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| 型号： | MAX1567ETL+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 28/35页 |
| 文件大小： | 0K |
| 描述： | IC DGTL CAM PWR-SUP 6CH 40TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 应用： | 控制器，数字式相机 |
| 输入电压： | 0.7 V ~ 5.5 V |
| 输出数： | 7 |
| 输出电压： | 1.25 V ~ 5 V |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 供应商设备封装： | 40-TQFN-EP（6x6） |
| 包装： | 管件 |
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Six-Channel, High-Efficiency, Digital
Camera Power Supplies
The inductor is typically selected to operate with contin-
uous current for best efficiency. An exception might be
if the step-up ratio, (V OUT / V IN ), is greater than 1 / (1 -
D MAX ), where D MAX is the maximum PWM duty factor
of 80%.
When using the step-up channel to boost from a low
input voltage, loaded startup is aided by connecting a
Schottky diode from the battery to PVSU. See the
Minimum Startup Voltage vs. Load Current graph in the
Typical Operating Characteristics .
Step-Up Inductor
In most step-up designs, a reasonable inductor value
(L IDEAL ) can be derived from the following equation,
which sets continuous peak-to-peak inductor current at
1/2 the DC inductor current:
L IDEAL = [2V IN(MAX) x D(1 - D)] / (I OUT x f OSC )
where D is the duty factor given by:
D = 1 - (V IN / V OUT )
Given L IDEAL , the consistent peak-to-peak inductor cur-
rent is 0.5 I OUT / (1 - D). The peak inductor current,
I IND(PK) = 1.25 I OUT / (1 - D).
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.
Step-Up Compensation
The inductor and output capacitor are usually chosen
first in consideration of performance, size, and cost. The
compensation resistor and capacitor are then chosen to
optimize control-loop stability. In some cases, it may
help to readjust the inductor or output-capacitor value to
get optimum results. For typical designs, the component
values in the circuit of Figure 1 yield good results.
The step-up converter employs current-mode control,
thereby simplifying the control-loop compensation.
When the converter operates with continuous inductor
current (typically the case), a right-half-plane zero
appears in the loop-gain frequency response. 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 right-half-plane zero.
The relevant characteristics for step-up channel com-
pensation are as follows:
? Transconductance (from FB to CC), gm EA (135μS)
? Current-sense amplifier transresistance, R CS
(0.3V/A)
? Feedback regulation voltage, V FB (1.25V)
? Step-up output voltage, V SU , in V
? Output load equivalent resistance, R LOAD , in ? =
V OUT / I LOAD
The key steps for step-up compensation are as follows:
1) Place f C sufficiently below the right-half-plane zero
(RHPZ) and calculate C C .
2) Select R C based on the allowed load-step transient.
R C sets a voltage delta on the C C pin that corre-
sponds to load-current step.
3) Calculate the output-filter capacitor (C OUT ) required
to allow the R C and C C selected.
4) Determine if C P is required (if calculated to be
>10pF).
For continuous conduction, the right-half-plane zero fre-
quency (f RHPZ ) is given by the following:
f RHPZ = V OUT (1 - D) 2 / (2 π x L x I LOAD )
where D = the duty cycle = 1 - (V IN / V OUT ), L is the
inductor value, and I LOAD is the maximum output cur-
rent. Typically target crossover (f C ) for 1/6 of the RHPZ.
For example, if we assume f OSC = 500kHz, V IN = 2.5V,
V OUT = 5V, and I OUT = 0.5A, then R LOAD = 10 ? . If we
select L = 4.7μH, then:
f RHPZ = 5 (2.5 / 5) 2 / (2 π x 4.7 x 10 -6 x 0.5) = 84.65kHz
Choose f C = 14kHz. Calculate C C :
C C = (V FB / V OUT )(R LOAD / R CS )(gm / 2 π x f C )(1 - D)
= (1.25 / 5)(10 / 0.3) x [135μS / (6.28 x 14kHz)] (2/5)
= 6.4nF
Choose 6.8nF.
Now select R C so transient-droop requirements are
met. As an 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 0.3V/A, the value of R C
that allows the required load-step swing is as follows:
R C = 0.3 I IND(PK) / 6.75μA
In a step-up DC-to-DC converter, if L IDEAL is used, out-
put current relates to inductor current by:
I IND(PK) = 1.25 I OUT / (1 - D) = 1.25 I OUT x V OUT / V IN
So, for a 500mA output load step with V IN = 2.5V and
V OUT = 5V:
R C = [1.25(0.3 x 0.5 x 5) / 2)] / 6.75μA = 69.4k ?
Note that the inductor does not limit the response in this
case since it can ramp at 2.5V / 4.7μH, or 530mA/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
28
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1567ETL+ | 功能描述:PMIC 解决方案 6Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安装风格:SMD/SMT 封装 / 箱体:QFN-24 封装:Reel |
| MAX1567ETL+T | 功能描述:PMIC 解决方案 6Ch Digital Camera Power Supply RoHS:否 制造商:Texas Instruments 安装风格:SMD/SMT 封装 / 箱体:QFN-24 封装:Reel |
| MAX1567ETL-T | 功能描述:PMIC 解决方案 RoHS:否 制造商:Texas Instruments 安装风格:SMD/SMT 封装 / 箱体:QFN-24 封装:Reel |
| MAX1567EVKIT | 制造商:Maxim Integrated Products 功能描述:6-CHANNEL HIGH EFFICIENCY DIGITAL CAMERA POWE - Bulk |
| MAX1567SUMEVKIT | 制造商:Maxim Integrated Products 功能描述:6-CHANNEL HIGH EFFICIENCY DIGITAL CAMERA POWE - Bulk |
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