mic44f18 Micrel Semiconductor, mic44f18 Datasheet - Page 8

• Manufacturer Part Number: mic44f18
• Description: Mic44f18,mic44f19,mic44f20 6a High Speed Mosfet Drivers In 2mm ? 2mm Package
• Manufacturer: Micrel Semiconductor

January 2007
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.
disabled, the VOUT pin is pulled low. The MIC44F19 is
an inverting driver that is optimized to drive P-channel
MOSFETs.
high, which turns off the P-channel MOSFET.
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.
Startup and UVLO
The UVLO circuit disables the output until the V
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
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
threshold is calculated as:
EN/UVLO
V
V
where
V
DD
DD
Hyst
0
0
1
1
enable
hysteresis
=
:
V
Enable
VDD
TH
=
IN
V
=
0
1
0
1
=
When disabled, the VOUT pin is pulled
Hysteresis
TH
Enable
V
Hysteresis
Hyst
×
MIC44F18
OUTPUT
⎡
⎢
⎣
1
LOW
LOW
LOW
+
×
HI
Threshold
⎡
⎢
⎣
R2
R1
=
1
+
Hysteresis
⎤
⎥
⎦
Voltage
R2
R1
⎤
⎥
⎦
MIC44F19
OUTPUT
DD
Voltage
LOW
HI
HI
HI
turn on (rising V
Voltage
DD
voltage and the
at
MIC44F20
OUTPUT
the
LOW
LOW
LOW
HI
VDD
When
The
DD
DD
)
pin
8
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.
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.
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.
Figure 2. UVLO Circuit
This prevents the
M9999-011207