REF3230 datasheet(9/21 Pages) TI2

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110

108

106

104

102

100

1.5

2.0

3.0

4.0

2.5

3.5

4.5

6.0

5.0

5.5

PowerSupply(V)

REF

REF3212, REF3220

REF3225, REF3230

REF3233, REF3240

www.ti.com

SBVS058C

– JUNE 2005 – REVISED AUGUST 2011

The REF32xx also features a low quiescent current of

The RC filter in Figure 23 can be used as a starting

100

μA, with a maximum quiescent current over

point for the REF3240. The values for R1 and C1

temperature of just 135

μA. The quiescent current

have been calculated so that the voltage at the

typically changes less than 2

μA over the entire supply

ENABLE pin reaches 0.7V after the input voltage has

range, as shown in Figure 22.

reached 4.15V; Table 1 lists these values. For output

voltage options other than 4.096V, the RC filter can

be made faster.

Table 1. Recommended R1 and C1 Values for the

REF3240

RISE TIME

R1 VALUE

C1 VALUE

2ms

150k

100nF

5ms

150k

220nF

10ms

330k

220nF

20ms

390k

330nF

50ms

680k

470nF

100ms

680k

1000nF

In this document, rise time is defined as the time until

an exponential input signal reaches 90% of its final

Figure 22. Supply Current vs Supply Voltage

voltage. For example, the 2ms value shown in

Table 1 is valid for an end value of 5V.

Supply voltages below the specified levels can cause

If the input voltage has a different shape or the end

the REF32xx to momentarily draw currents greater

value is not 5V, then the time until the minimum

than the typical quiescent current. This momentary

dropout voltage has been reached should be used to

current draw can be prevented by using a power

decide if the IN and ENABLE pins can be tied

supply with a fast rising edge and low output

together. Table 2 lists these times.

impedance.

Table 2. Minimum Dropout Voltage Times

For optimal startup when the IN pin and ENABLE pin

are tied together, keep the input voltage rise time less

DEVICE

TIME

than or equal to 2ms. For rise times greater than

REF3212

0.4ms

2ms, the ENABLE pin must be kept below 0.7V until

REF3220

0.5ms

the voltage at the IN pin has reached the minimum

operating voltage. One way to control the voltage at

REF3225

0.7ms

the ENABLE pin is with an additional RC filter, such

REF3230

0.9ms

as that shown in Figure 23. The RC filter must hold

REF3233

1.0ms

the voltage at the ENABLE pin below the threshold

REF3240

1.6ms

voltage until the voltage at the input pin has reached

the minimum operating voltage.

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.

SHUTDOWN

The REF32xx can be placed in a low-power mode by

pulling the ENABLE/SHUTDOWN pin low. When in

Shutdown mode, the output of the REF32xx becomes

a resistive load to ground. The value of the load

depends

the

model,

and

ranges

from

approximately 100k

Ω to 400kΩ.

Figure 23. Application Circuit to Control the

REF32xx ENABLE Pin

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