LT138A/LT338A
LM138/LM338
APPLICATIONS INFORMATION
negative side of the load. Although it may not be immedi-
ately obvious, best load regulation is obtained when the
top of the resistor divider, R1, is connected
directly
to the
case
not to the load.
This is illustrated in
Figure 3.
If R1
were connected to the load, the effective resistance be-
tween the regulator and the load would be:
LT338A
V
IN
V
IN
ADJ
V
OUT
CONNECT
R1 TO CASE
R1
R
L
R2
CONNECT
R2 TO LOAD
138A/338A F03
R2
+
R1
R
P
, R
P
=
Parasitic Line Re sistance
R1
Connected as shown, R
P
is not multiplied by the divider
ratio. R
P
is about 0.004Ω per foot using 16 gauge wire.
This translates to 4mV/ft at 1A load current, so it is
important to keep the positive lead between regulator and
load as short as possible, and use large wire or PC board
traces.
TYPICAL APPLICATIONS
Improving Ripple Rejection
LT338A
V
IN
+
1µF
*C1 IMPROVES RIPPLE REJECTION, X
C
SHOULD BE SMALL COMPARED TO R2
1.2V to 25V Adjustable Regulator
LT338A
V
IN
V
IN
ADJ
V
OUT
R1
240Ω
R2
5k
V
OUT
†
+
*NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS
**OPTIONAL, IMPROVES TRANSIENT RESPONSE
†
V
OUT
= 1.25V 1 + R2
R1
U
W
U
U
U
R
P
PARASITIC
LINE RESISTANCE
Figure 3. Connections for Best Load Regulation
V
IN
ADJ
V
OUT
R1
121Ω
1%
R2
365Ω
1%
5V
+
C
L
*
10µF
138A/338A TA03
C1*
1µF
+
C2**
1µF
138A/338A TA04
( )
7
LINER [ LINEAR TECHNOLOGY ]
