MIC5016_02 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – Low-Cost Dual High- or Low-Side MOSFET Driver

MIC5016/5017
Micrel
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
10µF
Control Input
ON
OFF
1/2 MIC5016
V+
NC
Input
NC
Source NC
Gnd
Gate
MBR2035CT
IRF540
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
Figure 12: High Side Driver WIth Load Protection
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
Push-Pull Driver With No Cross-Conduction (Figure 13) comparator to sense this voltage and feed the appropriate
As the turn-off time of the MIC5016/17 devices is much faster signal to the control inputs of the MIC5016 device. Obviously,
than the turn-on time, a simple dual push-pull driver with no it is very important to use a comparator with a fast slew rate
cross conduction can be made using one MIC5016 and one such as the LM393, and fast recovery diodes. 3mV of positive
MIC5017. The same control signal is applied to both inputs; feedback is used on the comparator to prevent oscillations.
the MIC5016 turns on with the positive signal, and the
MIC5017 turns on when it swings low.
10µF
12V
MIC5016 ^IRFZ40
12 _{V+ A Gate A} 4
10 _{V+ B Source A} 2
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
normal diode would have. Even greater savings can be had
by using FETs with lower R_DS(ON)s, but care must be taken
that the peak currents and voltages do not exceed the SOA
of the chosen FET.
14 _{In A Gate B} 6
IRFZ40
11 _{In B Source B} 5
Control Input 1
Control Input 2
3 _Gnd
12V
MIC5017 ^IRFZ40
12 _{V+ A Gate A} 4
10 _{V+ B Source A} 2
14 _{In A Gate B} 6
V_OUT A
110V AC
V_OUT B
25.2V
VCT
30mΩ
IRFZ40
Caltronics
T126C3
10Ω
10kΩ
56kΩ
10µF
1kΩ
1N914 (2)
1N914
MIC5016
12 _{V+ A Gate A} 4
10 _{V+ B Source A} 2
14 _{In A}
6
Gate B
11 _{In B Source B} 5
3 _Gnd
1RF540
*
4700µF
1RF540 *
VOUT =
18V, 3A
1N914
11 _{In B Source B} 5
10kΩ
1/2 LM393
1kΩ
* Parasitic body diode
3 _Gnd
Figure 13: Push-Pull Driver
Figure 14: High Efficiency 60 Hz
Synchronous Rectifier
October 1998
9
MIC5016/5017