MIC44F18 datasheet(9/17 Pages) MICREL

9 / 17 page

Micrel, Inc.

MIC44F18/19/20

February 2011

M9999-020111

Functional Description

The MIC44F18/19/20 family of drivers are high speed,

high current drivers that are designed to drive P-channel

and N-channel MOSFETs. The drivers come in both

inverting and non-inverting versions. The block diagram

of the MIC44Fxx driver is shown in Figure 1.

The MIC44F18 is a non-inverting driver.

When

disabled, the VOUT pin is pulled low. The MIC44F19 is

an inverting driver that is optimized to drive P-channel

MOSFETs.

When disabled, the VOUT pin is pulled

high, which turns off the P-channel MOSFET.

The

MIC44F20 is an inverting driver, whose VOUT pin is

pulled low when disabled. This allows it to drive an

N-channel MOSFETs and turn it off when the driver is

disabled. The logic table below summarizes the driver

operation.

EN/UVL

MIC44F18

OUTPUT

MIC44F19

OUTPUT

MIC44F20

OUTPUT

LOW

Startup and UVLO

The UVLO circuit disables the output until the VDD

supply voltage exceeds the UVLO threshold. Hysteresis

in the UVLO circuit prevents noise and finite circuit

impedance from causing chatter during turn-on and turn-

off.

As shown in figure 2, with the EN/UVLO pin open, an

internal resistor divider senses the VDD voltage and the

UVLO threshold is set at the minimum operating voltage

of the driver. The driver can be set to turn on at a higher

voltage by adding an external resistor to the UVLO pin.

With an external divider, the VDD turn on (rising VDD)

threshold is calculated as:

Voltage

Hysteresis

Enable

VDD

the

Voltage

Hysteresis

VDD

Voltage

Threshold

Enable

where

Hyst

Hysteresis

Hyst

hysteresis

enable

⎥⎦

⎤

⎢⎣

⎡ +

⎥⎦

⎤

⎢⎣

⎡ +

Because the external resistors are parallel with the

internal resistors, it is important to keep the value of the

external resistors at least 10 times lower than the typical

values of the internal resistors.

This prevents the

internal resistors from affecting the accuracy of the

enable calculation as well as preventing the large

tolerance of the internal resistors from affecting the

tolerance of the enable voltage setting.

Figure 2. UVLO Circuit

Input Stage

The MIC44Fxx family of drivers have a high impedance,

TTL compatible input stage. The tight tolerance of the

input threshold makes it compatible with CMOS devices

powered from any supply voltage between 3V and VDD.

Hysteresis on the input pin improves noise immunity and

prevents input signals with slow rise times from falsely

triggering the output. The amplitude of the input voltage

has no effect on the supply current draw of the driver.

The input voltage signal may go up to -5V below ground

without damaging the driver or causing a latch up

condition. Negative input voltages 0.7V below ground or

greater will cause an increase in propagation delay.

MIC44F18 Arkusz danych(PDF) 9 Page - Micrel Semiconductor

MIC44F18 Arkusz danych(HTML) 9 Page - Micrel Semiconductor

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Arkusz danych Pobierz

Link URL