Micrel, Inc.

MIC4604

June 25, 2013

8

Revision 1.0

Functional Description

The MIC4604 is a high-voltage, non-inverting, dual

MOSFET driver that is designed to independently drive

both high-side and low-side N-Channel MOSFETs. The

block diagram of the MIC4604 is shown in Figure 1.

Both drivers contain an input buffer with hysteresis, a

UVLO circuit, and an output buffer. The high-side output

buffer includes a high-speed level-shifting circuit that is

referenced to the HS pin. An internal diode is used as part

of a bootstrap circuit to provide the drive voltage for the

high-side output.

Startup and UVLO

The UVLO circuit forces the driver output low until the

supply voltage exceeds the UVLO threshold. The low-side

UVLO circuit monitors the voltage between the VDD and

VSS pins. The high-side UVLO circuit monitors the voltage

between the HB and HS pins. Hysteresis in the UVLO

circuit prevents noise and finite circuit impedance from

causing chatter during turn-on.

Input Stage

Both the HI and LI pins of the MIC4604 are referenced to

the VSS pin. The voltage state of the input signal does not

change the quiescent current draw of the driver.

The MIC4604 has a TTL-compatible input range and can

be used with input signals with amplitude less than the

supply voltage. The threshold level is independent of the

VDD supply voltage and there is no dependence between

feature makes the MIC4604 an excellent level translator

that will drive high-threshold MOSFETs from a low-voltage

PWM IC.

Low-Side Driver

A block diagram of the low-side driver is shown in

Figure 2. The low-side driver is designed to drive a ground

(VSS pin) referenced N-channel MOSFET. Low driver

impedances allow the external MOSFET to be turned on

and off quickly. The rail-to-rail drive capability of the output

A high level applied to LI pin causes the upper driver

MOSFET to turn on and VDD voltage is applied to the gate

of the external MOSFET. A low level on the LI pin turns off

the upper driver and turns on the low side driver to ground

the gate of the external MOSFET.

Figure 2. Low-Side Driver Block Diagram

High-Side Driver and Bootstrap Circuit

A block diagram of the high-side driver and bootstrap

circuit is shown in Figure 3. This driver is designed to drive

a floating N-channel MOSFET, whose source terminal is

referenced to the HS pin.

Figure 3. High-Side Driver and Bootstrap Circuit Block

Diagram

A low-power, high-speed, level-shifting circuit isolates the

low side (VSS pin) referenced circuitry from the high-side

(HS pin) referenced driver. Power to the high-side driver

and UVLO circuit is supplied by the bootstrap circuit while

the voltage level of the HS pin is shifted high.