6

Functional description

6.1

Gate driving power supply and UVLO

The STGAP2HD is a flexible and compact gate driver with 4 A output current and rail-to-rail outputs. The device

allows to implement either unipolar or bipolar gate driving.

Figure 3. Power supply configuration for unipolar and bipolar gate driving

Unipolar gate driving

Bipolar gate driving

VH

VL

GON_A

GNDISO_B

VH_B

GON_B

GOFF_B

CLAMP_B

GNDISO_A

VH_A

GOFF_A

CLAMP_A

VDD

GND

INA

INB

SD

iLOCK

BRAKE

I

S

O

L

A

T

I

O

N

Control

Logic

VH

VL

VH

VH

GON_A

GNDISO_B

VH_B

GON_B

GOFF_B

CLAMP_B

GNDISO_A

VH_A

GOFF_A

CLAMP_A

VDD

GND

INA

INB

SD

iLOCK

BRAKE

I

S

O

L

A

T

I

O

N

Control

Logic

Undervoltage protection is available on VH_x supply pin. A fixed hysteresis sets the turn-off threshold, thus

avoiding intermittent operation.

When VH_x voltage goes below the VHoff threshold, the output buffer goes into “safe state”. When VH_x voltage

reaches the VHon threshold, the device returns to normal operation and sets the output according to actual input

pins status.

The VDD and VH_x supply pins must be properly filtered with local bypass capacitors. The use of capacitors with

different values in parallel provides both local storage for impulsive current supply and high-frequency filtering.

The best filtering is obtained by using low-ESR SMT ceramic capacitors, which are therefore recommended. A

100 nF ceramic capacitor must be placed as close as possible to each supply pin, and a second bypass capacitor

with value in the range between 1 μF and 10 μF should be placed close to it.

6.2

Power-up, power-down and ‘safe state’

The following conditions define the “safe state”:

•

GOFF = ON state

•

GON = high impedance

Such conditions are maintained at power-up of the isolated side (VH_x < VHon) and during whole device power-

down phase (VH < VHoff), regardless of the value of the input pins.

The device integrates a structure which clamps the driver output to a voltage not higher than SafeClp when VH

voltage is not high enough to actively turn the internal GOFF MOSFET on. If VH_x positive supply pin is floating

or not supplied, the GOFF pin is therefore clamped to a voltage smaller than SafeClp.

If the supply voltage VDD of the control section of the device is not supplied, the output is put in safe state, and

remains in such condition until the VDD voltage returns within operative conditions.

After power-up of both isolated and low voltage side the device output state depends on the input pins' status.

STGAP2HD

Functional description

DS13652 - Rev 2

page 10/24