LM4040

Application Information

In a conventional shunt regulator application (Figure 1), an external series resistor (RS) is connected between the supply voltage, VS, and the

LM4040.

Figure 1

RS determines the current that flows through the load (IL) and the LM4040 (IR). Because load current and supply voltage

can vary, RS should be small enough to supply at least the minimum acceptable IR 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 IL

is at its minimum, RS should be large enough so that the current flowing through the LM4040 is less than 15mA.

RS is determined by the supply voltage, (VS), the load and operating current, (IL and IR), and the LM4040’s reverse

breakdown voltage, VR.

R

L

R

S

S

I

I

V

V

R

+

−

=

Printed Circuit Board Layout Considerations

The LM4040 device in the SOT23 package has the die attached to pin 3, which results in an electrical contact between

pin 2 and pin 3. Therefore, pin 3 of the SOT23 package must be left floating or connected to pin 2.

LM4040

Document number: DS33195 Rev. 8 - 2

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August 2019

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