XR77128 Datasheet, PDF (24/28 Pages) Exar Corporation – Quad Output Digital PWM/PFM

XR77128
There are three groups:
• Group 0 – is controlled by the chip ENABLE or an I²C
command. Channels assigned to this group will come
up with the ENABLE signal being high (plus additional
delay needed to load a configuration from Flash mem-
ory to run-time registers), and will go down with the
ENABLE signal being low. The control can always be
overridden with an I²C command.
• Group 1 – can be controlled by any GPIO/PSIO or an
I²C command. Channels assigned to this group will
start-up or shut-down following transitions of a signal
applied to the GPIO/PSIO set to control the group. The
control can always be overridden with an I²C command.
• Group 2 – can be controlled by any GPIO/PSIO or an
I²C command. Channels assigned to this group will
start-up or shut-down following transitions of a signal
applied to the GPIO/PSIO set to control the group. The
control can always be overridden with an I²C command.
Start-up
For each channel within a group a user can specify the fol-
lowing start-up characteristics:
• Ramp Rate – expressed in Volts per milliseconds. It
does not apply to LDOOUT.
• Order – position of a channel to come-up within the
group
• Wait PGOOD? – selecting this option for a channel
means the next channel in the order will not start ramp-
ing-up until this channel reaches the target level and its
Power Good flag is asserted.
• Delay – an additional time delay a user can specify to
postpone a channel start-up with respect to the previous
channel in the order. The delay is expressed in millisec-
onds with a range of 0ms to 255ms.
• Ramp Rate – expressed in Volts per milliseconds. It
does not apply to LDOOUT.
• Order – position of a channel to come-down within the
group
• Wait Stop Thresh? – selecting this option for a channel
means the next channel in the order will not start ramp-
ing down until this channel reaches the Stop Threshold
level.
• Delay – additional time delay a user can specify to post-
pone a channel shut-down with respect to the previous
channel in the order. The delay is expressed in millisec-
onds with a range of 0ms to 255ms.
Monitoring VCC and Temperature
Through I²C commands, the host can read back voltage
applied to the VCC pin and the die temperature respec-
tively. The VCC read back resolution is 200mV per LSB; the
die temperature read back resolution is 5C° per LSB. For
more on I²C commands refer to ANP-38.
Regulating Higher than 5.5V
To set the output voltage higher than 5.5V, the user needs
to add an external voltage divider. The resistors used in the
voltage divider should be below 20kΩ. In practice, the PA
5.2 design tool handles all the details and the user only has
to enter the desired output voltage. The PA 5.2 tool will rec-
ommend resistor divider values which can be modified by
the user.
Shut-down
For each channel within a group a user can specify the fol-
lowing shut-down characteristics:
External Driver Mode
XR77128 may be configured to drive external DrMOS or
similar devices using the GL pin. Although not supported by
PA 5.2 as of this publication date, future releases will sup-
port this feature. Exar’s technical support team can provide
assistance to enable the feature.
When the controller is in external driver mode, the PWM
signal is internally routed to the GL pin and can be used to
directly drive the PWM input of DrMOS devices according
© 2014 Exar Corporation
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exar.com/XR77128
Rev 1A