ADP150ACBZ-3.3-R7 datasheet(14/20 Pages) AD

14 / 20 page

ADP150

Rev. A | Page 14 of 20

THERMAL CONSIDERATIONS

In most applications, the ADP150 does not dissipate much heat

due to its 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 decreases 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 ADP150 must not exceed 125°C. To ensure that the junction

temperature stays below 125°C, be aware of the parameters that

contribute to the junction temperature changes. These parameters

include ambient temperature, power dissipation in the power

device, and thermal resistances between the junction and

ambient air (θJA). The θJA 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. Table 7 shows

typical θJA values of the 5-lead TSOT and 4-ball WLCSP packages

for various PCB copper sizes. Table 8 shows the typical ΨJB

value of the 5-lead TSOT and 4-ball WLCSP.

Table 7. Typical θJA Values

θJA (°C/W)

Copper Size (mm2)

TSOT

WLCSP

170

260

152

159

100

146

157

300

134

153

500

131

151

Device soldered to minimum size pin traces.

Table 8. Typical ΨJB Values

ΨJB (°C/W)

TSOT

WLCSP

42.8

58.4

Use Equation 2 to calculate the junction temperature.

TJ = TA + (PD × θJA)

(2)

where:

TA is the ambient temperature.

PD is the power dissipation in the die, given by

PD = [(VIN − VOUT) × ILOAD] + (VIN × IGND)

where:

ILOAD is the load current.

IGND is the ground current.

VIN and VOUT are input and output voltages, respectively.

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

ignored. Therefore, the junction temperature equation simplifies to

TJ = TA + {[(VIN − VOUT) × ILOAD] × θJA}

(3)

As shown in the previous equation, 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 that the junction temperature does not rise above 125°C.

Figure 33 to Figure 46 show the junction temperature calculations

for the different ambient temperatures, load currents, VIN-to-VOUT

differentials, and areas of PCB copper.

140

120

100

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

VIN – VOUT (V)

ILOAD = 1mA

ILOAD = 10mA

ILOAD = 25mA

ILOAD = 50mA

ILOAD = 75mA

ILOAD = 100mA

ILOAD = 150mA

MAX JUNCTION TEMPERATURE

Figure 33. TSOT, 500 mm2 of PCB Copper, TA = 25°C

140

120

100

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

VIN – VOUT (V)

ILOAD = 1mA

ILOAD = 10mA

ILOAD = 25mA

ILOAD = 50mA

ILOAD = 75mA

ILOAD = 100mA

ILOAD = 150mA

MAX JUNCTION TEMPERATURE

Figure 34. TSOT, 100 mm2 of PCB Copper, TA = 25°C

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