6

Functional description

6.1

Gate driving power supply and UVLO

The STGAP2GS is a flexible and compact gate driver with 3 A output current and rail-to-rail outputs. The device

allows implementation of either unipolar or bipolar gate driving.

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

VDD

I

S

O

L

A

T

I

O

N

VH

GOFF

GNDISO

VDD

GND

IN+

IN-

GON

+

VH

VDD

+

VH

+

VL

I

S

O

L

A

T

I

O

N

VH

GOFF

GNDISO

VDD

GND

IN+

IN-

GON

Unipolar gate driving

Bipolar gate driving

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

intermittent operation.

When VH voltage falls below the VHoff threshold, the output buffer enters a “safe state”. When VH 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 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 and 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 established at the end of the power-up of the isolated side (VH < VHon) and maintained until

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

When driving GaN switches, it is recommended to provide a smooth voltage transient to the VH supply pin during

power ON, and to limit the VH rising slope according to Table 3.

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 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 sides, the device output state depends on the status of the input

pins.

STGAP2GS

Functional description

DS14152 - Rev 1

page 8/20