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| 型号： | MAX1875EEG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 18/21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 Controllers with POR
V IN ( MIN ) = ?
? 1 - 1 . 5 ( 600 kHz )( 250 ns ) ?
V IN ( MIN ) = ?
? 1 - ( 600 kHz )( 250 ns ) ?
V IN ( MIN ) = ? OUT DROP 1 ? + V DROP 2 - V DROP 1
? ? 1- hf SW OFF ( MIN ) ? ?
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).
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
( ? 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 ?
t
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.
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 ?
?
+ 100 mV ? 100 mV = 6 . 58 V
Calculating again with h = 1 gives the absolute limit of
dropout:
? 5 V + 100 mV ?
?
+ 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 MAX1875/MAX1876 must oper-
ate in noisy environments can typically adjust their con-
troller ’ 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
switching losses and clean, stable operation. This is
especially true for dual converters where one channel
can affect the other. Refer to the MAX1875/MAX1876
EV kit data sheet for a specific layout example.
If possible, mount all of 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.
? Use a star ground connection on the power plane to
minimize the crosstalk between OUT1 and OUT2.
? Keep the high-current paths short, especially at the
ground terminals. This practice is essential for sta-
ble, jitter-free operation.
? Connect GND and PGND together close to the IC.
Do not connect them together anywhere else.
Carefully follow the grounding instructions under
step 4 of the Layout Procedure section.
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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 |
| MAX1875EEG+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 |
| MAX1875EEG-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 |
| MAX1875EVKIT | 功能描述:DC/DC 开关控制器 Evaluation Kit for the MAX1875 MAX1876 MAX1858 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 |
| MAX1876AEEG | 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 |
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