ZL8800_15 Datasheet, PDF (20/84 Pages) Intersil Corporation – Dual Channel/Dual Phase PMBus™ ChargeMode™ Control DC/DC Digital Controller

ZL8800
Phase Spreading
When multiple point of load converters share a common DC
input supply, it is desirable to adjust the clock phase offset of
each device such that not all devices have coincident rising
edges. Setting each converter to start its switching cycle at a
different point in time can dramatically reduce input capacitance
requirements. Since the peak current drawn from the input
supply is effectively spread out over a period of time, the peak
current drawn at any given moment is reduced and the power
losses proportional to I_RMS2 are reduced.
In order to enable phase spreading, all converters must be
synchronized to the same switching clock. Configuring the SYNC
pin is described in “Configurable Pins” on page 13. Selecting the
phase offset for the device is accomplished by selecting a device
address according to the following equation:
Phase offset = device address x 45°
This behavior is illustrated in Table 7:
ADDRESS LSB
0
1
2
3
4
5
6
7
TABLE 7.
PHASE OFFSET
(°)
ADDRESS LSB
0
8
45
9
90
A
135
B
180
C
225
D
270
E
315
F
PHASE OFFSET
(°)
0
45
90
135
180
225
270
315
The phase offset of each device may also be set to any value
between 0° and 360° in 22.5° increments using the
INTERLEAVE PMBus™ command.
Output Sequencing
A group of Intersil devices may be configured to power up in a
predetermined sequence. This feature is especially useful when
powering advanced processors, FPGAs and ASICs that require
one supply to reach its operating voltage prior to another supply
reaching its operating voltage in order to avoid latch-up from
occurring. Multidevice sequencing can be achieved by
configuring each device using the SEQUENCE PMBus™
command.
Multiple device sequencing is achieved by issuing PMBus™
commands to assign the preceding device in the sequencing
chain as well as the device that will follow in the sequencing
chain.
The enable (EN) pins of all devices in a sequencing group must be
tied together and driven high to initiate a sequenced turn-on of
the group. Enable must be driven low to initiate a sequenced
turnoff of the group.
Sequencing can also be accomplished by connecting the enable
pin of a sequel device to the power-good pin of a prequel device.
Sequencing is also achieved by using the TON_DELAY and
TON_RISE commands and choosing appropriate delay and rise
durations such that sequel devices start after their associated
prequel devices. The drawback to this method is that if a prequel
device fails to start properly, its sequel device will still start and
ramp on according to its delay and rise time settings.
Fault Spreading
Digital DC devices can be configured to broadcast a fault event
over the DDC bus to the other devices in the group. When a fault
occurs and the device is configured to shut down on a fault, the
device will shut down and broadcast the fault event over the DDC
bus. The other devices on the DDC bus will shut down together if
configured to do so, and will attempt to restart in their prescribed
order if configured to do so.
Active Current Sharing
The two channels of the ZL8800 can be used in parallel to create
a dual phase power rail. The device outputs will share the current
equally within a few percent.
Figure 9 shows a typical connection for a dual phase application.
When used in this configuration the ZL8800 can current share
between phases without utilizing output voltage droop.
V_IN
ZL8800
VIN
V_OUT
FIGURE 9. DUAL PHASE EXAMPLE
Temperature Monitoring Using XTEMP Pin
Each channel of the ZL8800 supports measurement of an
external device temperature using either a thermal diode
integrated in a processor, FPGA or ASIC, or using a discrete
diode-connected 2N3904 NPN transistor. Figure 10 on page 21
illustrates the typical connections required. A noise filtering
capacitor, not exceeding 100pF, should be connected across the
external temperature sensing device. The external temperature
sensors can be used to provide the temperature reading for
over-temperature and under-temperature faults. The external
sensors can also be used to provide more accurate temperature
compensation for inductor DCR current sensing by being placed
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FN7558.3
September 14, 2015