ADP1046AACPZ-R7 datasheet(20/88 Pages) AD

20 / 88 page

ADP1046A

Data Sheet

Rev. 0 | Page 20 of 88

SOFT START

The turning on and off of the ADP1046A is controlled by the

hardware PSON pin and/or the software PSON register,

depending on the configured settings in Register 0x2C.

When the user turns on the power supply (enables PSON),

the following soft start procedure occurs (see Figure 24).

1. The PSON signal is enabled at Time t0. If the part is

programmed to be always on (Register 0x2C[7:6] = 00),

PSON is enabled as soon as VCORE is above UVLO.

2. The ADP1046A waits for the programmed PS_ON delay

(set in Register 0x2C[4:3]).

3. The soft start begins to ramp up the internal digital reference.

The total duration of the soft start ramp is programmable

from 5 ms to 100 ms using Register 0x5F[7:5].

4. If the soft start from precharge function is enabled

(Register 0x5F[4] = 1), the soft start ramp starts from

the value of the output voltage sensed on VS1 or VS3±

(depending on the OrFET status), and the soft start ramp

time is reduced proportionally. If the soft start from pre-

charge function is disabled, the soft start ramp time is the

programmed value in Register 0x5F[7:5].

5. When the power supply voltage exceeds the VS1 under-

voltage protection (UVP) limit (set in Register 0x34[6:0]),

the UVP flag is reset.

6. The OrFET is turned on as soon as the OrFET enable thresh-

old is met. (The OrFET enable threshold is programmed in

VS1 to VS3±.

7. If no other fault conditions are present, the PGOODx

signals wait for the programmed debounce time (set in

flag must be unmasked in Register 0x7B and Register 0x7C

(Bit 7 must be set to 0).

8. If no OrFET is used, the power supply must be configured

to regulate using VS3 at all times (Register 0x33[2] = 1).

VS2 can be used as a secondary OVP mechanism.

Fault Condition During Soft Start

If a fault condition occurs during soft start, the controller responds

as programmed unless the flag is blanked. Flag blanking during

soft start is programmed in Register 0x0F. The ACSNS flag is

always blanked during soft start. The OTP, FLAGIN, OVP, and

OCP fault flags can be blanked during soft start by setting the

appropriate bits in Register 0x0F.

The UVP fault is blanked only for the debounce time during

soft start. Therefore, if the soft start period exceeds the debounce

time, the UVP fault is triggered and stored in the first flag ID

the first flag ID register clears the falsely triggered UVP condition.

Digital Compensation Filters During Soft Start

The ADP1046A has a dedicated soft start filter (SSF) that can be

used to fine-tune and optimize the dynamic response during

the output voltage ramp-up.

Before it ramps up the internal reference after the PSON signal

is enabled, the ADP1046A evaluates whether the OrFET should

be turned on or off by looking at the difference between VS1

and VS2. This step is done to determine whether the regulation

point should be VS1 or VS3± (see Figure 24).

•

If the regulation point is VS1, the soft start filter is used

by default during the ramp-up. At the end of the soft start

ramp, the part switches to the normal mode filter (NMF).

•

If the regulation point is VS3±, the part starts the ramp

using the normal mode filter (NMF).

In both cases, after the voltage reaches 12.5% of the nominal

output voltage value, the load current is evaluated.

•

If the load current is below the light load mode threshold,

the part switches to the light load mode filter (LLF).

•

If the load current is above the light load mode threshold,

the normal mode filter is used until the end of the soft start

ramp, even if the system subsequently enters light load

mode based on a change to the load current.

different filters during soft start as follows:

•

Force soft start filter (Bit 0). This option forces the part to

use the soft start filter even when the regulation point is

VS3. In some cases, this option allows better fine-tuning of

the ramp-up voltage. This option can also be selected when

an OrFET is not used.

•

Disable light load mode during soft start (Bit 1). This

option prevents the use of the light load mode filter during

soft start, even if the light load condition is met. The light

load mode filter is available for use after the end of the soft

start ramp.

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