Analyze and employ the skill in parameter of the voltage reference chip
The voltage reference chip is a kind of high-performance simulation chip, always use in various data collecting systems, realize high-accuracy data acquisition. Nearly all voltage reference chips are here in order to be realized ” High precision ” And diligent, but should really realize high precision in all kinds of application, need to find out about the meaning of the internal structure and every parameter of the voltage reference, and should know some essential application skills.
Classification of the voltage reference chip
Produce the structure differently according to the internal reference voltage, the voltage reference is divided into: Two kinds voltage references of band gap and regulator tube voltage references. Band gap voltage one the intersection of forward bias and PN junction and first and VT in benchmark architecture ‘ Thermoelectric force) The associated voltage connects in series, utilize negative temperature coefficient of PN junction to offset and realize temperature compensation with the positive temperature coefficient of VT. The tube-voltage benchmark architecture of voltage regulation is to connect a regulator tube of each surface breakdown and a PN junction in series, utilize positive temperature coefficient of the regulator tube to offset and realize temperature compensation with the negative temperature coefficient of the PN junction. Surface breakdown once helps to reduce the noise. Great of reference voltage (about 7V) of the voltage reference of the regulator tube ; And the reference voltage of the band gap voltage reference is lower, because employed more extensively on condition that required the low service voltage hereafter person.
On the basis of the external application structure, the voltage reference is divided into: Two kinds series type and parallel. While employing, the voltage reference of the series type is similar to stabilized voltage supply of three terminal, reference voltage and supporting connecting in series; The voltage reference of the parallel is similar to regulator tube, reference voltage and supporting connecting in parallel. The voltage references and regulator tube voltage references of band gap can all be applied to these two kinds of structure. The advantage of the voltage reference of the series type lies in, only demand to input the quiescent current that the power offers the chip, and offer the load current while existing in load; Voltage group criterion of the parallel demands to be greater than the quiescent current of the chip and summation of load current of the maximum in bias current set up, not fit for the application of low power consumption. The advantage of the voltage reference of the parallel lies in, adopt the electric current to bias and can satisfy very wide input voltage range, and is suitable for doing the Floating voltage reference.
The voltage reference chip parameter is analyzed
Set up Ken ‘ Beijing) The ICN25XX series voltage reference that the microelectronics will be put out soon, it is a series of high precision, the series type voltage reference of low power consumption, adopt smaller SOT23-3 to capsulate, offer 1.25V, 2.048V, 2.5V, 3.0V, 3.3V, 4.096V output voltage, and offer good temperature drift characteristic and noise characteristic.
Fig. 1. Voltage reference chip and parallel voltage reference chip synoptic diagram of series type
Table 1 has listed every parameter of the voltage reference chip correlated to precision. Should consider the original precision of the output voltage first. The voltage reference chips of different types, the original precision may be varied from 0.02% to 1%. This means they can reach different system accuracy, system accuracy that can adapt to 12 0.02%, 1% system accuracy that can adapt to 6 s. As to the system unable to normalize by oneself, need to choose the appropriate chip of original precision according to the accuracy requirement. Most system artificers can normalize and adjust the original trueness error through the software or hardware, so the original precision does not limit the applied key factor of the voltage reference chip.
Table 1. Specification of the voltage reference chip.
The temperature drift coefficient of the output voltage is an important parameter of weighing the voltage reference chip characteristic. It represents a average stream flow, can pass the output voltage of this parametric evaluation chip on the operating temperature -wide excursion, this parameter does not represent temperature variant slope of output voltage of a certain particular temperature point. Reduced by very much difficult method to normalize through the system of trueness error that the temperature drift lead to the fact.
The temperature drift characteristic that compensator circuit and regulation that the ICN25XX series voltage reference chip adopts the patent are with good circuit implementation: Here – 40 Does C reach 125 In C temperature range, is the drift coefficient of the temperature smaller than 10ppm/ C. Fig. 2 tests the typical temperature drift curve.
Fig. 2. ICN2520 typical temperature drift curve
The output voltage of the voltage reference chip will increase and change with duration, change according to exponential behavior at the same direction usually, duration the longer, change the smaller, so regard formula 1 as the long term stability of the voltage reference chip of the unit representation, in order to reflect the variable quantity of the output voltage is up to duration exponential decay. Long term stability is embodied in even a few years’ using process of several months, it is very difficult to guarantee by test when being dispatched from the factory. The ageing test for some time, in order to guarantee better long term stability that some chips will be before being dispatched from the factory. Normalize the system regularly, can avoid the error that long term stability brings. To the system that can’t be normalized regularly, will select the apparatus to have the voltage reference chip of good long term stability soon. Adopt the metal envelope encapsulated chip, because of getting rid of the influence of capsulating the stress, therefore generally have better long term stability.
The noise is another important parameter of weighing the characteristic of the voltage reference chip. Usually provide the noise parameter in two frequency domains of 10kHz in 0.1Hz to 10Hz and 10Hz, so that the artificer estimates the voltage reference in inner noises of frequency domain paid close attention to. The output noise is usually proportional to output voltage, regard ppm as the unit. 0.1Hz is mainly flicker noise to the noise of 10Hz, or is called 2 noises of formula, its noise amplitude is in inverse proportion to frequency, will generally provide the peak-to-peak value (P-P) of the internal noise of this frequency domain . Different semiconductor device glimmer noise characteristic differ significantly, for example the flicker noise of MOSFET is larger, and the flicker noise of bipolar transistor is much smaller, the regulator tube flicker noise of surface breakdown once is very light, so adopt the voltage reference chip of different technological design, the difference of noise characteristic of low frequency will be greater.
Fig. 3. Noise characteristic curves of ICN2520 voltage reference chip
It is mainly thermal noise 10Hz is and higher than the noise in this frequency domain to 10kHz frequency domain, the frequency character is basically smooth in the effective bandwidth, through the noise mean value (rms) provided Can estimate very easily out the inner thermal noise of a certain frequency domain. Increasing the electric current can reduce the noise effectively, so the fine noise characteristic often regards sacrificing power consumption as cost. Users can add Filtering capacitance or other smoothing circuit to limit noise bandwidth on the Ausgang of voltage reference, in order to improve the noise characteristic, thus reach the designing requirement.
The ICN25XX series voltage reference chip adopts the special internal structure, has reached the low noise level that the cmos process is usually very difficult to realize: 0.1Hz to 10Hz is 13ppm (P-P) ; 10Hz to 10kHz is 32ppm (rms) ; And kept CMOS technological power consumption advantage, the quiescent current is only 75A.
Some application will have requirements to the step response of the voltage reference chip. Step response includes three respects: Power up build-up time, dwarf signal output impedence ( High frequency) , big the intersection of signal and recover time ‘ Dynamic load) . The step response of voltage reference chip which different manufacturers introduce may have very big difference, good step response too often regard sacrificing power consumption as cost. The internal integrated buffer amplifier of ICN25XX series voltage reference, adopt the special construction, can offer good step response, linear regulation factor and load regulation, inner stability of the range that and can guarantee the Filtering capacitance of very large output.
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