Datasheet
ADS1672
www.ti.com
SBAS402D –JUNE 2008–REVISED JULY 2010
APPLICATIONS INFORMATION
across the VREFP and VREFN pins. The driving
To obtain the specified performance from the
amplifier must be able to provide this current as
ADS1672, the following layout and component
well as another 1mA caused by switching at
guidelines should be considered.
20MHz. It is therefore recommended that the
1. Power Supplies: The device requires two power
driving amplifier be able to provide at least 5mA,
supplies for operation: DVDD and AVDD. For
and enough decoupling capacitors be installed to
both supplies, use a 10mF tantalum capacitor,
attenuate instantaneous current spikes seen at
bypassed with a 0.1mF ceramic capacitor, placed
20MHz.
close to the device pins. Alternatively, a single
6. Analog Inputs: The analog input pins must be
10mF ceramic capacitor can be used. The
driven differentially to achieve specified
supplies should be relatively free of noise and
performance. A true differential driver or
should not be shared with devices that produce
transformer (ac applications) can be used for this
voltage spikes (such as relays, LED display
purpose. Route the analog inputs tracks (AINP,
drivers, etc.). If a switching power supply source
AINN) as a pair from the buffer to the converter
is used, the voltage ripple should be low (< 2mV).
using short, direct tracks and away from digital
The power supplies may be sequenced in any
tracks. A 750pF capacitor should be used directly
order.
across the analog input pins, AINP and AINN. A
2. Ground Plane: A single ground plane connecting
low-k dielectric (such as COG or film type) should
both AGND and DGND pins can be used. If
be used to maintain low THD. Capacitors from
separate digital and analog grounds are used,
each analog input to ground should be used.
connect the grounds together at the converter.
They should be no larger than 1/10 the size of
the difference capacitor (typically 100pF) to
3. Digital Inputs: Source terminate the digital inputs
preserve the ac common-mode performance.
to the device with 50Ω series resistors. The
resistors should be placed close to the driving
7. Component Placement: Place the power supply,
end of the digital source (oscillator, logic gates,
analog input, and reference input bypass
DSP, etc.) These resistors help reduce ringing on
capacitors as close as possible to the device
the digital lines, which may lead to degraded
pins. This placement is particularly important for
ADC performance.
the small-value ceramic capacitors.
Surface-mount components are recommended to
4. Analog/Digital Circuits: Place analog circuitry
avoid the higher inductance of leaded
(input buffer, reference) and associated tracks
components.
together, keeping them away from digital circuitry
(DSP, microcontroller, logic). Avoid crossing
Figure 39 to Figure 41 illustrate basic connections
digital tracks across analog tracks to reduce
and interfaces that can be used with the ADS1672.
noise coupling and crosstalk.
The THS4520 and THS4503 are good input drivers
5. Reference Inputs: Use a minimum 10mF
for the ADS1672. The THS4520 is a single-supply,
tantalum with a 0.1mF ceramic capacitor directly
high-speed, low-power, fully differential amplifier. The
across the reference inputs, VREFP and VREFN.
THS4503 is a high-speed, bipolar, fully differential
The reference input should be driven by a
amplifier. The wider supply range of the THS4503
low-impedance source. For best performance, the
provides better THD and SFDR performance over the
reference should have less than 3mV
RMS entire input range of the converter, while sacrificing
broadband noise. For references with higher
noise. The THS4520 offers comparable performance
noise, external reference filtering may be
with lower power and higher noise performance.
necessary. The ADS1672 has 800Ω of resistance
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