MIC5013 Datasheet, PDF (7/16 Pages) Micrel Semiconductor – Protected High- or Low-Side MOSFET Driver

MIC5013
Applications Information (Continued)
V_LOAD
Control Input
R_TH
10kΩ
V+=7 to 15V
MIC5013
1 _{Input Fault} 8
2 _{Thresh V+} 7
3 _{Sense Gate} 6
4 _{Source Gnd} 5
10µF
+
LOAD
V
R = ^TRIP
S_I
L
2200
R=
–1000
TH _V
TRIP
For this example:
IRF540
I =20A (trip current)
L
V = 200mV
TRIP
R
S
10mΩ
IRC 4LPW-5
(International Resistive Company)
Micrel
Figure 2. Low-Side Driver with
Current Shunt
Circuit Topologies
The MIC5013 is suited for use in high- or low-side driver
applications with over-current protection for both current-
sensing and standard MOSFETs. In addition, the MIC5013
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 the
Test Circuit) 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. 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. Each topology is described in this
section. Note that I_L, as used in the design equations, is the
load current that just trips the over-current comparator.
current comparator monitors RS and trips if I_L × R_S exceeds
V_TRIP. R is selected to produce the desired trip voltage.
As a guideline, keep V_TRIP within the limits of 100mV and
500mV (R_TH = 3.3kΩ to 20kΩ). Thresholds at the high end
offer the best noise immunity, but also compromise switch
drop (especially in low voltage applications) and power
dissipation.
The trip current is set higher than the maximum expected
load current—typically twice that value. Trip point accuracy
is a function of resistor tolerances, comparator offset (only
a few millivolts), and threshold bias voltage (V2). The values
shown in Figure 2 are designed for a trip current of 20
amperes. It is important to ground pin 4 at the current shunt
R_S, to eliminate the effects of ground resistance.
A key advantage of the low-side topology is that the load
supply is limited only by the MOSFET BVDSS rating.
Clamping may be required to protect the MOSFET drain
terminal from inductive switching transients. The MIC5013
Low-Side Driver with Current Shunt (Figure 2). The over- _V+=24V
Control Input
MIC5013
10µF ⁺
1 _{Input Fault} 8
R_{TH 2 Thresh V+ 7}
20kΩ _{3 Sense Gate 6}
4 _{Source Gnd} 5
V+
R1=
1mA
R2=100Ω
100mV+V
R=
TRIP
S
I_L
IRF541
100Ω
2200
R_TH = _V
–1000
TRIP
R1
24kΩ
R2
R
S
18mΩ
IRC 4LPW-5*
For this example:
I_L =10A (trip current)
V =100mV
TRIP
LOAD
*International Resistive Company
July 2000
Figure 3. High-Side Driver
with Current Shunt
7
MIC5013