Datasheet

4
LT1956/LT1956-5
1956f
Switch Peak Current Limit SHDN Pin Bias Current
Shutdown Supply Current
Lockout and Shutdown
Thresholds Shutdown Supply Current
Error Amplifier Transconductance
FB Pin Voltage and Current
Error Amplifier Transconductance Frequency Foldback
TYPICAL PERFOR A CE CHARACTERISTICS
UW
DUTY CYCLE (%)
1.0
SWITCH PEAK CURRENT (A)
1.5
2.0
2.5
20 40
TYPICAL
60 80
1956 G01
1000
GUARANTEED MINIMUM
JUNCTION TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
CURRENT (µA)
1.224
1.229
1.234
25 75
1956 G02
1.219
1.214
–25 0
50 100 125
1.209
1.204
1.5
2.0
1.0
0.5
0
VOLTAGE
CURRENT
JUNCTION TEMPERATURE (°C)
–50
250
200
150
100
12
6
0
25 75
1956 G03
–25 0
50 100 125
CURRENT (µA)
CURRENT REQUIRED TO FORCE SHUTDOWN
(FLOWS OUT OF PIN). AFTER SHUTDOWN,
CURRENT DROPS TO A FEW µA
AT 2.38V STANDBY THRESHOLD
(CURRENT FLOWS OUT OF PIN)
JUNCTION TEMPERATURE (°C)
–50
SHDN PIN VOLTAGE (V)
50 100
1956 G04
0
25 75
2.4
2.0
1.6
1.2
0.8
0.4
0
–25 125
LOCKOUT
START-UP
SHUTDOWN
INPUT VOLTAGE (V)
0
INPUT SUPPLY CURRENT (µA)
1956 G05
10 20 30 40 50 60
40
35
30
25
20
15
10
5
0
V
SHDN
= 0V
SHUTDOWN VOLTAGE (V)
0
0
INPUT SUPPLY CURRENT (µA)
50
100
150
200
250
300
0.1 0.2 0.3 0.4
1956 G06
0.5
V
IN
= 60V
V
IN
= 15V
JUNCTION TEMPERATURE
TRANSCONDUCTANCE (µmho)
1956 G07
2500
2000
1500
1000
500
0
–50
50 100
0
25 75–25 125
FREQUENCY (Hz)
GAIN (µMho)
PHASE (DEG)
3000
2500
2000
1500
1000
500
200
150
100
50
0
–50
100 10k 100k 10M
1956 G08
1k 1M
GAIN
PHASE
ERROR AMPLIFIER EQUIVALENT CIRCUIT
R
OUT
200k
C
OUT
12pF
V
C
R
LOAD
= 50Ω
V
FB
2 • 10
–3
)(
V
FB
(V)
0 0.2
SWITICHING FREQUENCY (kHz)
OR FB CURRENT (µA)
375
500
625
1.0
1956 G09
250
125
0
0.4
0.6
0.8
1.2
SWITCHING
FREQUENCY
FB PIN
CURRENT