate draws the current only few nanoamperes. Thus once the gate has been driven up to "ON"ON level, the current could be negligible. 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 also required to switch drain current on and off with the required speed. The required gate drive currents are calculated as follows. D1 s1 d1 Vi Cgd1 L VO Cgs1 Igd1 Ig1 Cgd2 d2 Igs1 g1 Ig2 Igd2 g2 D2 Igs2 Cgs2 s2 GND Vg 1 Vp h a s e +12V t Vg 2 +12V t Figure1. The gate driver must supply Igs to Cgs and Igd to Cgd In Figure 1, the current Ig1 and Ig2 are required to move the gate up to 12V.The operation consists of charging Cgd and Cgs. Cgs1 and Cgs2 are the capacitances from gate to source of the high side and the low side power MOSFETs, respectively. In general data sheets, the Cgs is referred as "Ciss" which is the input capacitance. Cgd1 and Cgd2 are the capacitances 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 showed below www.richtek.com 6 DS9602-03 March 2004 RT9602 lgs1 = C gs1 dVg1 C gs1 x 12 = dt tr1 (1) from equation. (3) and (4) l gs1 = lgs2 = C gs2 dVg2 C gs2 x 12 = dt tr2 (2 ) lgd1= Cg1 12V dV = Cgd1 tr1 dt (3) - 12 14 x 10 500 x 10 lgs2 = According to the design of RT9602, before driving the gate of the high side MOSFET up to 12V (or 5V), the low side MOSFET has to be off; and the high side MOSFET is turned off before the low side is turned on. From Figure 1, the body diode "D2" had been turned on before high side MOSFETs turned on 380 x 10 x 12 - 9 - 12 = 0.326 x (12 + 12) = 0.4(A)(8) - 9 30 x 10 the total current required from the gate driving source is Ig1 = Igs1 + Igd1 = (1.428 + 0.326) = 1.745(A) Ig2 = I gs2 + I gd2 = (0.88 + 0 .4 ) = 1.28(A) Figure 2. shows the schematic circuit of a two-phase synchronous-buck converter to implement the RT9602. The converter operates for the input rang from 5V to 12V. (4 ) 1.2uH Cb1 1uF C2 1uF C1 1000uF 12 Q1 It is helpful to calculate these currents in a typical case. Assume a synchronous rectified BUCK converter, input voltage Vi = 12V, Vg1 = Vg2 = 12V. The high side MOSFET is PHB83N03LT whose Ciss = 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 PHB83N03LT x 12 14 x10- 9 = 1.428 (A ) (5) 13 2uH 11 BOOT1 UGATE1 PHASE1 C5 1500uF PVCC PWM1 PHB95N03LT Q2 4 LGATE1 PWM2 9 C4 1uF C3 1000uF 8 Q3 L3 12V 5 1 PWM1 7 2 PWM2 UGATE2 PHASE2 GND LGATE2 PGND 3 6 PHB83N03LT 2uH C6 1500uF C7 10 1uF 14 VCC RT9602 Q4 Cb2 1uF PHB95N03LT 1660x10 R1 L1 Vin 12V L2 lgs1 = (10) By a similar calculation, we can also get the sink current required from the turned off MOSFET. D1 dV Vi + 12V = C gd2 dt t r2 - 12 (9) Layout Consider Before the low side MOSFET is turned on, the Cgd2 have been charged to Vi. Thus, as Cgd2 reverses its polarity and g2 is charged up to 12V, the required current is lgd2 = C gd2 (A)(7) BOOT2 10 D2 V CORE Figure 2. Two- Phase Synchronous-Buck Converter Circuit lgs2 = 2200x10- 12 x12 30x10- 9 DS9602-03 March 2004 = 0.88 (A) (6) www.richtek.com 7 RT9602 When layout the PC board, 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 junction of Q1, Q2, L2 and Q3, Q4, L4 should be very close. The connection from Q1, and Q3 drain to positive sides of C1, C2, C3, and C4; the connection from Q2, and Q4 source to the negative sides of C1, C2, C3, and C4 should be as short as possible. Next, the trace from Ugate1, Ugate2, Lgate1, and Lgate2 should also be short to decrease the noise of the driver output signals. Phase1 and phase2 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 C7 should be connected to PGND directly. Furthermore, the bootstrap capacitors (Cb1, Cb2) should always be placed as close to the pins of the IC as possible. Select the Bootstrap Capacitor Figure 3. shows part of the bootstrap circuit of RT9602. The VCB (the voltage difference between BOOT1 and PHASE1 on RT9602) 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 CB has to be selected properly. It is determined by following constraints. In practice, a low value capacitor CB will lead the overcharging that could damage the IC. Therefore to minimize the risk of overcharging and reducing the ripple on VCB, the bootstrap capacitor should not be smaller than 0.1F, and the larger the better. In general design, using 1F can provide better performance. At least one low-ESR capacitor should be used to provide good local de-coupling. Here, to adopt either a ceramic or tantalum capacitor is suitable. Power Dissipation For not exceeding the maximum allowable power dissipation to drive the IC beyond the maximum recommended operating junction temperature of 125C, it is necessary to calculate power dissipation appropriately. This dissipation is a function of switching frequency and total gate charge of the selected MOSFET. Figure 4. shows the power dissipation test circuit. CL and CU are the UGATE and LGATE load capacitors, respectively. The bootstrap capacitor value is 0.01F. +5V or +12V 0.01uF +5V or +12V UGATE1 2N7000 1uF +12V CU PHASE1 LGATE1 1uF 2N7000 33 CL PVCC PWM1 Vin RT9602 0.01uF BOOT1 PWM2 UGATE2 + UGATE1 PHASE1 CB VCB - PVCC CU PGND PHASE2 GND LGATE1 2N7000 LGATE2 2N7000 33 CL PGND Figure 4. RT9602 Power Dissipation Test Circuit Figure 3. Part of Bootstrap Circuit of RT9602 www.richtek.com 8 Figure 5. shows the power dissipation of the RT9602 as a function of frequency and load capacitance. The value of the CU and CL are the same and the frequency is varied from 100kHz to 600kHz. PVCC and VCC is 12V and connected together. Figure 6.shows the same characterization for PVCC tied to 5V instead of 12V. DS9602-03 March 2004 RT9602 The method to improve the thermal transfer is to increase the PC board copper area around the RT9602, first. Then, adding a ground pad under IC to transfer the heat to the peripheral of the board. Power Dissipation vs. Frequency 800 CU=CL 700 =5nF CU=CL=4nF Power (mW) 600 CU=CL=3nF 500 Power on Over-Voltage Protection Function The RT9602 provides a protect function which can avoid some short condition happened before power on. CU=CL=2nF 400 300 CU=CL=1nF The following discussion about the power on over-voltage protection function of RT9602 is based on the experiments of the high side MOSFET directly shorted to 12V. The test circuit as shown in the typical application circuit (with RT9241A/B dual-channel synchronous-rectified buck controller) the VCC and the phase signals are measured on the VCC pin and the phase pin of RT9602. The LGATE signal is measured on the gate terminal of MOSEFET. 200 100 PVcc=Vcc=12V 0 0 100 200 300 400 500 600 Frequency (kHz) Figure 5. Power Dissipation vs. Frequency (RT9602) Power Dissipation vs. Frequency 250 CU=CL=4nF Power(mW) 240 230 CU=CL 220 =5nF VVcc > CU=CL=2nF PPEASE > CU=CL=1nF 210 lLGATE > 200 hrountCurrent > CU=CL=3nF 190 180 Through 12V RT9809-20CV 170 Time (50ms) 50 100 150 200 250 300 350 400 450 Figure 7 High Side Direct Short Frequency(kHz) Figure 6. Power Dissipatin vs. Frequency, PVCC = 5V The operating junction temperature can be calculated from the power dissipation curves (Figure 5 and Figure 6). Assume the RT9602' s PVCC = VCC=12V, operating frequency is 200kHz, and the CU=CL=1.5nF which emulate the input capacitances of the high side and low side power MOSFETs. From Figure 5, the power dissipation is 500mW. In RT9602, the package thermal resistance JA is 127.67C/ W, the operating junction temperature is calculated as: TJ = 127.67 C/W x 500mW+ 25C = 88.84C where the 25 C is the ambient temperature. VVcc > PPEAS > lLGATE > lV CORE> (11) Time (50ms) Figure 8. High Side Direct Short DS9602-03 March 2004 www.richtek.com 9 RT9602 VVcc > PPEASE > lLGATE > lPWM1 > Time (25ms) Figure 9. High Side Direct Short Referring to Figure 7, when VCC exceeds 1.5V, RT9602 turns on the LGATE to clamp the Phase through the low side MOSFET. During the turn-on of the low side MOSFET, the current of ATX 12V is limited at 25A although the maximum current of ATX 12V listed on the case of ATX is 15A. After the ATX 12V shuts down, the VCC falls slowly. Please note that the trigger point of RT9602 is at 1.5V VCC, and the clamped value of phase is at about 2.4V. Next, reference to Figure 8, it is obvious that since the Phase voltage increases during the power-on, the VCORE increases correspondingly, but is gradually decreased as LGATE and VCC decrease. In Figure 9, during the turn-on of the low side MOSFET, the VCC is much less than 12V, thus the RT9241A/B keeps the PWM signal at high impedance state. www.richtek.com 10 DS9602-03 March 2004 RT9602 Outline Dimension H A M J B F C I D Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 8.534 8.738 0.336 0.344 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.178 0.254 0.007 0.010 I 0.102 0.254 0.004 0.010 J 5.791 6.198 0.228 0.244 M 0.406 1.270 0.016 0.050 14-Lead SOP Plastic Package RICHTEK TECHNOLOGY CORP. RICHTEK TECHNOLOGY CORP. Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 8F-1, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com DS9602-03 March 2004 www.richtek.com 11