Functional Block Diagram

10104514

Applications Information

The LM4050 is a precision micro-power curvature-corrected

bandgap shunt voltage reference. For space critical applica-

tions, the LM4050 is available in the sub-miniature SOT-23

surface-mount package. The LM4050 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 LM4050 remains stable. Re-

ducing design effort is the availability of several fixed reverse

breakdown voltages: 2.048V, 2.500V, 4.096V, 5.000V,

8.192V, and 10.000V. The minimum operating current in-

creases from 60 µA for the LM4050-2.0 to 100 µA for the

LM4050-10.0. All versions have a maximum operating cur-

rent of 15 mA.

LM4050s 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.

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

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

ply voltage and the LM4050. R

flows through the load (I

current and supply voltage may vary, R

enough to supply at least the maximum guaranteed I

RMIN

(spec. table) to the LM4050 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

minimum, R

flowing through the LM4050 is less than 15 mA.

R

operating current, (I

breakdown voltage, V

Typical Applications

10104515

FIGURE 1. Shunt Regulator

www.national.com

11