LD7538

13

Leadtrend Technology Corporation

LD7538-DS-00

November 2012

saturation; it would cause damage for acting beyond the

maximum safety operating area. It

’s necessary to check

the characteristic of MOSFET.

Fig. 23 shows a totem pole architecture for the circuit of

OUT. The output high level of OUT is at around VCC-1.5V.

Refer to on-region characteristics of the MOSFET, check

the saturation current of VGSH(MIN) to make sure the

saturation current is high enough to activate MOSFET to

operate in ohmic region. In order not to decrease the

voltage across VG, it’s recommended not to connect a

forward diode between the gate of the MOSFET and OUT

pin, for example like Fig 24.

In addition, pulling VCC level high can keep VGSH in high

level, for example:

1.

Increase NX value to pull VCC level high.

2.

Increase

VCC capacitance to improve VCC’s

performance to drop at startup transient, shown as Fig 25.

VDS

ID

Ohmic Region

Saturation Region

VGS1

VGS2

VGS3

VGS4

VGS5

VGS5 > VGS4 > VGS3 > VGS2 > VGS1

Cut-off region

Fig. 22

CS

GND

OUT

VGS

VS

VCC

VG

VD

VDS

RS

NX

CVCC

Fig. 23

CS

GND

OUT

VCC

VG

RS

NX

CVCC

Fig. 24

VCC

t

Large Capacitance of VCC Cap

Small Capacitance of VCC Cap

UVLO(on)

Fig. 25