MIC4100 datasheet(10/18 Pages) MICREL

10 / 18 page

Micrel, Inc.

MIC4100/1

Functional Description

The MIC4100 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 MIC4100 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

The MIC4100 and MIC4101 have different input stages,

which lets these parts cover a wide range of driver

applications. Both the HI and LI pins are referenced to the

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

change the quiescent current draw of the driver.

The MIC4100 has a high impedance, CMOS compatible

input range and is recommended for applications where

the input signal is noisy or where the input signal swings

the full range of voltage (from Vdd to Gnd). There is

typically 400mV of hysteresis on the input pins throughout

the VDD range. The hysteresis improves noise immunity

and prevents input signals with slow rise times from falsely

triggering the output. The threshold voltage of the

MIC4100 varies proportionally with the VDD supply

voltage.

The amplitude of the input signal affects the VDD supply

current. Vin voltages that are a diode drop less than the

VDD supply voltage will cause an increase in the VDD pin

current. The graph in Figure 2 shows the typical

dependence between IVDD and Vin for Vdd=12V.

Figure 2

The MIC4101 has a TTL compatible input range and is

recommended for use with inputs signals whose amplitude

is less than the supply voltage. The threshold level is

independent of the VDD supply voltage and there is no

dependence between IVDD and the input signal amplitude

with the MIC4101. This feature makes the MIC4101 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

3. 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

ensures a low Rdson from the external MOSFET.

A high level applied to LI pin causes the upper driver fet 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.

March 2006

M9999-031506

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