MIC4606 datasheet(20/40 Pages) MICROCHIP

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MIC4606

DS20005604D-page 20

 2017-2019 Microchip Technology Inc.

The bootstrap circuit consists of an internal diode and

external capacitor, CB. In a typical application, such as

the motor driver shown in Figure 6-3 (only Phase A is

illustrated), the AHS pin is at ground potential while the

low-side MOSFET is on. The internal diode allows

capacitor CB to charge up to VDD – VF during this time

(where VF is 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

internal diode is reverse biased, preventing capacitor

CB from discharging.

FIGURE 6-3:

MIC4606 Motor Driver Example.

6.6

Programmable Gate Drive

The MIC4606 offers programmable gate drive, which

means the MOSFET gate drive (gate-to-source voltage)

equals the VDD voltage. This feature offers designers

flexibility in driving the MOSFETs. Different MOSFETs

require different VGS characteristics for optimum

RDS(ON) performance. Typically, the higher the gate volt-

age (up to 16V), the lower the RDS(ON) achieved. For

example, a NTMSF4899NF MOSFET can be driven to

the ON state with a gate voltage of 5.5V, but RDS(ON) is

5.2 mΩ. If driven to 10V, RDS(ON) is 4.1 mΩ – a decrease

of 20%. In low-current applications, the losses due to

RDS(ON) are minimal, but in battery-powered high-

current motor drive applications, such as power tools,

the difference in RDS(ON) can cut into the efficiency

budget, reducing run time.

FIGURE 6-4:

MOSFET RDS(ON) vs. VGS.

AHS

AHB

AHO

ALO

LEVEL

SHIFT

AHI

ALI

PHASE

CVDD

PHASE A

MIC4606

PHASE

D = 30A

J = 25°C

1.1E-02

1E-02

9E-03

8E-03

7E-03

6E-03

5E-03

4E-03

3E-03

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

GS, GATE-TO-SOURCE VOLTAGE (V)

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