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參數(shù)資料
| 型號： | LTC3546IUFD#TR |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 4000 kHz SWITCHING FREQ-MAX, PQCC28 |
| 封裝： | 4 X 5 MM, PLASTIC, MO-220, QFN-28 |
| 文件頁數(shù)： | 8/28頁 |
| 文件大小： | 356K |
| 代理商： | LTC3546IUFD#TR |
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LTC3546
16
3546fb
the maximum RMS current. The RMS current calculation
is different if the part is used in-phase or out-of-phase.
For in-phase, there are two different equations:
VOUT1 > VOUT2:
I
II
D
I
D
I
D
RMS =
()+
2 1 2
2 11
2
1
11
22
2
–
(()
VOUT2 > VOUT1:
I
II
D
I
D
I
D
RMS =
()+
21 2
1 1
2
1
22
2
–
(()
Where:
D
V
and D
V
OUT
IN
OUT
IN
12
==
When D1 = D2, then the equation simplies to:
II
I
D
RMS =+
()
(
)
12
1–
or
II
I
VV
V
RMS
OUT
IN
OUT
IN
=+
()
12
–
where the maximum average output currents I1 and
I2 equals the peak current minus half the peak-to-peak
ripple current:
I1=ILIM1 –
ΔIL1
2
I2 =ILIM2 –
ΔIL2
2
These formula have a maximum at VIN = 2VOUT, where
IRMS = (I1 + I2)/2. This simple worst-case is commonly
used to determine the worst-case IRMS.
For out-of-phase (PHASE pin is at ground), the ripple
current can be lower than the in-phase.
In the out-of-phase case, the maximum IRMS does not oc-
cur when VOUT1 = VOUT2. The maximum typically occurs
when VOUT1 – VIN/2 = VOUT2 and when VOUT2 – VIN/2 =
VOUT1. As a good rule of thumb, the amount of worst-case
ripple is about 75% of the worst-case ripple in the in-phase
mode. Note, that when VOUT1 = VOUT2 = VIN/2 and I1 = I2,
the ripple is at its minimum.
Note that capacitor manufacturer’s ripple current ratings
are often based on only 2000 hours lifetime. This makes
it advisable to further derate the capacitor, or choose a
capacitor rated at a higher temperature than required.
Several capacitors may also be paralleled to meet the
size or height requirements of the design. An additional
0.1μF to 1μF ceramic capacitor is also recommended on
VIN for high frequency decoupling, when not using an all
ceramic capacitor solution.
Output Capacitor (COUT1 and COUT2) Selection
The selection of COUT1 and COUT2 is driven by the required
ESR to minimize voltage ripple and load step transients.
Typically, once the ESR requirement is satised, the
capacitance is adequate for ltering. The output ripple
(ΔVOUT) is determined by:
VOUT
IL ESR+
1
8 fO COUT
where fO = operating frequency, COUT = output capacitance
and ΔIL = ripple current in the inductor. The output ripple
is highest at maximum input voltage since ΔIL increases
with input voltage.
Once the ESR requirements for COUT have been met, the
RMS current rating generally far exceeds the IRIPPLE(P-P)
requirement, except for an all ceramic solution.
In surface mount applications, multiple capacitors may
have to be paralleled to meet the capacitance, ESR or RMS
current handling requirement of the application. Aluminum
electrolytic, special polymer, ceramic and dry tantalum
capacitors are all available in surface mount packages.
The OS-CON semiconductor dielectric capacitor avail-
able from Sanyo has the lowest ESR(size) product of any
aluminum electrolytic at a somewhat higher price. Special
polymer capacitors, such as Sanyo POSCAP, offer very
low ESR, but have a lower capacitance density than other
types. Tantalum capacitors have the highest capacitance
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相關代理商/技術參數(shù) |
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