1A Low-Voltage Low-Dropout Regulator

LM39100/39101/39102

HTC

9

Using Figure3, the minimum amount of required copper can be determined based on the required power

dissipation.Power dissipation in a linear regulator is calculated as fol-lows:

PD = (VIN – VOUT) IOUT + VIN·IGND

If we use a 2.5V output device and a 3.3V input at an output current of 1A, then our power dissipation is as follows:

PD = (3.3V – 2.5V) × 1A + 3.3V × 11mA

PD = 800mW + 36mW

PD = 836mW

From Figure3, the minimum amount of copper required too perate this application at a ∆T of 75°C is 160mm2.

Quick Method

Determine the power dissipation requirements for the design along with the maximum ambient temperature at which

the device will be operated. Refer to Figure4, which shows safe operating curves for three different ambient

temperatures:25°C, 50°C and 85°C. From these curves, the minimum amount of copper can be determined by

knowing the maxi-mum power dissipation required. If the maximum ambient temperature is 50°C and the power

dissipation is as above,836mW, the curve in Figure5 shows that the required area of copper is 160㎟.The

package is ideally 63°C/W, but it will vary depending upon the availability of copper ground plane to which it is

attached.