MIC4100 Datasheet, PDF (10/18 Pages) Micrel Semiconductor – 100V Half Bridge MOSFET Drivers

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 I_VDD 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 I_VDD 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
10
M9999-031506