ADM1266ACPZ-R7 datasheet(21/62 Pages) AD

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Data Sheet

ADM1266

Rev. A | Page 21 of 62

VOUT_COMMAND

VOUT_MARGIN_HIGH

VOUT_MARGIN_LOW

DAC ENABLE

OPERATION COMMAND

REG 0x01[7:6] = 00

OPERATION COMMAND

REG 0x01[7:6] = 10

REG 0x01[5:4] = 10

Figure 13. Margining Example 1

VOUT_COMMAND

VOUT_MARGIN_HIGH

VOUT_MARGIN_LOW

DAC ENABLE

MARGIN LOW

MARGIN OFF

MARGIN HIGH

MARGIN VOUT

TRANSITION

SPEED

TRANSITION

SPEED

TRANSITION

SPEED

Figure 14. Margining Example 2

Figure 13 and Figure 14 show examples of margining. When

margining is turned off, the DAC returns the output voltage to

the nominal level at the transition rate (0xDB) and then enters a

high-Z state.

To enable a smooth start of the margining process, the

ADM1266 uses a smart connect mode. Smart connect mode

calculates the DAC code that is equal to the feedback node such

that there is no current flowing in Resistor R3 (see Figure 12).

Smart connect mode prevents any sudden glitches in the output

voltage. Following smart connect mode, the DAC code is

changed as per the margin command.

The closed-loop margining process differs from open-loop

margining with the following differences:

•

The DAC is continuously repositioned until the 16 averages of

the high accuracy ADC monitoring the output rail result in

a value that equals the VOUT_MARGIN_x command.

This repositioning ensures that the output voltage does

indeed reach the command value. The output voltage is

sampled using the ADC at a rate of 5 ms. Therefore,

16 average readings complete in approximately 80 ms.

•

Whenever a margin command is issued, the DAC changes

its output based on the rate programmed in Register 0xDB.

Therefore, the output of the power supply rail also transitions

at this rate. All the DACs are controlled using the same rate.

During the closed-loop margining process, the UV and OV

faults are active and take the appropriate programmed action.

The DAC is disabled (high-Z state) immediately and does not

perform a soft disconnect.

One Shot Mode and Continuous Mode

The ADM1266 offers two modes of operation in closed-loop

margining: one shot and continuous mode.

In one shot mode, the process of closed-loop margining (see the

Closed-Loop Margining section) occurs once, that is, the DAC

changes the output voltage as per the margin command and

remains fixed, and no further changes in the DAC output are

allowed. In continuous mode, this process occurs continuously.

In one shot mode, a new margin command must be issued to

change the DAC output.

Continuous mode can be used for increasing the accuracy of a

power supply that suffers from wide tolerances in component or

reference voltage levels. Use this method when the ADC accuracy

is greater than the accuracy of the external components.

The Power Studio software provides all the extensive configura-

tions, from selecting the DAC range to margining commands.

Closed-Loop Margining Enable Timings

If the rail is in steady state and the ADM1266 receives the

operation command to go from the margin being off to the

servo VOUT_COMMAND (margin high or margin low), the

ADM1266 enables closed-loop margining. The ADM1266 also

performs the smart connection, waiting 5 ms for an updated

ADC reading before starting the ramp to obtain the desired

voltage level.

If the rail is in a steady state and the ADM1266 receives the

operation command to go from the servo VOUT_COMMAND

to margin high (margin low or margin off), the ADM1266

immediately starts the ramp to obtain the desired voltage level.

This process is also true when the starting point is margin high

or margin low.

If the device is programmed to wake up and immediately start

to the servo VOUT_COMMAND (margin high or margin low),

the ADM1266 enables the rail. After the rail clears the UV

threshold, the ADM1266 enables closed-loop margining and

performs smart connect after 20 ms to 25 ms. Then, the

ADM1266 waits 5 ms to obtain an updated ADC reading and

starts the ramp to obtain the desired voltage level.

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