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| 型号： | MAX1875AEEG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/22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 |
| 电源电压： | 4.5 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 Buck Controllers with
Sequencing/Prebias Startup and POR
V IN ( MIN ) = ? ?
Applications Information
Dropout Performance
When working with low input voltages, the output-volt-
age adjustable range for continuous-conduction opera-
tion is restricted by the minimum off-time (t OFF(MIN) ).
For best dropout performance, use the lowest (100kHz)
switching-frequency setting. Manufacturing tolerances
and internal propagation delays introduce an error to
the switching frequency and minimum off-time specifi-
cations. This error is more significant at higher frequen-
cies. Also, keep in mind that transient response
performance of buck regulators operated close to
dropout is poor, and bulk output capacitance must
often be added (see the V SAG equation in the Design
Procedure section).
Dropout design example:
V OUT = 5V
f SW = 600kHz
t OFF(MIN) = 250ns
V DROP1 = V DROP2 = 100mV
h = 1.5
? 5 V + 100 mV ?
? 1 - 1 . 5 ( 600 kHz )( 250 ns ) ?
+ 100 mV ? 100 mV = 6 . 58 V
Calculating again with h = 1 gives the absolute limit of
dropout:
1 - ( 600 kHz )( 250 ns ) ?
The absolute point of dropout is when the inductor cur-
rent ramps down during the minimum off-time ( ? I DOWN )
as much as it ramps up during the maximum on-time
?
V IN ( MIN ) = ?
?
5 V + 100 mV ?
?
V IN ( MIN ) = ? OUT DROP 1 ? + V DROP 2 - V DROP 1
( ? I UP ). The ratio h = ? I UP / ? I DOWN is an indicator of the
ability to slew the inductor current higher in response to
increased load, and must always be greater than 1. As
h approaches 1, the absolute minimum dropout point,
the inductor current cannot increase as much during
each switching cycle and V SAG greatly increases
unless additional output capacitance is used.
A reasonable minimum value for h is 1.5, but adjusting
this up or down allows tradeoffs between V SAG , output
capacitance, and minimum operating voltage. For a
given value of h, the minimum operating voltage can be
calculated as:
? V + V ?
? ? 1- hf SW t OFF ( MIN ) ? ?
where V DROP1 is the sum of the parasitic voltage drops
in the inductor discharge path, including synchronous
rectifier, inductor, and PC board resistances; V DROP2 is
the sum of the resistances in the charging path, includ-
ing high-side switch, inductor, and PC board resis-
tances; and t OFF(MIN) is from the Electrical
Characteristics . The absolute minimum input voltage is
calculated with h = 1.
If the calculated V+ (MIN) is greater than the required
minimum input voltage, then reduce the operating fre-
quency or add output capacitance to obtain an accept-
able V SAG . If operation near dropout is anticipated,
calculate V SAG to be sure of adequate transient
response.
+ 100 mV ? 100 mV = 6 V
Therefore, V IN must be greater than 6V, even with very
large output capacitance, and a practical input voltage
with reasonable output capacitance would be 6.58V.
Improving Noise Immunity
Applications where the MAX1858A/MAX1875A/
MAX1876A must operate in noisy environments can
typically adjust their controller ’s compensation to
improve the system ’s noise immunity. In particular,
high-frequency noise coupled into the feedback loop
causes jittery duty cycles. One solution is to lower the
crossover frequency (see the Compensation section).
PC Board Layout Guidelines
Careful PC board layout is critical to achieve low switch-
ing losses and clean, stable operation. This is especially
true for dual converters where one channel can affect
the other. Refer to the MAX1858 EV kit or MAX1875 EV
kit data sheet for specific layout examples.
If possible, mount all the power components on the top
side of the board with their ground terminals flush
against one another. Follow these guidelines for good
PC board layout:
? Isolate the power components on the top side from
the analog components on the bottom side with a
ground shield. Use a separate PGND plane under
the OUT1 and OUT2 sides (referred to as PGND1
and PGND2). Avoid the introduction of AC currents
into the PGND1 and PGND2 ground planes. Run the
power plane ground currents on the top side only.
20
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相关代理商/技术参数 |
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| MAX1875AEEG+ | 功能描述:电压模式 PWM 控制器 Dual 180 Out PWM Step-Down 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 |
| MAX1875AEEG+T | 功能描述:电压模式 PWM 控制器 Dual 180 Out PWM Step-Down 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 |
| MAX1875AEEG-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 |
| MAX1875EEG | 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 |
| MAX1875EEG+ | 功能描述:电压模式 PWM 控制器 Dual 180 Out PWM Step-Down 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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