AMC1304L05-Q1 Datasheet, PDF (21/39 Pages) Texas Instruments – High-Precision, Reinforced Isolated Delta-Sigma Modulators with LDO

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8 Detailed Description
AMC1304L05-Q1, AMC1304L25-Q1, AMC1304M05-Q1, AMC1304M25-Q1
SBAS799 – FEBRUARY 2017
8.1 Overview
The differential analog input (AINP and AINN) of the AMC1304-Q1 is a fully-differential amplifier feeding the
switched-capacitor input of a second-order, delta-sigma (ΔΣ) modulator stage that digitizes the input signal into a
1-bit output stream. The isolated data output (DOUT and DOUT_N) of the converter provides a stream of digital
ones and zeros that is synchronous to the externally-provided clock source at the CLKIN pin with a frequency in
the range of 5 MHz to 20.1 MHz. The time average of this serial bit-stream output is proportional to the analog
input voltage.
The Functional Block Diagram section shows a detailed block diagram of the AMC1304-Q1. The analog input
range is tailored to directly accommodate a voltage drop across a shunt resistor used for current sensing. The
SiO₂-based capacitive isolation barrier supports a high level of magnetic field immunity as described in the
ISO72x Digital Isolator Magnetic-Field Immunity application report (SLLA181A), available for download at
www.ti.com. The external clock input simplifies the synchronization of multiple current-sensing channels on the
system level. The extended frequency range of up to 20 MHz supports higher performance levels compared to
the other solutions available on the market.
8.2 Functional Block Diagram
LDOIN
Voltage Regulator
(LDO)
VCAP
DVDD
AINP
AINN
BUF
TX
-
û -Modulator
+
TX
BUF
DOUT
DOUT_N
(AMC1304Lx-Q1 only)
1.25-V
Reference
BUF
AMC1304-Q1
TX
CLKIN
CLKIN_N
(AMC1304Lx-Q1 only)
TX
AGND
DGND
Copyright © 2016, Texas Instruments Incorporated
8.3 Feature Description
8.3.1 Analog Input
The AMC1304-Q1 incorporates a front-end circuitry that contains a differential amplifier and sampling stage,
followed by a ΔΣ modulator. The gain of the differential amplifier is set by internal precision resistors to a factor of
4 for devices with a specified input voltage range of ±250 mV (this value is for the AMC1304x25-Q1), or to a
factor of 20 in devices with a ±50-mV input voltage range (for the AMC1304x05-Q1), resulting in a differential
input impedance of 5 kΩ (for the AMC1304x05-Q1) or 25 kΩ (for the AMC1304x25-Q1).
Consider the input impedance of the AMC1304-Q1 in designs with high-impedance signal sources that can
cause degradation of gain and offset specifications. The importance of this effect, however, depends on the
desired system performance. Additionally, the input bias current caused by the internal common-mode voltage at
the output of the differential amplifier causes an offset that is dependent on the actual amplitude of the input
signal. See the Isolated Voltage Sensing section for more details on reducing these effects.
Copyright © 2017, Texas Instruments Incorporated
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Product Folder Links: AMC1304L05-Q1 AMC1304L25-Q1 AMC1304M05-Q1 AMC1304M25-Q1