ISL68233IRAZ datasheet(20/103 Pages) RENESAS

20 / 103 page

ISL68222, ISL68233

4. Operating the Device

R16DS0036EU0100 Rev.1.00

Page 20 of 102

Oct.1.20

4.4

Enabling and Soft-Starting the Device

The ISL68222 and ISL68233 outputs can be enabled using the enable pin or PMBus. Enable method selection is

configured in PowerNavigator on a per-rail basis. The ISL68222 and ISL68233 begin their soft-start sequence

when they are 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

The ISL68222 and ISL68233 can be configured to disable in two ways:

• Immediate OFF: Immediately ceases regulation and tri-states PWM pins.

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

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

4.6

Phase Configuration and Automatic Phase Dropping

The ISL68222 and ISL68233 support two regulated outputs that control their five phases. Each rail is capable of

controlling up to five phases, but the rails can be configured for fewer phases. Unused phases should have their

CS and CSRTN pins grounded.

The ISL68222 and ISL68233 support Automatic Phase Dropping (APD) to optimize efficiency across the load

range. Figure 8 shows the typical characteristics of efficiency vs load current as the phase count is varied. The

diagram shows that for a typical multiphase system, optimal efficiency is achieved by using fewer phases as the

load current decreases.

The ISL68222 and ISL68233 continuously monitor output current, and if APD is enabled, the devices drop or add

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, five phases are active, and the load suddenly drops to a level needing only one phase; the

ISL68222 and ISL68233 begin 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. On Rail 1, phases are dropped beginning with the lowest 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

Figure 8. Efficiency vs Phase Number

ISL68233IRAZ Datasheet(PDF) 20 Page - Renesas Technology Corp