LTC3889 datasheet(67/118 Pages) AD

67 / 118 page

LTC3888/LTC3888-1/

LTC3888-2

Rev. B

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APPLICATIONS INFORMATION

RESISTOR CONFIGURATION PINS

As a factory default, the LTC3888 is programmed to use

external resistor configuration, allowing output voltage

(LTC3888/3888-2), output current limit (LTC3888-1),

PWM frequency and phasing, and the PMBus address to

be set without programming the part through its serial

interface or purchasing devices with custom EEPROM

contents. An 18.7kΩ resistor with a tolerance of 1% or

better must be wired between the RSET pin and GND.

This component establishes the correct bias level for the

Figure 43. Normalized RMS Input Ripple Current

0.1

0.2

0.3

0.4

388812 F43

0.5

0.6

DUTY FACTOR (VOUT/VIN)

0.1

0.3

0.5 0.6

0.2

0.4

0.7 0.8 0.9

1-PHASE

2-PHASE

DUTY FACTOR (VOUT/VIN)

0.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.3

0.5 0.6

388812 F44

0.2

0.4

0.7 0.8 0.9

1-PHASE

2-PHASE

Figure 44. Normalized Output Ripple Current

remaining RCONFIG pins, which are programmed with a

resistor to GND. The RCONFIG pins are only interrogated

at initial power up and during a reset, so modifying their

values on the fly is not recommended. RCONFIG pins on

the same IC can share a single resistor if they require

identical programming. Resistors with a tolerance of 1%

or better must be used to assure proper operation. Noisy

clock signals should not be routed near these pins.

Output voltage (LTC3888/3888-2), or output current limit

(LTC3888-1) can be set as shown in Table 10. For exam-

ple, setting this resistor to 4.42kΩ is equivalent to pro-

gramming a IOUT_OC_WARN_LIMIT value of 32A with

IOUT_OC_FAULT_LIMIT set to 40A for the (LTC3888-1).

Any of the single-IC master/slave configurations that the

LTC3888 supports can be programmed with PWM_CFG

using one of two frequencies as shown in Table 11. Phase

expansion is not supported when using an external resis-

tor to set master/slave configuration.

The LTC3888 address is selected based on the program-

ming of the two configuration pins ASEL0 and ASEL1

according to Table 12. ASEL0 programs the bottom four

bits of the device address for the LTC3888, and ASEL1

programs the three most-significant bits. Either portion

of the address can also be retrieved from the MFR_

ADDRESS value in EEPROM. If both pins are left open, the

full 7-bit MFR_ADDRESS value stored in EEPROM is used

to determine the device address. It is recommended that

each LTC3888 in a system have a unique address, and

the ASEL pins provide an efficient way to accomplish this

without a plethora of custom EEPPOM programming. The

LTC3888 also responds to 7-bit global addresses 0x5A

and 0x5B. MFR_ADDRESS and MFR_RAIL_ADDRESS

should not be set to either of these values.

LTC3889 Datasheet(PDF) 67 Page - Analog Devices

LTC3889 Datasheet(HTML) 67 Page - Analog Devices

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