Datasheet

LTC3634
20
3634fb
For more information www.linear.com/LTC3634
applicaTions inForMaTion
2-Phase, Single V
TT
Output Configuration
The two regulators on the LTC3634 can be easily com-
bined to provide a single 2-phase V
TT
termination supply
capable of sourcing and sinking up to 6A. The circuit is
shown in Figure 7.
In this circuit, V
FB1
is tied to INTV
CC
to put the LTC3634
into 2-phase operation. When set up for 2-phase operation,
the inputs to channel 1’s transconductance error amplifier
are switched to be the same as channel 2’s inputs (V
FB2
and VTTR), allowing it to be paralleled with channel 2’s
error amplifier. The ITH1 and ITH2 pins should be tied
together externally to force equal current sharing between
both channels.
Only one compensation network is needed on the ITH
node, although separate filter caps for each ITH pin may
be helpful depending on the board layout. In this parallel
configuration, it is important to note that the effective
g
m(EA)
and g
m(MOD)
are twice as large as that of a single
channel.
One advantage to this 2-phase configuration is that both
input and output current ripple is significantly reduced
compared to a single phase 6A converter solution, because
the current waveforms from each regulator are interleaved.
Refer to Application Note 77 for a full discussion and
analysis on PolyPhase
®
converters.
V
IN1
and V
IN2
may be powered from separate supply volt-
ages (see Figure 12). This is useful in cases where power
needs to be shared between two different sources. It is
important to note that when the V
TT
output sinks current,
it will backfeed through the converter and out of the V
IN
pins. Care must be taken to ensure that the input supplies
are able to handle this condition.
Efficiency Considerations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Percent efficiency can
be expressed as:
% Efficiency = 100% – (L1 + L2 + L3 +…)
where L1, L2, etc. are the individual losses as a percentage
of input power. Although all dissipative elements in the
circuit produce losses, three main sources usually account
for most of the losses in LTC3634 circuits: 1) conduction
losses, 2) switching losses and quiescent power loss 3)
transition losses and other losses.
Figure 7. Application Circuit for a 2-Phase, ±6A Single V
TT
Output
RUN1
RUN2
RT
INTV
CC
PHMODE
V
FB1
VDDQIN
ITH1
ITH2
LTC3634
3634 F07
L1
0.47µH
0.1µF
0.1µF
PGNDSGND
BOOST1
SW1
BOOST2
SW2
V
FB2
V
ON2
V
ON1
VTTR
MODE/SYNC
V
IN1
V
IN
3.6V TO 15V
V
IN2
L2
0.47µH
R1
160k
C
OUT2
100µF
×4
V
TT
V
DDQ
/2 AT ±6A
V
REF
V
DDQ
/2 AT ±10mA
10pF
6k
V
DDQ
SUPPLY
1000pF
C2
2.2µF
C1
47µF
×2
10pF
0.01µF