VREF

VIN

COUT

RZ

IBIAS

ISHUNT

ILOAD

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 (RZ in Figure 21). The value of

the resistor can be calculated using the following equation:

RZ = (VIN - VREF)/(IMIN_OPERATING + ILOAD_MAX)

(1)

RZ is chosen such that the total current flowing through RZ 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 VREF 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 IOUT

The LM4030 is designed to operate with or without a bypass capacitor (COUT 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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