MIC4607 datasheet(21/42 Pages) MICROCHIP

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DS20005610A-page 21

MIC4607

the forward voltage drop of the internal diode). After the

low-side MOSFET is turned off and the AHO pin turns

on, the voltage across capacitor CB is applied to the

gate of the high-side external MOSFET. As the

high-side MOSFET turns on, voltage on the AHS pin

rises with the source of the high-side MOSFET until it

reaches VIN. As the AHS and AHB pins rise, the inter-

nal diode is reverse biased, preventing capacitor CB

from discharging. During this time, the high-side MOS-

FET is kept ON by the voltage across capacitor CB.

FIGURE 5-3:

MIC4607 Motor Driver

Example.

5.6

Programmable Gate Drive

The MIC4607 offers programmable gate drive,

meaning the MOSFET gate drive (gate-to-source

voltage) equals the VDD voltage. This feature offers

designers flexibility in selecting the proper MOSFETs

for a given application. Different MOSFETs require

different VGS characteristics for optimum RDSON

performance. Typically, the higher the gate voltage (up

to 16V), the lower the RDSON achieved. For example,

as shown in Figure 5-4, a NTMSF4899NF MOSFET

can be driven to the ON state with a gate voltage of

5.5V but RDSON is 5.2 mΩ. If driven to 10V, RDSON is

4.1 mΩ – a decrease of 20%.

In low-current applications, the losses due to RDSON

are minimal, but in high-current motor drive applica-

tions such as power tools, the difference in RDSON can

lower the efficiency, reducing run time.

FIGURE 5-4:

MOSFET RDSON vs. VGS.

5.7

Overcurrent Protection Circuitry

The MIC4607 provides overcurrent protection for the

motor driver circuitry. It consists of:

• A comparator that senses the voltage across a

current-sense resistor

• A latch and timer that keep all gate drivers off

during a fault

• An open-drain pin that pulls low during the fault.

If an overcurrent condition is detected, the FLT/ pin is

pulled low and the gate drive outputs are latched off for

a time that is determined by the DLY pin circuitry. After

the delay circuitry times out, a high-going edge on any

of the LI pins (for the MIC4607-1 version) or a low-going

edge on any of the PWM pins (for the MIC4607-2

version) is required to reset the latch, de-assert the FLT/

pin and allow the gate drive outputs to switch.

For additional information, refer to the Timing Diagrams

section as well as the Functional Diagram section.

5.7.1

ILIM

The ILIM+ and ILIM- pins provide a Kelvin-sensed cir-

cuit that monitors the voltage across an external cur-

rent sense resistor. This resistor is typically connected

between the source pins of all three low-side MOSFETs

and power ground. If the peak voltage across this resis-

tor exceeds the VILIM+ threshold, it will cause all six out-

puts to latch off. Both pins should be shorted to VSS

ground if the overcurrent features is not used.

5.7.2

DLY

A capacitor connected to the DLY pin determines the

amount of time the gate drive outputs are latched off

before they can be restarted.

During normal operation, the DLY pin is held low by an

internal MOSFET. After an over-current condition is

detected, the MOSFET turns off and the external

capacitor is charged up by an internal current source.

The outputs remain latched off until the DLY pin voltage

reaches the VDLY+ threshold (typically 1.5V).

The delay time can be approximately calculated using

Equation 5-1.

EQUATION 5-1:

DLY

DLY -



DLY

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