ADM7160ACPZN3.3-R2 datasheet(14/24 Pages) AD

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ADM7160

Data Sheet

Rev. 0 | Page 14 of 24

SOFT START

The ADM7160 uses an internal soft start to limit the inrush

current when the output is enabled. The start-up time for the

3.3 V option is approximately 180 μs from when the EN active

threshold is crossed to when the output reaches 90% of its final

value. As shown in Figure 38, the start-up time is dependent on

the output voltage setting.

3.5

3.0

2.5

2.0

1.5

1.0

0.5

450

400

350

300

250

200

150

100

TIME (µs)

ENABLE

VOUT = 3.3V

VOUT = 2.8V

VOUT = 1.1V

Figure 38. Typical Start-Up Behavior

CURRENT-LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADM7160 is protected against damage due to excessive

power dissipation by current-limit and thermal overload pro-

tection circuits. The ADM7160 is designed to reach 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 limits the junction temperature to

a maximum of 150°C (typical). Under extreme conditions (that

is, high ambient temperature and power dissipation) when the

junction temperature begins to rise above 150°C, the output is

turned off, reducing the output current to 0 mA. When the junc-

tion temperature falls below 135°C, the output is turned on again,

and the output current is restored to its nominal value.

Consider the case where a hard short from VOUT to ground

occurs. At first, the ADM7160 reaches current limit, so that

only 300 mA is conducted into the short. If self-heating of the

junction causes its temperature to rise above 150°C, thermal

shutdown is activated, turning off the output and reducing the

output current to 0 mA. As the junction temperature cools and

falls below 135°C, the output turns on and conducts 300 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 300 mA and 0 mA that continues

as long as the short remains at the output.

Current-limit and thermal overload 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.

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