REF3212-EP_16 Datasheet, PDF (12/22 Pages) Texas Instruments – SOT23-6 SERIES VOLTAGE REFERENCES

REF3212-EP,
REF3230-EP,
REF3220-EP,
REF3233-EP,
REF3225-EP
REF3240-EP
Not
Recommended
New Designs
For
SBVS078B – OCTOBER 2006 – REVISED AUGUST 2011
www.ti.com
1
6
2
5
3
4
R₁
C₁
V_REF
V_IN
Figure 6. Application Circuit to Control the REF32xx ENABLE Pin
The RC filter in Figure 6 can be used as a starting point for the REF3240. The values for R₁ and C₁ have been
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
5ms
10ms
20ms
50ms
100ms
Table 2. Recommended R₁ and C₁ Values for the REF3240
R₁ VALUE
150kΩ
150kΩ
330kΩ
390kΩ
680kΩ
680kΩ
C₁ VALUE
100nF
220nF
220nF
330nF
470nF
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
REF3212
REF3220
REF3225
REF3230
REF3233
REF3240
TIME
0.4ms
0.5ms
0.7ms
0.9ms
1.0ms
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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