Applications Information
The LM4041 is a precision micro-power curvature-corrected
bandgap shunt voltage reference. For space critical applica-
tions, the LM4041 is available in the sub-miniature SOT-23
and SC70 surface-mount package. The LM4041 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 remains
stable. Design effort is further reduced with the choice of
either a fixed 1.2V or an adjustable reverse breakdown
voltage. The minimum operating current is 60 µA for the
LM4041-1.2 and the LM4041-ADJ. Both versions have a
maximum operating current of 12 mA.
where VO is the output voltage. The actual value of the
internal VREF is a function of VO. The “corrected” VREF is
determined by
VREF = ∆VO (∆VREF/∆VO) + VY
(2)
where
VY = 1.240 V and
∆VO = (VO − VY)
∆VREF/∆VO is found in the Electrical Characteristics and is
typically −1.55 mV/V. You can get a more accurate indication
of the output voltage by replacing the value of VREF in
equation (1) with the value found using equation (2).
LM4041s using the SOT-23 package have pin 3 connected
as the (-) output through the package’s die attach interface.
Therefore, the LM4041-1.2’s pin 3 must be left floating or
connected to pin 2 and the LM4041-ADJ’s pin 3 is the (-)
output.
Note that the actual output voltage can deviate from that
predicted using the typical value of ∆VREF/∆VO in equation
(2): for C-grade parts, the worst-case ∆VREF/∆VO is −2.5
mV/V. For D-grade parts, the worst-case ∆VREF/∆VO is −3.0
mV/V.
LM4041s using the SC70 package have pin 2 connected as
the (−) output through the packages’ die attach interface.
Therefore, the LM4041-1.2’s pin 2 must be left floating or
connected to pin 1, and the LM4041-ADJ’s pin 2 is the (−)
output.
Typical Applications
In a conventional shunt regulator application (Figure 1), an
external series resistor (RS) is connected between the sup-
ply voltage and the LM4041. RS determines the current that
flows through the load (IL) and the LM4041 (IQ). Since load
current and supply voltage may vary, RS should be small
enough to supply at least the minimum acceptable IQ to the
LM4041 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
LM4041 is less than 12 mA.
DS011392-22
FIGURE 1. Shunt Regulator
RS should be selected based on the supply voltage, (VS), the
desired load and operating current, (IL and IQ), and the
LM4041’s reverse breakdown voltage, VR.
The LM4041-ADJ’s output voltage can be adjusted to any
value in the range of 1.24V through 10V. It is a function of the
internal reference voltage (VREF) and the ratio of the external
feedback resistors as shown in Figure 2 . The output voltage
is found using the equation
DS011392-34
VO = VREF[(R2/R1) + 1]
VO = VREF[(R2/R1) + 1]
(1)
FIGURE 2. Adjustable Shunt Regulator
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