Si9978DW

Vishay Siliconix

S-60752—Rev. D, 05-Apr-99

FaxBack 408-970-5600, request 70011

4

www.siliconix.com

PIN CONFIGURATION

PIN DESCRIPTION

pin to allow connection of a decoupling capacitor. A minimum

of 1 µF is recommended.

The EN input allows normal operation when at logic “1”, and

turns all gate drive outputs off when at logic “0”.

When the

mode pin is at logic “1”, EN controls the entire H-bridge. When

the mode pin is at logic “0”, this pin becomes the ENABLE pin

for half-bridge A.

The function of this pin is determined by the MODE pin.

When the MODE pin is at logic “1”, it is the DIR pin, and when

As the DIR input, it is the direction control for the H-bridge,

and determines which diagonal pair of power MOSFETs is

anti-phase PWM control, the DIR input serves as the PWM

input.

When at logic “1”, the high-side MOSFET is turned on, and

when at logic “0”, the low-side MOSFET is turned on.

With the mode pin at logic “1”, this pin is the PWM input. It

controls the switching of the active diagonal pair. A logic “1”

turns the active MOSFETs on, while a logic “0” turns it off. The

QS input determines whether the bottom or both bottom and

top

MOSFETs

are

switched.

When

implementing

an

anti-phase PWM control, the PWM input is connected to a

logic “1”. When the mode pin is at logic “0”, this pin becomes

the ENABLE pin for half-bridge B.

With the mode pin at logic “1”, this input determines whether

the bottom MOSFETs of the H-bridge or both bottom and top

MOSFETs switch in response to the PWM signal. A logic “1”

on this input enables only the bottom MOSFETs. This is the

default condition as this pin is pulled up internally. When this

pin is pulled to ground, both the bottom and top MOSFETs are

enabled.

This input controls the B half-bridge when the MODE pin is at

logic “0”. When at logic “1”, the high-side MOSFET is turned

on, and when at logic “0”, the low-side MOSFET is turned on.

Pin 6: MODE

This input determines whether the Si9978 functions as an

H-bridge or as two independent half-bridges. When the

MODE pin is at logic “1”, the Si9978 functions as an H-bridge,

and when MODE is at logic “0”, it functions as two

independent half-bridges.

Pin 7: BRK

When this input and MODE are at logic “1”, both bottom gate

drives are switched high, turning on the bottom MOSFETs.

When this input is at logic “0”, the Si9978 operates normally.