[introduction] join the power source track of a taller voltage will slant the in-house circuit of buy linear manostat, make manostat can produce the low output tension of a 0.9V, this output voltage can bear 4A twinkling changes, change is very little.

Generally speaking, DC-DC switch manostat is fixed voltage output. Have method to use a number to control signal, is the trends that realizes power source to output voltage adjusted? How does article introduction use converter of ADI appropriative digital-to-analogue (DAC) LTC7106, the trends that realizes power source to output voltage is adjusted.

The trends that how realizes power source to output voltage is adjusted?

Resistor cent presses circuit + potentiometer

The trends that outputs voltage to DC-DC switch manostat is adjusted, the commonnest practice is to install resistor cent to press circuit. Pursue as follows, we use a potentiometer (Potentiometer) will replace divide among them press resistor RFB1, active voice adjusts the voltage of DC-DC switch manostat to output.

Graph 1: Use potentiometer will adjust DC-DC switch manostat to output (picture origin: ADI)

This method is very effective, but need our hand to move an operation. If need to use a number to control signal to control output voltage, a tweak is above feedback node VFB inputs or negaive electricity flows. Accordingly, we need a small-sized DAC that adjust output voltage technically for trends and develops.

Resistor cent presses circuit + DAC

We the DAC LTC7106 citing with ADI: Pursue as follows, LTC7106 presses circuit to export an electricity to resistor cent, make the voltage change that feedback of DCDC switch manostat makes crural VFB go up, make voltage of output of DC-DC switch manostat OK thereby control signal according to the number and change.

Graph 2: LTC7106 DAC accepts method of feedback of DC-DC power source (picture origin: ADI)

This kind of method raised a requirement to DAC. When DAC controls signal without the number, cannot have voltaic output, may make otherwise when DC-DC switch manostat is being started, needless voltage appears.

Special DAC can overcome this one phenomenon, for instance the LTC7106 of ADI is this kind of application technically namely and design. The number with significant short of controls signal, LTC7106 output brings crural IDAC to go up to do not have electric current (namely tall impedance) , during avoiding circuit to start thereby, the voltage that appears not to need.

LTC7106 is 7 DAC, can realize highest 1 LSB (lowest is effective) , the resolution of 1 μ A. We can design appropriate resistor cent to press circuit according to the character of DAC, will match the precision of DAC. We design example to explain through below.

Be based on the design example of LTC7106

Pursue as follows, use LTC7150S regards DC-DC switch as manostat, offer 1.5V voltage output. Assume we need power source to arrive in 1.5V between 1.0V now to power source output voltage undertakes trends is adjusted.

Graph 3: LTC7106 devises example (picture origin: ADI)

According to LTC7106 data manual, VFB=0.6V, because of this VOUT = 0.6V X [1 = (RFB1/RFB2) ]

Range of IDAC of LTC7106 output electric current is bigger, the precision of LTC7106 is better. It is normal that the IDAC of LTC7106 outputs limits to be in (Normal) below mode, can arrive – 63 μ A arrives + 63 μ A.

Choose RFB1=10k suppose? , RFB2=6.65k? , the basis is formulary:

We are OK derivation gives IDAC range: IDAC = (1.5V – 1.0V) / 10k? A of μ of = + 50.

Assume IDAC lowest is effective a LSB=1 μ A, the output voltage limits of Vout arrives for 1.5V 1.0V.

Use LTC7106 development board simplifies development technological process

We also can use LTC7106 development board DC2620A-A will shorten development technological process.

Graph 4: LTC7106 is developed board DC2620A-A

DC2620A-A can join through interface module DC1613A computer

Graph 5: DC2620A-A join computer (picture origin: ADI)

LTpowerPlay graph user interface can show on computer. The control signal on computer passes PMBus or I2C controls LTC7106.

Graph 6: LTpowerPlay graph user interface (picture origin: ADI)

LTpowerPlay still is offerred diagnose and debug a function, use at process designing or the power source in adjusting a system to run program, or power source problem is diagnosed when course of the power supply that start.

Article brief summary

Use LTC7106 is OK very the trends that allows implementation power source to output voltage is adjusted, move reliable. Those who need an attention is DAC output precision has an error, if LTC7106 is inside whole temperature limits, outputting ± 0.8% , negative output ± 1.5% . Must take care to design, inside the reasonable range that ensures control loop stability and output voltage ripple need to output voltage in place thereby.

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