TPS2811, TPS2812, TPS2813, TPS2814, TPS2815

DUAL HIGH-SPEED MOSFET DRIVERS

SLVS132D – NOVEMBER 1995 – REVISED NOVEMBER 1997

19

POST OFFICE BOX 655303

APPLICATION INFORMATION

Figures 33 through 47 illustrate the performance of the TPS2811 driving MOSFETs with clamped inductive

loads, similar to what is encountered in discontinuous-mode flyback converters. The MOSFETs that were tested

range in size from Hex-1 to Hex-4, although the TPS28xx family is only recommended for Hex-3 or below.

The test circuit is shown in Figure 32. The layout rules observed in building the test circuit also apply to real

applications. Decoupling capacitor C1 is a 0.1-

TPS2811, with short lead lengths. The connection between the driver output and the MOSFET gate, and

between GND and the MOSFET source, are as short as possible to minimize inductance. Ideally, GND of the

driver is connected directly to the MOSFET source. The tests were conducted with the pulse generator

frequency set very low to eliminate the need for heat sinking, and the duty cycle was set to turn off the MOSFET

when the drain current reached 50% of its rated value. The input voltage was adjusted to clamp the drain voltage

at 80% of its rating.

As shown, the driver is capable of driving each of the Hex-1 through Hex-3 MOSFETs to switch in 20 ns or less.

Even the Hex-4 is turned on in less than 20 ns. Figures 45, 46 and 47 show that paralleling the two drivers in

a package enhances the gate waveforms and improves the switching speed of the MOSFET. Generally, one

driver is capable of driving up to a Hex-4 size. The TPS2811 family is even capable of driving large MOSFETs

that have a low gate charge.

Regulator

R1

50

Ω

1

2

3

4

8

7

6

5

C1

0.1

µF

C2

4.7

µF

+

–

VDS

Q1

Current

Loop

L1

CR1

+

VI

VDS

VGS

VCC

Figure 32. TPS2811 Driving Hex-1 through Hex-4 Devices