LT1521/LT1521-3
LT1521-3.3/LT1521-5
TYPICAL PERFORMANCE CHARACTERISTICS
Ripple Rejection
100
90
80
RIPPLE REJECTION (dB)
I
LOAD
= 150mA
V
IN
= 6V + 50mV
RMS
RIPPLE
LOAD REGULATION (mV)
70
60
50
40
30
20
10
0
10
100
C
OUT
= 3.3µF
SOLID TANTALUM
1k
10k
FREQUENCY (Hz)
100k
1M
C
OUT
= 33µF
SOLID TANTALUM
LT1521-5
Transient Response
OUTPUT VOLTAGE
DEVIATION (V)
0.2
0.1
0
–0.1
–0.2
LOAD CURRENT
(mA)
LOAD CURRENT
(mA)
OUTPUT VOLTAGE
DEVIATION (V)
V
IN
= 6V
C
IN
= 0.1µF
C
OUT
= 1.5µF
0.2
0.1
0
–0.1
–0.2
150
100
50
0
50 100 150 200 250 300 350 400 450 500
TIME (µs)
LT1521 • TPC33
PIN FUNCTIONS
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
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
).
8
U W
Load Regulation
0
–5
–10
–15
LT1521*
–20
–25
–30
–35
V
IN
= V
OUT
(NOMINAL + 1V)
*V
ADJ
= V
OUT
0
50
75
25
TEMPERATURE (°C)
100
125
∆I
LOAD
= 1mA TO 300mA
LT1521-5
LT1521-3
LT1521-3.3
–40
–50 –25
LT1521 • TPC31
LT1521 • TPC32
LT1521-5
Transient Response
V
IN
= 6V
C
IN
= 0.1µF
C
OUT
= 33µF
300
200
100
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
TIME (ms)
LT1521 • TPC34
U
U
U
LINER [ LINEAR TECHNOLOGY ]
