ATL431 Datasheet, PDF (15/26 Pages) Texas Instruments – Low Iq Adjustable Precision Shunt Regulator

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ATL431, ATL432
SLVSCV5C – MARCH 2015 – REVISED SEPTEMBER 2015
9.2.1.2.2 Overdrive
Slow or inaccurate responses can also occur when the reference pin is not provided enough overdrive voltage.
This is the amount of voltage that is higher than the internal virtual reference. The internal virtual reference
voltage will be within the range of 2.5 V ±(0.5% or 1.0%) depending on which version is being used.
The more overdrive voltage provided, the faster the ATL43x will respond.
For applications where ATL43x is being used as a comparator, it is best to set the trip point to greater than the
positive expected error (that is, +1.0% for the A version). For fast response, setting the trip point to > 10% of the
internal V_ref should suffice. Figure 31 shows the transition from V_OH to V_OL based on the input voltage and can be
used as a guide for selecting the overdrive voltage.
For minimal voltage drop or difference from Vin to the ref pin, it is recommended to use an input resistor < 1 MΩ
to provide I_ref.
9.2.1.2.3 Output Voltage and Logic Input Level
In order for ATL43x to properly be used as a comparator, the logic output must be readable by the receiving logic
device. This is accomplished by knowing the input high and low level threshold voltage levels, typically denoted
by V_IH and V_IL.
As seen in Figure 31, ATL43x's output low level voltage in open-loop/comparator mode is ~2 V, which is
sufficient for some ≥ 5.0 V supplied logic. However, would not work for 3.3 V and 1.8 V supplied logic. In order to
accommodate this, a resistive divider can be tied to the output to attenuate the output voltage to a voltage legible
to the receiving low voltage logic device.
ATL43x's output high voltage is approximately V_sup due to ATL43x being open-collector. If V_sup is much higher
than the receiving logic's maximum input voltage tolerance, the output must be attenuated to accommodate the
outgoing logic's reliability.
When using a resistive divider on the output, be sure to make the sum of the resistive divider (R1 and R2 in
Figure 30) is much greater than R_sup in order to not interfere with ATL43x's ability to pull close to V_sup when
turning off.
9.2.1.2.3.1 Input Resistance
ATL43x requires an input resistance in this application in order to source the reference current (I_ref) needed from
this device to be in the proper operating regions while turning on. The actual voltage seen at the ref pin will be:
V_ref = V_in – I_ref × R_in
(1)
Because I_ref can be as high as 0.15 µA, TI recommends to use a resistance small enough that will mitigate the
error that I_ref creates from V_in. Also, the input resistance must be set high enough as to not surpass the absolute
maximum of 10 mA.
9.2.1.3 Application Curve
5.5
5.25
5
4.75
4.5
4.25
4
3.75
3.5
3.25
3
2.75
2.5
2.25
2
1.75
1.5
2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3
V_IN (V)
D001
R_IN = 100 kΩ
V_SUP = 5.0 V
R_SUP = 10 kΩ
Figure 31. Open Loop (Comparator Mode) V_OUT vs V_IN
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