XR77128 datasheet(21/28 Pages) EXAR

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XR77128

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Rev 1A

When the OVP level is reached and the fault is generated,

the host will be notified by the SUPPLY_FAULT_EVENT

interrupt generated by the controller. The host then can use

an I2C command to check which channel is at fault.

In addition, OVP fault can be monitored through any I/O.

A user can choose one of three options in response to an

OVP event: to shutdown the faulting channel, to shut down

faulting channel and to perform auto-restart of the channel,

or to restart the chip.

Choosing the “Restart Chip” option during development is

not recommended as it makes debug efforts difficult.

For the case of Shutdown and Auto-restart Channel, the

user has an option to specify startup timeout (the time in

which the fault is validated) and hiccup timeout (the period

after which the controller will try to restart the channel) peri-

ods in 1 ms increments with a maximum value of 255 ms.

Note: The Channel Fault Action response is the same for

an OVP or OCP event.

OCP

A user defined OCP fault level is set with 10mA increments

in PA 5.2. PA 5.2 uses calculations to give the user the

approximate DC output current entered in the current limit

field. However, the actual current limit trip value pro-

grammed into the part is limited to 280mV as defined in the

electrical characteristics. The maximum value the user can

program is limited by RDSON of the synchronous Power

FET and current monitoring ADC range. For example, using

a synchronous FET with RDSON of 30mΩ and the wider

ADC range, the maximum current limit programmed would

be:

XR77128 samples current approximately 30ns before the

synchronous FET turns off, so the actual measured DC out-

put current in this example would be 9.33A plus approxi-

mately half the inductor ripple.

The output current reported by the XR77128 is processed

through a seven sample median filter in order to reduce

noise.

When the OCP level is reached and the fault is generated,

the host will be notified by the SUPPLY_FAULT_EVENT

interrupt generated by the controller. The host then can use

an I2C command to check which channel is at fault.

In addition, OCP fault can be monitored through HW Flags

on GPIO0. The host can also monitor OCP warning flag

through HW Flags on GPIO0. The OCP warning level is

calculated by PA 5.2 as 85% of the OCP fault level.

A user can choose one of three options in response to an

OCP event: shut down the faulting channel, shut down the

faulting channel and perform auto-restart of the channel, or

restart the chip.

Choosing the “Restart Chip” option during development is

not recommended as it makes debug efforts difficult.

For the case of Shutdown and Auto-restart Channel, the

user has an option to specify startup timeout (the time in

which the fault is validated) and hiccup timeout (the period

after which the controller will try to restart the channel) peri-

ods in 1 ms increments with a maximum value of 255 ms.

Note: The Channel Fault Action response is the same for

an OCP or OVP event.

Start-up Time-out Fault

A channel will be at Startup Timeout Fault if it does not

come up in the time period specified in the “Startup Time-

out” box.

When the fault is generated, the host will be notified by the

SUPPLY_FAULT_EVENT interrupt generated by the con-

OCP Max (A)

280mV

30m



-----------------

9.33A

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