LTC3785-1 Linear Technology, LTC3785-1 Datasheet - Page 5

• Manufacturer Part Number: LTC3785-1
• Description: Buck-Boost Controller
• Manufacturer: Linear Technology

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TYPICAL PERFORMANCE CHARACTERISTICS
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
network is connected from this pin to the FB pin to com-
pensate the loop. See the section “Closing the Feedback
Loop” 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:
C
2.490
2.485
2.480
2.475
2.470
2.465
(Pin 2): Error Amp Output. A frequency compensation
V
OUT
–50
V
Temperature
IN
=
Start-Up Voltage vs
–25
1 225
.
TEMPERATURE (°C)
0
V
•
R
25
1
R
+
2
R
50
2
75
37851 G10
100
100
95
90
85
80
–50
V
Temperature
IN
Burst Quiescent Current vs
–25
TEMPERATURE (°C)
0
25
V
The overvoltage threshold is internally set 7.5% above
the regulated FB voltage and the undervoltage threshold
is internally set 7.5% below the FB regulated voltage. This
pin can be tied to FB but to optimize the response time it
is recommended that a separate voltage divider from V
be applied. The divider can be skewed from the feedback
value to achieve the desired UV or OV threshold.
I
to ground sets the current limit threshold from the I
and I
CCM (Pin 6): Continuous Conduction Mode Control Pin.
When set low, the inductor current is allowed to go slightly
negative (–15mV referenced to the I
When driven high, the reverse current limit is set to the similar
value of the forward current limit set by the I
RT (Pin 7): Oscillator Programming Pin. A resistor from
this pin to GND sets the free-running frequency of the IC.
f
LSET
OSC
SENSE
50
≅ 2.5e10/RT.
SSW1
(Pin 5): Current Limit Set. A resistor from this pin
(Pin 4): Overvoltage and Undervoltage Sense.
75
pins.
37851 G11
100
–2
–4
–6
–8
8
6
4
2
0
–50
OV and UV Thresholds vs
Temperature
–25
TEMPERATURE (°C)
LTC3785-1
0
OV THRESHOLD
UV THRESHOLD
SVOUT
25
LSET
– I
50
SSW2
pin.
75
pins).
37851 G12
SVIN
37851f
5
OUT
100