33937 datasheet(36/48 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

33937

FUNCTIONAL DEVICE OPERATION

LOGIC COMMANDS AND REGISTERS

DEADTIME COMMAND

Deadtime prevents the turn-on of both transistors in the

same phase until the deadtime has expired. The deadtime

timer starts when a FET is commanded off (see Figure 6 and

Figure 16). The deadtime control is disabled by enabling the

FULLON mode.

The deadtime is set by sending the DEADTIME command

(100x xxx1), and then sending a calibration pulse of CS. This

pulse must be 16 times longer than the required deadtime

(see Figure 21). Deadtime is measured in cycle times of the

internal time base, fTB. This measurement is divided by 16

and stored in an internal register to provide the reference for

timing the deadtime between high and low gate transactions

in the same phase.

For example: the internal time base is running at 20 MHz

and a 1.5 µs deadtime is required. First a DEADTIME

command is sent (using the SPI), then a CS is sent. The CS

pulse is 16*1.5 = 24 µs wide. The IC measures this pulse as

24000 ns/50 ns = 480 clock cycles and stores 480/16 = 30 in

the deadtime register. Until the next deadtime calibration is

performed, 30 clock cycles will separate the turn off and turn

on gate signals in the same phase. The worst case error

immediately after calibration will be +0/-1 time base cycle, for

this example +0 ns/-50 ns. Note that if the internal time base

drifts, the effect on dead time will scale directly.

Sending a ZERO DEADTIME command (100x xxx0) sets

the deadtime timer to 0. However, simultaneous turn-on of

High Side and Low Side FETs in the same phase is still

prevented unless the FULLON command has been

transmitted. There is no calibration pulse expected after

receiving the ZERO DEADTIME command.

After RESET, deadtime is set to the maximum value of 255

time base cycles (typically 15 µs).

The IC ignores any SPI data that is sent during the

calibration pulse. If there are any transitions on SI or SCLK

while the Deadtime CS pulse is low, a Framing Error will be

generated, however, the CS pulse will be used to calibrate

the deadtime

Figure 21. Deadtime Calibration

Table 14. .DEADTIME Command

SPI Data Bits

765

432

Write

100

ZERO/

CALIBRATE

Reset

xxx

SCLK

DEADTIME

Command

Deadtime Calibration Pulse

Deadtime

Command

SCLK

33937 Datasheet(PDF) 36 Page - Freescale Semiconductor, Inc

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