Datasheet

1-Hz Rate
V
Z
LM4040
R
S
V
IN
R
S
+
ǒ
V
S
* V
Z
Ǔ
(
I
L
) I
Z
)
LM4040
I
Z
+ I
L
I
L
I
Z
V
S
V
Z
R
S
LM4040-EP
www.ti.com SLOS746A – SEPTEMBER 2011– REVISED SEPTEMBER 2011
APPLICATION INFORMATION
Start-Up Characteristics
Figure 7. Test Circuit
Output Capacitor
The LM4040 does not require an output capacitor across cathode and anode for stability. However, if an output
bypass capacitor is desired, the LM4040 is designed to be stable with all capacitive loads.
SOT-23 Connections
There is a parasitic Schottky diode connected between pins 2 and 3 of the SOT-23 packaged device. Thus, pin 3
of the SOT-23 package must be left floating or connected to pin 2.
Cathode and Load Currents
In a typical shunt-regulator configuration (see Figure 8), an external resistor, R
S
, is connected between the
supply and the cathode of the LM4040. R
S
must be set properly, as it sets the total current available to supply
the load (I
L
) and bias the LM4040 (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-rated value of 15 mA.
R
S
is calculated according to Equation 1:
(1)
Figure 8. Shunt Regulator
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