LTM4677 datasheet(60/110 Pages) AD

60 / 110 page

LTC3888-1

Rev. 0

For more information www.analog.com

RESISTOR CONFIGURATION PINS

As a factory default, the LTC3888-1 is programmed to

use external resistor configuration, allowing output cur-

rent limit, 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 remaining RCONFIG pins, which are programmed

with a resistor to GND. The RCONFIG pins are only inter-

rogated at initial power up and during a reset, so modify-

ing 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 current limit can be set as shown in Table 10. For

example, setting this resistor to 4.42kΩ is equivalent to

programming a IOUT_OC_WARN_LIMIT value of 32A

with IOUT_OC_FAULT_LIMIT set to 40A.

Table 10. Resistor Programming of OC Warning and Fault Limits

RCONFIG (kΩ) IOUT_OC_WARN_LIMIT (A) IOUT_OC_FAULT_LIMIT (A)

OPEN

from EEPROM

11.8

10.2

9.31

8.66

7.87

7.15

6.49

5.9

5.11

4.42

3.74

3.09

2.43

1.74

1.02

GND

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

LTC3888-1 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.

APPLICATIONS INFORMATION

The LTC3888-1 address is selected based on the pro-

gramming of the two configuration pins ASEL0 and

ASEL1 according to Table 12. ASEL0 programs the bot-

tom four bits of the device address for the LTC3888-1,

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 LTC3888-1 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 LTC3888-1 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.

Table 11. PWM_CFG Resistor Programming

RCONFIG (kΩ)

MFR_PWM_CONFIG_LTC3888-1[3:0]

SWITCHING

FREQUENCY

(kHz)

BINARY

MASTER/SLAVE

OPEN

from EEPROM

11.8

0111

7 + 1

550

10.2

0110

6 + 2

9.31

0101

6 + 1

8.66

0100

5 + 3

7.87

0011

4 + 4 (or 8-phase)

7.15

0010

4 + 3