MIC5016/5017 Micrel
October 1998 5 MIC5016/5017
Applications Information
Functional Description
The MIC5016 is functionally compatible with the MIC5012,
and the MIC5017 is an inverting configuration of the MIC5016.
The internal functions of these devices are controlled via a
logic block (refer to block diagram) connected to the control
input (pin 14). When the input is off (low for the MIC5016, and
high for the MIC5017), 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. This is a feature not found on the MIC5012.
The charge pump incorporates a 100kHz oscillator and on-
chip pump capacitors capable of charging a 1,000pF load in
90µs typical. In addition to providing active regulation, the
internal 15V zener is included to prevent exceeding the V
GS
rating of the power MOSFET at high supply voltages.
The MIC5016/17 devices have been improved for greater
ruggedness and durability. All pins can withstand being
pulled 20 V 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 reaches 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 measure-
ments be affected, but 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 50 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 con-
tributing excess drop under load.
Low Voltage Testing As the MIC5016/5017 have 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 MIC5016 and MIC5017 are well suited for use with
standard power MOSFETs in both low and high side driver
configurations. In addition, the lowered supply voltage re-
quirements 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 IGBT 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 consider-
ably by bootstrapping 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.
High Side Driver (Figure 1) The high side topology shown
here 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.
Low Side Driver (Figure 2) A key advantage of this topology,
as previously mentioned, is speed. The MOSFET gate is
Figure 2. Low Side Driver
Load
1/2 MIC5016
OFF
ON
+3V to +30V
GateGnd
Source
Input
V+
10µF
