Datasheet

LTC3880/LTC3880-1
51
3880fc
For more information www.linear.com/LTC3880
APPLICATIONS INFORMATION
Clock. All phasing is with respect to the falling edge of
SYNC.
LTC3880 Chip 1 set the frequency to 425kHz with 90° and
270° phase shift:
R
TOP
= 20kΩ and R
BOTTOM
= 15kΩ
LTC3880 Chip 2 set the frequency to External Clock with
0° and 180° phase shift:
R
TOP
= open and R
BOTTOM
= 0Ω
Frequencies of 350kHz, 750kHz and 1000kHz can only be
set using NVM programming. If a 6-phase configuration
is desired, NVM programming will give optimal phasing.
All other configurations in frequency and phasing can be
achieved using the FREQ_CFG pin.
Address Selection Using RCONFIG
The LTC3880 address is selected using a combination of
the address stored in NVM and the ASEL pin. The MSB
of ASEL is the MSB in the NVM and the LSB is the ASEL
value. This allows 16 different LTC3880s on a single board
with one programmed address in NVM.
If the address stored in NVM is 0x4F, then the part address
can be set from 0x40 to 0x4F using ASEL. (The standard
default address is 0x4F). Do not set any part address to
0x5A or 0x5B because these are global addresses and all
parts will respond to them.
To choose address 0x40 R
TOP
is open and
R
BOTTOM
= 0Ω
To choose address 0x45 R
TOP
= 24.9k and
R
BOTTOM
= 7.32k
Table 14. FREQ_CFG (Phase Based on Falling Edge of SYNC)
R
TOP
(k) R
BOTTOM
(k) FREQUENCY (kHz)
θ
SYNC
TO θ
0
θ
SYNC
TO θ
1
DESCRIPTION
0 or Open Open NVM NVM NVM NVM
10 23.2 250 0 180 2-Phase
10 15.8 250 120 240 3-Phase
16.2 20.5 250 90 270 4-Phase
16.2 17.4 425 0 180 2-Phase
20 17.8 425 120 240 3-Phase
20 15 425 90 270 4-Phase
20 12.7 500 0 180 2-Phase
20 11 500 120 240 3-Phase
24.9 11.3 500 90 270 4-Phase
24.9 9.09 575 0 180 2-Phase
24.9 7.32 575 120 240 3-Phase
24.9 5.76 575 90 270 4-Phase
24.9 4.32 650 0 180 2-Phase
30.1 3.57 650 120 240 3-Phase
30.1 1.96 650 90 270 4-Phase
Open 0 External Clock 0 180 2-Phase