LTC3785 Datasheet, PDF (5/20 Pages) Linear Technology – 10V, High Effi ciency, Synchronous, No RSENSE Buck-Boost Controller

LTC3785
TYPICAL PERFOR A CE CHARACTERISTICS (T_A = 25°C unless otherwise noted)
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
3785 G10
V_IN Burst Quiescent Current vs
Temperature
100
95
90
85
80
–50 –25 0
25 50
TEMPERATURE (°C)
75 100
3785 G11
OV and UV Thresholds vs
Temperature
12
10
8
OV THRESHOLD
6
4
2
0
–2
–4
UV THRESHOLD
–6
–8
–50 –25 0 25 50
TEMPERATURE (°C)
75 100
3785 G12
PI FU CTIO S
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 10% above
the regulated FB voltage and the undervoltage threshold
is internally set 6.5% below the FB regulated voltage. This
pin can be tied to FB but to optimize the response time it
is recommended that a voltage divider from V_OUT be ap-
plied. 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 simi-
lar 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.
3785f
5