ZL2106ALCF datasheet(21/29 Pages) RENESAS

21 / 29 page

ZL2106

FN6852 Rev 6.00

Page 21 of 29

February 20, 2013

for more information on configuring tracking mode using PMBus

commands.

Figure 23 is an example of a basic pin-strap tracking

configuration. The VTRK pin is an analog input that, when

tracking mode is enabled, the voltage applied to the VTRK pin

performs as a reference for the device's output voltage. The

ZL2106 offers two modes of tracking: coincident and ratiometric.

Figures 20 and 21 illustrate the output voltage waveform for the

two tracking modes.

1. Coincident. This mode configures the ZL2106 to ramp its

output voltage at the same rate as the voltage applied to the

VTRK pin. Two options are available for this mode;

a. Track at 100% VOUT limited. Member rail tracks the reference

rail and stops when the member reaches its target voltage,

Figure 20 (A).

b. Track at 100% VTRK limited. Member rail tracks the

reference at the instantaneous voltage value applied to the

VTRK pin, Figure 20 (B).

2. Ratiometric. This mode configures the ZL2106 to ramp its

output voltage as a percentage of the voltage applied to the

VTRK pin. The default setting is 50%, but an external resistor

may be used to configure a different tracking ratio.

a. Track at 50% VOUT limited. Member rail tracks the reference

rail and stops when the member reaches 50% of the target

voltage, Figure 21 (A).

b. Track at 50% VTRK limited. Member rail tracks the reference

at the instantaneous voltage value applied to the VTRK pin

until the member rail reaches 50% of the reference rail

voltage, or if the member is configured to less than 50% of the

reference the member will achieve its configured target,

Figure 21 (B).

Tracking Overview

When the ZL2106 is configured to the voltage tracking mode, the

voltage applied to the VTRK pin acts as a reference for the

member device(s) output regulation. The soft-start values

(Rise/Fall times) are used to calculate the loop gain used during

the turn-on/turn-off ramps, therefore the minimum rise/fall time

has been constrained to 5ms to ensure accuracy. Tracking

accuracy can be improved by increasing the rise and fall times

beyond 5ms.

Tracking Groups

In a tracking group, the device configured to the highest voltage

within the group is defined as the reference device. The device(s)

that track the reference are called the member device(s). The

reference device will control the ramp delay and ramp rate of all

tracking devices and is not placed in the tracking mode.

The reference device is configured to the highest output voltage

for the group and all other device(s) output voltages are meant to

track and never exceed the reference device output voltage.

The reference device must be configured to have a minimum

Time-On Delay and Time-On Rise as shown in Equation 13.

This delay allows the member device(s) to prepare their control

loops for tracking following the assertion of ENABLE.

The member device Time-Off Delay has been redefined to

describe the time that the VTRK pin will follow the reference

voltage after enable is de-asserted. The delay setting sets the

timeout for the member's output voltage to turnoff in the event

that the reference output voltage does not achieve zero volts.

The member device(s) must have a minimum Time-Off Delay of

as shown in Equation 14.

It is assumed for a tracking group, that all of the ENABLE pins are

connected together and driven by a single logic source or PMBus

Broadcast Enable is used.

The configuration settings for Figures 20 and 21 are shown

below in Figure 22. In each case the reference and member rise

times are set to the same value.

FIGURE 19. BASIC I2C TRACKING CONFIGURATION

ZL2106

VTRK

SDA SCL

VOUT_M

MEMBER

ZL2106

SCL

SDA

VOUT_R

REFERENCE

SDA

SCL

FIGURE 20. COINCIDENT TRACKING

Track @ 100% Vout Limited

Vref > Vmem

Ton Dly

Toff Dly

VRef

Vmem

Track @ 100% Vtrk Limited

Vref = Vmem

Ton Dly

Toff Dly

VRef

Vmem

Coincident Tracking

Vref=1.8V

Vmem=0.9V

Vref=1.8V

Vmem=1.8V

FIGURE 21. RATIOMETRIC TRACKING

Track @ 50% Vout Limited

Vref = 1.8V

Vmem = 0.9V

Toff Dly

Ton Dly

Vmem

VRef

Track @ 50% Vtrk Limited

Vref = 1.8V

Vmem = 0.8V

Ratiometric Tracking

Vref=1.8V

Vmem=0.9V

Ton Dly

Toff Dly

Vref

Vmem

Vref=1.8V

Vmem=0.8V

(EQ. 13)

tONDLY(REF)  tONDLY(MEM) + tONRISE(REF) + 5ms  tONDLY(MEM) + 10ms

(EQ. 14)

tOFFDLY(MEM)  tOFFDLY(REF) + tOFFFALL(REF) + 5ms

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