ADP160/ADP161

Rev. 0 | Page 15 of 20

Consider the case where a hard short from OUT to ground occurs.

At first, the ADP160/ADP161 current limits so that only 320 mA is

conducted into the short. If self-heating of the junction 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 junction temperatures do not exceed 125°C.

THERMAL CONSIDERATIONS

In most applications, the ADP160/ADP161 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 large

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

ADP160/ADP161 must not exceed 125°C. To ensure the junction

temperature stays below this maximum value, the user needs to

be aware of the parameters that contribute to junction temperature

changes. These parameters include ambient temperature, power

dissipation in the power device, and thermal resistances between

on the package assembly compounds that are used and the amount

of copper used to solder the package GND pins to the PCB.

4-ball WLCSP for various PCB copper sizes. Table 9 shows the

TSOT

WLCSP

01

170

260

50

152

159

100

146

157

300

134

153

500

131

151

TSOT

WLCSP

42.8

58.4

The junction temperature of the ADP160/ADP161 can be

calculated 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 37 to

Figure 44 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 45 and Figure 46). Maximum junction

(5)

and 43°C/W for the 5-lead TSOT package.

140

120

100

80

60

40

20

0

0.3

4.8

4.3

3.8

3.3

2.8

2.3

1.8

1.3

0.8

MAXIMUM JUNCTION TEMPERATURE