ZL8802ALAFT datasheet(21/91 Pages) RENESAS

21 / 91 page

ZL8802

FN8760 Rev.3.00

Page 21 of 91

Nov 8, 2017

When current sharing up to 2 ZL8802s (4 phases total), the

ZL8802 uses a low-bandwidth, first-order digital current sharing

technique to balance the unequal device output loading by

aligning the load lines of member devices to a reference device.

Upon system start-up, the lowest numbered phase is defined as

the reference phase and all other phases are member phases.

The reference phase broadcasts its current over the DDC bus. The

member phases use the reference current information to trim

their reference voltages (VMEMBER) to balance the current

loading of each device in the system.

Figure 10 on page 20 shows that, for load lines with identical

slopes, the member reference 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 6:

Where R is the value of the droop resistance. The VOUT_DROOP

command is used to set the device output voltage droop to

achieve 4-, 6- or 8-phase current sharing.

4-, 6-, and 8-phase current sharing groups must have their DDC

and SYNC pins tied together to achieve current sensing and ensure

accurate phase offsets between current sharing phases.

Temperature Monitoring Using XTEMP Pin

Each channel of the ZL8802 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 11 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 close to the inductor. These

options for the external temperature sensors are selected using

the USER_CONFIG PMBus command.

Nonvolatile Memory and Security Features

The ZL8802 has internal nonvolatile memory where user

configurations are stored. Integrated security measures ensure

that the user can only restore the device to a level that has been

made available to them. During the initialization process, the

ZL8802 checks for stored values contained in its internal

nonvolatile memory. The ZL8802 offers two internal memory

storage units that are accessible by the user as follows:

User Store: The user store is the most commonly used store. It

provides the ability to modify certain power supply settings while

still protecting the equipment from modifying values that can

lead to a system level fault. The equipment manufacturer would

use the user store to achieve this goal.

Default Store: The default store is less commonly used. It

provides a means to protect the circuit from damage by

preventing the user from modifying certain values that are

related to the physical construction of the circuit. In this case, the

Original Equipment Manufacturer (OEM) would use the default

store in a protected mode and allow the user to restore the

device to its default settings. In this case the user store would be

available to the end-user for making changes, but would restrict

the user from restoring the device to the factory settings or

modifying the default store.

The user store takes priority over the Default Store. If there are

no values set in the user or default store, then the device will use

the pin-strap setting value.

For details regarding protection of the user and default stores,

see the PASSWORD PMBus command.

Monitoring Through SMBus

A system controller can monitor a wide variety of different

ZL8802 parameters through the SMBus interface. The device

can monitor for fault conditions by monitoring the SALRT pin,

which will be asserted when any number of preconfigured fault

conditions occur.

The device can also be monitored continuously for any number of

power conversion parameters including, but not limited to, the

following:

•Input voltage

•Output voltage

• Input current

•Output current

• Internal junction temperature

• Temperature of an external device

• Switching frequency

• Duty cycle

• Fault status information

The PMBus Host should respond to SALRT as follows:

1. ZL device pulls SALRT low.

2. PMBus host detects that SALRT is now low, and performs

transmission with Alert Response Address to find which ZL

device is pulling SALRT low.



MEMBER

REFERENCE

OUT

MEMBER









(EQ. 6)

FIGURE 11. EXTERNAL TEMPERATURE MONITORING

ZL8802

XTEMPxP

XTEMPxN

ZL8802

XTEMPxP

XTEMPxN

ASIC

100pF

2N3904

DISCRETE NPN

EMBEDDED THERMAL DIODE

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