1

2

3

6

5

4

V

REF

R

1

C

1

V

IN

REF3212-EP, REF3220-EP, REF3225-EP

REF3230-EP, REF3233-EP, REF3240-EP

SBVS078B

– OCTOBER 2006 – REVISED AUGUST 2011

www.ti.com

Figure 6. Application Circuit to Control the REF32xx ENABLE Pin

calculated so that the voltage at the ENABLE pin reaches 0.7V after the input voltage has reached 4.15V;

Table 2 lists these values. For output voltage options other than 4.096V, the RC filter can be made faster.

RISE TIME

2ms

150k

Ω

100nF

5ms

150k

Ω

220nF

10ms

330k

Ω

220nF

20ms

390k

Ω

330nF

50ms

680k

Ω

470nF

100ms

680k

Ω

1000nF

In this document, rise time is defined as the time until an exponential input signal reaches 90% of its final

voltage. For example, the 2ms value shown in Table 2 is valid for an end value of 5V.

If the input voltage has a different shape or the end value is not 5V, then the time until the minimum dropout

voltage has been reached should be used to decide if the IN and ENABLE pins can be tied together. Table 3 lists

these times.

Table 3. Minimum Dropout Voltage Times

DEVICE

TIME

REF3212

0.4ms

REF3220

0.5ms

REF3225

0.7ms

REF3230

0.9ms

REF3233

1.0ms

REF3240

1.6ms

Note that because the leakage current of the EN pin is in the range of a few nA, it can be disregarded in most

applications.

12

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© 2006–2011, Texas Instruments Incorporated

Product Folder Link(s): REF3212-EP, REF3220-EP, REF3225-EP REF3230-EP, REF3233-EP, REF3240-EP