ISL68227IRAZ datasheet(19/100 Pages) RENESAS

19 / 100 page

ISL68227

4. Operating the Device

FN9333 Rev.1.00

Page 19 of 99

Oct.1.20

4.4

Enabling and Soft-Starting the Device

The ISL68227 outputs can be enabled using the enable pin or PMBus. Enable method selection is configured in

PowerNavigator on a per rail basis. The ISL68227 begins its soft-start sequence when it is commanded to

regulate an output. Soft-start moves VOUT smoothly to the programmed VOUT_COMMAND. Soft-start timing is

programmed using the TON_DELAY (60h) and TON_RISE (61h) PMBus commands.

If a pre-existing voltage bias exists on the output, the PWM signals are held in tri-state until the soft-start ramp

reaches the prebias level. The tri-state prevents the converter from sinking current and pulling the prebias down.

No special configuration is required to enable this operation.

4.5

Disabling the Device

Similar to the enabling process, outputs can be disabled using the enable pin or PMBus on a per rail basis. The

ISL68227 can be configured to disable in two ways:

• Immediate OFF: Immediately ceases regulation and tri-state the PWM pins

• Soft OFF: Actively ramps the output voltage down to 0V before ceasing activity as programmed in the

TOFF_DELAY (64h) and TOFF_FALL (65h) PMBus commands.

4.6

Phase Configuration and Automatic Phase Dropping

The ISL68227 supports three regulated outputs that control its twelve phases. Each rail is capable of controlling

up to twelve phases, but the rails can be configured for fewer phases. Unused phases should have their CS and

CSRTN pins grounded.

The ISL68227 supports Automatic Phase Dropping (APD) to optimize efficiency across the load range. Figure 7

shows the typical characteristics of efficiency vs load current as the phase count is varied. The diagram shows

that optimal efficiency is achieved by using fewer phases as the load current decreases.

The ISL68227 continuously monitors output current, and if APD is enabled, the device drops or adds phases from

use as the load current varies.

Phases are dropped one at a time with a user-programmed delay between drop events. For example, if the delay

is set to 1ms, six phases are active, and the load suddenly drops to a level needing only one phase; the ISL68227

begins by dropping a single phase after 1ms. An additional phase is dropped each millisecond until only one

phase remains active. On Rail 0, phases are dropped beginning with the highest assigned phase.

Phases are automatically returned to service when load conditions require more phases. The phases are returned

to service in the opposite order they were dropped. Conditions that result in phase adding include increased load

current, rapid change sensed on the output voltage, and VOUT transition events. When rapid change is sensed on

the output voltage, the Fast Phase Add function prepares all dropped phases for activation so there is no delay if

all phases are needed to support a load transient.

Figure 7. Efficiency vs Phase Number

ISL68227IRAZ Datasheet(PDF) 19 Page - Renesas Technology Corp