LM4030AMF-2.5 NSC [National Semiconductor], LM4030AMF-2.5 Datasheet - Page 9

• Manufacturer Part Number: LM4030AMF-2.5
• Description: Ultra-High Precision Shunt Voltage Reference
• Manufacturer: NSC [National Semiconductor]

Application Information
THEORY OF OPERATION
The LM4030 is an ultra-high precision shunt voltage refer-
ence, 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
SOT23 package, the LM4030 exhibits excellent thermal hys-
teresis (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 pow-
ered 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 1.
COMPONENT SELECTION
A resistor must be chosen to set the maximum operating cur-
rent for the LM4030 (R
can be calculated using the following equation:
R
greater than the maximum load current plus the minimum op-
erating 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
ly with the shunted current (see Figure 2) leading to higher
rejection of noise emanating from the input supply and from
EMI (electro-magnetic interferrence).
Z
is chosen such that the total current flowing through R
FIGURE 2. Reverse Dynamic Impedance vs I
R
Z
FIGURE 1. Typical Application Circuit
= (V
IN
- V
REF
Z
)/(I
in Figure 1). The value of the resistor
MIN_OPERATING
REF
node scales inverse-
+ I
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LOAD_MAX
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)
OUT
Z
is
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The LM4030 is designed to operate with or without a bypass
capacitor (C
up to 10 μF. The use of a bypass capacitor can improve tran-
sient response and reduce broadband noise. Additionally, a
bypass capacitor will counter the rising reverse dynamic
impedance at higher frequencies improving noise immunity
(see Figure 3).
As with other regulators, an external capacitor reduces the
amplitude of the V
loading takes place. The capacitor should be placed as close
to the part as possible to reduce the effects of unwanted board
parasitics.
THERMAL HYSTERESIS
Thermal hysteresis is the defined as the change in output
voltage at 25°C after some deviation from 25°C. This is to say
that thermal hysteresis is the difference in output voltage be-
tween two points in a given temperature profile. An illustrative
temperature profile is shown in Figure 4.
This may be expressed analytically as the following:
Where
V
V
V
HYS
REF
REF1
FIGURE 3. Reverse Dynamic Impedance vs C
= Nominal preset output voltage
= Thermal hysteresis expressed in ppm
= V
FIGURE 4. Illustrative Temperature Profile
REF
OUT
before temperature fluctuation
in Figure 1) and is stable with capacitors of
REF
transient when a sudden change in
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OUT
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