LT3477 데이터 시트보기 (PDF) - Linear Technology

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LT3477

3A, DC/DC Converter with Dual Rail-to-Rail Current Sense

Linear Technology 

TYPICAL PERFOR A CE CHARACTERISTICS

LT3477

Current Sense Voltage

vs Temperature

104

103

102

101

100

VCM = 10V

99

98

VCM = 42V

97

96

–50 –25

0 25 50 75

TEMPERATURE (°C)

100 125

3477 G14

Current Sense Voltage

vs IADJ

120

VCM = 10V

100

80

60

40

20

0

0 100 200 300 400 500 600 700 800

IADJ VOLTAGE (mV)

2477 G13

PI FU CTIO S (QFN/TSSOP)

NC (Pins 1, 2, 20/Pins 18, 19, 20): No Connect Pin. Okay

to connect to ground or VIN, or to float.

VIN (Pin 3/Pin 1): Input Supply. Must be locally bypassed.

Powers the internal control circuitry.

RT (Pin 4/Pin 2): Timing Resistor Pin. Adjusts the switch-

ing frequency. Connect a 17.2k resistor between RT and

GND for a 1MHz switching frequency. Do not leave this pin

open. See Table 4 for additional RT values and switching

frequencies.

SHDN (Pin 5/Pin 3): Shutdown. Tie to 2V or greater to

enable the device. Tie below 0.3V to turn off the device.

SS (Pin 6/Pin 4): Soft-Start. Place a soft-start capacitor

here. Leave floating if not in use.

VC (Pin 7/Pin 5): Compensation Pin for Error Amplifier.

Connect a series RC from this pin to GND. Typical values

are 1kΩ and 4.7nF.

FBN (Pin 8/Pin 6): The Inverting Input to the Error Ampli-

fier. Connect resistive divider tap here for positive output

voltage.

FBP (Pin 9/Pin 7): The Noninverting Input to the Error

Amplifier. Connect resistive divider tap here for negative

output voltage.

VREF (Pin 10/Pin 8): Bandgap Voltage Reference. Inter-

nally set to 1.235V. Connect this pin to FBP if generating

a positive output or to an external resistor divider if

generating a negative voltage. This pin can provide up to

100µA of current and can be locally bypassed with a 100pF

capacitor.

IADJ2 (Pin 11/Pin 9): Second Current Sense Adjustment.

Setting IADJ2 to be less than 625mV leads to adjustment of

the sensed voltage of the second current sense amplifier

linearly. If IADJ2 is tied to higher than 650mV, the default

current sense voltage is 100mV. If current sense ampli-

fier 2 is not used, always tie IADJ2 to higher than 650mV.

IADJ1 (Pin 12/Pin 10): First Current Sense Adjustment.

Setting IADJ1 to be less than 625mV leads to adjustment of

the sensed voltage of the first current sense amplifier

linearly. If IADJ1 is tied to higher than 650mV, the default

current sense voltage is 100mV. If current sense ampli-

fier 1 is not used, always tie IADJ1 to higher than 650mV.

3477fb

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