Datasheet

LTC3880/LTC3880-1
60
3880fc
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
system power is not present the dongle will power the
LTC3880 through the V
DD33
supply pin. To initialize the
part when V
IN
is not applied and the V
DD33
pin is pow-
ered use global address 5B command 0xBD data 0x2B
followed by address 5B command 0xBD data 0xC4. The
part can now be communicated with, and the project file
updated. T
o write the updated project file to the NVM issue
a STORE_USER_ALL command. When VIN is applied,
a MFR_RESET must be issued to allow the PWM to be
enabled and valid ADCs to be read.
Because of the controllers limited current sourcing capabil-
ity, only the LTC3880s, their associated pull-up resistors
and the I
2
C pull-up resistors should be powered from the
ORed 3.3V supply. In addition any device sharing the I
2
C
bus connections with the LTC3880 should not have body
diodes between the SDA/SCL pins and their respective
V
DD
node because this will interfere with bus communica-
tion in the absence of system power. If VIN is applied the
dongle will
not supply the LTC3880s on the board. It is
recommended the RUN pins be held low to avoid providing
power to the load until the part is fully configured.
The LTC controller I
2
C connections are optoisolated from
the PC USB. The 3.3V from the controller and the LTC3880
V
DD33
pin must be driven to each LTC3880 with a separate
PFET. If V
IN
is not applied, the V
DD33
pins can be in parallel
because the on-chip LDO is off. The controller 3.3V cur-
rent limit is 100mA but typical V
DD33
currents are under
15mA. The V
DD33
does back drive the INTV
CC
/EXTV
CC
pin.
Normally this is not an issue if V
IN
is open.
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Figure 29