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| 型号： | MAX1585ETJ+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 23/29页 |
| 文件大小： | 0K |
| 描述： | IC DGTL CAM PWR SUP 5CH 32TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 60 |
| 应用： | 控制器，数字式相机 |
| 输入电压： | 0.7 V ~ 5.5 V |
| 输出数： | 5 |
| 输出电压： | 1.25 V ~ 5.5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-TQFN-EP（5x5） |
| 包装： | 管件 |
| 产品目录页面： | 1422 (CN2011-ZH PDF) |
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5-Channel Slim DSC Power Supplies
If Z COUT is not less than Z RHP / 10 (as is typical with
ceramic output capacitors) and continuous conduction
is required, then cross the loop over before Z RHP and f 0 :
f C < f 0SC / 10, and f C < Z RHP / 10
In that case:
C C = (V IN / V RAMP )(V FB / V OUT )(g M / (2 π x f C ))
Place:
1 / (2 π x R C x C C ) = 1 / (2 π x R LOAD x C OUT ), so that
R C = R LOAD x C OUT / C C
Or, reduce the inductor value for discontinuous operation.
AUX3 Step-Down Compensation
It is expected that most AUX3 step-down applications
employ continuous inductor current to optimize induc-
tor size and efficiency. To ensure stability, the control-
loop gain should cross over (drop below unity gain) at
a frequency (f C ) much less than that of the switching
frequency.
The relevant characteristics for voltage-mode step-
down compensation are as follows:
? Transconductance (from FB3 to CC3), g MEA (135μS)
? Oscillator ramp voltage, V RAMP (1.25V)
? Feedback regulation voltage, V FB (1.25V)
? Output voltage, V OUT3 , in V
? Output load equivalent resistance, R LOAD , in Ω =
V OUT3 / I LOAD
? Characteristic impedance of the LC output filter, R O
= (L / C) 1/2
The key steps for AUX3 step-down compensation are
as follows:
1) Place f C sufficiently below the switching frequency
(f OSC / 10).
2) Calculate C OUT .
3) Calculate the complex pole pair due to the output
LC filter.
4) Add two zeros to cancel the complex pole pair.
5) Add two high-frequency poles to optimize gain and
phase margin.
If we assume V IN = 5V, V OUT = 3.3V, and I OUT =
300mA, then R LOAD = 11 Ω . If we select f OSC = 500kHz
and L = 10μH, select the crossover frequency to be
1/10 the OSC frequency:
f C = f OSC / 10 = 50kHz
For 3.3V output, select R14 = 30.1k Ω and R15 =
18.2k Ω . See the Setting Output Voltages section.
Calculate the equivalent impedance, R EQ :
R EQ = R SOURCE + R L + ESR + R DS(ON)
where R SOURCE is the output impedance of the source
(this is the output impedance of the step-up converter
when the AUX3 step-down is powered from the step-
up), R L is the inductor DC resistance, ESR is the filter-
capacitor equivalent resistance, and R DS(ON) is the
on-resistance of the external MOSFET.
The output impedance of the step-up converter
(R SOURCE ) is approximately 1 Ω at f 0 . Since the sum of
R L + ESR + R DS(ON) is small compared to 1 Ω , assume
R EQ = 1 Ω . Choose C OUT so R O is less than R EQ / 2:
C OUT > L / [(R EQ / 2) 2 ] = 10μH / 0.25 = 40μF
Choose C OUT = 47μF:
C4 = (V IN / V RAMP )(1 / [2 π x R14 x f C ])
= (5 / 1.25)(1/ [2 π x 30.1k x 50kHz) = 423pF
Choose C4 = 470pF.
Cancel one pole of the complex pole pair by placing
the R4 C4 zero at 0.75 f 0 . The complex pole pair is at
the following:
f 0 = 1 / [2 π (L x C OUT ) 1/2 ]
= 1 / [2 π (10μH x 47μF) 1/2 ] = 7.345kHz
Choose R4 = 1 / (2 π x C4 x 0.75 x f 0 )
= 1 / (2 π x 470pF x 0.75 x 7.345kHz)
z
Choose R4 = 61.9k Ω (standard 1% value). Ensure that
R4 > 2 / g MEA = 14.8k Ω . If it is not greater, reselect
R14 and R15.
Cancel the second pole of the complex pole pair by
placing the R14 C20 zero at 1.25 x f 0 .
C20 = 1 / (2 π x R14 x 1.25 x f 0 )
= 1 / (2 π x 30.1k x 1.25 x 7.345kHz) = 576pF
Choose C20 = 560pF.
Roll off the gain below the switching frequency by plac-
ing a pole at f OSC / 2:
R22 = 1 / (2 π x C20 [f OSC / 2])
= 1 / (2 π x 560pF x 250kHz) = 1.137k Ω
Choose R22 = 1.2k Ω .
If the output filter capacitor has significant ESR, a zero
occurs at the following:
Z ESR = 1 / (2 π x C OUT x R ESR )
Use the R4 C22 pole to cancel the ESR zero:
C22 = C OUT x R ESR / R4
If C22 is calculated to be <10pF, it can be omitted.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1585ETJ+ | 功能描述:直流/直流开关转换器 5Ch Slim DSC Power Supply 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 |
| MAX1585ETJ+T | 功能描述:直流/直流开关转换器 5Ch Slim DSC Power Supply 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 |
| MAX1585ETJ-T | 功能描述:直流/直流开关转换器 5Ch Slim DSC Power Supply 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 |
| MAX1585EVKIT | 功能描述:直流/直流开关转换器 Evaluation Kit for the MAX1585 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 |
| MAX1586AETM | 功能描述:直流/直流开关调节器 PMICs w/Dynamic Core for PDAs RoHS:否 制造商:International Rectifier 最大输入电压:21 V 开关频率:1.5 MHz 输出电压:0.5 V to 0.86 V 输出电流:4 A 输出端数量: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:PQFN 4 x 5 |
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