ADP3191 datasheet(25/28 Pages) AD

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ADP3191

Rev. 0 | Page 25 of 28

SHUNT RESISTOR DESIGN

When replacing an existing ADP3181 design with the

ADP3191, the shunt resistor value needs to be determined.

A trade-off can be made between the power dissipated in the

shunt resistor and the UVLO threshold. Figure 19 shows the

typical resistor value needed to realize certain UVLO voltages.

It also gives the maximum power dissipated in the shunt

resistor for these UVLO voltages. The maximum power

dissipated is calculated using Equation 39.

()

(

)

()

SHUNT

MIN

MAX

−

(39)

where:

VIN(MAX) is the maximum voltage from the 12 V input supply.

(If the 12 V input supply is 12 V ±5%, then VIN(MAX) = 12.6 V.

If the 12 V input supply is 12 V ±10%, then VIN(MAX) = 13.2 V.)

The graph shows the power when VIN(MAX) = 12.6 V.

VCC(MIN) is the minimum VCC voltage of the ADP3191. It is

specified as 4.75 V.

RSHUNT is the shunt resistor value.

The CECC standard specification for power rating in surface

mount resistors is 0603 = 0.1 W, 0805 = 0.125 W, 1206 = 0.25 W.

Example:

UVLO voltage specification = 8 V.

From Figure 19, a shunt resistor value of 420 Ω is recommended.

From Figure 19, the power dissipation will be 140 mW. The user

can choose any of the following:

•

Two 840 Ω, 0603 resistors in parallel

•

Two 840 Ω, 0805 resistors in parallel

•

One 420 Ω, 1206 resistor

RSHUNT (Ω)

100

6.5

9.5

9.0

8.5

8.0

7.5

7.0

0.10

0.40

0.35

0.30

0.25

RSHUNT

PSHUNT

0.20

0.15

700

600

500

400

300

200

Figure 19. Typical Shunt Resistor Value and Power Dissipation

for Different UVLO Voltages

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