參數(shù)資料
型號(hào): LTC3727IG-1#TR
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 3 A SWITCHING CONTROLLER, 580 kHz SWITCHING FREQ-MAX, PDSO28
封裝: 5.30 MM, PLASTIC, SSOP-28
文件頁(yè)數(shù): 8/32頁(yè)
文件大?。?/td> 366K
代理商: LTC3727IG-1#TR
16
LTC3727/LTC3727-1
3727fc
The benefit of the LTC3727 multiphase can be calculated
by using the equation above for the higher power control-
ler and then calculating the loss that would have resulted
if both controller channels switch on at the same time. The
total RMS power lost is lower when both controllers are
operating due to the interleaving of current pulses through
the input capacitor’s ESR. This is why the input capacitor’s
requirement calculated above for the worst-case control-
ler is adequate for the dual controller design. Remember
that input protection fuse resistance, battery resistance
and PC board trace resistance losses are also reduced due
to the reduced peak currents in a multiphase 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 two 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.
The selection of COUT is driven by the required effective
series resistance (ESR). Typically once the ESR require-
ment is satisfied the capacitance is adequate for filtering.
The output ripple (
ΔVOUT) is determined by:
ΔΔ
V
I ESR
fC
OUT
L
OUT
+
1
8
Where f = operating frequency, COUT = output capaci-
tance, and
ΔIL= ripple current in the inductor. The output
ripple is highest at maximum input voltage since
ΔIL
increases with input voltage. With
ΔIL = 0.3IOUT(MAX) the
output ripple will typically be less than 50mV at max VIN
assuming:
COUT Recommended ESR < 2 RSENSE
and COUT > 1/(8fRSENSE)
The first condition relates to the ripple current into the
ESR of the output capacitance while the second term
guarantees that the output capacitance does not signifi-
cantly discharge during the operating frequency period
due to ripple current. The choice of using smaller output
capacitance increases the ripple voltage due to the
discharging term but can be compensated for by using
capacitors of very low ESR to maintain the ripple voltage
at or below 50mV. The ITH pin OPTI-LOOP compensation
components can be optimized to provide stable, high
performance transient response regardless of the output
capacitors selected.
Manufacturers such as Nichicon, Nippon Chemi-Con and
Sanyo can be considered for high performance through-
hole capacitors. The OS-CON semiconductor dielectric
capacitor available from Sanyo has the lowest (ESR)(size)
product of any aluminum electrolytic at a somewhat
higher price. An additional ceramic capacitor in parallel
with OS-CON capacitors is recommended to reduce the
inductance effects.
In surface mount applications multiple capacitors may
need to be used in parallel to meet the ESR, RMS current
handling and load step requirements of the application.
Aluminum electrolytic, dry tantalum and special polymer
capacitors are available in surface mount packages. Spe-
cial polymer surface mount capacitors offer very low ESR
but have lower storage capacity per unit volume than other
capacitor types. These capacitors offer a very cost-effec-
tive output capacitor solution and are an ideal choice when
combined with a controller having high loop bandwidth.
Tantalum capacitors offer the highest capacitance density
and are often used as output capacitors for switching
regulators having controlled soft-start. Several excellent
surge-tested choices are the AVX TPS, AVX TPS Series III
or the KEMET T510 series of surface mount tantalums,
available in case heights ranging from 1.2mm to 4.1mm.
Aluminum electrolytic capacitors can be used in cost-
driven applications providing that consideration is given
to ripple current ratings, temperature and long term reli-
ability. A typical application will require several to many
aluminum electrolytic capacitors in parallel. A combina-
tion of the above mentioned capacitors will often result in
maximizing performance and minimizing overall cost. Other
capacitor types include Nichicon PL series, NEC Neocap,
Cornell Dubilier ESRE and Sprague 595D series. Consult
manufacturers for other specific recommendations.
APPLICATIO S I FOR ATIO
WU
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