ADP150

Rev. A | Page 13 of 20

To guarantee the performance of the ADP150, it is imperative

that the effects of the dc bias, temperature, and tolerances on

the behavior of the capacitors be evaluated for each.

UNDERVOLTAGE LOCKOUT

The ADP150 has an internal undervoltage lockout circuit that

disables all inputs and the output when the input voltage is less

than approximately 2.0 V. This ensures that the ADP150 inputs

and output behave in a predictable manner during power-up.

ENABLE FEATURE

The ADP150 uses the EN pin to enable and disable the VOUT

pin under normal operating conditions. As shown in Figure 30,

turns on. When a falling voltage on EN crosses the inactive

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Figure 30. Typical EN Pin Operation

As shown in Figure 30, the EN pin has hysteresis built in. This

prevents on/off oscillations that can occur due to noise on the

EN pin as it passes through the threshold points.

The EN pin active/inactive thresholds are derived from the VIN

voltage; therefore, these thresholds vary with changing input

voltage. Figure 31 shows the typical EN active/inactive thresholds

when the input voltage varies from 2.2 V to 5.5 V.

1.1

0.4

0.5

0.6

0.7

0.8

0.9

1.0

5.5

5.3

4.8

4.3

3.8

3.3

2.8

2.3

RISING

FALLING

The ADP150 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 150 µs from the time the EN active

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

value. As shown in Figure 32, the start-up time is dependent on the

output voltage setting.

1

1

1

CH1 1V

CH2 1V

CH3 1V

CH4 1V

M40.0µs

A CH1

3.24V

T

240.000ns

1

T

EN

Figure 32. Typical Start-Up Time

CURRENT LIMIT AND THERMAL OVERLOAD

PROTECTION

The ADP150 is protected against damage due to excessive

power dissipation by current and thermal overload protection

circuits. The ADP150 is designed to limit current when the

output load reaches 260 mA (typical). When the output load

exceeds 260 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 150°C (typical). Under extreme

conditions (that is, high ambient temperature and power dissipation)

when the junction temperature starts to rise above 150°C, the

output is turned off, reducing the output current to zero. When

the junction temperature drops 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 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 device against accidental overload conditions. For reliable

operation, device power dissipation must be externally limited

so that the junction temperatures do not exceed 125°C.