ADP150ACBZ-2.8-R7 datasheet(14/20 Pages) AD

14 / 20 page

Data Sheet

ADP150

APPLICATIONS INFORMATION

analog.com

Rev. E | 14 of 20

Consider the case where a hard short from VOUT to GND occurs.

At first, the ADP150 limits current so that only 260 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 260 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 260 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 de-

vice against accidental overload conditions. For reliable operation,

device power dissipation must be externally limited so that the

junction temperatures do not exceed 125°C.

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 en-

ters thermal shutdown. It recovers only after the junction tempera-

ture 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 de-

vice, 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

Copper Size (mm2)

θJA (°C/W)

TSOT

WLCSP

170

260

152

159

100

146

157

300

134

153

Table 7. Typical θJA Values (Continued)

Copper Size (mm2)

θJA (°C/W)

TSOT

WLCSP

500

131

151

1 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 temper-

ature, input-to-output voltage differential, and continuous load cur-

rent, 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.

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

ADP150ACBZ-2.8-R7 Datasheet(PDF) 14 Page - Analog Devices

ADP150ACBZ-2.8-R7 Datasheet(HTML) 14 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Descarga

Enlace URL