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| 型号： | MAX1778EUG+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 26/39页 |
| 文件大小： | 0K |
| 描述： | IC DCDC CONV MULTI OUT 24TSSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 62 |
| 应用： | 转换器，TFT，LCD |
| 输入电压： | 2.7 V ~ 5.5 V |
| 输出数： | 5 |
| 输出电压： | 2.7 V ~ 13 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 24-TSSOP（0.173"，4.40mm 宽） |
| 供应商设备封装： | 24-TSSOP |
| 包装： | 管件 |
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MAX1778/MAX1880–MAX1885
Quad-Output TFT LCD DC/DC
Converters with Buffer
V RIPPLE ( C ) ≈ ? MAIN IN ? ?
?
? ? C OUT OSC ?
?
where η is the efficiency, f OSC is the oscillator frequen-
cy (see the Electrical Characteristics ), and I MAIN
includes the primary load current and the input supply
currents for the charge pumps (see the Charge-Pump
Input Power and Efficiency Considerations section), lin-
ear regulator, and VCOM buffer. Considering the typi-
cal application circuit, the maximum average DC load
current (I MAIN(MAX) ) is 300mA with an 8V output. Based
on the above equations and assuming 85% efficiency,
the inductance value is then chosen to be 4.7μH.
The inductor’s saturation current rating should exceed
the peak inductor current throughout the normal operat-
ing range. The peak inductor current is then given by:
Output-voltage ripple has two components: variations
in the charge stored in the output capacitor with each
LX pulse, and the voltage drop across the capacitor’s
equivalent series resistance (ESR) caused by the
current into and out of the capacitor:
V RIPPLE = V RIPPLE ( C ) + V RIPPLE ( ESR )
V RIPPLE ( ESR ) ≈ I PEAK R ESR ( COUT ) , AND
? V ? V ? ? I MAIN ?
V MAIN f
where I PEAK is the peak inductor current (see the
Inductor Selection section). For ceramic capacitors, the
? I MAIN ( MAX ) V MAIN ? ?
I PEAK = ? ? ? 1 +
?
?
2 ? ? η ?
V IN ( MIN ) ?
LIR ? ? 1 ?
? ? ?
output-voltage ripple is typically dominated by V RIP-
PLE(C) . The voltage rating and temperature characteris-
tics of the output capacitor must also be considered.
? I X V
?
P LR ? R L ? MAIN MAIN ?
Under fault conditions, the inductor current can reach
up to 1.85A (I LIM(MAX) ), see the Electrical
Characteristics). However, the controller’s fast current-
limit circuitry allows the use of soft-saturation inductors
while still protecting the IC.
The inductor’s DC resistance can significantly affect
efficiency due to the power loss in the inductor. The
power loss due to the inductor’s series resistance (P LR )
can be approximated by the following equation:
2
? V IN ?
where R L is the inductor’s series resistance. For best per-
formance, select inductors with resistance less than the
internal n-channel MOSFET on-resistance (0.35 ? typ).
Use inductors with a ferrite core or equivalent. To mini-
mize radiated noise in sensitive applications, use a
shielded inductor.
Output Capacitor
Output capacitor selection depends on circuit stability
and output-voltage ripple. A 10μF ceramic capacitor
works well in most applications (Tables 1 and 2).
Additional feedback compensation is required (see the
Feedback Compensation section) to increase the mar-
gin for stability by reducing the bandwidth further. In
cases where the output capacitance is sufficiently large,
additional feedback compensation is not necessary.
26
Feedback Compensation
For stability, add a pole-zero pair from FB to GND in the
form of a compensation resistor (R COMP ) in series with
a compensation capacitor (C COMP ), as shown in Figure
2. Select R COMP to be half the value of R2, the low-side
feedback resistor.
Integrator Capacitor
The MAX1778/MAX1880–MAX1885 contain an internal
current integrator that improves the DC load regulation
but increases the peak-to-peak transient voltage (see
the load-transient waveforms in the Typical Operating
Characteristics). For highly accurate DC load regula-
tion, enable the current integrator by connecting a
470pF ( ? OSC = 1MHz)/1000pF ( ? OSC = 500kHz)
capacitor to INTG. To minimize the peak-to-peak tran-
sient voltage at the expense of DC regulation, disable
the integrator by connecting INTG to REF. When using
the MAX1883–MAX1885, connect a 100k ? resistor to
GND when disabling the integrator.
Input Capacitor
The input capacitor (C IN ) in step-up designs reduces
the current peaks drawn from the input supply and
reduces noise injection. The value of C IN is largely
determined by the source impedance of the input sup-
ply. High source impedance requires high input capac-
itance, particularly as the input voltage falls. Since
step-up DC-DC converters act as “constant-power ”
loads to their input supply, input current rises as input
voltage falls. A good starting point is to use the same
capacitance value for C IN as for C OUT .
Maxim Integrated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1778EUG+ | 功能描述:直流/直流开关转换器 Quad-Output TFT LCD w/Buffer 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 |
| MAX1778EUG+T | 功能描述:直流/直流开关转换器 Quad-Output TFT LCD w/Buffer 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 |
| MAX1778EUG-T | 功能描述:直流/直流开关转换器 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 |
| MAX1778EVKIT | 功能描述:电源管理IC开发工具 MAX1778/80/81/82 Eval Kit RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX1779EUE | 功能描述:直流/直流开关转换器 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 |
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