Datasheet

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Adjustable Version
R
S
TL4051x (Adj)
V
S
R1
R2
V = V (1 + R2/R1)
Z REF
+
V
REF
-
Cathode and Load Currents
R
S
+
ǒ
V
S
* V
Z
Ǔ
(
I
L
) I
Z
)
(1)
TL4051x12
I + I
Z L
I
L
I
Z
V
S
V
Z
R
S
TL4051
PRECISION MICROPOWER SHUNT VOLTAGE REFERENCE
SLOS487 – JUNE 2007
APPLICATION INFORMATION (continued)
The adjustable version allows V
Z
to be set by a user-defined resistor divider. The output voltage, V
Z
, is set
according to the equation shown in Figure 3 .
Figure 3. Adjustable Shunt Regulator
In a typical shunt regulator configuration (see Figure 4 ), an external resistor, R
S
, is connected between the
supply and the cathode of the TL4051. R
S
must be set properly, as it sets the total current available to supply
the load (I
L
) and bias the TL4051 (I
Z
). In all cases, I
Z
must stay within a specified range for proper operation of
the reference. Taking into consideration one extreme in the variation of the load and supply voltage (maximum I
L
and minimum V
S
), R
S
must be small enough to supply the minimum I
Z
required for operation of the regulator, as
given by data sheet parameters. At the other extreme, maximum V
S
and minimum I
L
, R
S
must be large enough
to limit I
Z
to less than its maximum recommended rating of 12 mA.
R
S
is calculated as shown in Equation 1 .
Figure 4. Shunt Regulator
13
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