科技时代的发展LDO负载调整DC-DC已经成为趋势
2018-04-19 15:07:38
返回列表

科技时代的发展LDO负载调整DC-DC已经成为趋势

Improvement scheme

改进方案

As can be seen from Fig. 7, when adjusting the capacitance value of LDO output, the voltage dip will also become gentle. At the same time, the following two methods are adopted:

从图7可见,当调整LDO输出的电容值时,其电压跌落也会变得平缓,同时采取了以下两个办法:

LDO,DC-DC,MOSFETs,TVS,AC-DC,电压检测器,POWER IC,IGBT,MOS,负载开关,TOREX,茂捷,AOS,松木代理商_深圳市泰德兰电子有限公司

1) the LDO output series inductor is used to suppress the transient high current when the chip starts up through the saturation current of the inductor.

1)LDO输出串联电感,通过电感的饱和电流来抑制芯片启动时的瞬态大电流。


2) topology adjustment of input and output ends of the capacitor LDO, drop by the energy storage capacitor elimination.

2)调整LDO输入输出两端的电容的拓扑结构,通过电容储能来消除跌落。


Figure 8: an improved circuit

图8:改进后的电路

The load change rate of LDO is also a very important parameter, which is often a blind spot in the design. Finally, the author's circuit is shown in Figure 8. The inductor L1 and C77 are adjusted to 1000uF, and the restart is successfully solved.

LDO的负载变化率也是十分重要的参数,这往往也是设计中的一个盲区。最终笔者的电路如图8所示,增加了电感L1,C77调整到1000uF,重启的现象也成功解决。


summarize experience

经验总结


In the application of LDO chip, load adjustment rate is also a very important parameter. This parameter should be valued at the beginning of the selection of new product design. For the old products already used, when the load adjustment rate can not meet the requirements of actual use, the power design can meet the requirements of the system by controlling the instantaneous power of the back end load circuit and adjusting the topology structure of the LDO cascade, so that the product can run steadily.

在LDO芯片的应用中,负载调整率也是一个很重要的参数,在新产品设计的选型之初就应当重视这个参数。对老产品已经使用的芯片,当其负载调整率不能满足实际使用的要求时,通过控制后端负载电路的瞬间功率、调整LDO级联的拓扑结构等方法,可以使得电源设计满足系统要求,从而使产品稳定可靠地运行。


传统的DC-DC一般要求输入输出的压差在2~3V以上,随着时代的发展,这样的条件已经不能满足实际应用的需要。

The traditional DC-DC generally requires the input and output differential pressure to be over 2 ~ 3V. With the development of the times, such conditions can no longer meet the needs of practical applications.

例如在无线通信领域,GPRS模块常用到的电压是4V,经常是通过5V转换而来,输入输出的压差需低至1V。

For example, in the field of wireless communications, the voltage commonly used by GPRS modules is 4V, often through 5V conversion, and the input and output differential pressure should be as low as 1V.

针对这样的情况,于是LDO(Low dropout regulator)应运而生。

In view of this situation, LDO (Low dropout regulator) came into being.

LDO,DC-DC,MOSFETs,TVS,AC-DC,电压检测器,POWER IC,IGBT,MOS,负载开关,TOREX,茂捷,AOS,松木代理商_深圳市泰德兰电子有限公司

相对DC-DC而言,LDO的优点是噪音低,静态电流小。

Relative to DC-DC, LDO has the advantage of low noise and small quiescent current.

很多DC-DC在外围电路里还需要有电感和续流二极管,而LDO的典型电路非常简单,很多LDO只需在输入端及输出端各接一颗旁路电容就能够稳定工作,对于节省PCB的布局空间也很有优势。

Many DC-DC also need inductor and continuous current diode in the peripheral circuit, and the typical circuit of LDO is very simple. Many LDO only need to connect a bypass capacitor at the input and output side to work steadily, and it is also advantageous to save the layout space of PCB.

Ricoh推出的很多LDO,还具有如负载短路保护、过压关断、过热关断、反接保护等其它的功能。

Many of the LDO introduced by Ricoh also have other functions, such as load short circuit protection, overvoltage shutdown, overheat shutdown, reverse connection protection and so on.


很多硬件工程师在LDO的应用中主要考虑输入电压范围,输出电压和电流、压差、纹波、功耗、静态电流等,然而往往会忽略一个很重要的参数:负载调整率。

In the application of LDO, many hardware engineers mainly consider the range of input voltage, output voltage and current, voltage difference, ripple, power consumption, static current and so on. However, it often ignores a very important parameter: load adjustment rate.

本文就笔者在应用Ricoh的XC9516时由于忽视了负载调整率而来带的问题,并最终通过改进设计得到解决的过程,分享自己的一些经验。

In this paper, the author took the problem of ignoring the load adjustment rate when applying the XC9516 of Ricoh, and finally shared some experience through the process of improving the design.


问题描述

Problem description


笔者的电路如图1所示,系统12V转为5V,5V转换成3.3V和4V分别供MCU和通信模块。

The circuit of the author is shown in Figure 1. The system 12V is converted to 5V, and 5V is converted to 3.3V and 4V for MCU and communication module respectively.

由于通信模块是定时打开和关闭的,使用中发现只要U12(XC9516)的使能脚为低电平,系统就能正常工作,在MOD_EN拉高时,整个系统则被复位。

Since the communication module is opened and closed regularly, it is found that the system can work normally as long as the U12 (XC9516) can be used as a low level, and the whole system is reset when the MOD_EN is high.

图1:最初版原理图

Figure 1: the original schematic of the author's design


问题分析

problem analysis

LDO,DC-DC,MOSFETs,TVS,AC-DC,电压检测器,POWER IC,IGBT,MOS,负载开关,TOREX,茂捷,AOS,松木代理商_深圳市泰德兰电子有限公司

笔者最初是怀疑4V后端的电路短路,导致5V电源被拉底,但由于6台样机均会发生这个问题,4V短路的可能性被排除。

The author initially suspected that the back end of the 4V circuit was short circuited, causing the 5V power to be pulled down, but the possibility of 4V short circuit was ruled out because the 6 prototype would all have this problem.

实际上在电路中还有看门狗兼电源监控的设计,如图2所示,问题就发生在这里,其中的PW_EN脚直接控制5V转3.3V的LDO芯片。

In fact, there are also the watchdog and power monitoring design in the circuit, as shown in Figure 2, the problem occurs here, where the PW_EN foot directly controls the LDO chip of the 5V to 3.3V.

图2:看门狗电路

Figure 2: a watchdog circuit


笔者首先测量了系统各个电源在MOD_EN被拉高时的波形,得到波形如图3所示。

First, the waveforms of all the power sources in the MOD_EN are measured, and the waveforms are shown in Figure 3.

图3:系统各电源波形

Figure 3: the power waveform of the system


波形分析:图中从上至下依次为12V、5V、4V、3.3V波形,图中3.3V被拉低了184ms,需要进一步看一下5V和4V电源线上的尖峰细节。

Waveform analysis: from top to bottom, the graph is 12V, 5V, 4V, 3.3V waveform. 3.3V is lowered 184ms in the diagram. It needs to further look at the peak details of the 5V and 4V power lines.

将以上波形进行放大后,得到如图4所示波形图。

After enlarging the above waveform, we get the waveforms shown in Figure 4.

图4:系统各电源波形放大

Figure 4: power waveform magnification of the system

LDO,DC-DC,MOSFETs,TVS,AC-DC,电压检测器,POWER IC,IGBT,MOS,负载开关,TOREX,茂捷,AOS,松木代理商_深圳市泰德兰电子有限公司

波形分析:图中从上至下依次为12V、5V、4V、3.3V波形细节。

Waveform analysis: from top to bottom, the waveform is 12V, 5V, 4V and 3.3V.

图中5V电压被拉至2.3V,此电压低于2.63V时706会输出200mS复位信号。

The 5V voltage in the diagram is pulled to 2.3V. When the voltage is less than 2.63V, 706 will output the 200mS reset signal.

实测时间184mS,在测量的误差范围内,与706的电源监控复位时间相近,可继续监测706的复位信号,得到如图5、6所示波形。

The measured time 184mS, within the range of measurement error, is close to 706 of the power monitoring and reset time, and can continue to monitor the 706 reset signal, and get the waveform as shown in Figure 5 and 6.

图5:看门狗706的复位信号

Figure 5: the reset signal of the watchdog 706


波形分析:图中从上至下依次为12V、5V、4V、PW_EN波形细节。

Waveform analysis: from top to bottom, the waveform is 12V, 5V, 4V and PW_EN.

4V跳变的瞬间,RST输出了低电平复位信号,将5V转3.3V的LDO使能脚拉底。

At the instant of 4V jump, RST outputs a low level reset signal, and transfers the 5V to 3.3V LDO to the bottom.

图6:复位波形细节

Figure 6: reset waveform details


波形分析:在5V跌落后回升至3V前,看门狗706即输出了低电平复位信号,且复位信号分两段,在电源电压2.65V前后出现拐点,拐点前的跌落波形是随5V电源电压同步跌落;而拐点后的下降波形是看门狗芯片706监测到电源电压低于2.63V输出的复位信号。

Waveform analysis: before the 5V fall back to 3V, the watchdog 706 output the low level reset signal, and the reset signal is divided into two sections, the turn point appears before and after the power supply voltage 2.65V, the fall waveform before the turning point is synchronized with the 5V power supply voltage, and the drop wave after the turning point is watched by the dog chip 706 monitoring the power supply voltage below 2.6 The reset signal of the 3V output.

图7:XC9516手册上的负载调整率

The rate of load adjustment in figure 7:XC9516 manual

LDO,DC-DC,MOSFETs,TVS,AC-DC,电压检测器,POWER IC,IGBT,MOS,负载开关,TOREX,茂捷,AOS,松木代理商_深圳市泰德兰电子有限公司

通过查看XC9516的器件手册,发现其在负载突然变大时,输出电压由于不能及时调整而有瞬间的跌落。

By looking at the device manual of XC9516, it is found that when the load suddenly increases, the output voltage will drop instantaneously because it can not be adjusted in time.

对应到系统中,在使能4V电源LDO使能端的瞬间,因LDO后端有负载,瞬间电流的冲击,使得LDO输入和输出均有一定瞬间压降,系统把12V拉低至9.6V,更严重的是在50us内把5V电平拉低至2.6V以下,4.7V拉低到2.6V以下,引起电源监控芯片706输出复位信号,从而导致文头所述系统重启现象。

In the system, in the system, when the energy end of the 4V power LDO is made, the LDO input and output have a certain instantaneous voltage drop due to the load of the LDO back end and the impulse of the output. The system pulls the 12V down to 9.6V, and the more serious is to lower the 5V level to below 2.6V in 50uS, and 4.7V is lower to 2.6V below, causing the power monitoring chip 70. 6 output reset signal, which leads to system restart.





品质第一

品质第一

Quality first
价格合理

价格合理

price is reasonable
交货快捷

交货快捷

Fast delivery
服务至上

服务至上

Service-oriented
凝聚客户

凝聚客户

Convergence of customers
产品中心
AOS
茂捷
特瑞仕
松木
新洁能MOS管
解决方案
解决方案
关于我们
公司介绍
企业文化
组织架构
新闻中心
投诉建议
关注我们
微信公众号扫描
联系电话:0755-83322522
友情链接:电子元器件商城 合肥按摩椅专卖店 多级给水泵 电子负载 音频变压器 合肥大金中央空调 电子散热器 排针连接器 安全光栅 安检设备厂家 PE电熔管件 电池巡检仪 植物灯电源 电动洗地机 电位器厂家 工业液晶显示器 usb数据线厂家 光纤通信 香烟批发 触控一体机 湖南中央空调

QQ客服联系客服

联系电话0755-83322522