Datasheet

110
108
106
104
102
100
98
96
94
QuiescentCurrent( A)m
1.5 2.0 3.0 4.02.5 3.5 4.5 6.05.0 5.5
PowerSupply(V)
1
2
3
6
5
4
V
REF
R
1
C
1
V
IN
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
100μA, with a maximum quiescent current over
point for the REF3240. The values for R
1
and C
1
temperature of just 135μA. The quiescent current
have been calculated so that the voltage at the
typically changes less than 2μA 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 R
1
and C
1
Values for the
REF3240
RISE TIME R
1
VALUE C
1
VALUE
2ms 150kΩ 100nF
5ms 150kΩ 220nF
10ms 330kΩ 220nF
20ms 390kΩ 330nF
50ms 680kΩ 470nF
100ms 680kΩ 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 on the model, and ranges from
approximately 100kΩ to 400kΩ.
Figure 23. Application Circuit to Control the
REF32xx ENABLE Pin
Copyright © 2005–2011, Texas Instruments Incorporated 9