ADS5403 Datasheet, PDF (22/44 Pages) Texas Instruments – Single Channel 12-Bit 500Msps Analog to Digital Converter

ADS5403
SLAS944B – FEBRUARY 2013 – REVISED JANUARY 2014
www.ti.com
ANALOG INPUTS
The ADS5403 analog signal input is designed to be driven differentially. The analog input pins have internal
analog buffers that drive the sampling circuit. As a result of the analog buffer, the input pins present a high
impedance input across a very wide frequency range to the external driving source which enables great flexibility
in the external analog filter design as well as excellent 50Ω matching for RF applications. The buffer also helps to
isolate the external driving circuit from the internal switching currents of the sampling circuit which results in a
more constant SFDR performance across input frequencies.
The common-mode voltage of the signal input is internally biased to 1.9V using 500Ω resistors which allows for
AC coupling of the input drive network. Each input pin (INP, INM) must swing symmetrically between (VCM +
0.25V) and (VCM – 0.25V), resulting in a 1.0Vpp (default) differential input swing. The input sampling circuit has
a 3dB bandwidth that extends up to 1.2GHz.
2nH _0.5Ω
20Ω
INA_P
1.3pF
500Ω
1.4pF
INA_N
2nH _0.5Ω
Vcm= 1.9V
500Ω
20Ω
1.3pF
1.4pF
OVER-RANGE INDICATION
The ADS5403 provides a fast over-range indication on the OVRA/B pins. The fast OVR is triggered if the input
voltage exceeds the programmable overrange threshold and it gets presented after just 12 clock cycles enabling
a quicker reaction to an overrange event. The OVR threshold can be configured using SPI register writes.
The input voltage level at which the overload is detected is referred to as the threshold and is programmable
using the Over-range threshold bits. The threshold at which fast OVR is triggered is (full-scale × [the decimal
value of the FAST OVR THRESH bits] /16). After reset, the default value of the over-range threshold is set to 15
(decimal) which corresponds to a threshold of 0.56dB below full scale (20*log(15/16)).
OVR Detection Threshold
0
-5
-10
-15
-20
-25
0
2
4
6
8
10
12
14
16
Programmed Value (1-15)
22
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