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參數(shù)資料
| 型號(hào)： | SC480IMLTRT |
| 廠商： | Semtech Corporation |
| 英文描述： | Complete DDR1/2/3 Memory Power Supply |
| 中文描述： | 完全DDR1/2/3內(nèi)存供電 |
| 文件頁(yè)數(shù)： | 15/25頁(yè) |
| 文件大?。?/td> | 858K |
| 代理商： | SC480IMLTRT |
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15
2006 Semtech Corp.
www.semtech.com
POWER MANAGEMENT
SC480
For stability, place a 10
Ω
/1
μ
F series combination from
REF to VSSA. If REF load capacitance exceeds 1
μ
F, place
at least 10
Ω
in series with the load capacitance to prevent
instability. It is possible to use only one 10
Ω
resistor, by
connecting the load capacitors in parallel with the 1
μ
F,
and connecting the load REF to the capacitor side of the
10
Ω
resistor. (See the Typical Application Circuit on Page
1.) Note that this resistor creates an error term when REF
has a DC load. In most applications this is not a concern
since the DC load on REF is negligible.
Design Procedure
Prior to designing a switching output and making com-
ponent selections, it is necessary to determine the input
voltage range and output voltage speci
fi
cations. To dem-
onstrate the procedure, the output for the schematic in
Figure 7 on page 18
will be designed.
The maximum input voltage (V
) is determined by the
highest AC adaptor voltage. The minimum input voltage
(V
) is determined by the lowest battery voltage af-
ter accounting for voltage drops due to connectors, fuses
and battery selector switches. For the purposes of this
design example we will use a VBAT range of 8V to 20V to
design VDDQ.
Four parameters are needed for the design:
Nominal output voltage, V
. We will use 1.8V with
internal feedback resistors (FB pin tied to VCCA).
Static (or DC) tolerance, TOL
(we will use +/-2%).
Transient tolerance, TOL
and size of transient (we
will use +/-8% for a 10A to 5A load release for this
demonstration).
Maximum output current, I
OUT
(we will design for 10A).
Switching frequency determines the trade-off between
size and ef
fi
ciency. Increased frequency increases
the switching losses in the MOSFETs, and losses are a
function of VBAT
2
. Knowing the maximum input voltage
and budget for MOSFET switches usually dictates where
the design ends up. The default R
values of 1M
Ω
and
715k
Ω
are suggested only as a starting point.
The
fi
rst thing to do is to calculate the on-time, t
ON
, at
V
and V
BAT(MAX)
, since this depends only upon V
BAT
, V
OUT
and Rt
ON
.
1.
2.
3.
4.
s
9
10
50
)
MIN
(
BAT
V
OUT
V
3
10
37
tON
R
12
10
3.3
N)
ON_VBAT(MI
t
x
o
a
x
x
x
x
and,
s
9
10
50
)
MAX
(
BAT
V
OUT
V
3
10
37
tON
R
12
10
3.3
X)
ON_VBAT(MA
t
x
o
a
x
x
x
x
From these values of t
we can calculate the nominal
switching frequency as follows:
Hz
N)
ON_VBAT(MI
t
BAT(MIN)
V
OUT
V
(MIN)
SW_VBAT
f
·
¨
§
x
and,
Hz
X)
ON_VBAT(MA
t
BAT(MAX)
V
OUT
V
(MAX)
SW_VBAT
f
·
¨
§
x
t
ON
is generated by a one-shot comparator that samples
V
via R
, converting this to a current. This current is
used to charge an internal 3.3pF capacitor to V
. The
equations above re
fl
ect this along with any internal com-
ponents or delays that in
fl
uence t
ON
. For our example we
select R
tON
= 1M
Ω
:
t
ON_VBAT(MIN)
= 820ns and, t
ON_VBAT(MAX)
= 358ns
f
SW_VBAT(MIN)
= 274kHz and f
SW_VBAT(MAX)
= 251kHz
Now that we know t
we can calculate suitable values for
the inductor. To do this we select an acceptable inductor
ripple current. The calculations below assume 50% of I
OUT
which will give us a starting place.
H
OUT
I
0.5
(MIN)
ON_VBAT
§
t
OUT
V
BAT(MIN)
V
(MIN)
VBAT
L
·
¨
x
x
and,
H
OUT
I
0.5
X)
·
ON_VBAT(MA
§
x
t
OUT
V
BAT(MAX)
V
(MAX)
VBAT
L
¨
x
For our example:
L
VBAT(MIN)
= 1.02
μ
H and L
VBAT(MAX)
= 1.30
μ
H,
Application Information (Cont.)
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|---|---|
| SC4810B | High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
| SC4810BIMLTRT | High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
| SC4810BITSTRT | High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
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| SC4810EIMLTRT | High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SC4810B | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
| SC4810BIMLTRT | 制造商:Semtech Corporation 功能描述:Controller IC Leaded Process Compatible: |
| SC4810BITSTRT | 制造商:Semtech Corporation 功能描述:Controller IC |
| SC4810E | 制造商:SEMTECH 制造商全稱:Semtech Corporation 功能描述:High Performance Current Mode PWM Controller with Complementary Output, Programmable Delay |
| SC4810EIMLTRT | 制造商:Semtech Corporation 功能描述:Controller IC Leaded Process Compatible: |
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