ADP8863ACPZ-R7 datasheet(13/48 Pages) AD

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ADP8863

Rev. 0 | Page 13 of 48

Soft Start Feature

At startup (either from UVLO activation or fault/standby

recovery), the output is first charged by ISS (3.75 mA typical)

until it reaches about 92% of VIN. This soft start feature reduces

the inrush current that is otherwise present when the output

capacitance is initially charged to VIN. When this point is

reached, the controller enters G = 1× mode. If the output

voltage is not sufficient, then the automatic gain selection

determines the optimal point as defined in the Automatic Gain

Selection section.

OPERATING MODES

There are four different operating modes: active, standby,

shutdown, and reset.

Active Mode

In active mode, all circuits are powered up and in a fully

operational state. This mode is entered when Bit nSTBY (in

Standby Mode

Standby mode disables all circuitry except for the I2C receivers.

Current consumption is reduced to less than 1 μA. This mode is

entered when the nSTBY bit is set to 0 or when the nRST pin is

held low for more than 100 μs (maximum). When standby is

exited, a soft start sequence is performed.

Shutdown Mode

Shutdown mode disables all circuitry, including the I2C receivers.

Shutdown occurs when VIN is below the undervoltage thresholds.

When VIN rises above VIN(START) (2.05 V typical), all registers are

reset and the part is placed into standby mode.

Reset Mode

In reset mode, all registers are set to their default values and

the part is placed into standby. There are two ways to reset the

part: by power-on reset (POR) or using the nRST pin. POR is

activated any time that the part exits shutdown mode. After a

POR sequence is complete, the part automatically enters

standby mode.

After startup, the part can be reset by pulling the nRST pin low.

As long as the nRST pin is low, the part is held in a standby

state, but no I2C commands are acknowledged (all registers are

kept at their default values). After releasing the nRST pin, all

registers remain at their default values, and the part remains in

standby; however, the part does accept I2C commands.

The nRST pin has a 50 μs (typical) noise filter to prevent inad-

vertent activation of the reset function. The nRST pin must be

held low for this entire time to activate reset.

The operating modes function according to the timing diagram

in Figure 27.

STANDBY

nRST

SHUTDOWN

25µs TO 100µs NOISE FILTER

1×

1.5×

2×

SOFT START

10µs 100µs

VIN

VOUT

VIN

VIN CROSSES ~2.05V AND TRIGGERS POWER-ON RESET

BIT nSTBY IN REGISTER

MDCR GOES LOW

~100µs DELAY BETWEEN POWER-UP AND

WHEN I2C COMMANDS CAN BE RECEIVED

nRST MUST BE HIGH FOR 20µs (MAX)

BEFORE SENDING I2C COMMANDS

nRST IS LOW, WHICH FORCES STANDBY

LOW AND RESETS ALL I2C REGISTERS

GAIN CHANGES OCCUR ONLY WHEN NECESSARY,

BUT HAVE A MIN TIME BEFORE CHANGING

~3.75mA CHARGES

VOUT TO VIN LEVEL

Figure 27. Typical Timing Diagram

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