7

LT138A/LT338A

LM138/LM338

138afb

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:

R

RR

R

R

Parasitic Line

sis

ce

PP

21

1

+









=

,

Re

tan

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.

LT338A

PARASITIC

LINE RESISTANCE

R1

CONNECT

R1 TO CASE

CONNECT

R2 TO LOAD

138A/338A F03

ADJ

R2

Figure 3. Connections for Best Load Regulation

Improving Ripple Rejection

LT338A

R1

121

Ω

1%

R2

365

Ω

1%

1

µF

SHOULD BE SMALL COMPARED TO R2

10

µF

138A/338A TA03

ADJ

5V

+

+

1.2V to 25V Adjustable Regulator

LT338A

R1

240

Ω

C1*

1

µF

NEEDED IF DEVICE IS FAR FROM FILTER CAPACITORS

OPTIONAL, IMPROVES TRANSIENT RESPONSE

R2

5k

138A/338A TA04

ADJ

†

+

C2**

1

µF

*

**

+

R2

R1

1 +

()