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SPRUIF8 – June 2017
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Copyright © 2017, Texas Instruments Incorporated
AM438x ePOS EVM Hardware
4.4
APM Sense Resistors
The AM438x ePOS EVM has the following subsystems with current sense resistors (see
Table 3
). These
resistors allow measurement of power on each power rail, to check AM438x power requirements during
real-time software execution. The value of the resistors is selected to provide the best dynamic range
when using a TI INA226 converter. In fact, an INA226 converter is installed on the EVM for VDD_CORE,
VDD_MPU, VAM438X_DDR, V1_8D_AM438X, V3_3D_AM438X, and VDDS_DDR power supply rails of
the AM438x. Also, the measurement connections of all the sense resistors are attached to 2-pin standard
headers so that they can be read easily by a multimeter or connected to an INA226 converter EVM.
The AM438x ePOS EVM has the option to access the INA devices through the onboard AM438X I2C0
port by closing jumpers J101 and J102. By default, the INA226 converter is connected to the 5-pin header
J39. See the schematics for more details.
NOTE:
The value of the sense resistors for VDD_CORE and VDD_MPU were selected to give better
dynamic range for active power modes, rather than sleep or low power modes. If power is to
be measured for VDD_CORE or VDD_MPU for sleep or low-power modes, then this sense
resistor value must be changed to give better shunt voltage values.
Table 3. AM438x ePOS EVM APM Sense Resistors
Voltage Net
Sense Resistor Value
VDD_CORE
0.05
Ω
VDD_MPU
0.05
Ω
VAM438X_DDR
0.05
Ω
V1_8D_AM438X
0.05
Ω
V3_3D_AM438X
0.1
Ω
VDDS_DDR
0.05
Ω
5
Configuration and Setup
5.1
Boot Configuration
SYSBOOT pins on the AM438x can be configured a certain way using a 10-bit DIP switch on the EVM.
This SYSBOOT switch configures the AM438x to different settings. For instance, the boot method of the
processor can be set up by configuring the DIP switch to particular settings. The SW48 DIP switch has the
switches that set SYSBOOT[0...4, 6, 7, 17, 18]. Other SYSBOOT pin settings are done through resistors
pulled either high or low. See the AM438x TRM and data sheet for the actual definitions of each
SYSBOOT signal.
Table 4
provides the mapping of the boot strap pin and the corresponding switch bits.
Table 4. SYSBOOT DIP Switches
DIP Switch Bits (SW48)
Boot Strap
Bit 1
SYSBOOT18
Bit 2
SYSBOOT17
Bit 3
SYSBOOT7
Bit 4
SYSBOOT6
Bit 5
SYSBOOT4
Bit 6
SYSBOOT3
Bit 7
SYSBOOT2
Bit 8
SYSBOOT1
Bit 9
SYSBOOT0
Bit 10
NC (not connected)