Datasheet LTC3785 (Analog Devices) - 6

LTC3785 pin FuncTions
VSENSE (Pin 4):
Overvoltage and Undervoltage Sense.
SW2 (Pin 13):
Ground Reference for Driver D. Gate drive The overvoltage threshold is internally set 10% above from TG2 will reference to the common point of output the regulated FB voltage and the undervoltage threshold switches C and D. is internally set 6.5% below the FB regulated voltage. This
I
pin can be tied to FB but to optimize the response time it
SSW2 (Pin 14):
Reverse Current Limit Comparator Invert- ing Input. This pin is normally connected to the source of is recommended that a voltage divider from VOUT be ap- the N-channel MOSFET D (TG2 driven). plied. The divider can be skewed from the feedback value to achieve the desired UV or OV threshold.
VDRV (Pin 16):
Driver Supply for Ground Referenced Switches. Connect this pin to V
I
CC potential.
LSET (Pin 5):
Current Limit Set. A resistor from this pin to ground sets the current limit threshold from the ISVIN
BG1, BG2 (Pins 17, 15):
Bottom gate driver pins drive and ISSW1 pins. the ground referenced N-channel MOSFET switches B and C.
CCM (Pin 6):
Continuous Conduction Mode Control Pin. When set low, the inductor current is allowed to go slightly
ISSW1 (Pin 18):
Forward Current Limit Comparator Non- negative (–15mV referenced to the ISVOUT – ISSW2 pins). inverting Input. This pin is normally connected to the When driven high, the reverse current limit is set to the source of the N-channel MOSFET A (TG1 driven). similar value of the forward current limit set by the ILSET
SW1 (Pin 19):
Ground Reference for Driver A. Gate drive pin. from TG1 will reference to the common point of output
RT (Pin 7):
Oscil ator Programming Pin. A resistor from this switches A and B. pin to GND sets the free-running frequency of the IC.
TG1, TG2 (Pins 20, 12):
Top gate drive pins drive the  25000 top N-channel MOSFET switches A and D with a voltage f ≅ MHz OSC swing equal to VCC – VDIODE superimposed on the SW1  RT  and SW2 nodes respectively.
MODE (Pin 8):
Burst Mode Control Pin.
VBST1 (Pin 21):
Boosted Floating Driver Supply for the • MODE = High: Enable Burst Mode Operation. In Burst Buck Switch A. This pin will swing from a diode below Mode operation the operation is variable frequency, VCC up to VIN + VCC – VDIODE. which provides a significant efficiency improvement
ISVIN (Pin 22):
Forward Current Limit Comparator Invert- at light loads. The Burst Mode operation will continue ing Input. This pin is normally connected to the drain of until the pin is driven low. N-channel MOSFET A (TG1 driven). • MODE = Low: Disable Burst Mode operation and maintain
VCC (Pin 23):
Internal 4.35V LDO Regulator Output. The low noise, constant frequency operation. driver and control circuits are powered from this voltage
NC (Pin 9):
No Connect. There is no electrical connection to limit the maximum VGS drive voltage. Decouple this pin to this pin inside the package. to power ground with at least a 4.7µF ceramic capacitor. For low VIN applications, VCC can be bootstrapped from
ISVOUT (Pin 10):
Reverse Current Limit Comparator Non- VOUT through a Schottky diode. inverting Input. This pin is normally connected to the drain of the N-channel MOSFET D (TG2 driven).
VIN (Pin 24):
Input Supply Pin for the VCC Regulator. A ceramic capacitor of at least 10µF is recommended close
VBST2 (Pin 11):
Boosted Floating Driver Supply for Boost to the VIN and GND pins. Switch D. This pin will swing from a diode below VCC up to V
Ground (Exposed Pad Pin 25):
The GND and PGND pins OUT + VCC – VDIODE. are connected to the exposed pad which must be con- nected to the PCB ground for electrical contact and rated thermal performance. 3785fc Document Outline Features Applications Description Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Block Diagram Operation Applications Information Typical Application Package Description Revision History Typical Application Related Parts