Datasheet

V
REF
V
IN
C
OUT
R
Z
I
BIAS
I
SHUNT
I
LOAD
4
5
LM4030
www.ti.com SNVS552B –MARCH 2008–REVISED APRIL 2013
APPLICATION INFORMATION
THEORY OF OPERATION
The LM4030 is an ultra-high precision shunt voltage reference, having exceptionally high initial accuracy (0.05%)
and temperature stability (10ppm/°C). The LM4030 is available with fixed voltage options of 2.5V and 4.096V.
Despite the tiny SOT-23 package, the LM4030 exhibits excellent thermal hysteresis (75ppm) and long-term
stability (25ppm). The LM4030 is designed to operate without an external capacitor, but any capacitor up to 10
µF may be used. The LM4030 can be powered off as little as 120 µA (max) but is capable of shunting up to 30
mA continuously. The typical application circuit for the LM4030 is shown in Figure 21.
Figure 21. Typical Application Circuit
COMPONENT SELECTION
A resistor must be chosen to set the maximum operating current for the LM4030 (R
Z
in Figure 21). The value of
the resistor can be calculated using the following equation:
R
Z
= (V
IN
- V
REF
)/(I
MIN_OPERATING
+ I
LOAD_MAX
) (1)
R
Z
is chosen such that the total current flowing through R
Z
is greater than the maximum load current plus the
minimum operating current of the reference itself. This ensures that the reference is never starved for current.
Running the LM4030 at higher currents is advantageous for reducing noise. The reverse dynamic impedance of
the V
REF
node scales inversely with the shunted current (see Figure 22) leading to higher rejection of noise
emanating from the input supply and from EMI (electro-magnetic interferrence).
Figure 22. Reverse Dynamic Impedance vs I
OUT
The LM4030 is designed to operate with or without a bypass capacitor (C
OUT
in Figure 21) and is stable with
capacitors of up to 10 μF. The use of a bypass capacitor can improve transient response and reduce broadband
noise. Additionally, a bypass capacitor will counter the rising reverse dynamic impedance at higher frequencies
improving noise immunity (see Figure 23).
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