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LT3477

3477fc

IADJ VOLTAGE (mV)

200

400

600

800

2477 G13

100

120

100

300

500

700

VCM = 10V

TEMPERATURE (°C)

–50

103

3477 G14

100

–25

104

102

101

100

125

VCM = 10V

VCM = 42V

TYPICAL PERFORMANCE CHARACTERISTICS

Current Sense Voltage vs IADJ

Current Sense Voltage

vs Temperature

PIN FUNCTIONS (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 generat-

ing 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 ampliﬁer 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 ampliﬁer 1

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

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