STCMB1 datasheet(40/59 Pages) STMICROELECTRONICS

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Application information

STCMB1

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DocID028958 Rev 4

Figure 22. Adaptive dead time generation made more robust

Details of the adaptive dead time generator and its operation are given in the following.

The actual dead time TD that can be observed during the operation does not depend only

on the adjustment circuit of Figure 20 on page 36. This fact can be explained with the aid of

the oscilloscope picture shown in Figure 21 on page 38.

It shows a detailed view of the low-to-high transition of the half-bridge midpoint (waveform

labeled HB) along with the high-side gate drive (HVG) and the low-side gate drive (LVG).

Clearly, the comments that follow apply to the high-to-low transition as well.

There are three contributors to TD:



The turn-off delay tOFF of the power MOSFET, which depends on the input

characteristics of the specific MOSFET and the speed its gate is driven



The transition time TT the half-bridge midpoint takes for a rail-to-rail swing



The detection time tdet that elapses from the end of the half-bridge midpoint swing to

the gate drive signal of the other MOSFET going high; this includes the detection time

as well as the propagation delay along the downstream logic circuitry up to the driver

output.

It is important to point out that the value of TD_MIN specified in the electrical characteristics is

essentially tdet: therefore the minimum observable TD will always be longer. TD_MAX,

instead, is counted starting from the negative-going edge of the gate drive signal.

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