Generally speaking,
DC-DC switching regulators
have fixed voltage outputs. Is there a way to use digital control signals to dynamically adjust the power supply output voltage? This article describes how to use
ADI
's dedicated digital-to-analog converter (DAC)
LTC7106
to dynamically adjust the power supply output voltage.
How to achieve dynamic adjustment of power supply output voltage?
Resistor voltage divider circuit + potentiometer
The most common way to dynamically adjust the output voltage of a DC-DC switching regulator is to set up a resistor divider circuit. As shown in the figure below, we use a
potentiometer
to
replace
one of the voltage divider resistors to dynamically adjust the voltage output of the DC-DC switching regulator.
Figure 1: Using a potentiometer to adjust the output of a DC-DC switching regulator (Image source: ADI)
This method works well, but it requires manual operation. If we need to use a digital control signal to control the output voltage, a good way is to input a positive or negative current into the upper feedback node. Therefore, we need a small DAC specially developed for dynamically adjusting the output voltage.
Resistor voltage divider circuit + DAC
Let's take ADI's DAC
LTC7106
as an example: As shown in the figure below, LTC7106 outputs a current to the resistor divider circuit, causing the voltage on the feedback pin of the DCDC switching regulator to change, so that the output voltage of the DC-DC switching regulator can be changed according to the digital control signal.
Figure 2: The LTC7106 DAC is connected to the DC-DC power supply feedback path (Image source: ADI)
This method places a requirement on the DAC: when the DAC has no digital control signal, there can be no current output, otherwise unnecessary voltage may appear when the DC-DC switching regulator starts.
A dedicated DAC can overcome this phenomenon, such as ADI's LTC7106, which is designed specifically for this application. As long as there is no valid digital control signal, there is no current (i.e. high impedance) on the LTC7106 output pin IDAC, thus avoiding the appearance of unwanted voltage during circuit startup.
The LTC7106 is a 7-bit DAC that can achieve a resolution of up to 1 LSB (
least significant bit
) and 1 μA. We can design a suitable resistor divider circuit based on the characteristics of the DAC to match the accuracy of the DAC. Let's use a design example to illustrate this.
Design Example Based on LTC7106
As shown in the figure below,
LTC7150S
is used
as a DC-DC switching regulator to provide a 1.5V voltage output. Suppose we now need the power supply to dynamically adjust the power supply output voltage between 1.5V and 1.0V.
Figure 3: LTC7106 design example (Image source: ADI)
According to
the LTC7106 data sheet
,
The larger the LTC7106 output current IDAC amplitude, the better the accuracy of the LTC7106. The LTC7106 IDAC output range in normal mode can reach -63μA to +63μA.
Assuming that =10k
Ω
, =6.65k
Ω
are selected
, according to the formula:
We can deduce the IDAC range: IDAC = (1.5V–1.0V)/10kΩ
=
+50μA.
Assuming that the least significant bit of
IDAC
LSB = 1μA, the output voltage range of Vout is 1.5V to 1.0V.
Simplify the development process with the LTC7106 development board
We can also use the LTC7106 development board
DC2620A-A
to shorten the development process.
Figure 4: LTC7106 development board DC2620A-A
Figure 5: DC2620A-A connected to a computer (Image source: ADI)
The LTpowerPlay
graphical user interface
can be displayed on the computer
. The control signals from the computer control the LTC7106 via PMBus or
I2C
.
Figure 6: LTpowerPlay graphical user interface (Image source: ADI)
LTpowerPlay also provides diagnostic and debug capabilities for programming or adjusting the power management scheme in a system or diagnosing power supply problems when bringing up a supply rail.
Using LTC7106, it is easy to achieve dynamic adjustment of power supply output voltage and reliable operation. It should be noted that the DAC output accuracy has errors. For example, the positive output of LTC7106 is ±0.8% and the negative output is ±1.5% over the entire temperature range. Careful design must be made to ensure that the control loop stability and output voltage ripple are within the reasonable range of the required output voltage.
If you like this article, please like and share it! For more articles on power management, please click the link below. You are also welcome to leave a comment below to discuss.
Results of the May Points Lottery Announced
Monthly Points Prize Draw Program Launched in 2022
Gain support from many partners
Congratulations to the following
10 winners
!
This month's gift is:
Direct recharge for phone bills and data traffic￥
20
The results are announced as follows
✦
|
Name
|
Mobile Number
|
|
Chen Haihui
|
157*****175
|
|
Kong Fanzhi
|
181*****160
|
|
Shan Xinwei
|
139****038
|
|
Mao Jiacai
|
158*****620
|
|
Wang Jinbo
|
133*****079
|
|
Bai Jingdong
|
139****896
|
|
Song Zhangyu
|
134*****798
|
|
Tian Lifeng
|
159*****439
|
|
Lai Jingfeng
|
181*****191
|
|
Lugali
|
132*****323
|
Please reply as soon as possible with the mobile number you want to recharge
and telecom operators
Will be recharged within 14 days after the results are announced
Please wait
Do you also want to participate but are afraid of missing out on the chance to redeem the monthly lucky draw?
Come and register the alarm
Send reminder messages at the end of each month to remind you of the redemption date
If you
think this content is good
Please forward or share to
Moments
DK
Member Center
Center
Welfare
Have you joined?
Points can be exchanged for various gifts
Several new gifts have been added, while stocks last
if there is any problem
,
Welcome to contact Digi-Key
Digi-Key
Customer Service Team
China (RMB) Customer Service
Support > Contact Customer Service > WeChat Customer Service
QQ online real-time consultation | QQ number: 4009201199
China (US dollars) / Hong Kong Customer Service
china.support@digikey.com
Search for "digikey"
or "
Digikey Electronics"
on WeChat,
follow our official WeChat account and register as a member to receive engineers' tips every week, earn points, exchange for gifts, and enjoy benefits.
↙
Click "Read More" below to see more
Let me know you
're
watching
京公网安备 11010802033920号