參數(shù)資料
型號: LTC3827IG-1#TR
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 3 A DUAL SWITCHING CONTROLLER, 650 kHz SWITCHING FREQ-MAX, PDSO28
封裝: 5.30 MM, PLASTIC, SSOP-28
文件頁數(shù): 8/32頁
文件大?。?/td> 448K
代理商: LTC3827IG-1#TR
LTC3827-1
16
38271fe
APPLICATIONS INFORMATION
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 benet of a multiphase design
will only be fully realized when the source impedance of the
power supply/battery is included in the efciency testing.
The sources of the top MOSFETs should be placed within
1cm of each other and share a common CIN(s). Separating
the sources 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 LTC3827-1, 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 satised, the capacitance is adequate for ltering. The
output ripple (ΔVOUT) is approximated by:
VOUT IRIPPLE ESR +
1
8fCOUT
where f is the operating frequency, COUT is the output
capacitance and IRIPPLE is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since IRIPPLE increases with input voltage.
Setting Output Voltage
The LTC3827-1 output voltages are each set by an exter-
nal feedback resistor divider carefully placed across the
output, as shown in Figure 3. The regulated output voltage
is determined by:
VOUT = 0.8V 1+
RB
RA
To improve the frequency response, a feed-forward 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.
SENSE+ and SENSEPins
The common mode input range of the current comparator
is from 0V to 10V. Continuous linear operation is provided
throughout this range allowing output voltages from 0.8V
to 10V. The input stage of the current comparator requires
that current either be sourced or sunk from the SENSE pins
depending on the output voltage, as shown in the curve in
Figure 4. If the output voltage is below 1.5V, current will
ow out of both SENSE pins to the main output. In these
cases, the output can be easily pre-loaded by the VOUT
resistor divider to compensate for the current comparator’s
negative input bias current. Since VFB is servoed to the
0.8V reference voltage, RA in Figure 3 should be chosen
to be less than 0.8V/ISENSE, with ISENSE determined from
Figure 4 at the specied output voltage.
Figure 3. Setting Output Voltage
Figure 4. SENSE Pins Input Bias Current
vs Common Mode Voltage
1/2 LTC3827-1
VFB
VOUT
RB
CFF
RA
3827-1 F03
VSENSE COMMON MODE VOLTAGE (V)
0
–700
INPUT
CURRENT
(μA)
–600
–400
–300
–200
6789
200
38271 F04
–500
12345
10
–100
0
100
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