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RT9603
Synchronous-Rectified Buck MOSFET Drivers
General Description
The RT9603 is a high frequency, dual MOSFET drivers specifically designed to drive two power N-MOSFETs in a synchronous-rectified buck converter topology. The device combined with the RT924x series of multi-phase PWM controllers and MOSFETs form a complete core voltage regulator solution for advanced microprocessors. The output drivers in the RT9603 can efficiently switch power MOSFETs at frequencies up to 500kHz. It shall be taken into account the thermal consideration when the switching frequency above 500kHz. Each driver is capable of driving a 3nF load in 30/40ns rise/fall time with fast propagation delay from input transition to the gate of the power MOSFET. The device implements boot-strapping on the upper gate with only an external capacitor and a diode required. This reduces implementation complexity and allows the use of higher performance, cost effective NMOSFETs. Both drivers incorporate adaptive shoot-through protection to prevent upper and lower MOSFETs from conducting simultaneously and shorting the input supply. An unique feature of the RT9603 driver is the addition of over-voltage protection in the event of upper MOSFET direct shorted before power-on. The RT9603 detects the fault condition during initial start-up, the internal poweron OVP sense circuitry will rapidly drive the output lower MOSFET on before the multi-phase PWM controller takes control. As a result, the input supply will latch into the shutdown state, thereby prevent the processor from damaged.
Features
Drives Two N-MOSFETs Adaptive Shoot-Through Protection Supports High Switching Frequency Fast Output Rise Time Propagation Delay 40ns Tri-State Input for Bridge Shutdown Supply Over-Voltage Protection above Maximum Voltage Rating Supply Under-Voltage Protection Upper MOSFET Direct Shorted Protection Small SOP-8 Package RoHS Compliant and 100% Lead (Pb)-Free
Applications
Core Voltage Supplies for Intel Pentium(R) 4, AMD(R) AthlonTM Microprocessors High Frequency Low Profile DC-DC Converters High Current Low Voltage DC-DC Converters IA Equipments
Ordering Information
RT9603 Package Type S : SOP-8 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard)
Note : RichTek Pb-free and Green 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. 100%matte tin (Sn) plating.
Pin Configurations
(TOP VIEW)
BST VIN NC VCC 2 3 4 8 7 6 5 DRVH SW PGND DRVL
SOP-8
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RT9603
Typical Application Circuit
+12V R1 10 +12V D1
1N4148
1 4 C1 1uF 3 VCC NC BST C2
C3 1uF
C4 1000uF/16V
1uF
RT9603
DRVH SW DRVL
8 7 5 PHB95N03LT
Q1 PHB83N03LT L1 2uH Q2 R2 2.4K R3 ISNx 2.4K C5 x1500uF VCORE C6 x1500uF
PWM INPUT
2
VIN 6
PGND
ISPx
Note: The traces that run from the controller ISPx and ISNx pins, should be run together next to each other and Kelvin connected to the Q2. Place both R2 and R3 as close to the PWM Controller as possible.
Functional Pin Description
Pin No. Pin Name Pin Function Floating bootstrap supply pin for the upper gate drive. Connect the bootstrap capacitor 1 BST between this pin and the SW pin. The bootstrap capacitor provides the charge to turn on the upper MOSFET. Accepts a logic control signal. Connect this pin to the PWM output of the controller. 2 3 4 5 6 7 8 VIN NC VCC DRVL PGND SW DRVH If the PWM signal enters and remains within the shutdown window, the output drivers are disabled and both MOSFET gates are pulled and held low. No Internal Connection. Supply Input. Connect to +12V supply. Place a bypass capacitor from this pin to PGND. Lower gate drive output. Should be connected to the lower MOSFET gate. Common Ground. Upper driver return. Should be connected to the common node of upper and lower MOSFETs. The SW voltage is monitored for adaptive shoot-through protection. Upper gate drive output. Should be connected to the upper MOSFET gate.
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RT9603
Function Block Diagram
VCC
Internal 5V R VIN R Control Logic
BST Shoot-Through Protection DRVH SW Power-On OVP VCC Shoot-Through Protection DRVL PGND
Timing Diagram
VIN
TPDDRVH TRDRVH TFDRVH
DRVH
DRVL
TFDRVL TRDRVL TPDDRVL
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RT9603
Absolute Maximum Ratings
(Note 1) 15V 15V -5V to 15V -10V to 30V -0.3V to VCC+15V -0.3V to 42V GND - 0.3V to 7V VSW - 0.3V to VBST + 0.3V GND - 0.3V to VVCC + 0.3V 0.625W 160C/W 260C -40C to 150C 2kV 200V Supply Voltage, VCC ----------------------------------------------------------------------------------------BST to SW ----------------------------------------------------------------------------------------------------SW to GND DC ---------------------------------------------------------------------------------------------------------------< 200ns --------------------------------------------------------------------------------------------------------BST to GND DC ---------------------------------------------------------------------------------------------------------------< 200ns --------------------------------------------------------------------------------------------------------PWM Input Voltage -----------------------------------------------------------------------------------------DRVH ----------------------------------------------------------------------------------------------------------DRVL -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25C SOP-8 ----------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 4) SOP-8, JA ----------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 2) HBM (Human Body Mode) --------------------------------------------------------------------------------MM (Machine Mode) -----------------------------------------------------------------------------------------
Recommended Operating Conditions
(Note 3) Supply Voltage, VCC ----------------------------------------------------------------------------------------- 12V 10% Ambient Temperature Range ------------------------------------------------------------------------------- 0C to 70C Junction Temperature Range ------------------------------------------------------------------------------- 0C to 125C
Electrical Characteristics
(Recommended Operating Conditions, TA = 25C unless otherwise specified)
Parameter VCC Supply Current Power Supply Current Power-On Reset POR Threshold Hysteresis PWM Input Input Current Floating Voltage PWM_IN Threshold DRVH Rise Time DRVH Fall Time
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Symbol
Test Conditions
Min
Typ
Max
Units
IVCC
VBST = 12V, VPWM_IN = 0V
--
5
7
mA
VVCCRTH VVCCHYS IPWM_IN VPWMFL
VCC Rising
8.6 --
9.9 1.35
10.7 --
V V A V V V ns ns
VPWM_IN = 0V or 5V VCC = 12V
80 1.1 3.3 1.0 ---
127 2.1 3.7 1.26 30 40
150 3.7 4.3 1.5 ---
VPWMRTH PWM_IN Rising VPWMFTH PWM_IN Falling TRDRVH TFDRVH VVCC = 12V, 3nF load VVCC = 12V, 3nF load
To be continued
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RT9603
Parameter DRVL Rise Time DRVL Fall Time DRVH Turn-Off Propagation Delay DRVL Turn-Off Propagation Delay Shutdown Window Output Upper Drive Source Upper Drive Sink Lower Drive Source Lower Drive Sink RDRVH RDRVH RDRVL RDRVL VVCC = 12V VVCC = 12V VVCC = 12V VVCC = 12V Symbol TRDRVL TFDRVL TPDDRVH TPDDRVL Test Conditions VVCC= 12V, 3nF load VVCC = 12V, 3nF load VVCC = 12V, 3nF load VVCC = 12V, 3nF load Min ----1.0 ----Typ 30 30 40 35 -2 2.8 1.9 1.6 Max ----4.3 Units ns ns ns ns V
-----
Note 1. Stresses beyond those listed under "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 for extended periods may affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at T A = 25C on a low effective thermal conductivity test board of JEDEC 51-3 thermal measurement standard.
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RT9603
Application Information
The RT9603 is designed to drive both high side and low side N-MOSFET through externally input PWM control signal. It has power-on protection function which held DRVH and DRVL low before VCC up across the rising threshold voltage. After the initialization, the PWM signal takes the control. The rising PWM signal first forces the DRVL signal turns low then DRVH signal is allowed to go high just after a non-overlapping time to avoid shoot-through current. The falling of PWM signal first forces DRVH to go low. When DRVH and SW signal reach a predetermined low level, DRVL signal is allowed to turn high. The non-overlapping function is also presented between DRVH and DRVL signal transient. The PWM signal is acted as "High" if above the rising threshold and acted as "Low" if below the falling threshold. Any signal level enters and remains within the shutdown window is considered as "tri-state", the output drivers are disabled and both MOSFET gates are pulled and held low. If left the PWM signal (IN) floating, the pin will be kept at 2.1V by the internal divider and provide the PWM controller with a recognizable level. The RT9603 typically operates at frequency of 200kHz to 250kHz. It shall be noted that to place a 1N4148 or schottky diode between the VCC and BST pin as shown in the typical application circuit. 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 nano-amperes. Thus once the gate has been driven up to "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 d1 VIN Cgd1 Igs1 Ig2 Igd2 g1 g2 Igs2 Cgs2 s2 GND
Vg1 VSW +12V
s1 Cgs1 Cgd2 Igd1 Ig1 d2
L VOUT
D2
t Vg2 12V
t
Figure 1. Equivalent Circuit and Associated Waveforms 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 "Crss" 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:
l gs1 = C gs1
dVg1 C gs1 x 12 = dt t r1 dVg2 C gs2 x 12 = dt t r2
(1)
l gs2 = C gs2
(2)
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RT9603
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. Layout Consideration Figure 2 shows the schematic circuit of a two-phase synchronous buck converter to implement the RT9603. The converter operates from 5V to 12V of VIN.
L1 D1 + C2 1uF CB 1uF Q1 L2 2uH Q2
PHB83N03LT
lgd1 = C g1
dV 12V = C gd1 dt t r1
R1 4 VCC C4 10 1uF 12V
(3)
VIN 12V
1.2uH C1 1000uF
1 BST
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
DRVH SW
VCORE + C3 1500uF
7
RT9603
8
IN
2
PWM
PHB95N03LT
5
DRVL
PGND
6
lg d 2 = C g d 2
dV Vi + 12V = C gd2 dt t r2
(4 )
Figure 2. Two-Phase Synch. Buck Converter Circuit When layout the PCB, it should be very careful. The powercircuit section is the most critical one. If not configured properly, it will generate a large amount of EMI. The junction of Q1, Q2, L2 should be very close. Next, the trace from DRVH, and DRVL should also be short to decrease the noise of the driver output signals. SW 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 C4 should be connected to PGND directly. Furthermore, the bootstrap capacitors (CB) 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 RT9603. The VCB (the voltage difference between BST and SW on RT9603) 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.
It is helpful to calculate these currents in a typical case. Assume a synchronous rectified buck converter, input voltage VIN = 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
l gs1 =
1660 x 10
- 12 -9
x 12
14 x 10
2200 x 10
= 1.428 (A)
(5)
l gs2 =
- 12 -9
x 12
30 x 10
= 0.88 (A)
(6)
from equation. (3) and (4)
lgs1 = 380 x 10
- 12
x 12
14 x 10
-9
= 0.326 (A)
(7)
I gd2 =
500 x 10 -12 x (12 + 12) = 0.4(A) 30 x 10 - 9
(8)
the total current required from the gate driving source is
I g1 = I gs1 + I gd1 = (1.428 + 0.326) = 1.745(A)
(9)
I g2 = I gs2 + I gd2 = (0.88 + 0.4) = 1.28(A)
(10)
By a similar calculation, we can also get the sink current required from the turned off MOSFET.
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RT9603
1N4148
VIN
VCC BST DRVH SW VCC CB + VCB -
Figure 5 shows the power dissipation of the RT9603 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 1MHz.
Power Dissipation vs. Frequency
1000 900
CU=CL=3nF
Power Dissipation (mW)
DRVL PGND
800 700 600 500 400 300 200 100 0 0 200 400 600 800 1000
CU=CL=2nF
Figure 3. Part of Bootstrap Circuit of RT9603 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 decoupling. 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 DRVH and DRVL load capacitors, respectively. The bootstrap capacitor value is 0.01F.
10 +12V
1N4148
CU=CL=1nF
Frequency (kHz)
Figure 5. Power Dissipation vs. Frequency The operating junction temperature can be calculated from the power dissipation curves (Figure 5). Assume VCC=12V, operating frequency is 200kHz and the CU=CL=1nF which emulate the input capacitances of the high side and low side power MOSFETs. From Figure 5, the power dissipation is 100mW. For RT9603, the package thermal resistance JA is 160C/W, the operating junction temperature is calculated as : TJ = (160C/W x 100mW) + 25C = 41C where the ambient temperature is 25C. The method to improve the thermal transfer is to increase the PCB copper area around the RT9603 first. Then, adding a ground pad under IC to transfer the heat to the peripheral of the board. (11)
1uF CBST BST
+12V
VCC 1uF
DRVH
2N7002 CU 3nF
RT9603
SW 2N7002 PWM IN DRVL PGND
20 CL 3nF
Figure 4. Test Circuit
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RT9603
Over-Voltage Protection Function at Power-On An unique feature of the RT9603 driver is the addition of over-voltage protection in the event of upper MOSFET direct shorted before power-on. The RT9603 detects the fault condition during initial start-up, the internal poweron OVP sense circuitry will rapidly drive the output lower MOSFET on before the multi-phase PWM controller takes control. Figure 6 shows the measured waveforms with the high side MOSFET directly shorted to 12V.
VCC
SW
DRVL VCORE
Figure 6. Waveforms at High Side MOSFET Shorted Please note that the VCC trigger point to RT9603 is at 3V, and the clamped level on SW pin is at about 2.4V. Obviously since the SW pin voltage increases during initial start-up, the VCORE increases correspondingly, but it would quickly drop-off followed by DRVL and VCC decreased.
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RT9603
Outline Dimension
A
H M
J
B
F
C I D
Dimensions In Millimeters Symbol Min A B C D F H I J M 4.801 3.810 1.346 0.330 1.194 0.170 0.050 5.791 0.400 Max 5.004 3.988 1.753 0.508 1.346 0.254 0.254 6.200 1.270
Dimensions In Inches Min 0.189 0.150 0.053 0.013 0.047 0.007 0.002 0.228 0.016 Max 0.197 0.157 0.069 0.020 0.053 0.010 0.010 0.244 0.050
8-Lead SOP Plastic Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
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