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参数资料
| 型号： | MAX1858AEEG |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | Dual 180∑ Out-of-Phase Buck Controllers with Sequencing/Prebias Startup and POR |
| 中文描述： | DUAL SWITCHING CONTROLLER, 660 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封装： | 0.150 INCH, 0.25 INCH PITCH, MO-137AE, QSOP-24 |
| 文件页数： | 15/22页 |
| 文件大小： | 553K |
| 代理商： | MAX1858AEEG |
M
Dual 180° Out-of-Phase Buck Controllers with
Sequencing/Prebias Startup and POR
______________________________________________________________________________________
15
Setting the Output Voltage
For 1V or greater output voltages, set the MAX1858A/
MAX1875A/MAX1876A output voltage by connecting a
voltage-divider from the output to FB_ to GND (Figure
8). Select R_B (FB_ to GND resistor) to between 1k
and 10k
. Calculate R_A (OUT_ to FB_ resistor) with
the following equation:
where V
SET
= 1V (see the
Electrical Characteristics
)
and V
OUT
can range from V
SET
to 18V.
For output voltages below 1V, set the MAX1858A/
MAX1875A/MAX1876A output voltage by connecting a
voltage-divider from the output to FB_ to REF (Figure
8). Select R_C (FB to REF resistor) in the 1k
to 10k
range. Calculate R_A with the following equation:
where V
SET
= 1V, V
REF
= 2V (see the
Electrical
Characteristics
), and V
OUT
can range from 0 to V
SET
.
Setting the Switching Frequency
The controller generates the clock signal by dividing
down the internal oscillator or SYNC input signal when
driven by an external oscillator, so the switching frequen-
cy equals half the oscillator frequency (f
SW
= f
OSC
/2).
The internal oscillator frequency is set by a resistor
(R
OSC
) connected from OSC to GND. The relationship
between f
SW
and R
OSC
is:
where f
SW
is in Hz and R
OSC
is in
. For example, a
600kHz switching frequency is set with R
OSC
= 10k
.
Higher frequencies allow designs with lower inductor
values and less output capacitance. Consequently,
peak currents and I
2
R losses are lower at higher
switching frequencies, but core losses, gate-charge
currents, and switching losses increase.
A rising clock edge on SYNC is interpreted as a syn-
chronization input. If the SYNC signal is lost, the inter-
nal oscillator takes control of the switching rate,
returning the switching frequency to that set by R
OSC
.
This maintains output regulation even with intermittent
SYNC signals. When an external synchronization signal
is used, R
OSC
should set the switching frequency to
one-half SYNC rate (f
SYNC
).
Inductor Selection
Three key inductor parameters must be specified for
operation with the MAX1858A/MAX1875A/MAX1876A:
inductance value (L), peak-inductor current (I
PEAK
), and
DC resistance (R
DC
). The following equation assumes a
constant ratio of inductor peak-to-peak AC current to DC
average current (LIR). For LIR values too high, the RMS
currents are high, and therefore I
2
R losses are high.
Large inductances must be used to achieve very low LIR
values. Typically, inductance is proportional to resis-
tance (for a given package type), which again makes I
2
R
losses high for very low LIR values. A good compromise
between size and loss is a 30% peak-to-peak ripple cur-
rent to average-current ratio (LIR = 0.3). The switching
frequency, input voltage, output voltage, and selected
LIR determine the inductor value as follows:
where V
IN
, V
OUT
, and I
OUT
are typical values (so that
efficiency is optimum for typical conditions). The switch-
ing frequency is set by R
OSC
(see the
Setting the
Switching Frequency
section). The exact inductor value
is not critical and can be adjusted in order to make
trade-offs among size, cost, and efficiency. Lower
inductor values minimize size and cost, but also
improve transient response and reduce efficiency due
to higher peak currents. On the other hand, higher
inductance increases efficiency by reducing the RMS
current. However, resistive losses due to extra wire turns
can exceed the benefit gained from lower AC current
levels, especially when the inductance is increased
without also allowing larger inductor dimensions.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. The
L
V
V
V
V f
I
LIR
OUT
IN
OUT
=
(
)
-
R
Hz
f
OSC
SW
=
6 10
9
(
)
-
R A
_
R C
_
V
V
V
V
-
SET
REF
OUT
SET
=
-
R A
_
R B
_
V
V
OUT
SET
=
-1
MAX1858A
MAX1875A
MAX1876A
MAX1858A
MAX1875A
MAX1876A
OUT_
R_A
R_B
FB_
V
OUT_
> 1V
OUT_
R_C
R_A
FB_
REF
V
OUT_
< 1V
Figure 8. Adjustable Output Voltage
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1858AEEG+ | 功能描述:电压模式 PWM 控制器 Dual 180 Out Buck Controllers RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1858AEEG+T | 功能描述:电压模式 PWM 控制器 Dual 180 Out Buck Controllers RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| MAX1858AEEG-T | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1858EEG | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1858EEG+ | 功能描述:电压模式 PWM 控制器 Dual 180 Out Buck Controllers RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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