Si9978

Vishay Siliconix

Document Number: 70011

S-40804—Rev. E, 26-Apr-04

www.vishay.com

5

PIN DESCRIPTION (CONT’D)

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.

This is an open drain output which is active low. When the

MODE pin is at logic “1”, this pin functions as CL and indicates

that the H-bridge is in current limit. It stays low for the duration

of the current limit one-shot. With the MODE pin at logic “0”, it

serves as the FAULT output for half-bridge B to indicate when

an undervoltage or overcurrent condition is detected. When

indicating an overcurrent condition, the output stays low for the

duration of the current limit one-shot. The FAULT output resets

automatically when the condition clears.

This is an open drain output which is switched low when an

undervoltage or overcurrent condition is detected. When

indicating an overcurrent condition, the output stays low for the

duration of the current limit one-shot. When the MODE pin is

at logic “1”, this pin is the H-bridge FAULT output. With the

MODE pin at logic “0”, it serves as the FAULT output for

half-bridge A. The FAULT output resets automatically when the

condition clears.

Pin 10: NC

No internal connection.

The timing resistor and capacitor for the current limit one-shot

are connected to this pin. The values of the resistor and

capacitor determine the off time set by the one-shot. The

one-shot is triggered when the current limit comparator detects

an overcurrent condition.

The timing resistor and capacitor for the current limit one-shot

are connected to this pin. The values of the resistor and

capacitor determine the off time set by the one-shot. The

one-shot is triggered when the current limit comparator detects

an overcurrent condition.

These are the overcurrent sense inputs. Internally, they are

connected to the noninverting inputs of the current limit

comparators. Externally they are connected to the source(s) of

the low-side MOSFET(s) and the current sense resistor.

Pin 15: GND

The GND pin is the ground return for V+ and the ground

reference for the logic. Also, this is the ground reference input

for the current limit comparators and is connected to the

ground side of the internal 100-mV references. This pin should

be connected directly to the ground side of the current sensing

resistors.

These pins drive the gates of the low-side power MOSFETs.

These pins drive the gates of the high-side power MOSFETs.

These are the source connections of the high-side power

MOSFETs, the drain of the external low-side power MOSFET,

the negative terminal of the bootstrap capacitor, and the output

for each half-bridge.

These are the connections for the positive terminals of the

used for most applications.

Pin 24: V+

This is the only external power supply required for the Si9978,

and must be the same supply used to power the H-bridge it is

driving. The Si9978 powers the low-voltage logic, low-side

gate driver, and bootstrap/ charge pump circuits from

self-contained voltage regulators which require only a

bootstrap capacitor on the CAP pins.

No voltage sensing circuitry monitors V+ directly; however, the

low-voltage, internally generated supply and the bootstrap

voltage (which are derived from V+) are directly protected by

undervoltage monitors.