Datasheet

LT1945
3
1945fa
ELECTRICAL CHARACTERISTICS
The l denotes the specifi cations which apply over the full operating
temperature range, otherwise specifi cations are at T
A
= 25°C. V
IN
= 1.2V, V
SHDN
= 1.2V unless otherwise noted.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may
cause permanent damage to the device. Exposure to any Absolute Maximum
Rating condition for extended periods may affect device reliability and lifetime.
Note 2: The LT1945E is guaranteed to meet performance specifi cations
from 0°C to 70°C junction temperature. Specifi cations over the –40°C
to 85°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT1945I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3: Bias current fl ows out of the NFB1 pin.
Note 4: Bias current fl ows into the FB2 pin.
Note 5: See Figure 1 for Switcher 1 and Switcher 2 locations.
PARAMETER CONDITIONS MIN TYP MAX UNITS
SHDN Pin Current V
SHDN
= 1.2V
V
SHDN
= 5V
2
8
3
12
μA
μA
SHDN Input Voltage High 0.9 V
SHDN Input Voltage Low 0.25 V
Switch Leakage Current Switch Off, V
SW
= 5V 0.01 5 μA
TYPICAL PERFORMANCE CHARACTERISTICS
TEMPERATURE (°C)
–50
–25 0 25 50 75 100
SWITCH VOLTAGE (V)
1945 G01
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
I
SWITCH
= 500mA
I
SWITCH
= 300mA
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1945 G02
1.25
1.24
1.23
1.22
1.21
1.20
BIAS CURRENT (nA)
50
40
30
20
10
0
CURRENT
VOLTAGE
–25 0 25 50 75 100
TEMPERATURE (°C)
FEEDBACK VOLTAGE (V)
1945 G03
–1.25
–1.24
–1.23
–1.22
–1.21
–1.20
–50 –25 0
0
1
2
3
4
5
25 50 75 100
VOLTAGE
CURRENT
BIAS CURRENT (mA)
TEMPERATURE (°C)
SWITCH OFF TIME (ns)
1945 G04
550
500
450
400
350
300
250
–50 –25 0 25 50 75 100
V
IN
= 1.2V
V
IN
= 12V
TEMPERATURE (°C)
PEAK CURRENT (mA)
1945 G05
400
350
300
250
200
150
100
50
0
–50 –25 0 25 50 75 100
V
IN
= 12V
V
IN
= 1.2V
TEMPERATURE (°C)
QUIESCENT CURRENT (μA)
1945 G06
25
23
21
19
17
15
–50 –25 0 25 50 75 100
V
IN
= 12V
V
IN
= 1.2V
V
FB
= 1.23V
NOT SWITCHING
Switch Off Time Switch Current Limit Quiescent Current
Switch Saturation Voltage
(VCESAT)
FB2 Pin Voltage and
Bias Current
NFB1 Pin Voltage and
Bias Current