ST7MC2 datasheet(193/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROLLER (Cont’d)

10.6.9.3 Dead Time Generator

When using typical triple half bridge topology for

power converters, precautions must be taken to

avoid short circuits in half bridges. This is ensured

by driving high and low side switches with comple-

mentary signals and by managing the time be-

tween the switching-off and the switching-on in-

stants of the adjacent switches.

This time is usually known as deadtime and has to

be adjusted depending on the devices connected

to the PWM outputs and their characteristics (in-

trinsic delays of level-shifters, delays due to power

switches,...).

When driving motors in six-step mode, the dead-

time generator function also allows synchronous

rectification to be performed on the switch adja-

cent to the one where PWM is applied to reduce

conduction losses.

For each of the three PWM channels, there is one

6-bit Dead Time generator available.

It generates two output signals: A and B.

The A output signal is the same as the input phase

signal except for the rising edge, which is delayed

relative to the input signal rising edge.

The B output signal is the opposite of the input

phase signal except the rising edge which is de-

layed relative to the input signal falling edge.

Figure 111 shows the relationship between the

output signals of the deadtime register and its in-

puts.

If the delay is greater than the width of the active

phase (A or B) then the corresponding pulse is not

generated (see Figure 112 and Figure 113).

Figure 111. Dead Time waveforms

Figure 112. Dead time waveform with delay greater than the negative PWM pulse

Reference

Output A

Output B

Delay

Input signal

Input

Output A

Output B

Delay

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