LTC3855 LINER [Linear Technology], LTC3855 Datasheet - Page 17

• Manufacturer Part Number: LTC3855
• Description: Dual, Fast, Accurate Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

OPERATION
The system can be configured for up to 12-phase opera-
tion with a multichip solution. Typical configurations are
shown in Table 2 to interleave the phases of the channels.
Table 1
Table 2
Single-Output PolyPhase Configurations
To use LTC3838 for a 2-phase single output step-down
controller: Tie the V
Channel 2’s error amplifier and internally connect ITH2 to
ITH1. Tie the compensation R-C components to the ITH1
pin. The ITH2 pin can be either left open or shorted to ITH1
externally. The TRACK/SS2 and PGOOD2 pins become
defunct and can be left open. Note that the RUN1, RUN2,
DTR1, DTR2, VRNG1 and VRNG2 pins still function for
the two channels individually, therefore should be shorted
NUMBER OF
Channel 1
Channel 2
PHASMD
CLKOUT
PHASES
12
2
3
4
6
NUMBER OF
LTC3838
LTC3833
2, or 1 +
SGND
180°
60°
FB2
0°
1
2
3
6
(Refer to Functional Diagram)
pin to INTV
PIN CONNECTIONS
[PIN NAME (CHIP NUMBER)]
PHASMD(1) = FLOAT or SGND
PHASMD(1) = INTV
MODE/PLLIN(2) = CLKOUT(1)
PHASMD(1) = FLOAT
PHASMD(2) = FLOAT or SGND
MODE/PLLIN(2) = CLKOUT(1)
PHASMD(1) = SGND
PHASMD(2) = SGND
MODE/PLLIN(2) = CLKOUT(1)
PHASMD(3) = FLOAT or SGND
MODE/PLLIN(3) = CLKOUT(2)
PHASMD(1) = SGND
PHASMD(2) = SGND
MODE/PLLIN(2) = CLKOUT(1)
PHASMD(3) = FLOAT
MODE/PLLIN(3) = CLKOUT(2)
PHASMD(4) = SGND
MODE/PLLIN(4) = CLKOUT(3)
PHASMD(5) = SGND
MODE/PLLIN(5) = CLKOUT(4)
PHASMD(6) = FLOAT or SGND
MODE/PLLIN(6) = CLKOUT(5)
FLOAT
180°
90°
0°
CC
, which will disable
CC
INTV
240°
120°
0°
CC
externally for single-output applications. Set PHASMD
to SGND or FLOAT so that the two channels are 180°
out-of-phase. Efficiency losses may be substantially
reduced because the peak current drawn from the input
capacitor is effectively divided by the number of phases
used and power loss is proportional to the RMS current
squared. A 2-phase implementation can reduce the input
path power loss by up to 75%.
To make a single-output converter of three or more phases,
additional LTC3838 or LTC3833 chips can be used. The first
chip should be tied the same way as the 2-phase above. If
only one more channel of an additional LTC3838 is needed,
use Channel 1 for the additional phase:
• Tie the ITH1 pin to the ITH1 pin of the first chip
• Tie the RUN1 pin to the RUN pins of the first chip
• Tie the V
• Tie the V
• Tie the TRACK/SS1 pin to the TRACK/SS1 pin of the
If both channels are needed, the additional LTC3838 chip
should be tied the same way as the first LTC3838 chip to
disable the second channel’s EA:
• Tie the V
• Tie the ITH1 pin to the ITH1 pin of the first chip
• Tie the RUN pins to the RUN pins of the first chip
• Tie the V
• Tie the V
• Tie the TRACK/SS1 pin to the TRACK/SS1 pin of the
first chip
first chip
first chip
first chip
first chip
first chip
FB2
OUTSENSE1
OUTSENSE1
OUTSENSE1
OUTSENSE1
pin to the chip’s own INTV
+
–
+
–
pin to the V
pin to the V
pin to the V
pin to the V
OUTSENSE1
OUTSENSE1
OUTSENSE1
OUTSENSE1
LTC3838
CC
+
–
+
–
pin of the
pin of the
pin of the
pin of the
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