ADP1828YRQZ-R7 datasheet(25/32 Pages) AD

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ADP1828

Rev. 0 | Page 25 of 32

COMP

TRK

MASTER

VOLTAGE

RTRKT

RTRKB

0.6V

DETAIL VIEW OF

ADP1828

ERROR

AMPLIFIER

VOUT

RTOP

RBOT

Figure 41. Voltage Tracking

COINCIDENT TRACKING

The most common application is coincident tracking, used

in core vs. I/O voltage sequencing and similar applications.

Coincident tracking limits the slave output voltage to be the

same as the master voltage until it reaches regulation. Connect

the slave TRK input to a resistor divider from the master voltage

that is the same as the divider used on the slave FB pin. This

forces the slave voltage to be the same as the master voltage.

For coincident tracking, use the following equation:

RTRKT = RTOP and RTRKB = RBOT

where:

RTOP

and RBOT are the values chosen in the Compensating the

Voltage Mode Buck Regulator section.

See Figure 42 for an example of a coincident tracking circuit.

TRK

RTRKB

10kΩ

RTRKT

20kΩ

1.1V

ADP1828

ADP1829

ADP1828

RTOP

20kΩ

RBOT

10kΩ

CSS

1µF

CSS

150nF

3.3V

VOUT_MASTER

1.8V

VOUT_SLAVE

Figure 42. Example of a Coincident Tracking Circuit

TIME

SLAVE VOLTAGE

MASTER VOLTAGE

Figure 43. Coincident Tracking

CH1 5.00V

CH3 1.00V

CH2 1.00V

M 100ms

A CH1

2.60V

CH4 1.00V

VOUT_MASTER

EN FOR BOTH ADP1828

VOUT_SLAVE

TRK_SLAVE

Figure 44. Coincident Tracking of Figure 42

As the master voltage rises, the slave voltage also rises in the

same pattern. Eventually, the slave voltage reaches its regulation

voltage, where the internal reference takes over the regulation

while the TRK input continues to increase and thus removes

itself from influencing the output voltage. To ensure that the

output voltage accuracy is not compromised by the TRK pin

being too close in voltage to the 0.6 V reference, make sure

that the final value of the master voltage is greater than the

slave regulation voltage by at least 10%, or 60 mV as seen at the

FB node (the higher, the better). A difference of 60 mV between

TRK and the 0.6 V reference produces about 3 mV of offset in

the error amplifier, or 0.5%, at room temperature, while 100 mV

between them produces only 0.6 mV or 0.1% offset. For accurate

tracking, set the final voltage at TRK to less than or equal to

0.5 V. However, this condition would trip the PGOOD signal.

RATIOMETRIC TRACKING

Ratiometric tracking limits the output voltage to a fraction of

the master voltage. For example, the termination voltage for

DDR memories (VTT) is set to half the VDDQ voltage.

TIME

SLAVE VOLTAGE

MASTER VOLTAGE

Figure 45. Ratiometric Tracking

For ratiometric tracking, the simplest configuration is to tie the

TRK pin of the slave channel to the FB pin of the master channel.

The advantage of this is having the fewest components, but the

accuracy suffers as the TRK pin voltage becomes equal to the

internal reference voltage and an offset is imposed on the error

amplifier of about −18 mV at room temperature.

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