LM4040 datasheet(25/30 Pages) NSC

25 / 30 page

Applications Information

The LM4040 is a precision micro-power curvature-corrected

bandgap shunt voltage reference. For space critical applica-

tions, the LM4040 is available in the sub-miniature SOT-23

and SC70 surface-mount package. The LM4040 has been

designed for stable operation without the need of an external

capacitor connected between the “+” pin and the “−” pin. If,

however, a bypass capacitor is used, the LM4040 remains

stable. Reducing design effort is the availability of several

fixed reverse breakdown voltages: 2.048V, 2.500V, 3.000V,

4.096V, 5.000V, 6.000, 8.192V, and 10.000V. The minimum

operating current increases from 60 µA for the LM4040-

2.048 and LM4040-2.5 to 100 µA for the LM4040-10.0. All

versions have a maximum operating current of 15 mA.

LM4040s in the SOT-23 packages have a parasitic Schottky

diode between pin 2 (−) and pin 3 (Die attach interface

contact). Therefore, pin 3 of the SOT-23 package must be

left floating or connected to pin 2.

LM4040s in the SC70 have a parasitic Schottky diode be-

tween pin 1 (−) and pin 2 (Die attach interface contact).

Therefore, pin 2 must be left floating or connected to pin1.

The 4.096V version allows single +5V 12-bit ADCs or DACs

to operate with an LSB equal to 1 mV. For 12-bit ADCs or

DACs that operate on supplies of 10V or greater, the 8.192V

version gives 2 mV per LSB.

The typical thermal hysteresis specification is defined as the

change in +25˚C voltage measured after thermal cycling.

The device is thermal cycled to temperature -40˚C and then

measured at 25˚C. Next the device is thermal cycled to

temperature +125˚C and again measured at 25˚C. The re-

sulting V

OUT delta shift between the 25˚C measurements is

thermal hysteresis. Thermal hysteresis is common in preci-

sion references and is induced by thermal-mechanical pack-

age stress. Changes in environmental storage temperature,

operating temperature and board mounting temperature are

all factors that can contribute to thermal hysteresis.

In a conventional shunt regulator application (Figure 1),an

external series resistor (R

S) is connected between the sup-

ply voltage and the LM4040. R

S determines the current that

flows through the load (I

L) and the LM4040 (IQ). Since load

current and supply voltage may vary, R

S should be small

enough to supply at least the minimum acceptable I

Q to the

LM4040 even when the supply voltage is at its minimum and

the load current is at its maximum value. When the supply

voltage is at its maximum and I

L is at its minimum, RS should

be large enough so that the current flowing through the

LM4040 is less than 15 mA.

S is determined by the supply voltage, (VS), the load and

operating current, (I

L and IQ), and the LM4040’s reverse

breakdown voltage, V

Typical Applications

01132315

FIGURE 1. Shunt Regulator

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