MIC5060_10 Datasheet, PDF (8/12 Pages) Micrel Semiconductor – Ultra Small High-Side MOSFET Driver

Micrel, Inc.
MIC5060
drain supply and improves turn-on time. Since the supply
current in the “off” state is only a small leakage, the 100nF
bypass capacitor tends to remain charged for several
seconds after the MIC5060 is turned off. Faster speeds
can be obtained at the expense of supply voltage (the
overvoltage shutdown will turn the part off when the
bootstrapping action pulls the supply pin above 35V) by
using a larger capacitor at the junction of the two 1N4001
diodes. In a PWM application (this circuit can be used for
either PWM’ed or continuously energized loads), the chip
supply is sustained at a higher potential than the system
supply, which improves switching time.
Figure 1. 3V “Sleep-Mode” Switch
with a Logic-Level MOSFET
High Side Driver
The high side topology shown in Figure 1 is an
implementation of a “sleep-mode” switch for a laptop or
notebook computer, which uses a logic level FET. A
standard power FET can easily be substituted when
supply voltages above 4V are required.
Figure 2. Low Side Driver
Low Side Driver
A key advantage of this topology, as previously mentioned,
is speed. The MOSFET gate is driven to near supply
immediately when the MIC5060 is turned on. Typical
circuits reach full enhancement in 50µs or less with a 15V
supply.
Bootstrapped High Side Driver
The turn-on time of a high side driver can be improved to
faster than 40µs by bootstrapping the supply with the
MOSFET source. The Schottky barrier diode prevents the
supply pin from dropping more than 200mV below the
Figure 3. Bootstrapped High-Side Driver
High Side Driver with Current Sense
Although no current sense function is included on the
MIC5060, a simple current sense function can be realized
via the addition of one more active component; an
LM301A op amp used as a comparator. The positive rail of
the op amp is tied to V+, and the negative rail is tied to
ground. This op amp was chosen as it can withstand
having input transients that swing below the negative rail,
and has common mode range almost to the positive rail.
The inverting side of this comparator is tied to a voltage
divider, which sets the voltage to V+ – V_TRIP. The non
inverting side is tied to the node between the drain of the
FET and the sense resistor. If the overcurrent trip point is
not exceeded, this node will always be pulled above V+ –
V_TRIP, and the output of the comparator will be high which
feeds the control input of the MIC5060. Once the
overcurrent trip point has been reached, the comparator
will go low, which shuts off the MIC5060. When the short is
removed, feedback to the input pin insures that the
MIC5060 will turn back on. This output can also be level
February 2010
8
M9999-021610-C