TL4051_10 Datasheet, PDF (13/25 Pages) Texas Instruments – PRECISION MICROPOWER SHUNT VOLTAGE REFERENCE

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TL4051
PRECISION MICROPOWER SHUNT VOLTAGE REFERENCE
SLOS487 – JUNE 2007
Adjustable Version
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.
V_S
R_S
TL4051x (Adj)
+
V_REF ^R1
-
R2
V_Z = V_REF(1 + R2/R1)
Figure 3. Adjustable Shunt Regulator
Cathode and Load Currents
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.
R_S
+
ǒ_VS
(I_L
*
)
V_Z^Ǔ
I_Z)
(1)
V
S
R
S
V
Z
TL4051x12
I +I
Z
L
I
L
I
Z
Figure 4. Shunt Regulator
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