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3083

Adjustable 3A Single Resistor Low Dropout Regulator

Linear Technology 

LT3083

APPLICATIONS INFORMATION

The second technique for reducing power dissipation,

shown in Figure 8, uses a resistor in parallel with the

LT3083. This resistor provides a parallel path for current

flow, reducing the current flowing through the LT3083.

This technique works well if input voltage is reasonably

constant and output load current changes are small. This

technique also increases the maximum available output

current at the expense of minimum load requirements.

VIN

C1

VCONTROL

LT3083

IN

+

–

SET

RSET

RP

OUT

3083 F08

VOUT

C2

Figure 8. Reducing Power Dissipation Using a Parallel Resistor

As an example, assume: VIN = VCONTROL = 5V, VIN(MAX) =

5.5V, VOUT = 3.3V, VOUT(MIN) = 3.2V, IOUT(MAX) = 2A and

IOUT(MIN) = 0.7A. Also, assuming that RP carries no more

than 90% of IOUT(MIN) = 630mA.

Calculating RP yields:

RP

=

5.5V − 3.2V

0.63A

=

3.65Ω

(5% Standard Value = 3.6Ω)

The maximum total power dissipation is (5.5V – 3.2V) •

2A = 4.6W. However, the LT3083 supplies only:

2A − 5.5V − 3.2V = 1.36A

3.6Ω

Therefore, the LT3083’s power dissipation is only:

PDISS = (5.5V – 3.2V) • 1.36A = 3.13W

RP dissipates 1.47W of power. As with the first technique,

choose appropriate wattage resistors to handle and dis-

sipate the power properly. With this configuration, the

LT3083 supplies only 1.36A. Therefore, load current can

increase by 1.64A to a total output current of 3.64A while

keeping the LT3083 in its normal operating range.

3083fa

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