LTC3884 datasheet(17/26 Pages) AD

17 / 26 page

LTC7883

Rev. 0

For more information www.analog.com

Additional Identification Commands

The LTC7883 features a few new PMBus product identi-

fication commands as detailed in Table 2.

Switching Frequency and Phase

There is a high degree of flexibility for setting the PWM

operating frequency of the LTC7883. The switching fre-

quency of the PWM can be established with an internal

oscillator or an external time base. The internal phase-

locked loop (PLL) synchronizes PWM control to this

timing reference with proper phase relation, whether

the clock is provided internally or externally. The device

can also be configured to provide the master clock to

other ICs through PMBus command, EEPROM setting,

or external configuration resistors as outlined in appli-

cation Table 6. For PMBus or EEPROM configuration, an

LTC7883 unit is designated as a clock master by clearing

bit 4 of MFR_CONFIG_ALL_LTC3882-1. As clock master,

an LTC7883 unit will drive its open-drain SYNC pin at the

selected rate with a pulse width of 125ns. An external

pull-up resistor between SYNC and VDD33 is required in

this case. Only one unit connected to SYNC should be

designated to drive the pin. If more than one LTC7883 unit

sharing SYNC is programmed as clock master, just one

of the units is automatically elected to provide the clock.

The others disable their SYNC outputs and indicate this

with bit 10 of MFR_PADS_LTC3882-1.

OPERATION

Unlike the LTC3882-1, which only allows a fixed set of

predetermined frequencies, the LTC7883 FREQUENCY_

SWITCH command supports a continuous range of values

from 250kHz to 2.5MHz. The special case of 0x0000 for

External SYNC Only is not permitted by the LTC7883.

Sending this FREQUENCY_SWITCH command value will

result in a CML fault for invalid data.

The LTC7883 will automatically accept an external SYNC

input, disabling is own SYNC drive if necessary, as long as

the external clock frequency is greater than 1/2 of the pro-

grammed internal oscillator. Whether configured to drive

SYNC or not, an LTC7883 unit can continue PWM oper-

ation at the selected frequency (FREQUENCY_SWITCH)

using its own internal oscillator if an expected external

clock signal is not present.

The MFR_PWM_CONFIG_LTC3882-1 command can be

used to configure the phase of each channel. Desired

phase can also be set from EEPROM or external configu-

ration resistors as outlined in Table 6. Phase designates

the relationship between the falling edge of SYNC and the

internal clock edge that resets the PWM latch. That reset

turns off the top power switch, producing a PWM falling

edge. Additional small propagation delays to the PWM

control pins will apply.

Table 2. New Identification Commands

COMMAND NAME

CMD CODE

DESCRIPTION

TYPE

PAGED

DATA FORMAT

DEFAULT VALUE

UNIT A

UNIT B

ID_DEVICE_ID

0xAD

LTC7883 Model Number

R String

ASC

LTC7883A

LTC7883B

ID_DEVICE_REV

0xAE

LTC7883 Device Revision

Code

R String

ASC

C0001

LTC3884 Datasheet(PDF) 17 Page - Analog Devices

LTC3884 Datasheet(HTML) 17 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL