AN2123

Application schematic

11/15

7 Application schematic

The TD351 application design presented hereafter is based on the active Miller clamp concept. With this

function, the high-side driver can be supplied with a bootstrap system instead of using a floating positive/

negative supply. This concept is applicable to low- and medium-power systems, up to about 10 kW. Main

benefit of this is to reduce the global application cost by making the supply system simpler. Figures 16

shows the half bridge design concept using the TD35x.

It should be highlighted that the active Miller clamp is fully managed by the TD35x and doesn’t require any

special action from the system controller.

The TD351 is able to drive 1200 V IGBT modules up to 50 A or 75 A (depending on IGBT technology and

manufacturer). Key parameters to consider are the TD351 peak output current (0.75 A source / 1.0 A

sink) and the IGBT gate resistor.

The values of gate resistors should be chosen starting with the recommended values from the IGBT

manufacturer. Thanks to the active Miller clamp function, the gate resistor can be tuned independently

from the Miller effect, which normally puts some constraints on the gate resistor. The benefit is to optimize

the turn-on and turn-off behavior, especially regarding switching losses and EMI issues.

Table 1 shows the recommended gate resistors values from two major IGBT module manufacturers, and

the peak gate current (with a 15 V supply) required for 10 A to 100 A IGBT modules. Approximate

application power is indicated.

Figure 16. TD35x application concept

VH

VL

Rb

5

TD35x

OUT

CLAMP

24V

+

Cb

4.7u

VH

VL

TD35x

OUT

CLAMP

high side

IN

IN

4k7

15V

15V

Vreg

VREF

4k7

VREF