Datasheet

LTC3860
18
3860fc
APPLICATIONS INFORMATION
Multiphase Operation
When the LTC3860 is used in a single output, multiphase
application, the slave error amplifi ers must be disabled by
connecting their FB pins to V
CC
. All current limits should be
set to the same value using only one resistor to SGND per IC.
I
LIM2
should then be connected to V
CC
. These connections
are shown in Table 3. In a multiphase application all COMP,
RUN and TRACK/SS pins must be connected together.
For output loads that demand high current, multiple
LTC3860s can be daisychained to run out of phase to
provide more output current without increasing input and
output voltage ripple. The CLKIN pin allows the LTC3860
to synchronize to the CLKOUT signal of another LTC3860.
The CLKOUT signal can be connected to the CLKIN pin of
the following LTC3860 stage to line up both the frequency
and the phase of the entire system. Tying the PHSMD pin to
V
CC
, SGND or fl oating it generates a phase difference
(between CLKIN and CLKOUT) of 240°, 60° or 90° respec-
tively, and a phase difference (between CH1 and CH2) of
120°, 180° or 180°. Figure 7 shows the PHSMD connections
necessary for 3-, 4-, 6- or 12-phase operation. A total of
12 phases can be daisychained to run simultaneously out
of phase with respect to each other.
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
3860 F06a
R
S
ESLL
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
FILTER COMPONENTS PLACED
NEAR SENSE PINS
C
F
• 2R
F
≤ ESL/R
S
POLE-ZERO
CANCELLATION
V
LOGIC
V
CC
5V
IN
BG
GND
R
F
C
F
R
F
VINSNS
V
CC
PWM
ISNSPISNSN
LTC3860
GND
(6a) Using a Resistor to Sense Current
BOOST
TG
LTC4449
V
IN
12V
TS
V
OUT
3860 F06b
DCRL
R1*
INDUCTOR
V
LOGIC
V
CC
5V
IN
*PLACE R1 NEAR INDUCTOR
PLACE C1 NEAR ISNSP, ISNSN PINS
BG
GND
C1*
VINSNS
V
CC
PWM
ISNSPISNSN
LTC3860
GND
R1 • C1 =
L
DCR
(6b) Using the Inductor to Sense Current
Figure 6. Two Different Methods of Sensing Current
Table 3. Multiphase Confi gurations
CH1 CH2 FB1 FB2 I
LIM1
I
LIM2
Master Slave On Off
(FB = V
CC
)
Resistor
to GND
V
CC
Slave Slave Off
(FB = V
CC
)
Off
(FB = V
CC
)
Resistor
to GND
V
CC
Slave Additional
Output
Off
(FB = V
CC
)
On Resistor
to GND
Resistor
to GND