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參數(shù)資料
| 型號： | MAX1585ETJ |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 5-Channel Slim DSC Power Supplies |
| 中文描述： | 3.6 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, QCC32 |
| 封裝： | 5 X 5 MM, 0.80 MM HEIGHT, MO-220WHHD-2, TQFN-32 |
| 文件頁數(shù)： | 21/29頁 |
| 文件大?。?/td> | 632K |
| 代理商： | MAX1585ETJ |
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If Z
ESR
> f
C
, it can be ignored, as is typically the case
with ceramic output capacitors. If Z
ESR
is less than f
C
,
it should be cancelled with a pole set by capacitor C
P
connected from CCSU to GND:
C
P
= C
OUT
x R
ESR
/ R
C
If C
P
is calculated to be <10pF, it can be omitted.
Step-Down Component Selection
Step-Down Inductor
The external components required for the step-down
are an inductor, input and output filter capacitors, and
a compensation RC network.
The MAX1585/1585 step-down converter provides best
efficiency with continuous inductor current. A reason-
able inductor value (L
IDEAL
) can be derived from the
following:
L
IDEAL
= [2(V
IN
) x D(1 - D)] / I
OUT
x f
OSC
which sets the peak-to-peak inductor current at half the
DC inductor current. D is the duty cycle:
D = V
OUT
/ V
IN
Given L
IDEAL
, the peak-to-peak inductor current is 0.5 x
I
OUT
. The absolute peak inductor current is 1.25 x I
OUT
.
Inductance values smaller than L
IDEAL
can be used to
reduce inductor size; however, if much smaller values
are used, inductor current rises and a larger output
capacitance may be required to suppress output ripple.
Larger values than L
IDEAL
can be used to obtain higher
output current, but with typically larger inductor size.
Step-Down Compensation
The relevant characteristics for step-down compensa-
tion are as follows:
Transconductance (from FBSD to CCSD), g
MEA
(135μS)
Current-sense amplifier transresistance, R
CS
(0.6V/A)
Feedback regulation voltage, V
FB
(1.25V)
Step-down output voltage, V
SD
, in V
Output load equivalent resistance, R
LOAD
, in
= V
SD
/ I
LOAD
The key steps for step-down compensation are as fol-
lows:
1) Set the compensation RC zero to cancel the R
LOAD
C
OUT
pole.
2) Set the loop crossover below 1/10 the switching fre-
quency.
If we assume V
IN
= 3.5V, V
OUT
= 1.5V, and I
OUT
=
250mA, then R
LOAD
= 6
.
If we select f
OSC
= 500kHz and L = 22μH,
choose f
C
= 24kHz and calculate C
C
:
C
C
= (V
FB
/ V
OUT
)(R
LOAD
/ R
CS
)(g
M
/ 2
π
x f
C
)
= (1.25 / 1.5)(6 / 0.6) x (135μS / (6.28 x 40kHz))
= 4.5nF
Choose 4.7nF.
Now select R
C
so transient-droop requirements are met.
For example, if 4% transient droop is allowed, the input
to the error amplifier moves 0.04 x 1.25V, or 50mV. The
error-amp output drives 50mV x 135μS, or 6.75μA across
R
C
to provide transient gain. Since the current-sense
transresistance is 0.6V/A, the value of R
C
that allows the
required load step swing is as follows:
R
C
= 0.6 x I
IND(PK)
/ 6.75μA
In a step-down DC-DC converter, If L
IDEAL
is used, out-
put current relates to inductor current by the following:
I
IND(PK)
= 1.25 x I
OUT
So for a 250mA output load step with V
IN
= 3.5V and
V
OUT
= 1.5V:
R
C
= (1.25 x 0.6 x 0.25) / 6.75μA = 27.8k
Choose 27k
.
The inductor does somewhat limit the response in this
case since it ramps at (V
IN
- V
OUT
) / 22μH, or (3.5 - 1.5)
/ 22μH = 90mA/μs.
The output filter capacitor is then chosen so the C
OUT
R
LOAD
pole cancels the R
C
C
C
zero:
C
OUT
x R
LOAD
= R
C
x C
C
For the example:
C
OUT
= 27k
x 4.7nF / 6
= 21μF
Choose 22μF or greater.
If the output filter capacitor has significant ESR, a zero
occurs at:
Z
ESR
= 1 / (2
π
x C
OUT
x R
ESR
)
If Z
ESR
> f
C
, it can be ignored, as is typically the case
with ceramic output capacitors. If Z
ESR
is less than f
C
,
it should be cancelled with a pole set by capacitor C
P
connected from CCSD to GND:
C
P
= C
OUT
x R
ESR
/ R
C
If C
P
is calculated to be <10pF, it can be omitted.
AUX Controller Component Selection
External MOSFET
MAX1584/MAX1585 AUX1(step-up) controllers drive
external logic-level N-channel MOSFETs. AUX3 (step-
down) controllers drive P-channel MOSFETs. AUX2
(step-up) on the MAX1584 drives an N channel, while
AUX2 (inverting) on the MAX1585 drives a P channel.
M
5-Channel Slim DSC Power Supplies
______________________________________________________________________________________
21
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1585ETJ+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 5Ch Slim DSC Power Supply RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1585ETJ+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 5Ch Slim DSC Power Supply RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1585ETJ-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 5Ch Slim DSC Power Supply RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1585EVKIT | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Evaluation Kit for the MAX1585 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| MAX1586AETM | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 PMICs w/Dynamic Core for PDAs RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
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