ZL8802 datasheet(21/88 Pages) RENESAS

21 / 88 page

ZL8800

FN7558 Rev.6.00

Page 21 of 88

Nov 8, 2017

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 ZL8800 has internal nonvolatile memory that stores user

configurations. 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 ZL8800

checks for stored values contained in its internal non-volatile

memory. The ZL8800 offers two internal memory storage units

that are accessible by the user as follows:

• Default Store: A power supply module manufacturer may want

to protect the module from damage by preventing the user

from being able to modify certain values that are related to the

physical construction of the module. In this case, the module

manufacturer would use the Default Store and would allow the

user to restore the device to its default setting but would

restrict the user from restoring the device to the factory

settings.

• User Store: The manufacturer of a piece of equipment may

want to provide 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.

The User Store takes priority over the Default Store. If there are

no values set in the User or Default Store, the device will use the

pin-strap setting value.

DC/DC Converter Design

The ZL8800 operates as a voltage-mode, synchronous buck

converter with a selectable constant frequency pulse width

modulator (PWM) control scheme that uses external driver,

MOSFETs, capacitors, and an inductor to perform power

conversion.

Figure 12 illustrates the basic synchronous buck converter

topology showing the primary power train components. This

converter is also called a step-down converter, as the output

voltage must always be lower than the input voltage.

DUAL OUTPUT PWM PER CHANNEL

The ZL8800 has been designed to provide independent upper

and lower FET drive signals to a two-input MOSFET driver such as

the ZL1505.

The ZL8800 uses adaptive dead time control to improve the power

conversion efficiency. The ZL8800 monitors the power converter’s

operating conditions and continuously adjusts the turn-on and

turn-off timing of the high-side and low-side driver input signals to

optimize the overall efficiency of the power supply.

The ZL8800 can also be used with single-ended DrMOS

integrated driver and MOSFET devices. Power supplies using

DrMOS devices can be made smaller than discrete solutions

using separate drivers and MOSFETs, but at a slightly lower

efficiency. The option to use DrMOS or drivers and discrete

MOSFETs is set using the USER_CONFIG command.

Power Train Component Selection

The ZL8800 is a dual output or dual phase synchronous buck

converter that uses external drivers, MOSFETs, inductors, and

capacitors to perform the power conversion process. The proper

selection of the external components is critical for optimized

performance.

To select the appropriate external components for the desired

performance goals, the power supply requirements listed in

Table 8 must be known.

XTEMPxN

XTEMPxP

Discrete NPN

2N3904

XTEMPxN

XTEMPxP

Embedded Thermal Diode

µP

FPGA

DSP

ASIC

100 pF

100pF

FIGURE 11. EXTERNAL TEMPERATURE MONITORING

TABLE 8. POWER SUPPLY REQUIREMENTS

PARAMETER

EXAMPLE VALUE

Input Voltage (VIN)12V

Output Voltage (VOUT)1.2V

Output Current (IOUT)

30A

Output Voltage Ripple (Vorip)1% of VOUT

Output Load Step (Iostep)

50% of Io

Output Load Step Rate

10A/µs

Output Deviation Due to Load Step

±2%

Maximum PCB Temperature

85°C

Desired Efficiency

90%

Other Considerations

Optimize for small size

VOUT

ZL8800

VIN

FIGURE 12. SYNCHRONOUS BUCK CONVERTER

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