MIC5021BN Micrel Inc, MIC5021BN Datasheet - Page 8

• Manufacturer Part Number: MIC5021BN
• Description: IC DRIVER MOSFET HI SIDE HS 8DIP
• Manufacturer: Micrel Inc

Specifications of MIC5021BN

• Configuration: High-Side
• Input Type: Non-Inverting
• Delay Time: 500ns
• Number Of Configurations: 1
• Number Of Outputs: 1
• Voltage - Supply: 12 V ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: 8-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Current - Peak: -
• High Side Voltage - Max (bootstrap): -

MIC5021
External Protection
Resistors placed in series with each
the current drawn from the internal Schottky diodes during a
negative transient. This minimizes the forward drop across
the diodes.
During normal operation, sensing current from the sense pins
is unequal (5µA and 15µA). The internal Schottky diodes are
reverse biased and have no effect. To avoid skewing the trip
voltage, the current limiting resistors must drop equal volt-
ages at the trip point currents. See Figure 7. To minimize
resistor tolerance error, use a voltage drop lower than the
trip voltage of 50mV. 5mV is suggested.
External Schottky diodes are also recommended. See D2
and D3 in Figure 8. The external diodes clamp negative
transients better than the internal diodes because their larger
size minimizes the forward voltage drop at higher currents.
MIC5021
10µF
TTL Input
Figure 8. Protection from Inductive Kick
V
to avoid skewing
the 50mV trip point.
R 1 ≅ 3 × R 2
(5mV suggested)
1
2
3
4
R 1
V
Input
C
Gnd
= V
Figure 7. Resistor Voltage Drop
DD
T
1
2
3
4
MIC5021
R 2
V
Input
C
Gnd
DD
T
MIC5021
Sense-
Sense+
V
B O O S T
Gate
Sense-
Sense+
V
11DQ03
B O O S T
Gate
11DQ03
8
7
6
5
D2
8
7
6
5
D3
15µA
5µA
R 1
V
V
R 1
R 2
2.7
nF
1.0k
330Ω
R 1
R 2
D1
SENSE
+12V to +36V
R
N-Channel
Power MOSFET
Load
S
50mV nominal
(at trip)
N-Channel
Power MOSFET
R
S E N S E
connection limit
Inductive
Load
8
High-Side Sensing
Sensing the current on the high side of the MOSFET isolates
the
Lamp Driver Application
Incandescent lamps have a high inrush current (low resis-
tance) when turned on. The MIC5021 can perform a “soft
start” by pulsing the MOSFET (overcurrent condition) until
the filament is warm and its current decreases (resistance
increases). The sense resistor value is selected so the voltage
drop across the sense resistor decreases below the sense
threshold (50mV) as the filament becomes warm. The FET
is no longer pulsed and the lamp turns completely on.
A lamp may not fully turn on if the filament does not heat up
adequately. Changing the duty cycle, sense resistor, or both to
match the filament characteristics can correct the problem.
Soft start can be demonstrated using a #1157 dual filament
automotive lamp. The value of R
for soft start of the higher-resistance filament (measures ap-
prox. 2.1Ω cold or 21Ω hot).
TTL Input
TTL Input
SENSE
10µF
10µF
pins from the inductive spike.
"( )" values apply to demo circuit.
Figure 10. Lamp Driver with
Figure 9. High Side Sensing
1
2
3
4
1
2
3
4
V
Input
C
Gnd
See text.
Current Sensing
DD
T
Input
C
Gnd
V
MIC5021
DD
T
MIC5021
Sense-
Sense+
V
Sense+
Sense-
B O O S T
V
Gate
B O O S T
Gate
8
7
6
5
S
8
7
6
5
shown in Figure 10 allows
0.01
µF
+12V to +20V
0.01
µF
V+
(+12V)
N-Channel
Power MOSFET
(IRF540)
R
(0.041Ω)
(+12V)
R
(< 0.01Ω)
N-Channel
Power MOSFET
(IRFZ44)
S E N S E
S E N S E
Incandescent
Lamp (#1157)
Wirewound
Resistor
(3Ω)
Micrel, Inc.
July 2005