Datasheet

LT1977
5
1977fa
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switch Peak Current Limit
Soft-Start Current Threshold
vs FB Voltage
Frequency Foldback Percentage
TEMPERATURE (°C)
–50
1.5
PEAK SWITCH CURRENT (A)
2.0
2.5
3.0
3.5
–25 –0 25 50
1977 G10
75 100 125
FB VOLTAGE (V)
0
0
CURRENT (µA)
10
20
30
0.2
0.4
0.6 0.8
1977 G11
1.0
40
50
5
15
25
35
45
1.2
SOFT-START
DEFEATED
T
J
= 25°C
FB PIN VOLTAGE (V)
0
FOLDBACK PERCENTAGE (%)
60
80
100
1
1977 G12
40
20
50
70
90
30
10
0
0.25
0.5
0.75
1.25
Switch On Voltage (V
CESAT
)
LOAD CURRENT (A)
–0.1
0
VOLTAGE (mV)
50
150
200
250
500
350
0.3
0.7
0.9
1977 G13
100
400
450
300
0.1 0.5
1.1
1.3
1.5
T
J
= 125°C
T
J
= 25°C
T
J
= –50°C
INPUT VOLTAGE (V)
0
0
SUPPLY CURRENT (µA)
50
100
10
20
30 40
1977 F05
50
150
25
75
125
60
V
OUT
= 3.3V
T
A
= 25°C
Supply Current vs Input Voltage Minimum Input Voltage
Burst Mode Threshold
vs Input Voltage
INPUT VOLTAGE (V)
5
LOAD CURRENT (mA)
300
400
500
13
1977 G20
200
100
250
350
450
150
50
0
7
9
11
15
614
8
10
12
16 17 18 19
20
Burst Mode EXIT
(INCREASING LOAD)
Burst Mode ENTER
(DECREASING LOAD)
V
OUT
= 3.3V
L = 10µH
C
OUT
= 100µF
Minimum On Time Boost Current vs Switch Current
TEMPERATURE (°C)
–50
0
ON TIME (ns)
50
150
200
250
500
350
0
50
75
1977 G21
100
400
450
300
–25
25
100
125
LOAD CURRENT = 0.5A
LOAD CURRENT = 1A
SWITCH CURRENT (A)
0
0
BOOST CURRENT (mA)
5
15
20
25
1
45
1977 G22
10
0.5
0.25
1.25
0.75 1.5
30
35
40
LOAD CURRENT (A)
0
INPUT VOLTAGE (V)
5.0
5.5
6.0
1.6
1977 G19
4.5
4.0
3.0
0.40.2 0.8 10.6 1.2 1.4
3.5
7.5
6.5
7.0
5V START
5V RUNNING
3.3V START
3.3V RUNNING