9.1 Application Information

The LM4041-N is a precision micro-power curvature-corrected bandgap shunt voltage reference. For space-critical applications, the LM4041-N is available in the sub-miniature SOT-23 and SC70 surface-mount package. The LM4041-N 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 LM4041-N remains stable. Design effort is further reduced with the choice of either a fixed 1.2 V or an adjustable reverse breakdown voltage. The minimum operating current is 60 μA for the LM4041-N 1.2 V and the LM4041-N ADJ. Both versions have a maximum operating current of 12 mA.

LM4041-Ns using the SOT-23 package have pin 3 connected as the (–) output through the die attach interface of the package. Therefore, pin 3 of the LM4041-N 1.2 must be left floating or connected to pin 2 and pin 3 of the LM4041-N ADJ pinout.

The LM4041-N devices using the SC70 package have pin 2 connected as the (–) output through the die attach interface of the package. Therefore, the LM4041-N pin 2 of the LM4041-N 1.2 must be left floating or connected to pin 1, and the pin 2 of the LM4041-N ADJ is the (–) output.

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 resulting V_OUT delta shift between the 25°C measurements is thermal hysteresis. Thermal hysteresis is common in precision references and is induced by thermal-mechanical package 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 17), an external series resistor (R_S) is connected between the supply voltage and the LM4041-N. R_S determines the current that flows through the load (I_L) and the LM4041-N (I_Q). Because load current and supply voltage may vary, R_S must be small enough to supply at least the minimum acceptable I_Q to the LM4041-N 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, R_S must be large enough so that the current flowing through the LM4041-N is less than 12 mA.

R_S must be selected based on the supply voltage, (V_S), the desired load and operating current, (I_L and I_Q), and the reverse breakdown voltage of the LM4041-N, V_R.

Equation 1.

The output voltage of the LM4041-N SDJ can be adjusted to any value in the range of 1.24 V through 10 V. It is a function of the internal reference voltage (V_REF) and the ratio of the external feedback resistors as shown in Figure 19 . The output voltage is found using Equation 2.

The actual value of the internal V_REF is a function of V_O. The corrected V_REF is determined by Equation 3.

ΔV_REF/ΔV_O is found in the electrical characteristics tables in the Specificationsand is typically −1.55 mV/V. You can get a more accurate indication of the output voltage by replacing the value of V_REF in Equation 2 with the value found using Equation 3.