LM4040-N, LM4040Q-N
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SNOS633H –OCTOBER 2000–REVISED APRIL 2013
Functional Block Diagram
APPLICATIONS INFORMATION
The LM4040-N is a precision micro-power curvature-corrected bandgap shunt voltage reference. For space
critical applications, the LM4040-N is available in the sub-miniature SOT-23 and SC70 surface-mount package.
The LM4040-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 LM4040-N 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-N-2.048 and LM4040-N-2.5 to 100 μA for the 10.0-V LM4040-N. All versions have a maximum operating
current of 15 mA.
LM4040-Ns 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.
LM4040-Ns in the SC70 have a parasitic Schottky diode between 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 resulting VOUT 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 13) , an external series resistor (RS) is connected between
the supply voltage and the LM4040-N. RS determines the current that flows through the load (IL) and the
LM4040-N (IQ). Since load current and supply voltage may vary, RS should be small enough to supply at least
the minimum acceptable IQ to the LM4040-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 IL is at its minimum, RS should
be large enough so that the current flowing through the LM4040-N is less than 15 mA.
RS is determined by the supply voltage, (VS), the load and operating current, (IL and IQ), and the LM4040-N's
reverse breakdown voltage, VR.
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