MIC5014 Datasheet, PDF (6/9 Pages) Micrel Semiconductor – Low-Cost High- or Low-Side MOSFET Driver

MIC5014/5015
Micrel
Low Side Driver (Figure 2) A key advantage of this topology,
as previously mentioned, is speed. The MOSFET gate is
driven to near supply immediately when the MIC5014/15 is
turned on. Typical circuits reach full enhancement in 50µs or
less with a 15V supply.
Bootstrapped High Side Driver (Figure 3) 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 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 MIC5014/15 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.
+2.75V to +30V
1N5817
1N4001 (2)
100nF
Control Input
ON
OFF
MIC5015
1 _V+
NC ⁸
2 _Input
NC ⁷
3 _{Source NC} 6
4 _Gnd
Gate ⁵
1µF
1RF540
the short is removed, feedback to the input pin insures that the
MIC5014 will turn back on. This output can also be level
shifted and sent to an I/O port of a microcontroller for intelli-
gent control.
Current Shunts (R_S). Low valued resistors are necessary for
use at R_S. Resistors are available with values ranging from 1
to 50mΩ, at 2 to 10W. If a precise overcurrent trip point is
not necessary, then a nonprecision resistor or even a mea-
sured PCB trace can serve as R_S. The major cause of drift in
resistor values with such resistors is temperature coefficient;
the designer should be aware that a linear, 500 ppm/°C
change will contribute as much as 10% shift in the overcurrent
trip point. If this is not acceptable, a power resistor designed
for current shunt service (drifts less than 100 ppm/°C), or a
Kelvin-sensed resistor may be used.^†
12V
10µF
MIC5014
1 _V+
NC ⁸
2 _Input
NC ⁷
3 _{Source NC} 6
4 _Gnd
Gate ⁵
R_S
0.06Ω
On
I_TRIP = V_TRIP/R_S
= 1.7A
V_TRIP = R1/(R1+R2)
R1
1kΩ
R4
1kΩ
LM301A
R2
120kΩ 2.2kΩ
Figure 4. High Side Driver with Overcurrent Shutdown
Figure 3. Bootstrapped Hgh-Side Driver
High Side Driver With Current Sense (Figure 4) Although no
current sense function is included on the MIC5014/15 devices,
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
MIC5014 (polarities should be reversed if the MIC5015 is
used). One the overcurrent trip point has been reached, the
comparator will go low, which shuts off the MIC5014. When the
† Suppliers of Precision Power Resistors:
Dale Electronics, Inc., 2064 12th Ave., Columbus, NE 68601. (402) 565-
3131
International Resistive Co., P.O. Box 1860, Boone,NC 28607-1860.
[phone]
Isotek Corp., 566 Wilbur Ave. Swansea, MA 02777. [phone]
Kelvin, 14724 Ventura Blvd., Ste. 1003, Sherman Oaks, CA 91403-3501.
[phone]
RCD Components, Inc., 520 E. Industrial Pk. Dr., Manchester, NH 03103.
[phone]
Ultronix, Inc., P.O. Box 1090, Grand Junction, CO 81502 [phone]
High Side Driver With Delayed Current Sense (Figure 5)
Delay of the overcurrent detection to accomodate high inrush
loads such as incandescent or halogen lamps can be accom-
plished by adding an LM3905 timer as a one shot to provide
an open collector pulldown for the comparator output such
that the control input of the MIC5015 stays low for a preset
amount of time without interference from the current sense
circuitry. Note that an MIC5015 must be used in this applica-
tion (figure 5), as an inverting control input is necessary. The
delay time is set by the RC time constant of the external
components on pins 3 and 4 of the timer; in this case, 6ms was
chosen.
An LM3905 timer was used instead of a 555 as it provides a
clean transition, and is almost impossible to make oscillate.
Good bypassing and noise immunity is essential in this circuit
to prevent spurious op amp oscillations.
5-142
1997