UCD8220PWPR datasheet(21/32 Pages) TI

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UCD8220, UCD8620

SLUS652B – MARCH 2005 – REVISED SEPTEMBER 2005

When the CS voltage is below ILIM, the driver output

restart the device in the event that it is not operating

follows the PWM command. The CLF digital output

properly. But these peripherals typically do not react

flag is monitored by the host controller to determine

fast enough to save the power stage. The UCD87K’s

when a current limit event occurs, and to then apply

local current limit comparator provides the required

the appropriate algorithm to obtain the desired current

fast protection for the power stage.

limit profile (i.e. straight line, fold back, hickup, or

The CS threshold is 25 mV below the ILIM voltage. If

latch-off).

the user attempts to command zero current while the

A benefit of this local protection feature is that the

CS pin is at ground, the CLF flag latches high until

UCD8620 devices protects the power stage if the

the CLK pin receives a pulse. At start-up, it is

software code in the digital controller becomes cor-

necessary to ensure that the ILIM pin is always

rupted. If the controller’s PWM output stays high, the

greater than the CS pin for the handshaking to work.

local current sense circuit turns off the driver output

If for any reason the CS pin comes to within 25 mV of

when an overcurrent event occurs. The system then

the ILIM pin during start-up, then the CLF flag is

goes into retry mode because most DSP and

latched high and the digital controller must poll the

microcontrollers

have

on-board

watchdog,

UCD8620 device, by sending it a narrow CLK pulse.

brown-out, and other supervisory peripherals to

If a fault condition is not present, the CLK pulse

resets the CLF signal to low indicating that the

UCD8620 device is ready to process power pulses.

UCD8220PWPR Datasheet(PDF) 21 Page - Texas Instruments