ADP2140 datasheet(20/32 Pages) AD

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ADP2140

Data Sheet

Rev. B | Page 20 of 32

SELECTED FEATURES

SHORT-CIRCUIT PROTECTION

The ADP2140 includes frequency foldback to prevent output

current runaway on a hard short. When the voltage at the feed-

back pin falls below 50% of the nominal output voltage, indicating

the possibility of a hard short at the output, the switching frequency

is reduced to 1/2 of the internal oscillator frequency. The reduc-

tion in the switching frequency gives more time for the inductor

to discharge, preventing a runaway of output current.

UNDERVOLTAGE LOCKOUT

To protect against battery discharge, undervoltage lockout

circuitry is integrated on the ADP2140. If the input voltage

drops below the 2.15 V UVLO threshold, the ADP2140 shuts

down and both the power switch and synchronous rectifier turn

off. When the voltage rises again above the UVLO threshold,

the soft start period initiates and the part is enabled.

THERMAL PROTECTION

In the event that the ADP2140 junction temperatures rises above

150°C, the thermal shutdown circuit turns off the converter.

Extreme junction temperatures can be the result of high current

operation, poor circuit board design, and/or high ambient tem-

perature. A 20°C hysteresis is included; thus, when thermal

shutdown occurs, the ADP2140 does not return to operation

until the on-chip temperature drops below 130°C. When

emerging from a thermal shutdown, soft start initiates.

SOFT START

The ADP2140 has an internal soft start function that ramps the

output voltage in a controlled manner upon startup, thereby

limiting the inrush current. This prevents possible input voltage

drops when a battery or a high impedance power source is con-

nected to the input of the converter.

CURRENT LIMIT

The ADP2140 has protection circuitry to limit the direction and

amount of current to 1000 mA flowing through the power switch

and synchronous rectifier. The positive current limit on the power

switch limits the amount of current that can flow from the input

to the output, and the negative current limit on the synchronous

rectifier prevents the inductor current from reversing direction

and flowing out of the load.

The ADP2140 also provides a negative current limit to prevent

an excessive reverse inductor current when the switching section

sinks current from the load in forced continuous conduction

mode. Under negative current limit conditions, both the high-

side and low-side switches are disabled.

POWER-GOOD PIN

The ADP2140 has a dedicated pin (PG) to signal the state of the

monitored output voltages. The voltage monitor circuit has an

active high, open-drain output requiring an external pull-up

resistor typically supplied from the I/O supply rail, as shown

in . The voltage monitor circuit has a small amount

of hysteresis and is deglitched to ensure that noise or external

perturbations do not trigger the PG line.

LDO SECTION

The ADP2140 low dropout linear regulator uses an advanced

proprietary architecture to achieve low quiescent current, and

high efficiency regulation. It also provides high power supply

rejection ratio (PSRR), low output noise, and excellent line and

load transient response with just a small 1 μF ceramic output capa-

citor. The wide input voltage range of 1.65 V to 5.5 V allows it to

operate from either the input or output of the buck. Supply current

in shutdown mode is typically 0.3 µA.

Internally, the LDO consists of a reference, an error amplifier, a

feedback voltage divider, and a pass device. The output current

is delivered via the pass device, which is controlled by the error

amplifier, forming a negative feedback system ideally driving

the feedback voltage to be equal to the reference voltage. If the

feedback voltage is lower than the reference voltage, the negative

feedback drives more current, increasing the output voltage. If

the feedback voltage is higher than the reference voltage, the

negative feedback drives less current, decreasing the output

voltage. The positive supply for all circuitry, except the pass

device, is the VIN1 pin.

The LDO has an internal soft start that limits the output voltage

ramp period to approximately 130 µs.

The LDO is available in 0.8 V, 1.0 V, 1.1 V, 1.2 V, 1.3 V, 1.5 V, 2.5 V,

2.8 V, 3.0 V, and 3.3 V output voltage options.

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