ADP1055ACPZ-R7 datasheet(20/140 Pages) AD

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ADP1055

Data Sheet

Rev. A | Page 20 of 140

incorporates this phase delay into its calculations. Note that the

GUI does not account for other delays such as gate driver and

propagation delays.

DIGITAL FILTER PROGRAMMING REGISTERS

Three sets of registers allow three different filters to be

programmed.



Normal mode filter (used for CCM or heavy load and

configured in Register 0xFE01 to Register 0xFE04)



Light load mode filter (configured in Register 0xFE05 to



Soft start filter (configured in Register 0xFE09 to

The software GUI allows the user to program the light load

mode filter in the same manner as the normal mode filter. It is

recommended that the GUI be used for this purpose.

DIGITAL COMPENSATION FILTERS DURING SOFT

START

The ADP1055 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.

During soft start, the ADP1055 determines the load condition

and after the voltage reaches 12.5% of the nominal output

voltage value, it determines the current load condition and

switches filters accordingly to the light load mode threshold

(Register 0xFE5F[3:1]). If the load current is below the light

load mode threshold, the ADP1055 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 device subsequently enters light

load mode based on a change to the load current.

Other configurations can be programmed to use different filters

during soft start, as follows:



Force soft start filter (Register 0xFE51[2]). This option forces

the ADP1055 to use the soft start filter. In some cases, this

option allows better fine-tuning of the ramp-up voltage.



Disable light load mode during soft start (Register 0xFE51[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.

Figure 23 shows the use of filters during soft start.

Figure 23. Digital Filters During Soft Start (Low Temperature Filter Not Shown)

As shown in Figure 23, in Zone 1, the ADP1055 starts with the

normal mode filter or the soft start filter. Zone 2 begins when the

voltage reaches 12.5% of the nominal output voltage value. At this

point, the ADP1055 checks whether the system is in light load

mode, and the choice of filter is based on the following criteria:



If the system is in light load mode, the ADP1055 switches

to the light load mode filter (unless the option to disable

the LLM filter was previously selected).



If the system is not in light load mode, the ADP1055

continues to use the filter used in Zone 1: the normal mode

filter or the soft start filter.

The ADP1055 changes to the LLM filter if the load changes

during Zone 2 (voltage rises from 12.5% to 100% of the soft

start ramp. The filter does not revert to LLM if the load drops

until after the end of soft start.

In Zone 3 the filter changes to the NMF or LLM filter, depending

on the load.

FILTER TRANSITION

To avoid output voltage glitches and to provide a seamless

transition from one filter to another, the ADP1055 supports

programmable filter transitions. This feature allows a gradual

transition from one filter to another. Filter transitions are

programmed using Register 0xFE4A[2:0]. When the ADP1055

switches filters, the switching action is changed in 32 steps. The

step size can be programmed over several cycles (1tSW to 32tSW)

to avoid glitches in the output. The filter used depends on the

state of the synchronous rectifiers and whether the system is in

continuous conduction mode (CCM) or discontinuous conduction

mode (DCM) (see Table 5).

Table 5. State of Synchronous Rectifiers and Filter Used

State of SRx Outputs

Load

Regular Mode

Diode Emulation Mode

Filter Used

Medium to heavy load

SRs in CCM

Normal mode filter (Register 0xFE01 to Register 0xFE04).

Below LLM threshold

SRs in LLM

Diode emulation SRs

LLM filter (Register 0xFE05 to Register 0xFE08.) When diode

emulation mode is in use, the LLM filter is activated after the LLM

threshold is crossed.

Deep LLM

SRs are off

LLM filter (Register 0xFE05 to Register 0xFE08).

PS ON

12.5% REF

NMF/SSF

ZONE 1

LLF

NMF/SSF

LLM/NMF

BASED ON

LOAD

LLM/NMF

BASED ON

LOAD

NMF/SSF

RAMP TIME

0x5F

VOUT

ZONE 3

ZONE 2

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