LTC3860_15 Datasheet, PDF (18/36 Pages) Linear Technology – Dual, Multiphase Step-Down Voltage Mode DC/DC Controller with Current Sharing

LTC3860
APPLICATIONS INFORMATION
VINSNS
5V
V_CC
LTC3860
PWM
GND ISNSN ISNSP
C_F
R_F
V_LOGIC BOOST
V_CC
TG
LTC4449
IN
TS
BG
GND
V_IN
12V
SENSE RESISTOR
PLUS PARASITIC
INDUCTANCE
L
R_S ESL
C_F • 2R_F ≤ ESL/R_S
POLE-ZERO
CANCELLATION
V_OUT
R_F
FILTER COMPONENTS PLACED
NEAR SENSE PINS
3860 F06a
(6a) Using a Resistor to Sense Current
VINSNS
5V
LTC3860
V_CC
PWM
GND ISNSN ISNSP
C1*
V_LOGIC BOOST
V_CC
TG
LTC4449
IN
TS
BG
GND
V_IN
12V
INDUCTOR
L DCR
R1*
V_OUT
R1 • C1 = ^L *PLACE R1 NEAR INDUCTOR
DCR _{PLACE C1 NEAR ISNSP, ISNSN PINS}
3860 F06b
(6b) Using the Inductor to Sense Current
Figure 6. Two Different Methods of Sensing Current
Multiphase Operation
When the LTC3860 is used in a single output, multiphase
application, the slave error amplifiers 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
18
and the phase of the entire system. Tying the PHSMD pin to
V_CC, SGND or floating 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.
Table 3. Multiphase Configurations
CH1
CH2
FB1
FB2
Master
Slave
Slave
Slave
On
Off
(FB = V_CC)
Slave
Off
Off
(FB = V_CC) (FB = V_CC)
Additional Off
On
Output (FB = V_CC)
I_LIM1
Resistor
to GND
Resistor
to GND
Resistor
to GND
I_LIM2
V_CC
V_CC
Resistor
to GND
3860fc