LTC3701EGN#TR Linear Technology, LTC3701EGN#TR Datasheet - Page 12

• Manufacturer Part Number: LTC3701EGN#TR
• Description: IC DC/DC CNTRLR STPDN DUAL16SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3701EGN#TR

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 10 V
• Current - Output: 1A
• Frequency - Switching: 550kHz
• Voltage - Input: 2.5 ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -
• Other names: LTC3701EGNTR

APPLICATIO S I FOR ATIO
LTC3701
C
The selection of C
ture and its impact on the worst-case RMS current drawn
through the input network (battery/fuse/capacitor). It can
be shown that the worst-case capacitor RMS current
occurs when only one controller is operating. The control-
ler with the highest (V
in the formula below to determine the maximum RMS
capacitor current requirement. Increasing the output cur-
rent drawn from the other controller will actually decrease
the input RMS ripple current from its maximum value. The
out-of-phase technique typically reduces the input
capacitor’s RMS ripple current by a factor of 30% to 70%
when compared to a single phase power supply solution.
In continuous mode, the source current of the P-channel
MOSFET is a square wave of duty cycle (V
(V
capacitor sized for the maximum RMS current of one
channel must be used. The maximum RMS capacitor
current is given by:
This formula has a maximum at V
I
monly used for design because even significant deviations
do not offer much relief. Note that capacitor manufactur-
ers’ ripple current ratings are often based on only 2000
hours of life. This makes it advisable to further derate the
capacitor, or to choose a capacitor rated at a higher
temperature than required. Several capacitors may be
paralleled to meet size or height requirements in the
design. Due to the high operating frequency of the LTC3701,
ceramic capacitors can also be used for C
consult the manufacturer if there is any question.
The benefit of the LTC3701 2-phase operation can be cal-
culated by using the equation above for the higher power
controller and then calculating the loss that would have
resulted if both controller channels switched on at the
same time. The total RMS power lost is lower when both
controllers are operating due to the reduced overlap of
12
RMS
IN
IN
C
V
and C
IN
+ V
IN
I
= I
MAX
Required I
D
OUT
). To prevent large voltage transients, a low ESR
V
OUT
D
/2. This simple worst-case condition is com-
Selection
V
OUT
IN
RMS
U
is simplified by the 2-phase architec-
OUT
V
D
)(I
U
V
OUT
IN
–
) product needs to be used
V
OUT
IN
W
= 2V
/ 1 2
OUT
+ V
OUT
IN
U
. Always
D
, where
+ V
D
)/
current pulses required through the input capacitor’s ESR.
This is why the input capacitor’s requirement calculated
above for the worst-case controller is adequate for the
dual controller design. Also, the input protection fuse re-
sistance, battery resistance, and PC board trace resistance
losses are also reduced due to the reduced peak currents
in a 2-phase system. The overall benefit of a multiphase
design will only be fully realized when the source imped-
ance of the power supply/battery is included in the effi-
ciency testing. The sources of the P-channel MOSFETs
should be placed within 1cm of each other and share a
common C
duce undesirable voltage and current resonances at V
A small (0.1 F to 1 F) bypass capacitor between the chip
V
suggested. A 10 resistor placed between C
the V
channels.
The selection of C
resistance (ESR). Typically, once the ESR requirement is
satisfied, the capacitance is adequate for filtering. The
output ripple ( V
where f is the operating frequency, C
capacitance and I
tor. The output ripple is highest at maximum input voltage
since I
Low Supply Operation
Although the LTC3701 can function down to approximately
2V, the maximum allowable output current is reduced when
V
change as the supply is reduced down to 2V. Also shown
is the effect of V
Setting Output Voltage
The LTC3701 output voltages are each set by an external
feedback resistive divider carefully placed across the
output capacitor (see Figure 6). The resultant feedback
signal is compared with an internal 0.8V reference by the
IN
IN
pin and ground, placed close to the LTC3701, is also
decreases below 3V. Figure 5 shows the amount of
V
IN
OUT
RIPPLE
pin provides further isolation between the two
IN
(s). Separating the sources and C
I
RIPPLE
increases with input voltage.
IN
OUT
RIPPLE
on V
OUT
) is approximated by:
ESR
REF
is driven by the effective series
is the ripple current in the induc-
as V
8
fC
IN
1
OUT
goes below 2.3V.
OUT
is the output
IN
IN
may pro-
(C1) and
3701fa
IN
.