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| 型号： | MAX1878ETC+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 10/12页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK BST SYNC ADJ 12TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 75 |
| 类型： | 降压（降压），升压（升压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 1.25 V ~ 28 V |
| 输入电压： | 2 V ~ 5.5 V |
| PWM 型： | 电压模式 |
| 频率 - 开关： | 500kHz |
| 电流 - 输出： | 500mA |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-WQFN 裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 12-TQFN-EP（4x4） |
Dual-Output Step-Down and LCD Step-Up
Power Supply for PDAs
Inductor Selection
The MAX1878 is optimized to use a 10μH inductor over
the entire operating range. Smaller inductance values
typically offer smaller physical size for a given series
resistance or saturation current. Circuits using larger
inductance values may startup at lower input voltages
and exhibit less ripple, but also provide reduced output
power. This occurs when the inductance is sufficiently
large to prevent the maximum current limit from being
reached before the maximum on-time expires. The
inductor’s saturation current rating should be greater
than the peak switching current. However, it is generally
acceptable to bias the inductor into saturation by as
much as 20%, although this will slightly reduce efficien-
cy. Choose a low DC-resistance inductor to improve effi-
ciency. For the above reasons choose the step-up
converter inductor in the range of 10μH to 33μH
depending on the input voltage (4μH per volt of V IN ).
Step-Up Converter Diode Selection
The high maximum switching frequency of 500kHz
requires a high-speed rectifier such as the 1N4148. To
maintain high efficiency, the average current rating of
the diode should be greater than the peak switching
current. Choose a reverse breakdown voltage greater
than the output voltage. A Schottky diode is not recom-
mended as the lower forward voltage does little to
improve efficiency whereas the higher reverse leakage
current decreases efficiency.
Input Bypass Capacitors
Bypass V IN with a 10μF low-ESR surface-mount ceram-
ic capacitor to PGND and PGNDLCD as close to the IC
as possible. This input bypass capacitor reduces peak
currents and noise at the input voltage source. Connect
AIN1 and AIN2 together and bypass with a low-ESR
1μF surface-mount ceramic capacitor to AGND. A low
resistance (10 Ω ) from IN to AIN1 and AIN2 creates a
lowpass RC filter and provides low-noise analog input
power to the MAX1878.
Output Filter Capacitors
The MAX1878 is a voltage mode converter and requires
ripple at FB and FBLCD for stable regulation. For most
applications, bypass V LCD with a 0.1μF small ceramic
surface-mount capacitor to PGNDLCD. For small
ceramic capacitors, the output ripple voltage is domi-
nated by the capacitance value. If tantalum or electrolyt-
ic capacitors are used, the higher ESR increases the
output ripple voltage. Decreasing the ESR reduces the
output ripple voltage and the peak-to-peak transient
voltage. Surface-mount capacitors are generally pre-
ferred because they lack the inductance and resistance
of their through-hole equivalents. Bypass V MAIN with a
10μF to 47μF tantalum capacitor to PGND. Choose a
capacitor with 200m Ω to 300m Ω ESR to provide stable
switching while minimizing output ripple. A 22μF filter
capacitor works well for most applications.
Ripple Regulation
For proper switching control the ripple at FB and FBLCD
must be greater than 25mV. Use R6 and C6 as shown in
Figure 1 to inject ripple into FB. To insure sufficient ripple
on FBLCD, connect C5 as shown in Figure 1.
PC Board Layout and Grounding
High switching frequencies make PC board layout a
very important part of design. Good design minimizes
excessive EMI on the feedback paths and voltage gra-
dients in the ground plane, both of which can result in
instability or regulation errors. Connect the inductors,
input filter capacitors, and output filter capacitors as
close to the device as possible, and keep their traces
short, direct, and wide. The external voltage-feedback
networks should be very close to the feedback pins,
within 0.2 inches (5mm). Keep noisy traces, such as LX
and LXLCD, away from the voltage feedback networks;
also keep them separate, using grounded copper.
The exposed backside pad and corner tabs of the
TQFN package are internally connected to analog
ground. For heat dissipation, connect the exposed
backside pad to a large analog ground plane, prefer-
ably on a surface of the board that receives good air-
flow. Connect all power grounds and all analog
grounds to separate ground planes in a star ground
configuration. Connect the analog ground plane and
the power ground plane together at a single point. The
MAX1878 evaluation kit data sheet includes a proper
PC board layout and routing scheme.
10
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相关代理商/技术参数 |
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| MAX1878ETC+ | 功能描述:直流/直流开关转换器 Dual-Output Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1878ETC+T | 功能描述:直流/直流开关转换器 Dual-Output Step-Down RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1878EVKIT | 功能描述:直流/直流开关转换器 Evaluation Kit for the MAX1878 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1879EUA | 功能描述:电池管理 1-Cell Li+ Pulse Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
| MAX1879EUA+ | 功能描述:电池管理 1-Cell Li+ Pulse Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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