Datasheet

LT3477
5
3477fc
I
ADJ
VOLTAGE (mV)
0
0
VOLTAGE SENSE (mV)
20
40
60
80
200 400
600
800
2477 G13
100
120
100 300
500
700
V
CM
= 10V
TEMPERATURE (°C)
–50
CURRENT SENSE VOLTAGE (mV)
103
25
3477 G14
100
98
–25 0 50
97
96
104
102
101
99
75 100 125
V
CM
= 10V
V
CM
= 42V
TYPICAL PERFORMANCE CHARACTERISTICS
Current Sense Voltage vs I
ADJ
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 V
IN
, or to fl oat.
V
IN
(Pin 3/Pin 1): Input Supply. Must be locally bypassed.
Powers the internal control circuitry.
R
T
(Pin 4/Pin 2): Timing Resistor Pin. Adjusts the switch-
ing frequency. Connect a 17.2k resistor between R
T
and
GND for a 1MHz switching frequency. Do not leave this pin
open. See Table 4 for additional R
T
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 fl oating if not in use.
V
C
(Pin 7/Pin 5): Compensation Pin for Error Amplifi er.
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-
fi er. Connect resistive divider tap here for positive output
voltage.
FBP (Pin 9/Pin 7): The Noninverting Input to the Error
Amplifi er. Connect resistive divider tap here for negative
output voltage.
V
REF
(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.
I
ADJ2
(Pin 11/Pin 9): Second Current Sense Adjustment.
Setting I
ADJ2
to be l es s t han 625mV leads to adju st ment of
the sensed voltage of the second current sense amplifi er
linearly. If I
ADJ2
is tied to higher than 650mV, the default
current sense voltage is 100mV. If current sense amplifi er 2
is not used, always tie I
ADJ2
to higher than 650mV.
I
ADJ1
(Pin 12/Pin 10): First Current Sense Adjustment.
Setting I
ADJ1
to be less than 625mV leads to adjustment
of the sensed voltage of the fi rst current sense amplifi er
linearly. If I
ADJ1
is tied to higher than 650mV, the default
current sense voltage is 100mV. If current sense amplifi er 1
is not used, always tie I
ADJ1
to higher than 650mV.