Datasheet
8
LT1521/LT1521-3
LT1521-3.3/LT1521-5
1521335fb
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
OUT (Pin 1): The output pin supplies power to the load. A
minimum output capacitor of 1.5µF is required to prevent
oscillations, but larger values of output capacitor will be
necessary to deal with larger load transients. See the
Applications Information section for more on output
capacitance and reverse output characteristics.
SENSE (Pin 2): For fixed voltage versions of the LT1521
(LT1521-3, LT1521-3.3, LT1521-5), the sense pin is the
input to the error amplifier. Optimum regulation will be
obtained at the point where the sense pin is connected to
PIN FUNCTIONS
UUU
LT1521-5
Transient Response
TIME (µs)
0
OUTPUT VOLTAGE
DEVIATION (V)
LOAD CURRENT
(mA)
0.2
0.1
0
–0.1
–0.2
150
100
50
400
LT1521 • TPC33
10050 150 250 350 450
200
300
500
V
IN
= 6V
C
IN
= 0.1µF
C
OUT
= 1.5µF
FREQUENCY (Hz)
RIPPLE REJECTION (dB)
100
90
80
70
60
50
40
30
20
10
0
10 1k 10k 1M
LT1521 • TPC31
100 100k
I
LOAD
= 150mA
V
IN
= 6V + 50mV
RMS
RIPPLE
C
OUT
= 33µF
SOLID TANTALUM
C
OUT
= 3.3µF
SOLID TANTALUM
Ripple Rejection
Load Regulation
TEMPERATURE (°C)
–50
LOAD REGULATION (mV)
25
LT1521 • TPC32
–25 0 50
0
–5
–10
–15
–20
–25
–30
–35
–40
75 100 125
∆I
LOAD
= 1mA TO 300mA
LT1521-3.3
LT1521-3
LT1521*
LT1521-5
V
IN
= V
OUT
(NOMINAL + 1V)
*V
ADJ
= V
OUT
LT1521-5
Transient Response
TIME (ms)
0
OUTPUT VOLTAGE
DEVIATION (V)
LOAD CURRENT
(mA)
0.2
0.1
0
–0.1
–0.2
300
200
100
4.0
LT1521 • TPC34
1.00.5 1.5 2.5 3.5 4.5
2.0
3.0
5.0
V
IN
= 6V
C
IN
= 0.1µF
C
OUT
= 33µF
the output pin of the regulator. In critical applications small
voltage drops caused by the resistance (R
P
) of PC traces
between the regulator and the load, which would normally
degrade regulation, may be eliminated by connecting the
sense pin to the output at the load as shown in Figure 1
(Kelvin Sense Connection). Note that the voltage drop
across the external PC traces will add to the dropout
voltage of the regulator. The sense pin bias current is 5µA
at the nominal regulated output voltage. This pin is inter-
nally clamped to –0.6V (one V
BE
).