ADP223ACPZ-R7 datasheet(20/24 Pages) AD

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ADP222/ADP223/ADP224/ADP225

Data Sheet

Rev. B | Page 20 of 24

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

2000

4000

6000

8000

10000

TIME (µs)

ENABLE

VOUT, NO QOD

VOUT, WITH QOD

Figure 71. Typical Turn-Off Time with and Without QOD Function

CURRENT LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADP222/ADP223/ADP224/ADP225 are protected against

damage due to excessive power dissipation by current and

thermal overload protection circuits. The ADP222/ADP223/

ADP224/ADP225 are designed to current limit when the output

load reaches 300 mA (typical). When the output load exceeds

300 mA, the output voltage is reduced to maintain a constant

current limit.

Thermal overload protection is included, which limits the

junction temperature to a maximum of 155°C (typical). Under

extreme conditions (that is, high ambient temperature and

power dissipation) when the junction temperature starts to rise

above 155°C, the output is turned off, reducing the output current

to 0. When the junction temperature drops below 140°C, the

output is turned on again, and output current is restored to its

nominal value.

Consider the case where a hard short from VOUTx to ground

occurs. At first, the ADP222/ADP223/ADP224/ADP225 cur-

rent limits, so that only 300 mA is conducted into the short. If

self-heating of the junction is great enough to cause its tempera-

ture to rise above 155°C, thermal shutdown activates, turning

off the output and reducing the output current to 0 mA. As the

junction temperature cools and drops below 135°C, the output

turns on and conducts 300 mA into the short, again causing the

junction temperature to rise above 155°C. This thermal oscilla-

tion between 140°C and 155°C causes a current oscillation

between 300 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 ADP222/ADP223/ADP224/ADP225

do 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 155°C, the converter

enters thermal shutdown. It recovers only after the junction

temperature has decreased below 140°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 ADP222/ADP223/ADP224/ADP225 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 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 pin to the PCB.

Table 6 shows typical θJA values of the 8-lead LFCSP package for

various PCB copper sizes, and Table 7 shows the typical ΨJB value

of the 8-lead LFCSP.

Table 6. Typical θJA Values

Copper Size (mm2)

θJA (°C/W)

251

175.1

100

135.6

500

77.3

1000

65.2

6400

Device soldered to minimum size pin traces.

Table 7. Typical ΨJB Value

Model

ΨJB (°C/W)

8-Lead LFCSP

18.2

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