ADP2140 datasheet(21/32 Pages) AD

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Data Sheet

ADP2140

Rev. B | Page 21 of 32

APPLICATIONS INFORMATION

POWER SEQUENCING

The ADP2140 has a flexible power sequencing system

supporting two distinct activation modes:



Individual activation control is where EN1 controls only

the buck regulator and EN2 controls only the LDO. A high

level on Pin EN1 turns on the buck and a high level on

Pin EN2 turns on the LDO. A logic low level turns off the

respective regulator.



Autosequencing is where the two regulators turn on in a

specified order and delay after a low-to-high transition on

the EN1 pin.

Select the activation mode (individual or autosequence) by

decoding the state of Pin EN2. The individual activation mode

is selected when the EN2 pin is driven externally or hardwired

to a voltage level (VIN1 or PGND). The autosequencing mode

is selected when the EN2 pin remains unconnected (floating).

To minimize quiescent current consumption, the mode selection

executes one time only during the rising edge of VIN1. The

detection circuit then activates for the time needed to assess the

EN2 state, after which time the circuit is disabled until VIN1 falls

below 0.5 V.

When EN2 is unconnected, the internal control circuit provides

a termination resistance to ground. The 100 kΩ termination

resistance is low enough to guarantee insensitivity to noise and

transients. The termination resistor is disabled in the event that

the EN2 pin is driven externally to a logic level high (individual

activation mode assumed) to reduce the quiescent current con-

sumption.

When the autosequencing mode is selected, the EN1 pin is used to

start the on/off sequence of the regulators. A logic high sequences

the regulators on whereas a logic low sequences the regulators

off. The regulator activation order is associated with the voltage

selected for the buck regulator and the LDO.

When the turn on or turn off autosequence starts, the start-up

delay between the first and the second regulator is fixed to 5 ms

in PWM mode (tREG12, as shown in Figure 71 and Figure 72).

When the application requires activating and deactivating the

regulators at the same time, use the individual activation mode,

which connects the EN1 and EN2 pins together, as shown in

Figure 75.

Table 6. Power Sequencing Modes

EN21

EN1

Description

Individual mode: both regulators are off.

Individual mode: buck regulator is on.

Individual mode: LDO regulator is on.

Individual mode: both regulators are on.

Rising edge

Autosequence: Buck regulator turns on,

then the LDO regulator turns on. The LDO

voltage is less than the buck voltage.

Rising edge

Autosequence: LDO regulator turns on,

then the buck regulator turns on. The LDO

voltage is greater than the buck voltage.

Rising edge

Autosequence: If the buck voltage is 1.875 V,

then the LDO regulator always turns on first.

Falling edge

Autosequence: The LDO and buck regula-

tors turn off at the same time.

1 NC means not connected.

Figure 70 to Figure 75 use the following symbols, as described in

Table 7.

Table 7. Timing Symbols

Symbol

Description

Typical

Value

tSTART

Time needed for the internal circuitry

to activate the first regulator

60 μs

tSS

Regulator soft start time

330 μs

tRESET

Time delay from power-good

condition to the release of PG

5 ms

tREG12

Delay time between buck and LDO

activation

5 ms

EN1

VBUCK

EN2

VLDO

92% VBUCK

92% VLDO

85% VLDO

tSS

tRESET

tSS

TIME

Figure 70. Individual Activation Mode

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