CXAS42304 is a high-performance single channel analog front-end chip, specifically optimized for electronic temperature guns and high-precision low-frequency measurement applications. The chip adopts advanced ∑ - Δ conversion technology to achieve 24 bit lossless code performance and can directly process weak differential signals from sensors. It integrates a programmable gain amplifier (fixed gain 128 times) and a digital filter internally, supporting fully differential analog input and external reference voltage input. It is worth mentioning that the chip is equipped with a high-precision digital temperature sensor, which can directly measure the temperature of the chip, providing convenience for temperature compensation and system monitoring.
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[ CXAS42304 ]"
CXAS42304 high-precision electronic thermometer dedicated analog front-end chip: single channel 24 bit ADC detailed explanation
In the fields of medical electronics, industrial measurement and control, and consumer electronics, high-precision temperature measurement and low-frequency signal acquisition impose strict requirements on analog front-end chips. CXAS42304 is a single channel analog front-end chip designed specifically for electronic thermometers and high-precision low-frequency measurement systems, integrating 24 bitΣ -Δ ADC、 Low noise amplifiers and on-chip temperature sensors provide system designers with a complete solution that is highly integrated, low-power, and high-precision. This article will comprehensively analyze the technical characteristics, application design, and system advantages of CXAS42304, helping engineers achieve high-performance measurement system design.
1、 Chip Overview and Market Positioning
CXAS42304 is a high-performance single channel analog front-end chip, specifically optimized for electronic temperature guns and high-precision low-frequency measurement applications. The chip adopts advanced&Sigma technology; -Δ Conversion technology enables 24 bit lossless code performance and can directly process weak differential signals from sensors. It integrates a programmable gain amplifier (fixed gain 128 times) and a digital filter internally, supporting fully differential analog input and external reference voltage input. It is worth mentioning that the chip is equipped with a high-precision digital temperature sensor, which can directly measure the temperature of the chip, providing convenience for temperature compensation and system monitoring.
Compared with the multi-channel version, CXAS42304 achieves smaller package size and lower system cost through optimized architecture while maintaining high performance, making it particularly suitable for portable devices with limited space, such as electronic thermometers, environmental monitors, and industrial sensor nodes.
2、 Core functional features
· Single channel fully differential inputSupports a pair of fully differential analog inputs, effectively suppressing common mode interference
· 24 bit high-precision ADCNo loss of code performance, ensuring measurement accuracy
· On-chip temperature sensorDirectly output digital temperature values to simplify system design
· Fixed high gain128 times low-noise amplifier, suitable for amplifying small signals
· Excellent linearityNonlinear error is only± 0.001%, ensuring full range accuracy
· Strong anti-interference abilitySynchronous suppression of 50Hz/60Hz power interference
· Built in clock oscillatorNo need for external crystals or clock circuits
· Simple serial interfaceTwo line communication (PD_SCK and DOUT)
· Wide voltage operation2.6V-5.5V single power supply
· Multiple packaging optionsSOP8, DIP8, TSSOP8 meet different installation requirements
3、 Pin function and system connection
CXAS42304 adopts a compact 8-pin package with clear pin definitions for easy system layout:
· VREF (Pin 1)Reference voltage input, supports 1.8V to AVDD range
· AGND (Pin 2)Simulated ground, providing reference ground for analog circuits
· AIN -/- AIN+(pin 3/4)Differential analog input negative/positive terminal
· PD_SCK (Pin 5)Power off control and serial clock input
· DOUT (pin 6)Serial data output
· DVDD/AVDD (pins 7/8): Digital/Analog Power Input
In practical applications, it is important to note that the AVDD voltage should not be higher than the DVDD voltage, and all unused digital input pins should be connected to appropriate levels to avoid floating.
4、 Electrical characteristics and performance parameters
Under recommended working conditions, CXAS42304 exhibits excellent measurement performance:
· Effective resolutionProvide 16 bit noise free accuracy at a 10Hz output rate
· Input voltage rangeThe differential input range is± 0.5× (VREF/128)V
· Common mode input rangeAGND+0.9V to AVDD-1.3V
· temperature measurement15 bit effective accuracy, range -40 ℃ to+85 ℃
· Power consumption characteristicsWhen powered by 3V, the working current is only 1080 A, and the standby current is as low as 0.5 A
· ESD protectionHBM mode 4000V, MM mode 300V
These parameters ensure that the chip can maintain stable and reliable performance even in harsh environments, making it particularly suitable for battery powered portable devices.
4.1. Absolute maximum rated value range
Note: If the device is forced to operate beyond the conditions listed in this table, it may cause permanent damage to the device. This table only lists the working conditions
The limit of stress does not mean that the device can operate under the conditions listed in the table, or other conditions that exceed the specified operating range
Under the item. Long term operation at absolute limits may affect the lifespan of the device.
4.2. Recommended working conditions range
(at -40 ℃~+85 ℃) Unless otherwise specified
5、 Serial Communication and Data Reading Mechanism
CXAS42304 achieves simplified two-wire serial communication through PD_SCK and DOUT. When DOUT becomes low, it indicates that the conversion data is ready. At this time, the host should input 25-27 clock pulses through PD_SCK: the first 24 pulses are used to read the current conversion data (from the highest bit to the lowest bit), and the 25-27 pulses are used to select the input source and rate for the next conversion.
The specific configuration is as follows:
· 25 pulsesSelect differential signal input, 10Hz output rate
· 26 pulses: Select temperature measurement, 10Hz output rate
· 27 pulsesSelect differential signal input, 10Hz output rate
The communication timing parameters are strictly defined, such as T1 (from DOUT falling edge to PD_SCK rising edge) with a minimum of 0.1 μ s, T3&# 39; The PD_SCK high-level time should be within the range of 0.2-50 ms, and the design should ensure compliance with these timing requirements.
The serial communication cable is connected by pin PD_SCK; And DOUT Composition, used for outputting data, selecting output data rate and input signal.
When the data output pin DOUT is at a high level, it indicates that A/D; The converter is not ready to output data yet. At this time, the serial clock input
The signal PD_SCK should be at a low level. When DOUT changes from high level to low level, PD_SCK should input 25 to 27 different clocks
Pulse (Figure 3). The rising edge of the first clock pulse will read out the highest bit (MSB) of the output 24 bit data until the 24th; At that moment
The clock pulse is completed, and the 24 bit output data is outputted bit by bit from the highest bit to the lowest bit. The 25th to 27th clock pulses are used to select the next one
The output data rate and input signal of the A/D conversion are shown in Table 4. The number of input clock pulses for PD_SCK should not be less than 25 or more than
27, otherwise it will cause serial communication errors.
When A/D; When the input signal or output data rate of the converter changes, the A/D converter requires 4 data output cycles to stabilize.
DOUT After 4 data output cycles, it will change from high level to low level and output valid data.
5.2. Output noise
Table 6 Indicates the number of noise free bits output by CXAS42304. The provided data is applicable to both AVDD and VREF with 5V bipolar input range
Surrounding. These data are typical values and were generated under simulated differential input voltage of 0V.
5.3. Analog input
5.3.1. Channel Analog Input Range:
CXAS42304 includes one analog input pair, namely AIN+and AIN -. Input pairs provide differential inputs that can handle single and bipolar input signals
Enter the channel. It should be noted that bipolar input signals are referenced to the AIN terminal.
The analog differential input voltage range is± 0.5 × (VREF/128) V, the absolute value of the analog input voltage is at; AGND+0.9V and
AVDD-1.3V.
5.3.2 Benchmark Input:
VREF provides the reference input for CXAS42304. The reference voltage input range is 1.8V to AVDD.
5.4 System clock and AD data update rate
5.4.1 System Clock:
The system clock of CXAS42304 is provided by an internal oscillator, which is a high-precision oscillator with ultra-low dependence on VDD and temperature.
5.4.2 AD data update rate:
CXAS42304 provides an output data rate of 10Hz.
5.5. Output Data
The output data encoding of CXAS42304 is binary complement, ranging from 800000H (minimum value) to 7FFFFFH (maximum value).
6、 Detailed explanation of temperature measurement function
One of the outstanding features of CXAS42304 is its built-in digital temperature sensor. The sensor provides 15 bit effective accuracy, with a typical temperature measurement accuracy of 20.4 readings per degree Celsius. The temperature measurement range is -40 ℃ to+85 ℃, covering the vast majority of application scenarios.
Precautions for use:
· There is a difference in the zero point and gain between chips, and calibration needs to be determined based on the application scenario
· When used for temperature control, it is recommended to perform zero and gain calibration
· When used for system temperature compensation, only focus on linearity and usually do not require calibration
· Temperature measurement and analog input measurement share the same data interface, switched by PD_SCK pulse number
The digital temperature sensor inside the CXAS42304 chip can be directly used to read the temperature inside the chip, that is, the system. It is effective (stable)
The number of digits is 15; Position. The typical temperature measurement accuracy is 20.4 degrees per degree (℃); Number of readings (15 digits). The temperature measurement range is -40 ℃~85 ℃. make
When using a digital temperature sensor, it should be noted that the temperature sensor inside the chip has significant zero and gain differences between chips. If using
To measure absolute temperature, both zero point and gain need to be calibrated. If measuring temperature is used for system temperature related performance compensation, then zero and gain are
No calibration is required, as long as the linearity of temperature measurement meets the requirements.
7、 Low power management and system clock
The chip provides intelligent power management function:
· Normal working mode: Fully functional enabled, typical power consumption 1080μ A @ 3V
· power-down modePD_SCK maintains a high level for over 512 seconds before entering, reducing power consumption to 0.5 A
· Quick wake-upRecovering from power down mode to normal working mode only requires 4 data output cycles
The system clock is provided by an internal high-precision oscillator, which has extremely low dependence on power supply voltage and temperature changes, ensuring the stability of output data rate (fixed 10Hz) without the need for external clock components.
7.2. Reset and power down mode
When the chip is powered on, the power on automatic reset circuit inside the chip will automatically reset the chip. But at this point, the tested object is uncertain (i.e
Whether in differential input measurement state or temperature measurement state, customers can use the PD_SCK pin after 10ms of power on
Send the specified number of clocks to specify the input status.
Pin PD_SCK input is used to control the power-off of CXAS42304. When PD_SCK is at a low level, the chip is in normal working condition.
If PD_SCK changes from low level to high level and remains at high level for more than 512 seconds, CXAS42304 enters power down mode (see Figure 4). when
When PD_SCK returns to low level, the chip will enter normal working state again. After the chip returns from the power-off state to the normal working state,
The selection of input signals remains unchanged.
After the chip enters normal working state from reset or power-off state, the A/D converter needs 4 data output cycles to stabilize. DOUT
After 4 data output cycles, it will change from high level to low level and output valid data.
8、 Typical application scenarios
CXAS42304 is widely used in the following fields:
· Medical ElectronicsElectronic thermometers, ear thermometers, medical monitoring equipment
· Industrial MeasurementTemperature transmitter, pressure sensor signal conditioning, industrial control
· environmental monitoringTemperature and humidity recorder, meteorological station, indoor environmental monitoring
· consumer electronicsSmart home sensors, wearable devices
Its high integration significantly reduces the number of external components, lowers system complexity, and overall costs.
9、 Packaging selection and design considerations
The chip offers three packaging options:
· DIP8Suitable for prototype development and educational applications
· SOP8Balancing size and welding process, with the strongest universality
· TSSOP8Ultra thin and ultra small package, suitable for applications with extremely limited space
When designing, attention should be paid to the PCB layout, and decoupling capacitors should be placed as close as possible to the AVDD and DVDD pins. Analog and digital grounds should be appropriately separated, and high-quality capacitor filtering should be used at the reference input terminal.
10、 Development support and reference design
JTM-IC provides complete development support for CXAS42304, including data manuals, application notes, and reference designs. The C language reference code provided in the article demonstrates the basic process of chip initialization and data reading, which engineers can use to quickly develop application systems.
After the chip is powered on, a 10ms delay is required for initialization, and the input state is configured by sending a specific pulse sequence. When reading data, it is necessary to ensure that the timing complies with the specifications, especially after channel switching, waiting for 4 data output cycles to stabilize the system.
Reference program
C language: (for reference only)
/*CXAS42304. h header file*/
#ifndef _CXAS42304_H_
#define __H_
#define CH1_10HZ 0x01
#define CH1_40HZ 0x02
#define CH2_TEMP 0x03
#define CH1_10HZ_CLK twenty-five
#define CH1_40HZ_CLK twenty-seven
#define CH2_TEMP_CLK twenty-six
unsigned long Read_CXAS42304(unsigned char next_select);
#endif
/*CXAS42304. c program file*/
#include " CXAS42304.h"
#include " global.h" //Define ports
#include " delay.h" //Delay subroutine
Void Initial_CXAS42304 (void)//CXAS42304 needs to initialize input signal or output data rate after 10mS power on
{
delay_ms(10); //Delay of 10ms
Switch (Next_Select)//Initialization: Determine the next data update rate or switch channels
{
case CH1_10HZ:
for(i = 0;i < 25;i++)
{
SET_SCK_H(); //Define in the global. h file to set the SCK pin to output a high level
delay_us(5); //Delay by 5 microseconds, customize this function according to different MCUs
SET_SCK_L(); //Define in the global. h file to set the SCK pin to output a low level
delay_us(5);
}
break;
case CH1_40HZ:
for(i = 0;i < 27;i++)
{
SET_SCK_H(); //Define in the global. h file to set the SCK pin to output a high level
delay_us(5); //Delay by 5 microseconds, customize this function according to different MCUs
SET_SCK_L(); //Define in the global. h file to set the SCK pin to output a low level
delay_us(5);
}
break;
case CH2_TEMP_CLK:
for(i = 0;i < 26;i++)
{
SET_SCK_H(); //Define in the global. h file to set the SCK pin to output a high level
delay_us(5); //Delay by 5 microseconds, customize this function according to different MCUs
SET_SCK_L(); //Define in the global. h file to set the SCK pin to output a low level
delay_us(5);
}
break;
}
unsigned long Read_CXAS42304(unsigned char next_select)
{
unsigned char i = 0;
unsigned long data_temp = 0;
for(i = 0;i < 24;i++)
{
SET_SCK_H(); //Define in the global. h file to set the SCK pin to output a high level
data_temp < <= 1;
delay_us(5); //Delay by 5 microseconds, customize this function according to different MCUs
If (READ-PORT&(1<< PIN_SOUT)//Determine if DOUT is at a high level
data_temp |= 1;
SET_SCK_L(); //Define in the global. h file to set the SCK pin to output a low level
}
Switch (Next_Select)//Determine the next data update rate or switch channels
{
case CH1_10HZ:
SET_SCK_H();
delay_1us();
SET_SCK_L();
break;
case CH1_40HZ:
SET_SCK_H();
delay_1us();
SET_SCK_L();
delay_1us();
SET_SCK_H();
delay_1us();
SET_SCK_L();
delay_1us();
SET_SCK_H();
delay_1us();
SET_SCK_L();
break;
case CH2_TEMP:
SET_SCK_H();
delay_1us();
SET_SCK_L();
delay_1us();
SET_SCK_H();
delay_1us();
SET_SCK_L();
break;
default:
break;
}
return(data_temp); //Return the data read from CXAS42304
}
11、 Conclusion
CXAS42304 is an ideal choice for electronic thermometers and high-precision low-frequency measurement systems due to its high precision, low power consumption, small size, and integrated temperature measurement capabilities. Both medical device manufacturers and industrial sensor developers can benefit from the excellent performance of this chip. Choosing CXAS42304 means choosing the comprehensive advantages of reliability, high cost-effectiveness, and fast time to market.
JTM-IC, as a professional integrated circuit supplier, is committed to providing customers with high-quality chips and comprehensive technical support. Welcome to visit our official websitejtm-ic.comObtain detailed information, sample application, and technical support for CXAS42304.
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