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| 型号： | MAX1585ETJ+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 21/29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 ESR > f C , it can be ignored, as is typically the case
with ceramic output capacitors. If Z ESR is less than f C ,
it should be cancelled with a pole set by capacitor C P
connected from CCSU to GND:
C P = C OUT x R ESR / R C
If C P is calculated to be <10pF, it can be omitted.
Step-Down Component Selection
Step-Down Inductor
The external components required for the step-down
are an inductor, input and output filter capacitors, and
a compensation RC network.
The MAX1585/1585 step-down converter provides best
efficiency with continuous inductor current. A reason-
able inductor value (L IDEAL ) can be derived from the
following:
L IDEAL = [2(V IN ) x D(1 - D)] / I OUT x f OSC
which sets the peak-to-peak inductor current at half the
DC inductor current. D is the duty cycle:
D = V OUT / V IN
Given L IDEAL , the peak-to-peak inductor current is 0.5 x
I OUT . The absolute peak inductor current is 1.25 x I OUT .
Inductance values smaller than L IDEAL can be used to
reduce inductor size; however, if much smaller values
are used, inductor current rises and a larger output
capacitance may be required to suppress output ripple.
Larger values than L IDEAL can be used to obtain higher
output current, but with typically larger inductor size.
Step-Down Compensation
The relevant characteristics for step-down compensa-
tion are as follows:
? Transconductance (from FBSD to CCSD), g MEA
(135μS)
choose f C = 24kHz and calculate C C :
C C = (V FB / V OUT )(R LOAD / R CS )(g M / 2 π x f C )
= (1.25 / 1.5)(6 / 0.6) x (135μS / (6.28 x 40kHz))
= 4.5nF
Choose 4.7nF.
Now select R C so transient-droop requirements are met.
For example, if 4% transient droop is allowed, the input
to the error amplifier moves 0.04 x 1.25V, or 50mV. The
error-amp output drives 50mV x 135μS, or 6.75μA across
R C to provide transient gain. Since the current-sense
transresistance is 0.6V/A, the value of R C that allows the
required load step swing is as follows:
R C = 0.6 x I IND(PK) / 6.75μA
In a step-down DC-DC converter, If L IDEAL is used, out-
put current relates to inductor current by the following:
I IND(PK) = 1.25 x I OUT
So for a 250mA output load step with V IN = 3.5V and
V OUT = 1.5V:
R C = (1.25 x 0.6 x 0.25) / 6.75μA = 27.8k Ω
Choose 27k Ω .
The inductor does somewhat limit the response in this
case since it ramps at (V IN - V OUT ) / 22μH, or (3.5 - 1.5)
/ 22μH = 90mA/μs.
The output filter capacitor is then chosen so the C OUT
R LOAD pole cancels the R C C C zero:
C OUT x R LOAD = R C x C C
For the example:
C OUT = 27k Ω x 4.7nF / 6 Ω = 21μF
Choose 22μF or greater.
If the output filter capacitor has significant ESR, a zero
occurs at:
?
?
Current-sense amplifier transresistance, R CS (0.6V/A)
Feedback regulation voltage, V FB (1.25V)
Z ESR = 1 / (2 π x C OUT x R ESR )
If Z ESR > f C , it can be ignored, as is typically the case
? Step-down output voltage, V SD , in V
? Output load equivalent resistance, R LOAD , in
Ω = V SD / I LOAD
The key steps for step-down compensation are as fol-
lows:
1) Set the compensation RC zero to cancel the R LOAD
C OUT pole.
2) Set the loop crossover below 1/10 the switching fre-
quency.
If we assume V IN = 3.5V, V OUT = 1.5V, and I OUT =
250mA, then R LOAD = 6 Ω .
If we select f OSC = 500kHz and L = 22μH,
with ceramic output capacitors. If Z ESR is less than f C ,
it should be cancelled with a pole set by capacitor C P
connected from CCSD to GND:
C P = C OUT x R ESR / R C
If C P is calculated to be <10pF, it can be omitted.
AUX Controller Component Selection
External MOSFET
MAX1584/MAX1585 AUX1(step-up) controllers drive
external logic-level N-channel MOSFETs. AUX3 (step-
down) controllers drive P-channel MOSFETs. AUX2
(step-up) on the MAX1584 drives an N channel, while
AUX2 (inverting) on the MAX1585 drives a P channel.
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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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