6

FN2853.5

April 4, 2006

Direct Drive of MOSFETs

Figure 11 shows interfaces between the ICL7667 and typical

switching regulator ICs. Note that unlike the DS0026, the

ICL7667 does not need a dropping resistor and speedup

capacitor between it and the regulator IC. The ICL7667, with

its high slew rate and high voltage drive can directly drive the

gate of the MOSFET. The SG1527 IC is the same as the

SG1525 IC, except that the outputs are inverted. This

inversion is needed since ICL7667 is an inverting buffer.

Transformer Coupled Drive of MOSFETs

Transformers are often used for isolation between the logic

and control section and the power section of a switching

regulator. The high output drive capability of the ICL7667

enables it to directly drive such transformers. Figure 11

shows a typical transformer coupled drive circuit. PWM ICs

with either active high or active low output can be used in

this circuit, since any inversion required can be obtained by

reversing the windings on the secondaries.

Buffered Drivers for Multiple MOSFETs

In very high power applications which use a group of

MOSFETs in parallel, the input capacitance may be very large

and it can be difficult to charge and discharge quickly. Figure

13 shows a circuit which works very well with very large

circuit may not be needed at frequencies greater than 10kHz

18

16

14

12

10

8

6

4

2

0

-2

0246

810

12

14

16

18

20

680pF

630pF

212pF

FIGURE 9. MOSFET GATE DYNAMIC CHARACTERISTICS

FIGURE 10A.

FIGURE 10B.

FIGURE 10. DIRECT DRIVE OF MOSFET GATES

SG1527

GND

B

A

ICL7667

+V

-V

15V

IRF730

IRF730

TL494

GND

C2

C1

ICL7667

+V

-V

15V

IRF730

IRF730

E2

E1

+15V

1K

1K

ICL7667