LTC2644芯片初步测试

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• LTC2644 Datasheet

01 LTC2644芯片特性

一、前言

  LTC2644是一款高精度的PAC芯片，  可以将 PWM 波形转换成与占空比成正比的模拟电压。  正好手边有一个小电路中使用了这颗芯片。  下面将其拆卸下来进行测试， 为后面的应用设计提供基础。

二、测试电路

AD\Test\2024\March\TestLTC2644STM32.SchDoc

  设计测试电路原理图，  利用STM32F103单片机输出PWM信号，  TIME1 的 第1，第4 PWM通道控制LTC2644。 输出模拟电压信号通过 P-OUT端口输出。  设置IDLSEL为低电平， 在PWM空闲状态下， 输出电压电平与PWM静态逻辑电平对应。  设置REFSEL为低电平， 选择内部2.5V参考电压。  使用AS1117将输入5V电源转换成3.3V 工作电源。  LED指示单片机工作状态，  利用UART BOOTLOADER进行软件下载。 下面设计PCB板。  使用单面布板， 这样可以利用一分钟制板方法快速获得测试电路收。 布通之后的PCB， 带有三个跳线。

三、焊接测试

  将电路板固定在调试台上，  提供5V工作电压。 由于这个单片机是拆卸的原来电路板上旧的单片机，  所以现在单片机上电之后已经开始工作了。 这说明电路板一切正常。

四、动态特性

  设置PWM占空比线性增加， 输出锯齿波。  输出的正弦波也非常完美。

五、输出精度

  测试 LTC2644的线性精度，  设定PWM占空比从1% 上升到 10%， 测量输出电压。  测量结果显示， 输出电压与PWM 占空比之间呈现线性关系。  对PWM占空比与电压进行线性拟合。 数据符合的非常好。  测量数据与拟合数值见得误差都在 0.25mV之内。 这个数据波动对于 满量程2.5V来说， 精度非常高。

from headm import * from tsmodule.tsvisa import * from tsmodule.tsstm32 import * pwm = list(range(100)) vdim = [] dm3068open() for p in pwm: stm32cmd("pwm %d"%(p+1)) time.sleep(1.5) v = dm3068vdc() vdim.append(v) tspsave('measure', pwm=pwm, vdim=vdim) printff(p, v) plt.plot(pwm, vdim, lw=3) plt.xlabel("PWM") plt.ylabel("Voltage(V)") plt.grid(True) plt.tight_layout() plt.show() 

pwm=[0.00,1.00,2.00,3.00,4.00,5.00,6.00,7.00,8.00,9.00,10.00,11.00,12.00,13.00,14.00,15.00,16.00,17.00,18.00,19.00,20.00,21.00,22.00,23.00,24.00,25.00,26.00,27.00,28.00,29.00,30.00,31.00,32.00,33.00,34.00,35.00,36.00,37.00,38.00,39.00,40.00,41.00,42.00,43.00,44.00,45.00,46.00,47.00,48.00,49.00,50.00,51.00,52.00,53.00,54.00,55.00,56.00,57.00,58.00,59.00,60.00,61.00,62.00,63.00,64.00,65.00,66.00,67.00,68.00,69.00,70.00,71.00,72.00,73.00,74.00,75.00,76.00,77.00,78.00,79.00,80.00,81.00,82.00,83.00,84.00,85.00,86.00,87.00,88.00,89.00,90.00,91.00,92.00,93.00,94.00,95.00,96.00,97.00,98.00,99.00] vdim=[0.00,0.01,0.01,0.01,0.01,0.02,0.02,0.02,0.02,0.03,0.03,0.03,0.03,0.04,0.04,0.04,0.04,0.05,0.05,0.05,0.05,0.06,0.06,0.06,0.06,0.07,0.07,0.07,0.07,0.08,0.08,0.08,0.08,0.09,0.09,0.09,0.09,0.10,0.10,0.10,0.10,0.11,0.11,0.11,0.11,0.12,0.12,0.12,0.12,0.13,0.13,0.13,0.13,0.14,0.14,0.14,0.14,0.15,0.15,0.15,0.15,0.16,0.16,0.16,0.16,0.17,0.17,0.17,0.17,0.18,0.18,0.18,0.18,0.19,0.19,0.19,0.19,0.20,0.20,0.20,0.20,0.21,0.21,0.21,0.21,0.22,0.22,0.22,0.22,0.23,0.23,0.23,0.23,0.24,0.24,0.24,0.24,0.25,0.25,0.25] 

from headm import *
from scipy.optimize        import curve_fit

pwm, vdim = tspload('measure', 'pwm', 'vdim')

def linefun(x, a, b):
    return a*x + b

param = (1/e-3, 0)
param, conv = curve_fit(linefun, pwm, vdim, p0=param)
printf(param)

vfit = linefun(pwm, *param)
err = [v1-v2 for v1,v2 in zip(vdim, vfit)]

plt.plot(pwm, err, lw=3, label='Error')

plt.xlabel("PWM")
plt.ylabel("Voltage(V)")
plt.grid(True)
plt.legend(loc="upper right")
plt.tight_layout()
plt.show()

※ 总结. ※

  本文对于 LTC2644 这款PAC芯片进行了测试，  无论是动态响应， 还是输出线性精度， 都非常高。   相比前几天测试的 GP8101来说， 性能的确高了一大截。

■ 相关文献链接:

• LTC2644 Datasheet

● 相关图表链接:

• 图1.2.1 测试电路原理图
• 图1.5.1 占空比从1%到10%过程中对应的输出电压
• 图1.5.2 对测量数据进行线性拟合
• 图1.5.3 测量结果线性拟合误差