LM4041
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.
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.
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.
In a conventional shunt regulator application
(Figure 1),
an
external series resistor (R
S
) is connected between the sup-
ply voltage and the LM4041. R
S
determines the current that
flows through the load (I
L
) and the LM4041 (I
Q
). 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
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 I
L
is at its minimum, R
S
should
be large enough so that the current flowing through the
LM4041 is less than 12 mA.
R
S
should be selected based on the supply voltage, (V
S
), the
desired load and operating current, (I
L
and I
Q
), and the
LM4041’s reverse breakdown voltage, V
R
.
where V
O
is the output voltage. The actual value of the
internal V
REF
is a function of V
O
. The “corrected” V
REF
is
determined by
V
REF
=
∆V
O
(∆V
REF
/∆V
O
) + V
Y
(2)
where
V
Y
= 1.240 V and
∆V
O
= (V
O
− V
Y
)
∆V
REF
/∆V
O
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 V
REF
in
equation (1) with the value found using equation (2).
Note that the actual output voltage can deviate from that
predicted using the typical value of
∆V
REF
/∆V
O
in equation
(2): for C-grade parts, the worst-case
∆V
REF
/∆V
O
is −2.5
mV/V. For D-grade parts, the worst-case
∆V
REF
/∆V
O
is −3.0
mV/V.
Typical Applications
DS011392-22
FIGURE 1. Shunt Regulator
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 (V
REF
) and the ratio of the external
feedback resistors as shown in
Figure 2
. The output voltage
is found using the equation
V
O
= V
REF
[(R2/R1) + 1]
(1)
DS011392-34
V
O
= V
REF
[(R2/R1) + 1]
FIGURE 2. Adjustable Shunt Regulator
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