Datasheet
SLVS132F − NOVEMBER 1995 − REVISED OCTOBER 2004
19
www.ti.com
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-µF ceramic device, connected between V
CC
and GND of the 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
+
−
V
DS
Q1
Current
Loop
L1
CR1
+
V
I
V
DS
V
GS
V
CC
Figure 32. TPS2811 Driving Hex-1 through Hex-4 Devices