Texas Instruments LMP91300NPN User Manual

1. INTRODUCTION ......................................................................................................... 1
2. SETUP ......................................................................................................................... 1
3. QUICK START ............................................................................................................ 1
4. BOARD LAYOUT ........................................................................................................ 3
5. SCHEMATIC ................................................................................................................ 4
6. BILL OF MATERIALS ................................................................................................. 5
1. Introduction
The Texas Instruments LMP91300NPN evaluation board allows a designer to use the LMP91300 in an
inductive sensor. The LMP91300SWIFEVM can be used with the LMP91300NPN to program and burn the
registers of the LMP91300 using the SWIF (Single Wire InterFace) protocol.
2. Setup
Supply and Ground – Power and ground from the LMP91300SWIFEVM are connected to the right side of
the board. See the Board Layout section. If another method besides the LMP91300SWIFEVM is used to
power the LMP91300NPN board, the supply must be <36V as D3 is a 36V zener.
Load – A load can be connected to the middle pad on the right side of the board.
LC Tank – The left side of the board has pads for mounting a capacitor and coil to form an LC tank.
3. Quick Start
When a new sensor is being used the registers should be setup using the following procedure. Instructions
on how to determine the value to put in each register are described in the Register Information section of the
LMP91300 datasheet.
1. Set RP_MAX in the OSC_CONFIG_0 register.
2. Set PADC_TIMEC and RP_MIN in the OSC_CONFIG_1 register.
3. Set RESONATOR_MIN_FREQ in the OSC_CONFIG_2 register.
4. Set UNDER_RANGE_SWITCH_EN, OSC_AMP, and RESPONSE_TIME in the OSC_CONFIG_3_INIT
and OSC_CONFIG_3_FNL registers. The same values should be written to both registers. Setting
OSC_AMP to 4V and RESPONSE_TIME to 6144 should give the most accurate results. Note that the power
on default for OSC_AMP is 11:Reserved so OSC_AMP must be changed to either 1V, 2V, or 4V.
5. Select the value of the CF capacitor:
a. Start with a default value of 10nF for CF.
b. Move the metal target far away from the LC tank.
c. Connect a scope probe to the INB (pin 21) and CFB (pin 17) pins. Since the CFB pin is very sensitive
to capacitive loading, it is recommended to use an active probe. As an alternative, a passive probe with
a 1kΩ series resistance between the tip and the CFB pin can be used.
October 3, 2013
LMP91300NPN User's Guide
LMP91300NPN User's Guide
User's Guide
October 3, 2013
1