MIC5012
Micrel
Applications Information
(Continued)
7 to 15V
1N5817
15V
33kΩ
33pF
1N4001 (2)
100nF
+
10µF
100kΩ
4N35
100kΩ
1kΩ
To MIC5012
Input
MPSA05
1/2 MIC5012
V+
Control Input
Input
Source
Gnd
Gate
IRF540
10mA
Control Input
Figure 4. Improved
Opto-Isolator Performance
LOAD
24V
Figure 3. Bootstrapped
High-Side Driver
100kΩ
ON
CR2943-NA102A
(GE)
OFF
+
1/2 MIC5012
V+
Input
Source
Gnd
Gate
10µF
IRFP044 (2)
5
330kΩ
LOAD
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. Always 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.
April 1998
Figure 5. 50-Ampere
Industrial Switch
Circuit Topologies
The MIC5012 is suited for use with standard MOSFETs in
high- or low-side driver applications. In addition, the MIC5012
works well in applications where, for faster switching times,
the supply is bootstrapped from the MOSFET source out-
put. Low voltage, high-side drivers (such as shown in Figure
1) are the slowest; their speed is reflected in the gate turn-
on time specifications. The fastest drivers are the low-side
and bootstrapped high-side types (Figures 2 and 4). Load
current switching times are often much faster than the time
to full gate enhancement, depending on the circuit type, the
MOSFET, and the load. Turn-off times are essentially the
same for all circuits (less than 10µs to V
GS
= 1V). The choice
of one topology over another is based on a combination of
considerations including speed, voltage, and desired sys-
tem characteristics.
High-Side Driver
(Figure 1). The high-side topology works
well down to V
+
= 7V with standard MOSFETs. From 4.75
to 7V supply, a logic-level MOSFET can be substituted
since the MIC5012 will not reach 10V gate enhancement
(10V is the maximum rating for logic-compatible MOSFETs).
5-119
MICREL [ MICREL SEMICONDUCTOR ]
