MIC44F18_11 Datasheet, PDF (9/17 Pages) Micrel Semiconductor – 6A, 13V High Speed MOSFET Drivers with Enable Input

Micrel, Inc.
MIC44F18/19/20
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.
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.
EN/UVL
O
IN
MIC44F18
OUTPUT
MIC44F19
OUTPUT
0
0
LOW
HI
0
1
LOW
HI
1
0
LOW
HI
1
1
HI
LOW
MIC44F20
OUTPUT
LOW
LOW
HI
LOW
Startup and UVLO
The UVLO circuit disables the output until the V_DD
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 V_DD 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 V_DD turn on (rising V_DD)
threshold is calculated as:
V_DDenable
=
V_TH
×
⎢⎣⎡¹⁺
R1⎤
R2^⎥⎦
V_DDhysteresis
=
V_Hyst
×
⎢⎣⎡¹⁺
R1⎤
R2^⎥⎦
where: V_TH = EnableThresholdVoltage
VDD_Hysteresis = HysteresisVoltageat the VDDpin
V_Hyst = EnableHysteresisVoltage
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.
February 2011
9
M9999-020111