MIC5013 Datasheet, PDF (6/16 Pages) Micrel Semiconductor – Protected High- or Low-Side MOSFET Driver

MIC5013
Block Diagram
Input 1
Fault 8
V+
7
CHARGE
PUMP
LOGIC
CURRENT
SENSE
LATCH
QR
S
MIC5013
+
–
V. REG
V+
I2
+
V_TRIP 1k
–
5
Ground
1k
2
Threshold
500Ω
6 Gate
12.5V
3 Sense
4 Source
Micrel
Applications Information
Functional Description (refer to block diagram)
The various MIC5013 functions are controlled via a logic
block connected to the input pin 1. When the input is low, all
functions are turned off for low standby current and the gate
of the power MOSFET is also held low through 500Ω to an
N-channel switch. When the input is taken above the turn-
on threshold (3.5V typical), the N-channel switch turns off
and the charge pump is turned on to charge the gate of the
power FET. A bandgap type voltage regulator is also turned
on which biases the current sense circuitry.
The charge pump incorporates a 100kHz oscillator and on-
chip pump capacitors capable of charging 1nF to 5V above
supply in 60µs typical. The charge pump is capable of
pumping the gate up to over twice the supply voltage. For
this reason, a zener clamp (12.5V typical) is provided
between the gate pin 6 and source pin 4 to prevent exceed-
ing the V_GS rating of the MOSFET at high supplies.
The current sense operates by comparing the sense volt-
age at pin 3 to an offset version of the source voltage at pin
4. Current I2 flowing in threshold pin 2 is mirrored and
returned to the source via a 1kΩ resistor to set the offset, or
trip voltage. When (V_SENSE – V_SOURCE) exceeds V_TRIP, the
current sense trips and sets the current sense latch to turn
off the power FET. An integrating comparator is used to
reduce sensitivity to spikes on pin 3. The latch is reset to turn
the FET back on by “recycling” the input pin 1 low and then
high again.
A resistor R_TH from pin 2 to ground sets I2, and hence V_TRIP.
An additional capacitor C_TH from pin 2 to ground creates a
higher trip voltage at turn-on, which is necessary to prevent
high in-rush current loads such as lamps or capacitors from
false-tripping the current sense.
When the current sense has tripped, the fault pin 8 will be
high as long as the input pin 1 remains high. However, when
the input is low the fault pin will also be low.
Construction Hints
High current pulse circuits demand equipment and assem-
bly techniques that are more stringent than normal low
current lab practices. The following are the sources of
pitfalls most often encountered during prototyping: Sup-
plies: many bench power supplies have poor transient
response. Circuits that are being pulse tested, or those that
operate by pulse-width modulation will produce strange
results when used with a supply that has poor ripple
rejection, or a peaked transient response. Monitor the
power supply voltage that appears at the drain of a high-
side driver (or the supply side of the load in a low-side driver)
with an oscilloscope. It is not uncommon to find bench
power supplies in the 1kW class that overshoot or under-
shoot by as much as 50% when pulse loaded. Not only will
the load current and voltage measurements be affected, but
it is possible to over-stress various components—espe-
cially electrolytic capacitors—with possibly catastrophic
results. A 10µF supply bypass capacitor at the chip is
recommended.
Residual Resistances: Resistances in circuit connections
may also cause confusing results. For example, a circuit
may employ a 50mΩ power MOSFET for low drop, but
careless construction techniques could easily add 50 to
100mΩ resistance. Do not use a socket for the MOSFET. If
the MOSFET is a TO-220 type package, make high-current
drain connections to the tab. Wiring losses have a profound
effect on high-current circuits. A floating millivoltmeter can
identify connections that are contributing excess drop un-
der load.
MIC5013
6
July 2000