LTC4449 datasheet(66/108 Pages) LINER

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LTC3882-1

Rev A

For more information www.analog.com

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-I2C/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

severaltutorials.Completeinformationisavailableathttp://

www.linear.com/ltpowerplay.

Interfacing to the DC1613

The LTC DC1613 USB-to-I2C/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

LTC3882-1EEPROMand/orLTpowerPlayconfigurationfile.

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 VCC system supply

(5V to 12V). If VCC is applied, the DC1613 will not supply

the LTC3882-1s on the board. If the DC2086 is used, PFETs

with lower RDS(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 VDD33 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 I2C

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

I2C 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 I2C bus with the LTC3882-1

should not have body diodes between their SDA/SCL pins

andtheirrespectivelogicsupply,becausethiswillinterfere

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 VIN = 36V,

VOUT = 3.3V, and IOUT = 40A. A fully discrete power stage

designisemployedtoallowbetteroptimizationgiventhese

demanding requirements. Assume that a secondary 5V

supply will be available in the system for the LTC3882-1

VCC supply. The necessary local bypassing is then pro-

vided for the VDD33 (2.2µF) and VDD25 (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 VDD33

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 VDD33 in

this case.

First, the regulated output is established by programming

the VOUT_COMMAND stored in EEPROM to 3.3V.

LTC4449 Datasheet(PDF) 66 Page - Linear Technology

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