TPS40400 datasheet(39/72 Pages) TI

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OUT(PGOOD _ OFF)

POWER _ GOOD _ OFF 2-

TPS40400

www.ti.com

SLUS930B

– APRIL 2011 – REVISED OCTOBER 2011

Supported POWER_GOOD_OFF Levels

Low Threshold

High Threshold

92%

108%

90%(1)

110%

88%

112%

(1)

Default value

For example, with a 1.2 V nominal output voltage, the POWER_GOOD_OFF command can set the lower

threshold to 1.104 V, 1.0 8V or 1.056 V. Doing this automatically sets the upper thresholds to 1.296 V, 1.32 V

and 1.344 V respectively.

The effective value of this command is determined by the settings of the VOUT_MODE command. In this device,

the VOUT_MODE is fixed to Linear with an exponent of

–10 (decimal) so the effective lower power good turn on

threshold requested are:

(24)

The nominal output voltage is set by external resistors and a 600 mV error amplifier reference. It is critical that

the correct value be programmed into VOUT_SCALE_LOOP for the correct POWER_GOOD_ON threshold to be

selected.

Normally, the POWER_GOOD_ON threshold is set higher than the POWER_GOOD_OFF threshold. If the

POWER_GOOD_ON threshold is set to a value equal to or less than the POWER_GOOD_OFF threshold, the

device:

•

Sets the CML bit in the STATUS_BYTE

•

Sets the Invalid data bit in STATUS_CML

•

Notifies the host via SMBALRT pin

It is the user's responsibility to make sure that chsen POWER_GOOD_ON and POWER_GOOD_OFF thresholds

are reasonable with respect to each other. For values written outside the supported ranges are ACK'ed but

cause the SMBALRT line to assert and the CML bit to be set in the STATUS_WORD. The invalid data bit is also

set in the STATUS_CML results. The actual POWER_GOOD_OFF threshold is set to the nearest supported

extreme value. For instance, with VOUT_SCALE_LOOP set to 0.5 for a typical 1.2-V output supply, setting

POWER_GOOD_OFF to 0.5 results in the threshold being set to the 88% value.

The POWER_GOOD_OFF command has two data bytes formatted as two's complement binary integer:

Command

POWER_GOOD_OFF

Format

Linear, two's complement binary

Bit Position

Access

r/w

Function

High Byte

Low Byte

Default Value

The default value sets the power good turn off threshold to 1.08 V which maps to the 90% low threshold and

108% high threshold.

TON_RISE (61h)

The TON_RISE command sets the time in ms, from when the output starts to rise until the voltage has entered

the regulation band. There are several discreet settings that this command supports. Commanding a value other

than one of these values results in the nearest supported value being selected.

The supported TON_RISE times over PMBus are as follows. Note that the actual soft-start time is longer than

the entered value. Typically the nominal value seen in operation is approximately 15% longer that the time

entered.

•

600

µs

•

900

µs

•

1.2 ms

•

1.8 ms

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