ZL9101M

13

FN7669.1

January 26, 2011

calibrating out the physical parasitic mismatches due to power

train components and PCB layout.

Upon system start-up, the module with the lowest member position as

selected in ISHARE_CONFIG is defined as the reference module. The

remaining modules are members. The reference module broadcasts its

current over the DDC bus. The members use the reference current

loading of each module in the system.

Figure 12 shows that, for load lines with identical slopes, the

member voltage is increased towards the reference voltage

which closes the gap between the inductor currents.

The relation between reference and member current and voltage

is given by the following equation:

where R is the value of the droop resistance.

The ISHARE_CONFIG command is used to configure the module

for active current sharing. The default setting is a stand-alone

non-current sharing module. A current sharing rail can be part of

a system sequencing group.

For fault configuration, the current share rail is configured in a

quasi-redundant mode. In this mode, when a member module

fails, the remaining members will continue to operate and

attempt to maintain regulation. Of the remaining modules, the

module with the lowest member position will become the

reference. If fault spreading is enabled, the current share rail

failure is not broadcast until the entire current share rail fails.

The phase offset of (multi-phase) current sharing modules is

automatically set to a value between 0° and 337.5° in 22.5°

increments as follows:

Please refer to Application Note AN2034 for additional details on

current sharing.

Phase Adding/Dropping

The ZL9101M allows multiple power converters to be connected

in parallel to supply higher load currents than can be addressed

using a single-phase design. In doing so, the power converter is

optimized at a load current range that requires all phases to be

operational. During periods of light loading, it may be beneficial

to disable one or more phases in order to eliminate the current

drain and switching losses associated with those phases,

resulting in higher efficiency.

The ZL9101M offers the ability to add and drop phases using a

PMBus command in response to an observed load current

change. All phases in a current share rail are considered active

prior to the current sharing rail ramp to power-good.

Any member of the current sharing rail can be dropped. If the

reference module is dropped, the remaining active module with

the lowest member position will become the new reference.

Additionally, any change to the number of members of a current

sharing rail will precipitate autonomous phase distribution within

the rail where all active phases realign their phase position

based on their order within the number of active members.

If the members of a current sharing rail are forced to shut down

due to an observed fault, all members of the rail will attempt to

re-start simultaneously after the fault has cleared.

A system controller can monitor a wide variety of different

The module can monitor for any number of power conversion

parameters including but not limited to the following:

• Input voltage/Output voltage

•Output current

• Internal temperature

• Switching frequency

• Duty cycle

Please refer to Application Note AN2033 for details on how to

Snapshot Parameter Capture

The ZL9101M offers a special feature that enables the user to

capture parametric data during normal operation or following a

fault. The Snapshot functionality is enabled by setting bit 1 of

MISC_CONFIG to 1.

See AN2033 for details on using SnapShot in addition to the

parameters supported. The Snapshot feature enables the user to

read parameters via a block read transfer through the SMBus.

This can be done during normal operation, although it should be

noted that reading the 22 bytes will occupy the SMBus for some

time.

The SNAPSHOT_CONTROL command enables the user to store

the snapshot parameters to Flash memory in response to a

pending fault as well as to read the stored data from Flash

memory after a fault has occurred. Table 3 describes the usage

of this command. Automatic writes to Flash memory following a

fault are triggered when any fault threshold level is exceeded,

provided that the specific fault’s response is to shut down

(writing to Flash memory is not allowed if the device is configured

to re-try following the specific fault condition). It should also be

the time when the controller is writing the data to Flash memory;

-R

-R

FIGURE 12. ACTIVE CURRENT SHARING

()

MEMBER

REFERENCE

OUT

MEMBER

I

I

R

V

V

−

×

+

=

(EQ. 2)

Phase Offset

SMBus Address 4:0

[]

Current

–

=

(EQ. 3)

Share Position∗22.5

°