參數(shù)資料
型號(hào)： LTC3890MPUH#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
封裝： 5 X 5 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-220WHHD, QFN-32
文件頁(yè)數(shù)： 11/38頁(yè)
文件大?。?/td> 381K
代理商： LTC3890MPUH#TRPBF
LTC3890
19
3890fa
APPLICATIONS INFORMATION
RMS capacitor current requirement. Increasing the out-
put current 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 top MOSFET
is a square wave of duty cycle (VOUT)/(VIN). To prevent
large voltage transients, a low ESR capacitor sized for the
maximum RMS current of one channel must be used. The
maximum RMS capacitor current is given by:
CIN Required IRMS ≈
IMAX
VIN
VOUT
() VIN –VOUT
()
1/ 2
(1)
This formula has a maximum at VIN = 2VOUT, where IRMS
= IOUT/2. This simple worst-case condition is commonly
used for design because even significant 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 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 LTC3890, ceramic capacitors
can also be used for CIN. Always consult the manufacturer
if there is any question.
The benefit of the LTC3890 2-phase operation can be cal-
culated by using Equation 1 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 benefit of a multiphase design will
only be fully realized when the source impedance of the
power supply/battery is included in the efficiency testing.
The drains of the top MOSFETs should be placed within
1cm of each other and share a common CIN(s). Separating
the drains and CIN may produce undesirable voltage and
current resonances at VIN.
A small (0.1μF to 1μF) bypass capacitor between the chip
VIN pin and ground, placed close to the LTC3890, is also
suggested. A 10Ω resistor placed between CIN (C1) and
the VIN pin provides further isolation between the two
channels.
The selection of COUT is driven by the effective series
resistance (ESR). Typically, once the ESR requirement
is satisfied, the capacitance is adequate for filtering. The
output ripple (ΔVOUT) is approximated by:
ΔVOUT ≈ΔIL ESR +
1
8 f COUT
where f is the operating frequency, COUT is the output
capacitance and ΔIL is the ripple current in the inductor.
The output ripple is highest at maximum input voltage
since ΔIL increases with input voltage.
Setting Output Voltage
The LTC3890 output voltages are each set by an external
feedback resistor divider carefully placed across the out-
put, as shown in Figure 5. The regulated output voltage
is determined by:
VOUT = 0.8V 1+
RB
RA
To improve the frequency response, a feedforward ca-
pacitor, CFF, may be used. Great care should be taken to
route the VFB line away from noise sources, such as the
inductor or the SW line.
1/2 LTC3890
VFB
VOUT
RB
CFF
RA
3890 F05
Figure 5. Setting Output Voltage
相關(guān)PDF資料
PDF描述
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LTC3890HUH#PBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
LTC3890HUH#TRPBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
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