Datasheet LTC3805 (Analog Devices) - 7

LTC3805
pin Functions SSFLT (Pin 1):
Soft-Start Pin. A capacitor placed from
ISENSE (Pin 7):
Performs two functions: for current mode this pin to GND (Exposed Pad) controls the rate of rise of control, it monitors the switch current, using the voltage converter output voltage during start-up. This capacitor is across an external current sense resistor. Pin 7 also injects also used for time out after a fault prior to restart. a current ramp that develops slope compensation voltage
I
across an optional external programming resistor.
TH (Pin 2):
Error Amplifier Compensation Point. Normal operating voltage range is clamped between 0.7V and 1.9V.
OC (Pin 8):
Overcurrent Pin. Connect this pin to the ex-
FB (Pin 3):
Receives the feedback voltage from an external ternal switch current sense resistor. An additional resistor resistor divider across the output. programs the overcurrent trip level.
RUN (Pin 4):
An external resistor divider connects this
VCC (Pin 9):
Supply Pin. A capacitor must closely decouple pin to V VCC to GND (Exposed Pad). IN and sets the thresholds for converter operation.
FS (Pin 5):
A resistor connected from this pin to ground
GATE (Pin 10):
Gate Drive for the External N-channel sets the frequency of operation. MOSFET. This pin swings from GND to VCC.
SYNC (Pin 6):
Input to synchronize the oscillator to an
GND (Exposed Pad Pin 11):
Ground. A capacitor must external source. closely decouple GND to VCC (Pin 9). The exposed pad must be soldered to electrical ground on PCB for electrical contact and rated thermal performance.
block DiagraM
9 4 VCC RUN SOFT-START RAMP 800mV UNDERVOLTAGE REFERENCE LOCKOUT SSFLT 1 SHUTDOWN SOFT-START OVERCURRENT FAULT 10µA COMPARATOR OC 8 + 100mV – – CURRENT COMPARATOR GATE ERROR R SWITCHING + AMPLIFIER + DRIVER GATE Q LOGIC AND BLANKING 10 S CIRCUIT FB 3 – SLOPE SHUTDOWN COMP 20mV CURRENT OSCILLATOR RAMP ITH CLAMPS GND ISENSE 11 1.2V 7 ITH FS SYNC 2 5 6 3805 BD 3805fg 7 Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration 0rder Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Application Package Description Revision History Typical Application Related Parts