Datasheet

LTC3785
5
3785fc
Typical perForMance characTerisTics
V
IN
Start-Up Voltage
vs Temperature
V
IN
Burst Quiescent Current
vs Temperature
OV and UV Thresholds
vs Temperature
V
FB
vs Temperature
Normalized Oscillator Frequency
vs Temperature Oscillator Frequency vs RT
T
A
= 25°C, unless otherwise noted.
pin FuncTions
RUN/SS (Pin 1): Run Control and Soft-Start Input. An
internal 1µA charges the soft-start capacitor and will
charge to approximately 2.5V. During a current limit fault,
the soft-start capacitor will incrementally discharge. Once
the pin drops below 1.225V the IC will enter fault mode,
turning off the outputs for 32 times the soft-start time. If
>5µA (at RUN/SS = 1.225V) is applied externally, the part
will latch off after a fault is detected. If >40µA (at RUN/SS
= 1.225V) is applied externally, current limit faults will not
discharge the SS capacitor.
V
C
(Pin 2): Error Amp Output. A frequency compensa-
tion network is connected from this pin to the FB pin to
compensate the loop. See Closing the Feedback Loop in
the Applications Information section for guidelines.
FB (Pin 3): Feedback Pin. Connect resistor divider tap
here. The feedback reference voltage is typically 1.225V
The output voltage can be adjusted from 2.7V to 10V ac-
cording to the following formula:
V
OUT
=1.225V •
R1+R2
R2
TEMPERATURE (°C)
–50
1.2255
1.2245
1.2250
1.2240
1.2235
1.2230
1.2225
1.2220
1.2215
25 75
3785 G07
–25 0
50 150125100
V
FB
(V)
TEMPERATURE (°C)
–50 25 75
–25 0
50 150125100
–1.0
CHANGE FROM 25°C (%)
–0.6
–0.2
0.2
3785 G08
0.6
1.0
–0.8
–0.4
0
0.4
0.8
RT (kΩ)
20
0
OSCILLATOR FREQUENCY (kHz)
200
400
600
800
1000
1200
40 60 80 100
3785 G09
TEMPERATURE (°C)
–50 25 75
–25 0
50 150125100
2.465
V
IN
START-UP VOLTAGE (V)
2.470
2.475
2.480
2.485
2.490
3785 G10
TEMPERATURE (°C)
–50 25 75
–25 0
50 150125100
V
IN
CURRENT (µA)
3785 G11
80
85
100
90
95
TEMPERATURE (°C)
–50 25 75
–25 0
50 150125100
–8
THRESHOLD (%)
–4
0
4
3785 G12
8
12
–6
–2
2
6
10
OV THRESHOLD
UV THRESHOLD