MIC5060_10 Datasheet, PDF (7/12 Pages) Micrel Semiconductor – Ultra Small High-Side MOSFET Driver

Micrel, Inc.
MIC5060
Application Information
Functional Description
The internal functions of the MIC5060 is controlled via a
logic block (refer to block diagram) connected to the
control input (pin 2). When the input is off (low), all
functions are turned off, and the gate of the external power
MOSFET is held low via two N-Channel switches. This
results in a very low standby current, 15µA typical, which is
necessary to power an internal bandgap.
When the input is driven to the “ON” state, the N-Channel
switches are turned off, the charge pump is turned on, and
the P-Channel switch between the charge pump and the
gate turns on, allowing the gate of the power FET to be
charged. The op amp and internal zener form an active
regulator which shuts off the charge pump when the gate
voltage is high enough.
The charge pump incorporates a 100kHz oscillator and on-
chip pump capacitors capable of charging a 1000pF load
in 90µs typical. In addition to providing active regulation,
the internal 15V zener is included to prevent exceeding the
VGS rating of the power MOSFET at high supply voltages.
The MIC5060 device has been improved for greater
ruggedness and durability. All pins can withstand being
pulled 20V below ground without sustaining damage, and
the supply pin can withstand an overvoltage transient of
60V for 1s. An overvoltage shutdown has also been
included, which turns off the device when the supply
exceeds 35V.
Construction Hints
High current pulse circuits demand equipment and
assembly techniques that are more stringent than normal,
low current lab practices. The following are the sources of
pitfalls most often encountered during prototyping:
Supplies: 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. Always
monitor the power supply voltage that appears at the drain
of a high side driver (or the supply side of the load for a
low side driver) with an oscilloscope. It is not uncommon to
find bench power supplies in the 1kW class that overshoot
or undershoot by as much as 50% when pulse loaded. Not
only will the load current and voltage measurements be
affected, but also it is possible to overstress various
components, especially 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 voltage drop, but
unless careful construction techniques are used, one could
easily add 50mΩ to 100mΩ resistance. Do not use a
socket for the MOSFET. If the MOSFET is a TO-220 type
package, make high current connections to the drain tab.
Wiring losses have a profound effect on high-current
circuits. A floating milliohmeter can identify connections
that are contributing excess drop under load.
Low Voltage Testing
As the MIC5060 has relatively high output impedances, a
normal oscilloscope probe will load the device. This is
especially pronounced at low voltage operation. It is
recommended that a FET probe or unity gain buffer be
used for all testing.
Circuit Topologies
The MIC5060 is well suited for use with standard power
MOSFETs in both low and high side driver configurations.
In addition, the lowered supply voltage requirements of
these devices make them ideal for use with logic level
FETs in high side applications with a supply voltage of 3V
to 4V. (If higher supply voltages [>4V] are used with logic
level FETs, an external zener clamp must be supplied to
ensure that the maximum V_GS rating of the logic FET [10V]
is not exceeded.) In addition, a standard I_GBT can be driven
using these devices.
Choice of one topology over another is usually based on
speed vs. safety. The fastest topology is the low side
driver, however, it is not usually considered as safe as
high side driving as it is easier to accidentally short a load
to ground than to V_CC. The slowest, but safest topology is
the high side driver; with speed being inversely
proportional to supply voltage. It is the preferred topology
for most military and automotive applications. Speed can
be improved considerably by bootstrapping from the
supply.
All topologies implemented using these devices are well
suited to driving inductive loads, as either the gate or the
source pin can be pulled 20V below ground with no effect.
External clamp diodes are unnecessary, except for the
case in which a transient may exceed the overvoltage trip
point.
February 2010
7
M9999-021610-C