LT8705 Просмотр технического описания (PDF) - Linear Technology

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LT8705

80V VIN and VOUT Synchronous 4-Switch Buck Boost DC/DC Controller

Linear Technology 

LT8705

PIN FUNCTIONS (QFN/TSSOP)

SHDN (Pin 1/Pin 4): Shutdown Pin. Tie high to enable

device. Ground to shut down and reduce quiescent current

to a minimum. Do not float this pin.

RT (Pin 12/Pin 15): Timing Resistor Pin. Adjusts the switch-

ing frequency. Place a resistor from this pin to ground to

set the free-running frequency. Do not float this pin.

CSN (Pin 2/Pin 5): The (–) Input to the Inductor Current

Sense and Reverse-Current Detect Amplifier.

CSP (Pin 3/Pin 6): The (+) Input to the Inductor Current

Sense and Reverse-Current Detect Amplifier. The VC pin

voltage and built-in offsets between CSP and CSN pins, in

conjunction with the RSENSE resistor value, set the current

trip threshold.

LDO33 (Pin 4/Pin7): 3.3V Regulator Output. Bypass this

pin to ground with a minimum 0.1μF ceramic capacitor.

FBIN (Pin 5/Pin 8): Input Feedback Pin. This pin is con-

nected to the input error amplifier input.

FBOUT (Pin 6/Pin 9): Output Feedback Pin. This pin

connects the error amplifier input to an external resistor

divider from the output.

IMON_OUT (Pin 7/Pin 10): Output Current Monitor Pin. The

current out of this pin is proportional to the output current.

See the Operation and Applications Information sections.

VC (Pin 8/Pin 11): Error Amplifier Output Pin. Tie external

compensation network to this pin.

SS (Pin 9/Pin 12): Soft-Start Pin. Place at least 100nF of

capacitance here. Upon start-up, this pin will be charged

by an internal resistor to 2.5V.

CLKOUT (Pin 10/Pin 13): Clock Output Pin. Use this pin to

synchronize one or more compatible switching regulator

ICs to the LT8705. CLKOUT toggles at the same frequency

as the internal oscillator or as the SYNC pin, but is ap-

proximately 180° out of phase. CLKOUT may also be used

as a temperature monitor since the CLKOUT duty cycle

varies linearly with the part’s junction temperature. The

CLKOUT pin can drive capacitive loads up to 200pF.

SYNC (Pin 11/Pin 14): To synchronize the switching fre-

quency to an outside clock, simply drive this pin with a

clock. The high voltage level of the clock needs to exceed

1.3V, and the low level should be less than 0.5V. Drive this

pin to less than 0.5V to revert to the internal free-running

clock. See the Applications Information section for more

information.

BG1, BG2 (Pins 14, 16/Pins 17, 19): Bottom Gate Drive.

Drives the gates of the bottom N-channel MOSFETs be-

tween ground and GATEVCC.

GATEVCC (Pin 15/Pin 18): Power Supply for Gate Drivers.

Must be connected to the INTVCC pin. Do not power from

any other supply. Locally bypass to GND.

BOOST1, BOOST2 (Pins 23, 17/Pins 28, 20): Boosted

Floating Driver Supply. The (+) terminal of the bootstrap

capacitor connects here. The BOOST1 pin swings from a

diode voltage below GATEVCC up to VIN + GATEVCC. The

BOOST2 pin swings from a diode voltage below GATEVCC

up to VOUT + GATEVCC

TG1, TG2 (Pins 22, 18/Pins 26, 21): Top Gate Drive. Drives

the top N-channel MOSFETs with voltage swings equal

to GATEVCC superimposed on the switch node voltages.

SW1, SW2 (Pins 21, 19/Pins 24, 22): Switch Nodes. The

(–) terminals of the bootstrap capacitors connect here.

SRVO_FBIN (Pin 25 QFN Only): Open-Drain Logic Out-

put. This pin is pulled to ground when the input voltage

feedback loop is active.

SRVO_IIN (Pin 26 QFN Only): Open-Drain Logic Output.

The pin is pulled to ground when the input current loop

is active.

SRVO_IOUT (Pin 27 QFN Only): Open-Drain Logic Out-

put. The pin is pulled to ground when the output current

feedback loop is active.

SRVO_FBOUT (Pin 28 QFN Only): Open-Drain Logic Out-

put. This pin is pulled to ground when the output voltage

feedback loop is active.

EXTVCC (Pin 29/Pin 30): External VCC Input. When EXTVCC

exceeds 6.4V (typical), INTVCC will be powered from this

pin. When EXTVCC is lower than 6.22V (typical), INTVCC

will be powered from VIN.

CSNOUT (Pin 30/Pin 32): The (–) Input to the Output Cur-

rent Monitor Amplifier. Connect this pin to VOUT when not

in use. See Applications Information section for proper

use of this pin.

8705p

For more information www.linear.com/8705

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