Diodes LM4041 - Manual (Page 5)

LM4041
PRECISION MICROPOWER SHUNT VOLTAGE REFERENCES
LM4041
Document number: DS32020 Rev. 8 - 2
5 of 7
www.diodes.com
September 2011
© Diodes Incorporated
Application Information
In a conventional shunt regulator application (Figure 1), an
external series resistor (R
S
) is connected between the
supply voltage, V
S
, and the LM4041.
R
S
determines the current that flows through the load (I
L
)
and the LM4041 (I
R
). Since load current and supply
voltage may vary, R
S
should be small enough to supply at
least the minimum acceptable I
R
to the LM4040 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
LM4040 is less than 12 mA.
R
S
is determined by the supply voltage, (V
S
), the load and
operating current, (I
L
and I
Q
), and the LM4040’s reverse
breakdown voltage, V
R
.
R L
R S
S
I I
V V
R
+
−
=
The LM4041 comes in two varients:
•
LM4041 with fixed 1.225V output
•
LM4041_ADJ with variable output voltage.
The LM4041-ADJ’s output voltage can be adjusted to any
value in the range of 1.24V through 10V. The output
voltage is set by the ratio of two external feedback
resistors as shown in Figure 2 and the internal reference
voltage (V
R
).
The output voltage is found using the equation:
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+ × =
1
2
R O
R
R
1 V V
Printed circuit board layout considerations
LM4041 with fixed output voltage in the SOT23 package
has the die attached to pin 1, which results in an electrical
contact between pin 2 and pin 1. Therefore, pin 1 of the
SOT23 package must be left floating or connected to
pin 2.
LM4041 with fixed output voltage in the SC70-5 package
have the die attached to pin 2, which results in an
electrical contact between pin 2 and pin 1. Therefore, pin
2 must be left floating or connected to pin1.
R
S
V
S
I
R
+
I
L
I
R
I
L
V
R
Figure 1
R
S
V
S
I
R
+ I
L
I
R
I
L
V
R
V
O
Figure 2