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| 型号： | MAX1802EHJ+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 20/28页 |
| 文件大小： | 0K |
| 描述： | IC PWR SPLY STEP DOWN 32-TQFP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 360 |
| 应用： | 控制器，数字式相机 |
| 输入电压： | 2.5 V ~ 11 V |
| 输出数： | 5 |
| 输出电压： | 1.25 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-TQFP |
| 供应商设备封装： | 32-TQFP（5x5） |
| 包装： | 托盘 |
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Digital Camera Step-Down
Power Supply
Use discontinuous current when the step-up ratio
(V OUT / V IN ) is greater than 1 / (1 - D MAX ).
Continuous Inductor Current
A reasonable inductor value (L IDEAL ) can be derived
from the following equation, which sets continuous
peak-to-peak inductor current at 1/3 the DC inductor
current:
The output capacitor is required to keep the output volt-
age ripple small and to ensure regulation control-loop
stability. The output capacitor must have low imped-
ance at the switching frequency. Tantalum and ceramic
capacitors are good choices. Tantalum capacitors typi-
cally have high capacitance and medium-to-low equiv-
alent series resistance (ESR) so that ESR dominates the
impedance at the switching frequency. In turn, the out-
L IDEAL =
3 ( V IN ( MAX ) ? V DSN ) D ( 1 ? D )
I OUT f OSC
put ripple is approximately:
V RIPPLE ≈ I L( p-p) ESR
where I L (p-p) is the peak-to-peak inductor current.
where D, the duty cycle, is given by:
Ceramic capacitors typically have lower ESR than tan-
talum capacitors, but with relatively small capacitance
D ≈ 1 ?
V IN
V OUT + V D
that dominates the impedance at the switching fre-
quency. In turn, the output ripple is approximately:
In these equations, V DSN is the voltage drop across the
N-channel MOSFET switch, and V D is the forward volt-
age drop across the rectifier. Given L IDEAL , the consis-
tent peak-to-peak inductor current is 0.33 I OUT / (1 - D).
The maximum inductor current is 1.17 I OUT / (1 - D).
Inductance values smaller than L IDEAL can be used;
however, the maximum inductor current will rise as L is
reduced, and a larger output capacitance will be
required to maintain the same output ripple.
The inductor current will become discontinuous if I OUT
decreases by more than a factor of six from the value
used to determine L IDEAL .
Discontinuous Inductor Current
In the discontinuous mode, each MAX1802 auxiliary
controller regulates the output voltage by adjusting the
duty cycle to allow adequate power transfer to the load.
To ensure regulation under worst-case load conditions
(maximum I OUT ), choose:
V RIPPLE ≈ I L( p-p) Z C
where I L (p-p) is the peak-to-peak inductor current, and
Z C ≈ 1 / (2 π f OSC C OUT ).
See the Compensation Design section for a discussion
of the influence of output capacitance and ESR on reg-
ulation control-loop stability.
The capacitor voltage rating must exceed the maximum
applied capacitor voltage. For most tantalum capaci-
tors, manufacturers suggest derating the capacitor by
applying no more than 70% of the rated voltage to the
capacitor. Ceramic capacitors are typically used up to
the voltage rating of the capacitor. Consult the manu-
facturer ’ s specifications for proper capacitor derating.
MOSFET Selection
The MAX1802 main converter and auxiliary controllers
drive external logic-level P- and/or N-channel MOSFETs
as the circuit switching elements. The key selection
parameters are:
L =
V OUT D MAX
2 I OUT f OSC
? On-resistance (R DS(ON) )
? Maximum drain-to-source voltage (V DS(MAX) )
? Total gate charge (Q g )
The peak inductor current is V IN D MAX / (L f OSC ).
The inductor ’ s saturation current rating should meet or
exceed the calculated peak inductor current.
Input and Output Filter Capacitors
The input capacitor (C IN ) reduces the current peaks
drawn from the battery or input power source. The
impedance of the input capacitor at the switching fre-
quency should be less than that of the input source so
that high-frequency switching currents do not pass
through the input source.
? Reverse transfer capacitance (C RSS )
Because the main converter ’ s external MOSFETs are
used for current sense, they directly determine the out-
put current capability and efficiency of the main con-
verter. It is important to select the appropriate external
MOSFETs for the main converter. The P-channel on-
resistance (R DSP ) at minimum input voltage (V VDDM )
must be low enough so that the converter can produce
the desired output current as determined by the
I OUT(MAX) equation in the Main DC-DC Converter sec-
tion. The N-channel on-resistance (R DSN ) determines
20
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| MAX1802EHJ+ | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller 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 |
| MAX1802EHJ+T | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller 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 |
| MAX1802EHJ-T | 功能描述:直流/直流开关转换器 Step-Up Slave DC/DC Controller 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 |
| MAX1804EUB | 功能描述:电流和电力监控器、调节器 RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX1804EUB+ | 功能描述:电流和电力监控器、调节器 Feedback Integrator for Power Supply RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
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