LTC1612 Просмотр технического описания (PDF) - Linear Technology

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LTC1612

Synchronous, Step-Down 800kHz PWM DC/DC Converter

Linear Technology 

LT1612

ELECTRICAL CHARACTERISTICS The q denotes specifications which apply over the full operating

temperature range, otherwise specifications are TA = 25°C, VIN = VSHDN = 3V

SYMBOL PARAMETER

SHDN Pin Current

BOOST Pin Current

Switch Current Limit (Note 4)

CONDITIONS

SHDN = 2V

SHDN = 5V

BOOST = VIN + 2V

Duty Cycle = 0%

MODE = OV

MIN

q

q

600

TYP MAX

10

15

30

45

4

710 900

UNITS

µA

µA

mA

mA

MODE = 5V

550 650 900

mA

Burst Mode Operation Current Limit

MODE = 0V

180

mA

Switch Voltage Drop

Rectifier Voltage Drop

SW Pin Leakage

ISW = 500mA

IRECT = 500mA

VSW = 5V

200 280

mV

300 400

mV

q

1

µA

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 2: The LT1612E is guaranteed to meet performance specifications

from 0°C to 70°C. Specifications over the –40°C to 85°C operating

temperature range are assured by design, characterization and correlation

with statistical process controls.

Note 3: Bias current flows out of the FB pin.

Note 4: Duty cycle affects current limit due to slope compensation.

PIN FUNCTIONS

VC (Pin 1): Compensation Pin. This is the current sink/

source output of the error amplifier. By connecting an RC

network from this pin to ground, frequency response can

be tuned for a wide range of circuit configurations. The

voltage at this pin also sets the current limit, and if

grounded, the switch will remain in the OFF state.

FB (Pin 2): Feedback Pin. This pin is the negative input to

the error amplifier. Connect the resistor divider tap to this

point which sets VOUT according to:

VOUT = 0.62V (1 + R1/R2)

VIN (Pin 3): Supply Pin. Bypass capacitor C1 must be right

next to this pin.

GND (Pin 4): Ground Pin. Connect directly to local ground

plane.

SW (Pin 5): Switch Pin. Connect inductor and boost

capacitor here. Minimize trace area at this pin to keep EMI

down.

BOOST (Pin 6): This is the supply pin for the switch driver

and must be above VIN by 1.5V for proper switch opera-

tion. Connect the boost capacitor to this pin.

MODE (Pin 7): Burst Mode Operation Disable Pin. For

continuous switching operation (low noise), pull this pin

above 2V. For Burst Mode operation which gives better

light load efficiency, tie to ground. Output ripple voltage in

Burst Mode operation is typically 30mVP-P. See applica-

tions section for more information about this function.

SHDN (Pin 8): Shutdown Pin. Pull this pin low for shut-

down mode. Tie to a voltage between 2V and 5.5V for

normal operation.

3

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