Both the AD7417 and AD7418 are 10-bit, 4-channel and single-channel ADCs with an on-chip temperature sensor that can operate on a single 2.7 V to 5.5 V supply. The device contains a 15µs successive approximation converter, a 5-channel multiplexer, a temperature sensor, a clock oscillator, a sample-and-hold, and a reference (2.5 V). The AD7416 is only available in an 8-lead package for temperature monitoring devices. The temperature sensor on the device can be accessed through multiplexer channel 0. When channel 0 is selected and conversion starts, the generated ADC code at the end of the conversion measures the ambient temperature (±1°C at 25°C). On-chip registers can be programmed to have high and low temperature limits, and an open-drain over-temperature indicator (OTI) provides an output that becomes active over-limit when programmed. The configuration register allows to program the meaning of the OTI output (active high or active low) and its mode of operation (comparator or interrupt). A programmable fault queue counter allows the number of out-of-limit measurements that must occur in noisy environments to falsely trigger the OTI output before the triggering OTI output is set to block. The C 174 ; compatible serial interface allows the AD7416/AD7417/AD7418 registers to be written and read back. Three of them can select the LSB of the AD7416/AD7417 serial bus address, connecting up to eight AD7416/AD7417 devices to a bus.

The AD7417 is available in a narrow body, 0.15-inch, 16-lead, small outline package (SOIC) and a 16-lead, thin shrink, small outline package (TSSOP). The AD7416 and AD7418 are available in 8-lead SOIC and MSOP packages.

feature

10-bit ADC with 15µs conversion time and 30µs conversion time

Single and 4 single-ended analog input channels

On-chip temperature sensor: -40°C to +125°C

On-chip track-and-hold

temperature indicator

Automatic power off at the end of conversion

Wide operating power supply range: 2.7 V to 5.5 V.

A generation

2C compatible serial interface

Selectable serial bus address allows connection of up to 8

AD7416/AD7417 devices are single bus

AD7416 is a good alternative to LM75

application

Data collection through ambient temperature monitoring

Industrial Process Control

car

battery charging application

personal computer

AD7416 function block diagram

AD7417 function block diagram

AD7418 function block diagram

Product Highlights

1. The AD7416/AD7417/AD7418 have an on-chip temperature sensor that can accurately measure the ambient temperature (±1°C at 25°C, ±2°C temperature). The measurable temperature range is -40°C to +125°C. The over temperature indicator is implemented by

The ADC code is digitally compared to the contents of channel 0 (temperature sensor) on-chip TOTI setpoint register.

2. The AD7417 provides a space-saving 10-bit analog-to-digital converter with four external voltage input channels, an on-chip temperature sensor, an on-chip voltage reference and a clock oscillator.

3. The automatic power-down function enables the AD7416/AD7417/AD7418 to achieve excellent power performance. At lower throughput rates, the device can be programmed to operate in a low-power shutdown mode, allowing further power savings.

Theory of Operation

circuit information

Both the AD7417 and AD7418 are single- and quad-channel with 15µs conversion time, 10-bit ADC single sensor for on-chip temperature, reference and serial interface logic function chips. The AD7416 has no analog input channels for temperature measurement only. The ADC section consists of a conventional successive approximation converter around the capacitor DAC. The AD7416, AD7417, and AD7418 are capable of operating from a 2.7 V to 5.5 V supply. The AD7417 and AD7418 accept an analog input range of 0 V to +VREF. On-chip temperature sensors can accurately measure the temperature of ambient equipment. The working measurement range of the temperature sensor is -40°C to +125°C. These parts require a 2.5 V reference voltage either from the part's own internal reference or from an external reference source.

Converter Details

Conversions are initiated on the AD7417/AD7418 by pulsing the CONVST input. The device's conversion clock is internally generated and no external clock is required unless reading and writing to the serial port. On-chip track and hold enter hold mode from track mode and the conversion sequence begins on the falling edge of the CONVST signal. The AD7418 also initiates a conversion in auto-conversion mode every time a read or write to the AD7416/AD7417 occurs. In this case, the internal clock oscillator (restarts the running conversion sequence) at the end of a read or write operation. Track and hold enters hold mode approximately 3µs after the read or write operation completes and then initiates the conversion. This conversion result is available after 15µs or 30µs, depending on whether the analog input channel or the temperature sensor is selected. The acquisition time for track and hold for the AD7417/AD7418 is typically 400 ns. Temperature measurement is done by selecting channel 0 with the on-chip multiplexer and converting this channel. The conversion on channel 0 takes 30µs to complete.

Temperature measurement is described in the Measurement section. The on-chip reference is not available to the user, but REFIN can be overloaded by an external reference source (2.5 V only). All unused analog inputs should be connected to the voltage nominal analog input range to avoid noise pickup. For lowest power consumption, unused analog inputs should be connected to GND.

Typical Connection Diagram

The figure below shows a typical connection diagram for the AD7417. Using the A0, A1 and A2 pins allows the user to select from up to 8 AD7417 devices on the same serial bus if desired. An external 2.5 V reference can be connected to the REFIN pin. If an external reference is used, a 10µF capacitor should be connected between REFIN and GND. SDA and SCL form a 2-wire I2C compatible interface. For applications where power consumption is a concern, in a. Automatic power down at the end should use transitions to improve power performance (see the Operating Modes section.)

analog input

The figure below shows the structure of the AD7417 and AD7418 equivalent circuits for analog inputs. D1, diode and D2, provide ESD protection for the analog input. Care must be taken to ensure that the analog input signal never exceeds the supply rails by more than 200 mV to prevent these diodes from becoming forward biased and starting to conduct current into the substrate. The maximum current these diodes can carry without irreversible damage to the part is 20mA. Capacitor C2 in the figure below is typically around 4pF due mainly to pin capacitance. Resistor R1 is a lumped element consisting of the on-resistance of the multiplexer and a switch. This resistance is typically 1kΩ. Capacitor C1 is the ADC sampling capacitor and has a capacitance of 3 pF.

on-chip reference

The AD7417/AD7418 built-in 1.2 V bandgap reference is amplified by a switched capacitor amplifier, resulting in an output of 2.5 V. The amplifier is only powered on at the beginning of the conversion phase and powered off at the end of the conversion. On-chip reference selected by connecting

Connect the REFIN pin to analog ground, which causes SW1 (see diagram below) to turn on and the reference amplifier to power up during conversions. Therefore, the on-chip reference is not external and an external 2.5 V reference can be connected to the REFIN pin. This has an effect circuit that turns off the on-chip reference.

temperature measurement

A common method of measuring temperature is to use the voltage of a diode or base-emitter NTC transistor, operating at a constant current. Unfortunately, this technique requires calibration to remove the absolute value of the effect VBE, which varies from device to device. The technique employed by the AD7416/AD7417/AD7418 is to measure the current change in VBE while the device is operating at two different currents. This is made by

VBEKT/q1nN

where:

K is Boltzmann's constant.

q is the charge on the electron (1.6 x 10-19 coulombs).

T is the absolute temperature of Kelvins.

N is the ratio of the two currents.

The figure above shows the method used by the AD7416/AD7417/AD7418 to measure device temperature. Measuring ΔVBE, the sensor (substrate transistor) switches currents as I and N×I between operations. The resulting waveform is passed through a chopper-stabilized amplifier that performs functional amplification and rectification of the waveform to produce a DC voltage proportional to ΔVBE. This voltage is measured by the ADC to give a 10-bit twos complement temperature output. The temperature resolution of the ADC is 0.25°C, which is equivalent to 1 LSB of the ADC. The ADC can theoretically measure a temperature range of 255°C; the guaranteed temperature range is -40°C to +125°C. The conversion result is stored in the temperature value register (0x00) as a 16-bit word. Temperature conversion formula using 10 MSBs

Temperature value register

Positive temperature = ADC code / 4 (1)

Negative temperature = (ADC code - 512 )/4(2)

The MSB is removed from the ADC code in Equation 2.

Internal register structure

AD7417/AD7418 have 7 internal registers as shown below

Six of them are data registers and one is an address pointer register. The AD7416 has five internal registers (the ADC and Config2 registers do not apply to the AD7416).

address pointer register

The address pointer register is an 8-bit register that stores an address to one of the six data registers. The first data byte of each serial write operation of the AD7416/AD7417/AD7418 is the address of one of the data registers, i.e. stored in the address pointer register, and selects the data register to write subsequent data bytes. Only the three LSBs of the address pointer register are used to select a data register.