LM4040
PRECISION MICROPOWER SHUNT VOLTAGE REFERENCE
www.ti.com
SLOS456J–JANUARY 2005–REVISED SEPTEMBER 2006
APPLICATION INFORMATION (continued)
Cathode and Load Currents
In a typical shunt-regulator configuration (see Figure 9), an external resistor, RS, is connected between the
supply and the cathode of the LM4040. RS must be set properly, as it sets the total current available to supply
the load (IL) and bias the LM4040 (IZ). In all cases, IZ 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 IL
and minimum VS), RS must be small enough to supply the minimum IZ required for operation of the regulator, as
given by data-sheet parameters. At the other extreme, maximum VS and minimum IL, RS must be large enough
to limit IZ to less than its maximum-rated value of 15 mA.
RS is calculated according to Equation 1:
ǒ
Ǔ
VS * VZ
RS +
(
)
IL ) IZ
(1)
V
S
R
S
I + I
Z L
I
L
V
Z
I
Z
LM4040
Figure 9. Shunt Regulator
28
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