ISL68233IRAZ datasheet(21/103 Pages) RENESAS

21 / 103 page

ISL68222, ISL68233

4. Operating the Device

R16DS0036EU0100 Rev.1.00

Page 21 of 102

Oct.1.20

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.

Any command to change the output voltage set point uses all phases, including VOUT transition events. After the

output voltage change is complete, phases begin dropping as configured.

To ensure dropped phases have sufficient bootstrap capacitor charge to turn on the high-side MOSFET after a

long period of inactivity, a bootstrap refresh function periodically turns on the low-side MOSFET of each dropped

phase to refresh the bootstrap capacitor.

To produce the most optimal efficiency across a wide range of output loading, the modulator supports automatic

dropping or adding of phases and diode emulation (in a single-phase state). Use of APD and diode emulation are

optional. If automatic phase dropping is enabled, the number of active phases at any time is determined solely by

load current.

4.7

Diode Emulation and PFM Operation

As described in Phase Configuration and Automatic Phase Dropping, the ISL68222 and ISL68233 support APD

to optimize phase usage as load demand decreases. When the regulator drops to 1-phase operation, it supports

diode emulation and Pulse Frequency Modulation (PFM) operation to further maximize efficiency performance.

Traditionally, use of such efficiency boosting techniques have come at the expense of transient response, but the

ISL68222 and ISL68233 are able to meet all transient demands directly from diode emulation/PFM operation.

Diode emulation and PFM operation are supported when a single phase is active. If constant frequency operation

is needed at light loads, the feature can be disabled. If enabled, the low-side MOSFET conducts when the current

is flowing from source-to-drain and does not allow a reverse current, emulating an ideal diode. As Figure 9 shows,

when the inductor current is positive, the LGATE is held on and allows current to flow in the low resistance

channel of the LFET. When current reaches zero, the LFET is turned off to prevent a reverse current in the

inductor. The controller modulates the LFET state through the PWM pin of the respective regulator channel by

tri-stating the PWM when the load current reaches zero, which commands the MOSFET driver to turn off both the

HFET and LFET.

In single-phase diode emulation operation, the ISL68222 and ISL68233 deliver inductor current pulses with a

user-programmed pulse width. By programming the pulse width, the output voltage ripple can be tuned to meet

expectations for any system type. Pulse frequency is then modulated to maintain output voltage regulation as

shown in Figure 10. The transition from single phase PFM to multiphase constant frequency operation is

managed seamlessly by the ICs.

Figure 9. Diode Emulation PWM Signaling

Figure 10. Single Phase Light Load PFM Operation

ISL68233IRAZ Datasheet(PDF) 21 Page - Renesas Technology Corp