LM4040 Micrel Semiconductor, LM4040 Datasheet - Page 12

• Manufacturer Part Number: LM4040
• Description: Precision Micropower Shunt Voltage Reference
• Manufacturer: Micrel Semiconductor

LM4040/4041
Applications Information
The LM4040 and LM4041 have been designed for stable
operation without the need of an external capacitor con-
nected between the (+) and (–) pins. If a bypass capacitor is
used, the references remain stable.
Schottky Diode
LM4040-x.x and LM4041-1.2 in the SOT-23 package have a
parasitic Schottky diode between pin 2 (–) and pin 3 (die
attach interface connect). Pin 3 of the SOT-23 package must
float or be connected to pin 1. LM4041-ADJs use pin 3 as the
(–) output.
Conventional Shunt Regulator
In a conventional shunt regulator application (see Figure 1),
an external series resistor (R
supply voltage and the LM4040-x.x or LM4041-1.2 reference.
R
the reference (I
vary, R
minimum acceptable I
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
the current flowing through the LM4040-x.x is less than
15mA, and the current flowing through the LM4041-1.2 or
LM4041-ADJ is less than 12mA.
R
operating current, (I
breakdown voltage (V
LM4040/4041
S
S
determines the current that flows through the load (I
is determined by the supply voltage (V
L
is at its minimum, R
S
should be small enough to supply at least the
Figure 3. Voltage Level Detector
Q
). Since load current and supply voltage may
R
LM4041-ADJ
s
= (V
L
R
and I
Q
).
s
– V
to the reference even when the
S
Q
D1
should be large enough so that
), and the reference’s reverse
R
S
) / (I
–5V
) is connected between the
+
R3
200
–
L
+ I
FB
< –12V
LED ON
Q
)
R1
120k
R2
1M
S
), the load and
L
) and
12
Adjustable 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
feedback resistors as shown in Figure 2. The output is found
using the equation
(1)
where V
the internal V
determined by
(2)
where V
in the Electrical Characteristics and is typically –1.3mV/V and
V
(1) with the value found using equation (2).
Note that actual output voltage can deviate from that pre-
dicted using the typical V
grade parts, the worst-case V
V
The following example shows the difference in output voltage
resulting from the typical and worst case values of
Let V
is 1.223V. Choosing a value of R1 = 10k , R2 = 63.272k .
Using the worst case V
grade parts, the output voltage is actually 8.965V and 8.946V
respectively. This results in possible errors as large as 0.39%
for the C-grade parts and 0.59% for the D-grade parts. Once
again, resistor values found using the typical value of
adjustment.
V
V
Y
Y
REF
REF
is equal to 1.233V. Replace the value of V
= 1.248V.
O
= +9V. Using the typical values of V
/ V
/ V
O
O
is the desired output voltage. V
is the desired output voltage. The actual value of
O
O
Figure 4. Voltage Level Detector
:
REF
will work in most cases, requiring no further
D1
V
V
is a function of V
O
REF
= V
LM4041-
´ = V
REF
ADJ
REF
O
REF
´ [ (R2/R1) + 1 ]
–5V
REF
( V
/ V
+
–
R3
330
/ V
) and the ratio of the external
REF
FB
REF
O
O
. The “corrected” V
> –12V
LED ON
O
/ V
for the C-grade and D-
/ V
in equation (2); for C-
R1
120k
R2
1M
O
O
REF
) + V
is –2.5mV/V and
REF
REF
January 2000
/ V
Y
´ in equation
/ V
O
O
is found
, V
Micrel
REF
REF
is