SPX2810 datasheet(6/9 Pages) SIPEX

6 / 9 page

Date: 5/25/04

SPX2810 1A Low Dropout Linear Regulator

Figure 11. 12.5V Regulator with Shutdown

Figure 10. Improving Ripple Rejection

Figure 12. Recommended Connections for Best Results

Output Voltage

The output of the adjustable regulator can be set to any voltage between 1.25V and 10V. The value

of V

OUT can be quickly approximated using the formula (Figure 9)

OUT=1.25 *(R1 + R2)/R1.

A small correction to this formula is required depending on the values of resistors R1 and R2, since

adjustable pin current (approx 50

µA) flows through R2. When I

ADJ is taken into account, the formula

becomes

OUT = VREF(1+ (R2/R1)) + IADJ * R2, where VREF=1.25V.

Layout Considerations

Parasitic line resistance can degrade load regulation. In order not to affect the behavior of the regulator,

it is best to connect R

1 to the case as illustrated in Figure 11. For the same reason, R2 should be

connected to the negative side of the load.

SPX2810

R 2

R 1

Connect R

to Load

R L

Connect R1 to

Case of Regulator

RP Parasitic Line

Resistance

OUT

ADJ

SPX2810

10µF

Ω

330Ω

4.7µF

ADJ

OUT

(Note A)

TTL

Input

2N3904

DROPOUT (MAX)

Note A: V

IN(MIN)

= (Intended V

OUT

) + (V

)

SPX2810

10µF

10µF*

1kΩ,

330Ω

4.7µF

improves ripple rejection.

should be ~ R1 at ripple frequency

ADJ

OUT

(Note A)

OUT

Note A: V

IN(MIN) = (Intended VOUT

) + (V DROPOUT (MAX))

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