uPI Semiconductor Corp., http://www.upi-semi.com

Rev. F03, File Name: uP6281-DS-F0300

uP6281

3

Functional Description

The uP6281 is a dual, high voltage MOSFET driver optimized

for driving two N-Channel MOSFETs in a synchronous-

rectified buck converter. Each driver is capable of driving a

5000pF load with 30ns transition time. This device combined

with uPI multi-phase buck PWM controller forms a complete

core voltage regulator for advanced microprocessors.

The uP6281 features adaptive anti-shoot-through protection

that prevents cross-conduction of the external MOSFET

while maintains minimum deadtime for optimized efficiency.

Both gate drives are turned off by pulling low OD# pin or

high-impedance at PWM pin, preventing rapid output

capacitor discharge during system shutdowns.

Other feature is supply input under voltage lockout. The

uP6281 is available in thermal enhanced PSOP-8L or

WDFN3x3-8L packages.

Output Disable

Logic low of OD# disables the gate drivers and keep both

output low. Tie the OD# pin to controller power directly if

the output disable function is not used.

PWM Input

The PWM pin is a tri-state input. Logic high turns on the

high-side gate driver and turns off the low side gate driver

once the POR of VCC is granted and OD# is kept high.

Logic low turns off the high side gate driver and turns off

the low side gate driver.

High impedance input at PWM pin will keep both high-side

and low-side gate drivers low and turns off both MOSFETs.

The PWM pin voltage is kept around 2.0V by internal bias

resistors when floating.

Low Side Driver

The low-side driver is designed to drive a ground-referenced

N-Channel MOSFET. The bias to the low-side driver is

internally connected to VCC supply and GND. The low-

side driver output is out of phase with the PWM input when

it is enabled. The low side driver is held low if the OD# pin

is pulled low or high-impedance at PWM pin.

High-Side Driver

The high-side driver is designed to drive a floatingN-Channel

MOSFET. The bias voltage to the high-side driver internally

connected to BOOT and PHASE pins. An external

bootstrap supply circuit that is connected between BOOT

and PHASE pins provides the bias current for the high-

side gate driver.

The bootstrap capacitor C

BOOT is charged to VCC when

PHASE pin is grounded by turning on the low-side

MOSFET. The PHASE raises to V

IN when the high-side

MOSFET is turned on, forcing the BOOT pin voltage to V

IN

+ V

CC that provides voltage to hold the high-side MOSFET

on.

The high-side gate driver output is in phase with the PWM

input when it is enabled. The high-side driver is held low if

the OD# pin is pulled low or high-impedance at PWM pin.

Adaptive Shoot Through Protection

The adaptive shoot-through circuit prevents the high-side

and low-side MOSFETs from being ON simultaneously and

conducting destructive large current. It is done by turning

on one MOSFET only after the other MOSFET is off already

with adequately delay time.

At the high-side off edge, UGATE and PHASE voltages

are monitored for anti-shoot-through protection. The uP6281

will not begin to output low-side driver high until both (V

UGATE

- V

PHASE) and VPHASE are lower than 1.2V, making sure the

high-side MOSFET is turned off completely.

At the low-side off edge, LGATE voltage is monitored for

anti-shoot-through protection. The uP6281 will not begin

to output high-side driver high until V

LGATE is lower than

1.2V, making sure the low-side MOSFET is turned off

completely.