LT1158
APPLICATIONS INFORMATION
from a true short. This is done by using the current limit to
control cold filament current in conjunction with the self-
protection circuit of Figure 9. The reduced cold filament
current also extends the life of the filament.
down the top MOSFET. The LT1158 will then go into the
automatic restart mode described in Self-Protection with
Automatic Restart above.
The time constant for an incandescent filament is tens
A good guideline is to choose R
to set I at ap-
of milliseconds, which means that t
will have
SENSE
SC
SHUTDOWN
proximately twice the steady state “on” current of the
lamp(s). t is then made long enough to guar-
antee that the lamp filaments heat and drop out of current
limit before the enable capacitor discharges to the enable
low threshold. For a short-circuit, the enable capacitor
will continue to discharge below the threshold, shutting
to be longer than in most other applications. This places
increased SOA demands on the MOSFET during a short
circuit, requiring that a larger than normal device be used.
A protected high current lamp driver application is shown
in Figure 18.
SHUTDOWN
TYPICAL APPLICATIONS
5V TO 10V INPUT (USE LOGIC-LEVEL Q1, Q2)
8V TO 20V INPUT (USE STANDARD Q1, Q2
AND CONNECT BOOST DIODE TO PIN 1)
1N4148
100k
s
16
1
2
3
4
5
6
7
8
+
BOOST DR
BOOST
500μF
Q1
VP0300
LOW ESR
15
14
13
12
11
10
9
+
V
T GATE DR
T GATE FB
T SOURCE
0.01μF
SHORT-CIRCUIT
CURRENT = 8A
INSERT FOR
ZERO POWER
SHUTDOWN
0.1μF
680k
BIAS
L1
R
S
22μH
0.015Ω
+3.3V/6A
OUTPUT
ENABLE
FAULT
INPUT
GND
+
100k
+
–
+
10μF
LT1158
100Ω
2N2222
1000μF
LOW ESR
+
SENSE
CMOS
ON/OFF
100Ω
–
SENSE
Q2
+
V
Q1, Q2: IRLZ44 (LOGIC-LEVEL)
IRFZ44 (STANDARD)
B GATE FB
B GATE DR
1.62k
1%
24k
1N4148
1
510Ω
L1: HURRICANE LAB
HL-KK122T/BB
8
7
6
5
1000pF
0.05μF
1k
2
R : VISHAY/DALE TYPE LVR-3
S
4.99k
1%
VISHAY/ULTRONIX RCS01, SM1
ISOTEK CORP. ISA-PLAN SMR
LT1431
3
4
200pF
CONSTANT OFF TIME CURRENT MODE CONTROL LOOP
1
V
OUT
FREQUENCY =
WHERE t
≈ 10μs
OFF
1 –
(
)
t
V
IN
LT1158 F10
OFF
Figure 10. High Efficiency 3.3V Step-Down Switching Regulator (Requires No Heatsinks)
1158fb
16
LINEAR_DIMENSIONS [ Linear Dimensions ]
