DS9603-00  November 2003
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Features
l
Drives Two N-Channel MOSFETs l Adaptive Shoot-Through Protection l Supports High Switching Frequency - Fast Output Rise Time    - Propagation Delay 40ns
l Tri-State Input for Bridge Shutdown
l Supply Over-Voltage Protection above Maximum Voltage Rating
l Supply Under-Voltage Protection
l Upper MOSFET Direct Shorted Protection l Small SOP-8 Package
Applications
l
Core Voltage Supplies for Intel Pentium ® 4, AMD ®Athlon TM  Microprocessors
l High Frequency Low Profile DC-DC Converters l High Current Low Voltage DC-DC Converters l
IA Equipments
Synchronous-Rectified Buck MOSFET Drivers
General Description
The RT9603 is a high frequency, dual MOSFET drivers specifically designed to drive two power N-Channel 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 N-Channel MOSFETs.
Both drivers incorporate adaptive shoot-through protect-ion to prevent upper and lower MOSFETs from conduct-ing 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 power-on 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.
Pin Configurations
(TOP VIEW)
SOP-8
BST VCC
NC IN DRVH DRVL
PGND SW
RT9603
C : Commercial Standard
Ordering Information
Typical Application Circuit
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
+12V VCORE
ISPx ISNx
PWM INPUT
DS9603-00  November 2003
www.richtek
Function Block Diagram
Timing Diagram
IN
DRVH DRVL
VCC
BST
DRVH SW
DRVL PGND
Absolute Maximum Ratings (Note 1)
l Supply Voltage (V CC)------------------------------------------------------------------------------------15V
l BST to SW------------------------------------------------------------------------------------------------15V
l SW to GND-----------------------------------------------------------------------------------------------−4V to 15V
l PWM Input Voltage-------------------------------------------------------------------------------------GND - 0.3V to 7V
l DRVH------------------------------------------------------------------------------------------------------V SW - 0.3V to V BST + 0.3V
l DRVL-------------------------------------------------------------------------------------------------------GND - 0.3V to V VCC + 0.3V l Package Thermal Resistance
SOP-8, θJA------------------------------------------------------------------------------------------------67°C/W
adaptivel Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------260°C
l Storage Temperature Range-------------------------------------------------------------------------−40°C to 150°C
l ESD Susceptibility (Note 2)
HBM--------------------------------------------------------------------------------------------------------2kV
Recommended Operating Conditions (Note 3)
l Supply Voltage, V CC-------------------------------------------------------------------------------------------------12V ±10%
l Ambient Temperature Range-------------------------------------------------------------------------------------0°C to 70°C
l Junction Temperature Range------------------------------------------------------------------------------------0°C to 125°C
Electrical Characteristics
(Recommended Operating Conditions, T A= 25°C unless otherwise specified)
To be continued
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 1.5kΩ resistor into each pin.
Note 3. The device is not guaranteed to function outside its operating conditions.
DS9603-00  November 2003www.richtek
Applications Information
The RT9603 is designed to drive both high side and low side N-Channel 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 V gs 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.In Figure 1, the current I g1 and I g2 are required to move the gate up to 12V. The operation consists of charging C gd and C gs. C gs1 and C
gs2
are the capacitances from gate to source of the high side and the low side power MOSFETs, respectively. In general data sheets, the C gs is referred as "C rss" which is the input capacitance. C gd1 and C gd2are the capacitances from gate to drain of the high side and the low side power MOSFETs, respectively and referred to the data sheets as "C rss" the reverse transfer capacitance. For example, t r1and t r2are the rising time of the high side and the low side power MOSFETs respec
tively, the required current I gs1and I gs2
,
are showed below:
(2)
t
12
C
dt
dVg2
C
l
(1)
t
12
C
dt
dVg1
C
l
r2
gs2
gs2
gs2
r1
gs1
gs1
gs1
×
=
=
×
=
=
Figure 1. Equivalent Circuit and Associated Waveforms V
V
V OUT V
GND

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