Data Sheet

ADP165/ADP166

Consider the case where a hard short from VOUT to ground

occurs. At first, the ADP165/ADP166 limit current so that only

320 mA is conducted into the short.

If self-heating of the junction temperature is great enough to

cause its temperature to rise above 150°C, thermal shutdown

activates, turning off the output and reducing the output current

to zero. As the junction temperature cools and drops below 135°C,

the output turns on and conducts 320 mA into the short, again

causing the junction temperature to rise above 150°C. This thermal

oscillation between 135°C and 150°C causes a current oscillation

between 320 mA and 0 mA that continues as long as the short

remains at the output.

Current and thermal limit protections are intended to protect

the device against accidental overload conditions. For reliable

operation, device power dissipation must be externally limited

so that junction temperatures do not exceed 125°C.

THERMAL CONSIDERATIONS

In most applications, the ADP165/ADP166 do not dissipate

much heat due to their high efficiency. However, in applications

with high ambient temperature and high supply voltage to

output voltage differential, the heat dissipated in the package

is high enough that it can cause the junction temperature of

the die to exceed the maximum junction temperature of 125°C.

When the junction temperature exceeds 150°C, the converter enters

thermal shutdown. It recovers only after the junction temperature

has decreased below 135°C to prevent any permanent damage.

Therefore, thermal analysis for the chosen application is very

important to guarantee reliable performance over all conditions.

The junction temperature of the die is the sum of the ambient

temperature of the environment and the temperature rise of the

package due to the power dissipation, as shown in Equation 2.

To guarantee reliable operation, the junction temperature of the

ADP165/ADP166 must not exceed 125°C. To ensure that the

junction temperature stays below this maximum value, the user

must be aware of the parameters that contribute to junction

temperature changes. These parameters include ambient

temperature, power dissipation in the power device, and thermal

number is dependent on the package assembly compounds that

are used and the amount of copper used to solder the package

GND pins to the PCB.

LFCSP, and the 4-ball WLCSP for various PCB copper sizes.

LFCSP, and 4-ball WLCSP.

TSOT

LFCSP

WLCSP

170

175.1

260

50

152

135.6

159

100

146

77.3

157

300

134

65.2

153

500

131

51

151

1

Device soldered to minimum size pin traces.

Package

Unit

5-Lead TSOT

42.8

(°C/W)

6-Lead LFCSP

17.9

(°C/W)

4-Ball WLCSP

58.4

(°C/W)

Calculate the junction temperature of the ADP165/ADP166

from the following equation:

(2)

where:

(3)

where:

Power dissipation due to ground current is quite small and can be

ignored. Therefore, the junction temperature equation simplifies to

the following:

(4)

As shown in Equation 4, for a given ambient temperature, input-

to-output voltage differential, and continuous load current, there

exists a minimum copper size requirement for the PCB to ensure

the junction temperature does not rise above 125°C. Figure 43 to

Figure 57 show the junction temperature calculations for the

differentials, and areas of PCB copper.

In the case where the board temperature is known, use the

temperature rise (see Figure 55 to Figure 57). Maximum junction

(5)

42.8°C/W for the 5-lead TSOT package, and 58.4°C/W for the

4-ball WLCSP package.

Rev. A | Page 17 of 23