Datasheet

IN0A
IN0B
VDD
Core
GND
SCL
SDA
I
2
C
CLKIN
ADDR
INTB
SD
Resonant
Circuit
Driver
IN1A
IN1B
Resonant
Circuit
Driver
IN0A
IN0B
VDD
GND
SCL
SDA
I
2
C
CLKIN
ADDR
INTB
SD
Resonant
Circuit
Driver
IN3A
IN3B
Resonant
Circuit
Driver
f
REF
f
IN
Core
f
REF
f
IN
40 MHz
40 MHz
Copyright © 2016, Texas Instruments Incorporated
10
LDC1612
,
LDC1614
SNOSCY9A DECEMBER 2014REVISED MARCH 2018
www.ti.com
Product Folder Links: LDC1612 LDC1614
Submit Documentation Feedback Copyright © 2014–2018, Texas Instruments Incorporated
7 Detailed Description
7.1 Overview
The LDC1612/LDC1614 is an inductance-to-digital converter (LDC) that measures the oscillation frequency of
multiple LC resonators. The device outputs a digital value that is proportional to frequency, with 28 bits of
measurement resolution. This frequency measurement can be converted to an equivalent inductance, or mapped
to the movement of an conductive object. The LDC1612/LDC1614 supports a wide range of inductance and
capacitor combinations with oscillation frequencies varying from 1 kHz to 10 MHz with equivalent parallel
resistances as low as 1.0 kΩ. The device includes a stable internal reference to reduce overall system cost, while
also providing the option to drive a clean external oscillator for improved measurement noise. The conversion
time of the LDC1612/LDC1614 is configurable per channel, where longer conversion times provide higher
effective resolution.
The LDC1612/LDC1614 is configured through a 400-kbit/s I2C bus and includes the ADDR input pin to select an
address. The power supply of the device ranges from 2.7 V to 3.6 V. The only external components necessary
for operation are the supply bypassing capacitors and I2C pull-ups.
7.2 Functional Block Diagram
Figure 10. Block Diagrams for the LDC1612 (Left) and LDC1614 (Right)
The LDC1612/LDC1614 is composed of front-end resonant circuit drivers, followed by a multiplexer that
sequences through the active channels, connecting them to the core that measures and digitizes the sensor
frequency
SENSOR
). The core uses a reference frequency
REF
) to measure the sensor frequency. ƒ
REF
is
derived from either the internal reference clock (oscillator), or an externally supplied clock. The digitized output
for each channel is proportional to the ratio of ƒ
SENSOR
REF
. The I2C interface is used to support device
configuration and to transmit the digitized frequency values to a host processor. The LDC can be placed in an
inactive shutdown mode to reduce current consumption by setting the SD pin to V
DD
. The INTB pin may be
configured to notify the host of changes in system status.
7.3 Feature Description
7.3.1 Multi-Channel and Single Channel Operation
The LDC1612/LDC1614 provides flexibility in channel sampling. It can continuously convert on any available
single channel or automatically sequence conversions across multiple channels. When operated in multi-channel
mode, the LDC sequentially samples the selected channels. In single channel mode, the LDC continuously
samples only the selected channel.