MIC5031 Просмотр технического описания (PDF) - Micrel

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MIC5031

High-Speed High-Side MOSFET Driver

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MIC5031

Functional Description

Refer to “Functional Diagram.”

The MIC5031 is a noninverting device. Applying a CMOS

logic high signal to EN (enable input) activates the driver’s

internal circuitry. Applying a TTL logic high signal to CTL

(control input) produces gate drive output. The G (gate)

output is used to turn on an external N-channel MOSFET.

Control

CTL (control) is a TTL compatible input. The threshold is

approximately 1.4V, independent of the supply voltage.

The falling edge of a signal applied to CTL also resets the

overcurrent lockout latch.

Enable

EN (enable) is a CMOS compatible input. EN enables or

disables all internal circuitry. The enable threshold is approxi-

mately half the supply voltage. The MIC5031 supply current

is near zero when the driver is disabled (low). See “Applica-

tions Information: Power-Up Sequence.”

Charge Pump

The charge pump produces a voltage that is higher than the

supply voltage. This higher voltage is required to drive the

external N-channel MOSFET in high-side switch circuits.

The charge pump consists of an oscillator and a voltage

tripler. When the driver is enabled, the charge pump is

switched on and off to regulate its output voltage.

External capacitors C1 and C2 are required. The charge

pump will not operate without these capacitors.

Bootstrap Capacitor

The external bootstrap capacitor is necessary to achieve the

fastest gate rise times. The bootstrap capacitor (C3) supplies

additional current at a higher voltage to the gate drive

regulator as the MOSFET is switched on.

When the MOSFET is off, the gate drive regulator voltage is

applied to the boost capacitor . As the MOSFET turns on, the

MOSFET source-to-ground voltage increases. The increas-

ing source voltage is added to the voltage across the capaci-

tor for a voltage doubling effect.

Gate Drive Regulator

The gate drive regulator manages the voltage from the

bootstrap capacitor, the supply, and the charge pump.

The gate drive regulator charges the bootstrap capacitor

when the MOSFET is off and limits the voltage from the

bootstrap capacitor as the MOSFET is switched on. It also

performs skip-mode control by switching the charge pump on

and off to regulate the gate drive output voltage.

Gate Output

When the MIC5031 is enabled and CTL is high, the gate

driver steers regulated voltage to G (gate output). When CTL

is low, the gate driver grounds G. This respectively charges

or discharges the external MOSFET’s gate, .

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Current Sense

Refer to the “Voltage Reference (Simplified)” diagram.

The MIC5031 detects an overcurrent condition by comparing

the voltage drop across the external MOSFET to a reference

voltage drop created across R1. If VDS exceeds VR1, a

comparator (not shown) shuts off the external MOSFET by

way of the current limit delay, lockout latch, and logic.

The bandgap reference, op amp and NPN create a constant

voltage (1.23V) across R2. This results in a constant current,

IR2, through R2. Ignoring a small amount of base current, the

same current (IR2) flows through R1. R1 is selected to

achieve the desired reference voltage drop, VR1. Refer to the

applications section for formulas.

Supply

1.23V

Bandgap

Reference

VR1 IR2 R1

RV

RI

IR2 R2

1.23V

External

N-Channel VDS

MOSFET

Voltage Reference (Simplified)

An overcurrent condition also activates the fault flag output

when the lockout latch is activated.

Overcurrent-Shutdown Delay

The overcurrent-shutdown delay circuit permits a delay be-

tween overcurrent detection and latch activation for high-

inrush current loads.

The delay can be increased by adding capacitance from DLY

to GND.

Open-Load Detect

The open load detect resistor is an external high-value pull-

up resistor that causes the source voltage of the external

MOSFET to increase when the load is missing.

The MIC5031 monitors the S-pin voltage only when the gate

driver is off. If the voltage on the S-pin rises above the open-

load detect threshold, the fault flag is activated.

Overtemperature Detect

The overtemperature detect circuit switches the logic to turn

the output off at approximately 140°C. An overtemperature

shutdown condition is restored to normal automatically When

the device cools to about 130°C (10°C hysteresis).

An overtemperature condition also activates the fault flag

output.

Fault Flag

FLT (fault flag) is an open-collector NPN transistor. Fault is

active (pulls collector near ground) upon overcurrent, open-

load, or overtemperature.

August 1999

5

MIC5031

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