MIC4609 datasheet(22/34 Pages) MICROCHIP

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MIC4609

DS20005531A-page 22

 2016 Microchip Technology Inc.

FIGURE 4-8:

Overcurrent Fault Sequence.

4.8.1

ISNS

The ISNS pin may be used to monitor motor winding

currents. The measurement is referenced to the

VSS pin and can sense the voltage across a low-side

current sense resistor or it may be connected to a

current sense transformer. The current sense resistor

is typically connected between the source pins

(MOSFET) or emitter pins (IGBT) of all three low-side

switches and power ground.

If the peak voltage on the ISNS pin exceeds the VISNS

threshold, it will cause all six outputs to latch off. A

blanking circuit on the ISNS comparator output

prevents noise from falsely tripping the overcurrent

circuit. The ISNS pin is internally pulled down to VSS

but may be externally connected to VSS ground for

improved noise immunity if the overcurrent feature is

not used.

4.8.2

RCIN

A capacitor connected to the RCIN pin determines the

amount of time the gate drive outputs are latched off

before they can be restarted.

During normal operation, the RCIN pin is internally

pulled low. Once an overcurrent condition is detected,

the RCIN pin capacitor is charged up by an internal

current source until the voltage reaches the

VRCIN+ threshold and the latch is reset. The outputs are

then enabled.

The delay time can be approximated by applying

Equation 4-1.

EQUATION 4-1:

4.8.3

FAULT

This open-drain output is asserted low for an

overcurrent condition or when the VDD voltage is below

the

UVLO

threshold.

will

de-assert

high-impedance state once the VDD rises above the

UVLO threshold or when the RCIN pin voltage has

reached the VRCIN+ threshold. During normal

operation, the internal pull-down MOSFET of the pin is

high impedance. A pull-up resistor must be connected

to this pin.

FAULT

RCIN Threshold

ISNS Threshold

Blanking

Time

ISNS

RCIN

Normal

Operation

Normal

Operation

OC Fault

tDLY

CRCIN VRCIN+



IRCIN

-----------------------------------------

Where:

CRCIN = External capacitance on the RCIN pin

IRCIN = RCIN pin current source

(typically 0.44 µA)

VRCIN+ = Internal comparator threshold

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