LM4051 National Semiconductor, LM4051 Datasheet - Page 9

• Manufacturer Part Number: LM4051
• Description: Precision Micropower Shunt Voltage Reference
• Manufacturer: National Semiconductor

Applications Information
The LM4051 is a precision micro-power curvature-corrected
bandgap shunt voltage reference. For space critical applica-
tions, the LM4051 is available in the sub-miniature SSOT-23
surface-mount package. The LM4051 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 LM4051 remains stable. De-
sign effort is further reduced with the choice of either a fixed
1.2V or an adjustable reverse breakdown voltage. The mini-
mum operating current is 60 µA for the LM4051-1.2 and the
LM4051-ADJ. Both versions have a maximum operating cur-
rent of 12 mA.
LM4051s using the SSOT-23 package have pin 3 connected
as the (-) output through the package’s die attach interface.
Therefore, the LM4051-1.2’s pin 3 must be left floating or
connected to pin 2 and the LM4051-ADJ’s pin 3 is the (-) out-
put.
In a conventional shunt regulator application (Figure 1) , an
external series resistor (R
ply voltage and the LM4051. R
flows through the load (I
current and supply voltage may vary, R
enough to supply at least the minimum acceptable I
LM4051 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
be large enough so that the current flowing through the
LM4051 is less than 12 mA.
R
desired load and operating current, (I
LM4051’s reverse breakdown voltage, V
The LM4051-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
feedback resistors as shown in Figure 2 . The output voltage
is found using the equation
S
should be selected based on the supply voltage, (V
V
O
= V
L
REF
) and the LM4051 (I
S
) is connected between the sup-
REF
[(R2/R1) + 1]
L
S
) and the ratio of the external
is at its minimum, R
determines the current that
L
R
S
.
and I
should be small
Q
). Since load
Q
), and the
S
Q
should
S
to the
), the
(1)
(2)
9
where V
nal V
mined by
where
typically −1.55 mV/V. You can get a more accurate indication
of the output voltage by replacing the value of V
tion (1) with the value found using equation (3).
Typical Applications
V
REF
REF
/ V
O
FIGURE 2. Adjustable Shunt Regulator
is a function of V
O
is the output voltage. The actual value of the inter-
is found in the Electrical Characteristics and is
V
FIGURE 1. Shunt Regulator
REF
= V
V
O
Y
( V
O
= 1.22V
. The “corrected” V
REF
DS101222-22
/ V
DS101222-34
O
) + V
Y
REF
REF
www.national.com
is deter-
in equa-
(3)