LTC3785-1 Datasheet, PDF (5/20 Pages) Linear Technology – 10V, High Effi ciency, Buck-Boost Controller with Power Good

TYPICAL PERFORMANCE CHARACTERISTICS
V_IN Start-Up Voltage vs
Temperature
2.490
2.485
2.480
2.475
2.470
2.465
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
37851 G10
V_IN Burst Quiescent Current vs
Temperature
100
95
90
85
80
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
37851 G11
LTC3785-1
OV and UV Thresholds vs
Temperature
8
6
OV THRESHOLD
4
2
0
–2
–4
–6
UV THRESHOLD
–8
–50
–25 0 25 50
TEMPERATURE (°C)
75 100
37851 G12
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 compensation
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:
V_OUT
=
1.225V
•
R1+ R2
R2
V_SENSE (Pin 4): Overvoltage and Undervoltage Sense.
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_OUT
be applied. The divider can be skewed from the feedback
value to achieve the desired UV or OV threshold.
I_LSET (Pin 5): Current Limit Set. A resistor from this pin
to ground sets the current limit threshold from the I_SVIN
and I_SSW1 pins.
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_SVOUT – I_SSW2 pins).
When driven high, the reverse current limit is set to the similar
value of the forward current limit set by the I_LSET pin.
RT (Pin 7): Oscillator Programming Pin. A resistor from
this pin to GND sets the free-running frequency of the IC.
f_OSC ≅ 2.5e10/RT.
37851f
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