LTC3882-1
66
Rev A
For more information
APPLICATIONS INFORMATION
LTpowerPlay can also be used offline (no hardware pres-
ent) to build multiple IC configuration files that can be
saved and later reloaded. LTpowerPlay uses the DC1613
USB-to-I
2
C/SMBus/PMBus controller to communicate
with a system for evaluation, development or debug. The
software also features automatic update to remain up-
to-date with the latest device drivers and documentation
available from Linear Technology. A great deal of context
sensitive help is available within LTpowerPlay, along with
several tutorials. Complete information is available at
Interfacing to the DC1613
The LTC DC1613 USB-to-I
2
C/SMBus/PMBus controller
can be interfaced to the LTC3882-1 on any board for
programming, telemetry and system debug. This includes
the DC1936 from Linear Technology, or any customer
target system. The controller, when used in conjunction
with LTpowerPlay, provides a powerful way to debug an
entire power system. Faults are quickly diagnosed using
telemetry, fault status registers and the fault log. The final
configuration can be quickly developed and stored to the
LTC3882-1 EEPROM and/or LTpowerPlay configuration file.
The DC1613 can communicate with, program and even
power one or more LTC3882-1s, regardless of whether
system supplies are up. The DC2086 Powered Program-
ming Adapter can be used to extend the power sourcing
capability of the DC1613. Figure 47 illustrates an applica-
tion schematic for in-system programming of multiple
LTC3882-1s normally powered from a V
CC
system supply
(5V to 12V). If V
CC
is applied, the DC1613 will not supply
the LTC3882-1s on the board. If the DC2086 is used, PFETs
with lower R
DS(ON)
, such as the SiA907EDJT, should be
used in place of the TP0101K devices. Figure 48 shows an
example when the system normally provides 3.3V directly
to the LTC3882-1(s).
If system supplies are not up in either of these circuits, the
DC1613 will power the LTC3882-1 V
DD33
supply, allowing
in-circuit configuration or manufacturing customization.
These circuits also facilitate remote diagnostics, control
and reprogramming of the LTC3882-1 while the host
system is fully operational, permitting very flexible in-
system debugging.
If the system supply is restored while power is still applied
by the DC1613 or DC2086, the LTC3882-1 can often be
ready to initiate output soft-start before sufficient supply
bias for the power stage has been established. Create
additional LTC3882-1 delay with TON_DELAY or use a
common system RUN line to control both the LTC3882-1
and its related power stages based on acceptable operat-
ing parameters, as shown in Figure 55. The DC1613 I
2
C
connections are opto-isolated from the host PC USB. The
DC1613 3.3V current limit is only 100mA, so it should
only be used to power one or two LTC3882-1s in-system.
Because of this limited current sourcing capability, only
the LTC3882-1s, their associated pull-up resistors and the
I
2
C pull-up resistors should be powered from the isolated
3.3V supply provided by the DC1613. Using the DC2086
will enable in-system programming of several tens of
LTC3882-1 devices without normal system power applied.
Any other device sharing the I
2
C bus with the LTC3882-1
should not have body diodes between their SDA/SCL pins
and their respective logic supply, because this will interfere
with bus communication in the absence of system power.
Hold the RUN pins low externally to avoid providing power
to the load until the part is fully configured.
Design Example
As a design example, consider a 132W 2-phase applica-
tion such as the one shown in Figure 53, where V
IN
= 36V,
V
OUT
= 3.3V, and I
OUT
= 40A. A fully discrete power stage
design is employed to allow better optimization given these
demanding requirements. Assume that a secondary 5V
supply will be available in the system for the LTC3882-1
V
CC
supply. The necessary local bypassing is then pro-
vided for the V
DD33
(2.2µF) and V
DD25
(1µF) LDO outputs.
These LDO outputs should not be shared with other ICs
that might have outputs of the same name, because they
have independent, internal control loops. When V
DD33
is used as the LTC3882-1 supply input, it may be shared
with other ICs operating from that 3.3V supply. Local HF
bypassing of at least 0.1µF is still required on V
DD33
in
this case.
First, the regulated output is established by programming
the VOUT_COMMAND stored in EEPROM to 3.3V.
