LTC3865EFE#TRPBF Linear Technology, LTC3865EFE#TRPBF Datasheet - Page 23

• Manufacturer Part Number: LTC3865EFE#TRPBF
• Description: IC BUCK SYNC ADJ DUAL 38TSSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3865EFE#TRPBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 5 V
• Frequency - Switching: 250kHz ~ 770kHz
• Voltage - Input: 4.5 ~ 38 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 38-TSSOP Exposed Pad, 38-eTSSOP, 38-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -

APPLICATIONS INFORMATION
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 signifi cant deviations
do not offer much relief. Note that capacitor manufacturers’
ripple current ratings are often based on only 2000 hours
of life. This makes it advisable to further derate the capaci-
tor, 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 LTC3865, ceramic capacitors
can also be used for C
if there is any question.
The benefi t of the LTC3865/LTC3865-1 2-phase operation
can be calculated 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
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 resistance,
battery resistance, and PC board trace resistance losses
are also reduced due to the reduced peak currents in a
2-phase system. The overall benefi t of a multiphase design
will only be fully realized when the source impedance of the
power supply/battery is included in the effi ciency testing.
The sources of the top MOSFETs should be placed within
1cm of each other and share a common C
the sources and C
current resonances at V
A small (0.1μF to 1μF) bypass capacitor between the chip V
pin and ground, placed close to the LTC3865/LTC3865-1,
is also suggested. A 2.2Ω to 10Ω resistor placed between
C
the two channels.
RMS
IN
C
(C1) and the V
IN
= I
Re
OUT
quired I
/2. This simple worst-case condition is com-
IN
IN
RMS
pin provides further isolation between
may produce undesirable voltage and
IN
≈
. Always consult the manufacturer
IN
I
MAX
V
.
IN
⎡ ⎣
(
V
OUT
IN
)(
V
= 2V
IN
IN
(s). Separating
–
V
OUT
OUT
, where
)
⎤ ⎦ ⎦
1 2 /
IN
The selection of C
resistance (ESR). Typically, once the ESR requirement
is satisfi ed, the capacitance is adequate for fi ltering. The
output ripple (ΔV
where f is the operating frequency, C
capacitance and I
tor. The output ripple is highest at maximum input voltage
since I
Setting Output Voltage
The LTC3865/LTC3865-1 output voltages are each set
by the voltages at VID pins. Each of the VID pins can be
fl oated, or INTV
voltages are needed at the output (Table 1).
If the desired output voltage is not one of the preset
values, select 0.6V and use 1% resistors to divide V
as shown in Figure 9. The regulated output voltage is
determined by:
To improve the frequency response, a feed-forward ca-
pacitor, C
route the V
the inductor or the SW line.
Δ
V
OUT
V
OUT
RIPPLE
=
FF
≈
0 6
OSENSE
, may be used. Great care should be taken to
I
.
RIPPLE
increases with input voltage.
V
Figure 9. Setting Output Voltage
CC
•
1/2 LTC3865
LTC3865/LTC3865-1
⎛
⎝ ⎜
OUT
RIPPLE
or grounded, depending on what preset
line away from noise sources, such as
1
OUT
⎛
⎝ ⎜
+
V
ESR
) is approximated by:
OSENSE
R
R
is driven by the effective series
B
A
is the ripple current in the induc-
+
⎞
⎠ ⎟
8
fC
V
1
OUT
OUT
R
R
3865
B
A
F09
⎞
⎠ ⎟
OUT
C
FF
is the output
23
OUT
3865fb
,