LM4041 datasheet(12/19 Pages) NSC

12 / 19 page

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 (IQ). 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, RS should

be large enough so that the current flowing through the

LM4041 is less than 12 mA.

S should be selected based on the supply voltage, (VS), the

desired load and operating current, (I

L and IQ), and the

LM4041’s reverse breakdown voltage, V

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

O =VREF[(R2/R1) + 1]

(1)

where V

O is the output voltage. The actual value of the

internal V

REF is a function of VO. The “corrected” VREF is

determined by

REF = ∆VO (∆VREF/∆VO)+VY

(2)

where

Y = 1.240 V and

∆V

O =(VO −VY)

∆V

REF/∆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 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/∆VO in equation

(2): for C-grade parts, the worst-case

∆V

REF/∆VO is −2.5

mV/V. For D-grade parts, the worst-case

∆V

REF/∆VO is −3.0

mV/V.

Typical Applications

DS011392-22

FIGURE 1. Shunt Regulator

DS011392-34

O =VREF[(R2/R1) + 1]

FIGURE 2. Adjustable Shunt Regulator

LM4041 Datasheet(PDF) 12 Page - National Semiconductor (TI)

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