MIC5016/5017
High Side Driver With Load Protection
(Figure 12) Al-
though the MIC5016/17 devices are reverse battery pro-
tected, the load and power FET are not in a typical high side
configuration. In the event of a reverse battery condition, the
internal body diode of the power FET will be forward biased.
This allows the reversed supply to drive the load.
An MBR2035CT dual Schottky diode was used to eliminate
this problem. This particular diode can handle 20A continu-
ous current and 150A peak current; therefore it should survive
the rigors of an automotive environment. The diodes are
paralleled to reduce the switch loss (forward voltage drop).
12V
Micrel
This scheme works with no additional components as the
relative time difference between the rise and fall times of the
MIC5014 is large. However, this does mean that there is
considerable deadtime (time when neither driver is turned
on). If this circuit is used to drive an inductive load, catch
diodes must be used on each half to provide an alternate path
for the kickback current that will flow during this deadtime.
This circuit is also a simple H-bridge which can be driven with
a PWM signal on the input for SMPS or motor drive applica-
tions in which high switching frequencies are not desired.
Synchronous Rectifier
(Figure 14) In applications where
efficiency in terms of low forward voltage drops and low diode
reverse-recovery losses is critical, power FETs are used to
achieve rectification instead of a conventional diode bridge.
Here, the power FETs are used in the third quadrant of the IV
characteristic curve (FETs are installed essentially “back-
wards”). The two FETs are connected such that the top FET
turns on with the positive going AC cycle, and turns off when
it swings negative. The bottom FET operates opposite to the
top FET.
In the first quadrant of operation, the limitation of the device
is determined by breakdown voltage. Here, we are limited by
the turn-on of a parasitic p-n body drain diode. If it is allowed
to conduct, its reverse recovery time will crowbar the other
power FET and possibly destroy it. The way to prevent this
is to keep the IR drop across the device below the cut-in
voltage of this diode; this is accomplished here by using a fast
comparator to sense this voltage and feed the appropriate
signal to the control inputs of the MIC5016 device. Obviously,
it is very important to use a comparator with a fast slew rate
such as the LM393, and fast recovery diodes. 3mV of positive
feedback is used on the comparator to prevent oscillations.
10µF
1/2 MIC5016
V+
Control Input
ON
OFF
MBR2035CT
NC
NC
NC
Gate
IRF540
Input
Source
Gnd
Figure 12: High Side Driver WIth Load Protection
Push-Pull Driver With No Cross-Conduction
(Figure 13)
As the turn-off time of the MIC5016/17 devices is much faster
than the turn-on time, a simple dual push-pull driver with no
cross conduction can be made using one MIC5016 and one
MIC5017. The same control signal is applied to both inputs;
the MIC5016 turns on with the positive signal, and the
MIC5017 turns on when it swings low.
At 3A, with an R
DS
(ON) of 0.077Ω, our forward voltage drop
per FET is ~ 0.2 V as opposed to the 0.7 to 0.8 V drop that a
12V
normal diode would have. Even greater savings can be had
IRFZ40
MIC5016
10µF
by using FETs with lower R
DS
(ON)s, but care must be taken
12
V+ A Gate A 4
that the peak currents and voltages do not exceed the SOA
10
2
V+ B Source A
of the chosen FET.
14
11
Control Input 1
3
In A
Gate B
6
5
10µF
MIC5016
1N914
12
10
14
11
V
CT
30mΩ
56kΩ
Caltronics
T126C3
10Ω
10kΩ
10kΩ
1/2 LM393
1kΩ
* Parasitic body diode
1N914 (2)
1N914
V+ A
Gate A
4
2
6
5
1RF540
4700µF
*
Load
IRFZ40
In B Source B
Gnd
1RF540
V
OUT
A
110V AC
25.2V
*
V
OUT
=
18V, 3A
1kΩ
V+ B Source A
In A
Gate B
Control Input 2
12V
MIC5017
12
10
14
11
3
V+ A
IRFZ40
Gate A 4
2
6
5
V
OUT
B
In B Source B
3 Gnd
V+ B Source A
In A
Gate B
IRFZ40
In B Source B
Gnd
Figure 13: Push-Pull Driver
Figure 14: High Efficiency 60 Hz
Synchronous Rectifier
5-154
October 1998
MICREL [ MICREL SEMICONDUCTOR ]
