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| 型号： | MAX1858EEG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/21页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 24-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 660kHz |
| 占空比： | 90% |
| 电源电压： | 4.75 V ~ 23 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
Dual 180° Out-of-Phase PWM Step-Down
Controller with Power Sequencing and POR
R _ A = - R _ C ? SET OUT ?
L = OUT IN OUT
For output voltages below 1V, set the MAX1858 output
voltage by connecting a voltage-divider from the output
to FB_ to REF (Figure 6). Select R_C (FB to REF resis-
tor) in the 1k ? to 10k ? range. Calculate R_A with the
following equation:
? V - V ?
? V REF - V SET ?
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:
between size and loss is a 30% peak-to-peak ripple
current to average-current ratio (LIR = 0.3). The switch-
ing frequency, input voltage, output voltage, and
selected LIR determine the inductor value as follows:
V (V - V )
V IN f SW I OUT LIR
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
6 × 10 9
R OSC =
? - Hz
S
f SW
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
I PEAK LOAD ( MAX ) + ?
? LIR ?
? 2 ? LOAD ( MAX )
V ITH DS ( ONMAX ) × I LOAD ( MAX ) × ? 1 -
> R
?
?
2 ?
where f SW is in Hz, f OSC 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 MAX1858: 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 val-
ues. Typically inductance is proportional to resistance
(for a given package type) which again makes I 2 R loss-
es high for very low LIR values. A good compromise
inductor ’ s saturation rating must exceed the peak-
inductor current at the maximum defined load current
(I LOAD(MAX) ):
= I ? I
Setting the Valley Current Limit
The minimum current-limit threshold must be high enough
to support the maximum expected load current with the
worst-case low-side MOSFET on-resistance value since
the low-side MOSFET ’ s on-resistance is used as the cur-
rent-sense element. The inductor ’ s valley current occurs
at I LOAD(MAX) minus half of the ripple current. The cur-
rent-sense threshold voltage (V ITH ) should be greater
than voltage on the low-side MOSFET during the ripple-
current valley:
? LIR ?
,
where R DS(ON) is the on-resistance of the low-side
MOSFET (N L ). Use the maximum value for R DS(ON)
from the low-side MOSFET ’ s data sheet, and additional
margin to account for R DS(ON) rise with temperature is
also recommended. A good general rule is to allow
0.5% additional resistance for each ° C of the MOSFET
junction temperature rise.
______________________________________________________________________________________
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相关代理商/技术参数 |
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|---|---|
| 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 |
| MAX1858EEG+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 |
| MAX1858EEG-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 |
| MAX1858EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1858 MAX1875 MAX1876 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 |
| MAX185ACNG | 功能描述:模数转换器 - ADC RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
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