Datasheet

LT3085
7
3085fb
TYPICAL PERFORMANCE CHARACTERISTICS
Error Amplifi er Gain and Phase
FREQUENCY (Hz)
10
GAIN (dB)
PHASE (deg)
9
15
21
100k
3085 G28
3
–3
6
12
18
0
–6
–9
–72
72
216
–216
–360
–144
0
144
–288
–432
–504
100
1k
10k
1M
I
LOAD
= 500mA
I
LOAD
= 100mA
I
LOAD
= 100mA
I
LOAD
= 500mA
Ripple Rejection - SET Pin Current
FREQUENCY (Hz)
0
RIPPLE REJECTION (dB)
60
150
10k 100k10010 1k 1M
3085 G29
30
90
120
45
135
15
75
105
C
SET
= 0.1μF
C
SET
= 0
R
SET
= 100k
V
IN
= V
CONTROL
= V
OUT (NOMINAL)
+2V
RIPPLE = 50mV
P–P
PIN FUNCTIONS
V
CONTROL
(Pin 4/Pin 5): This pin is the supply pin for the
control circuitry of the device. The current fl ow into this
pin is about 1.7% of the output current. For the device to
regulate, this voltage must be more than 1.2V to 1.35V
greater than the output voltage (see V
CONTROL
Dropout
Voltage in the Electrical Characteristics table and graphs
in the Typical Performance Characteristics). The LT3085
requires a bypass capacitor at V
CONTROL
if more than six
inches away from the main input fi lter capacitor. The output
impedance of a battery rises with frequency, so include
a bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1μF to 10μF suffi ces.
IN (Pins 5, 6/Pins 7, 8): This is the collector to the power
device of the LT3085. The output load current is supplied
through this pin. For the device to regulate, the voltage at
this pin must be more than 0.1V to 0.5V greater than the
output voltage (see V
IN
Dropout Voltage in the Electrical
Characteristics table and graphs in the Typical Perfor-
mance Characteristics). The LT3085 requires a bypass
capacitor at IN if more than six inches away from the main
input fi lter capacitor. The output impedance of a battery
rises with frequency, so include a bypass capacitor in
battery-powered circuits. A bypass capacitor in the range
of 1μF to 10μF suffi ces.
NC (NA/Pin 6): No Connection. The No Connect pin has
no connection to internal circuitry and may be tied to V
IN
,
V
CONTROL
, V
OUT
, GND, or fl oated.
OUT (Pins 1, 2/Pins 1, 2, 3): This is the power output
of the device. There must be a minimum load current of
1mA or the output may not regulate. A minimum 2.2μF
output capacitor is required for stability.
SET (Pin 3/Pin 4): This pin is the non-inverting input to the
error amplifi er and the regulation set point for the device.
A fi xed current of 10μA fl ows out of this pin through a
single external resistor, which programs the output voltage
of the device. Output voltage range is zero to the absolute
maximum rated output voltage. Transient performance can
be improved and output noise can be decreased by adding
a small capacitor from the SET pin to ground.
Exposed Pad (Pin 7/Pin 9): OUT. Tie directly to Pins 1, 2/
Pins 2, 3 directly at the PCB.
(DCB/MS8E)