AD7416/AD7417/AD7418
(continued from page 1)
situations where a change in the selected input channel takes
place or where there is a step input change on the input voltage
applied to the selected AIN input of the AD7417 or AD7418. It
means that the user must wait for the duration of the track-and-
hold acquisition time after the end of conversion or after a channel
change/step input change to AIN before starting another conver-
sion, to ensure that the part operates to specification.
An I2C compatible serial interface allows the AD7416/AD7417/
AD7418 registers to be written to and read back. The three LSBs
of the AD7416/AD7417’s serial bus address can be selected,
which allows up to eight AD7416/AD7417s to be connected to
a single bus.
The AD7417 is available in a narrow body, 0.15'', 16-lead, small
outline IC (SOIC) and in a 16-lead, thin shrink, small outline
package (TSSOP). The AD7416 and AD7418 are available in
8-lead SOIC and MSOP packages.
CIRCUIT INFORMATION
The AD7417 and AD7418 are single-channel and four-channel,
15 µs conversion time, 10-bit ADCs with on-chip temperature
sensor, reference, and serial interface logic functions on a single
chip. The AD7416 has no analog input channel and is intended
for temperature measurement only. The ADC section consists
of a conventional successive approximation converter based
around a capacitor DAC. The AD7416, AD7417, and AD7418
are capable of running on a 2.7 V to 5.5 V power supply, and
the AD7417 and AD7418 accept an analog input range of 0 V
to +VREF. The on-chip temperature sensor allows an accurate
measurement of the ambient device temperature to be made.
The working measurement range of the temperature sensor is
–40°C to +125°C. The parts require a 2.5 V reference that can
be provided from the part’s own internal reference or from an
external reference source.
PRODUCT HIGHLIGHTS
1. The AD7416/AD7417/AD7418 have an on-chip temperature
sensor that allows an accurate measurement of the ambient
temperature ( 1°C @ 25°C, 2°C overtemperature) to be
made. The measurable temperature range is –40°C to +125°C.
An overtemperature indicator is implemented by carrying
out a digital comparison of the ADC code for Channel 0
(temperature sensor) with the contents of the on-chip over-
temperature register.
2. The AD7417 offers a space-saving 10-bit A/D solution with
four external voltage input channels, an on-chip temperature
sensor, an on-chip reference, and clock oscillator.
3. The automatic power-down feature enables the AD7416/
AD7417/AD7418 to achieve superior power performance. At
slower throughput rates, the part can be programmed to
operate in a low power shutdown mode, allowing further
savings in power consumption.
CONVERTER DETAILS
Conversion is initiated on the AD7417/AD7418 by pulsing the
CONVST input. The conversion clock for the part is internally
generated so no external clock is required except when reading
from and writing to the serial port. The on-chip track-and-hold
goes from track to hold mode and the conversion sequence is
started on the falling edge of the CONVST signal. A conversion
is also initiated in the automatic conversion mode every time a
read or write operation to the AD7416/AD7417/AD7418 takes
place. In this case, the internal clock oscillator (which runs the
automatic conversion sequence) is restarted at the end of the
read or write operation. The track-and-hold goes into hold
approximately 3 µs after the read or write operation is complete
and a conversion is then initiated. The result of the conversion
is available either 15 µs or 30 µs later, depending on whether an
analog input channel or the temperature sensor is selected. The
track-and-hold acquisition time of the AD7417/AD7418 is 400 ns.
TERMINOLOGY
Relative Accuracy
Relative accuracy or endpoint nonlinearity is the maximum
deviation from a straight line passing through the endpoints of
the ADC transfer function.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (0000 . . . 000)
to (0000 . . . 001) from the ideal, i.e., GND + 1 LSB.
Offset Error Match
This is the difference in offset error between any two channels.
A temperature measurement is made by selecting the Channel 0
of the on-chip mux and carrying out a conversion on this channel.
A conversion on Channel 0 takes 30 µs to complete. Tempera-
ture measurement is explained in the Temperature Measurement
section of this data sheet.
Gain Error
This is the deviation of the last code transition (1111 . . . 110)
to (1111 . . . 111) from the ideal, i.e., VREF – 1 LSB, after the
offset error has been adjusted out.
The on-chip reference is not available to the user, but REFIN
can be overdriven by an external reference source (2.5 V only).
Gain Error Match
This is the difference in gain error between any two channels.
All unused analog inputs should be tied to a voltage within the
nominal analog input range to avoid noise pickup. For mini-
mum power consumption, the unused analog inputs should be
tied to GND.
Track-and-Hold Acquisition Time
Track-and-hold acquisition time is the time required for the
output of the track-and-hold amplifier to reach its final value,
within 1/2 LSB, after the end of conversion (the point at which
the track-and-hold returns to track mode). It also applies to
–8–
REV. G
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