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參數(shù)資料
| 型號： | MAX1587 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | High-Efficiency, Low-IQ PMICs with Dynamic Core for PDAs and Smart Phones |
| 中文描述： | 高效率，低智商與動態(tài)的PDA和智能手機PMIC的核心 |
| 文件頁數(shù)： | 24/32頁 |
| 文件大小： | 656K |
| 代理商： | MAX1587 |
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M
High-Efficiency, Low-I
Q
PMICs with
Dynamic Core for PDAs and Smart Phones
24
______________________________________________________________________________________
The voltage change is a conventional RC exponential
described by:
Vo(t) = Vo(0) + dV(1 – exp(-t / (100k
C
RAMP
)))
A useful approximation is that it takes approximately 2.2
RC time constants for V3 to move from 10% to 90% of
the voltage difference. For C
RAMP
= 1500pF, this time
is 330μs. For 1V to 1.3V change, this equates to
1mV/μs. See the
Typical Operating Characteristics
for
examples of different ramp-rate settings.
The maximum capacitor value that can be used at
RAMP is 2200pF. If larger values are used, the V3 ramp
rate is still controlled according to the above equation,
but when V3 is first activated, POK indicates an “in reg-
ulation” condition before V3 reaches its final voltage.
The RAMP pin is effectively the reference for REG3.
FB3 regulates to 1.28 times the voltage on RAMP.
Design Procedure
Setting the Output Voltages
The outputs V1 and V2 have preset output voltages, but
can also be adjusted using a resistor voltage-divider. V1
has 3.3V and 3.0V presets. To set V1 to 3.0V, connect
FB1 to IN. To set to 3.3V, connect FB1 to GND. V2 can
be preset to 1.8V or 2.5V on the MAX1586A and
MAX1587A. To set V2 to 1.8V on the MAX1586A and
MAX1587A, connect FB2 to IN. To set to 2.5V, connect
FB2 to GND. V2 can preset to 3.3V or 2.5V on the
MAX1587B. To set V2 to 3.3V on the MAX1587B, connect
FB2 to IN. To set to 2.5V, connect FB2 to GND.
To set V1 or V2 to other than the preset output voltages,
connect a resistor voltage-divider from the output volt-
age to the corresponding FB input. The FB_ input bias
current is less than 100nA, so choose the low-side (FB_-
to-GND) resistor (R
L
) to be 100k
or less. Then calcu-
late the high-side (output-to-FB_) resistor (R
H
) using:
R
H
= R
L
[(V
OUT
/ 1.25) – 1]
The V3 (VCC_CORE) output voltage is set from 0.7V to
1.475V in 25mV steps by the I
2
C serial interface. See
the
Serial Interface
section for details.
Linear regulator V4 provides a fixed 1.3V output volt-
age. Linear regulator V5 provides a fixed 1.1V output
voltage. V4 and V5 voltages are not adjustable.
The output voltage of linear regulator V6 (VCC_USIM) is
set to 0V, 1.8V, 2.5V, or 3.0V by the I
2
C serial interface.
See the
Serial Interface
section for details.
Linear regulator V7 (VCC_BATT) tracks the voltage at
V1 as long as ON1 is high and V1 is in regulation. When
ON1 is low or V1 is not in regulation, V7 switches to the
backup battery (V
BKBT
).
Inductor Selection
The external components required for the step-down
are an inductor, input and output filter capacitors, and a
compensation RC network.
The MAX1586/MAX1587 step-down converters provide
best efficiency with continuous inductor current. A rea-
sonable inductor value (L
IDEAL
) is derived from:
L
IDEAL
= [2(V
IN
) x D(1 - D)] / (I
OUT(MAX)
x f
OSC
)
This sets the peak-to-peak inductor current at 1/2 the
DC inductor current. D is the duty cycle:
D = V
OUT
/ V
IN
Given L
IDEAL
, the peak-to-peak inductor ripple current
is 0.5 x I
OUT
. The peak inductor current is 1.25 x
I
OUT(MAX)
. Make sure the saturation current of the
inductor exceeds the peak inductor current and the
rated maximum DC inductor current exceeds the maxi-
mum output current (I
OUT(MAX)
). Inductance values
larger than L
IDEAL
can be used to optimize efficiency or
to obtain the maximum possible output current. Larger
inductance values accomplish this by supplying a
given load current with a lower inductor peak current.
Typically, output current and efficiency are improved
for inductor values up to about two times L
IDEAL
. If the
inductance is raised too much, however, the inductor
size may become too large, or the increased inductor
resistance may reduce efficiency more than the gain
derived from lower peak current.
Smaller inductance values allow smaller inductor sizes,
but also result in larger peak inductor current for a
given load. Larger output capacitance may then be
needed to suppress the increase in output ripple
caused by larger peak current.
Capacitor Selection
The input capacitor in a DC-DC converter reduces cur-
rent peaks drawn from the battery or other input power
source and reduces switching noise in the controller.
The impedance of the input capacitor at the switching
frequency should be less than that of the input source
so high-frequency switching currents do not pass
through the input source.
The output capacitor keeps output ripple small and
ensures control-loop stability. The output capacitor
Table 3. Serial Address
SRAD
A7
A6
A5
A4
A3
A2
A1
A0
RD/W
0
1
0
0
0
0
1
1
0
0
1
1
0
0
0
1
0
0
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1587AETL | 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 |
| MAX1587AETL+ | 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 |
| MAX1587AETL+T | 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 |
| MAX1587AETL-T | 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 |
| MAX1587AEVKIT | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 MAX1587A Evaluation Kit/Evaluation System 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 |
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