NXP Semiconductors
UM10946
LPCXpresso board for LPC4367/43S67/18S37 family of MCUs
UM10946
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 1.0
— 18 November 2015
11 of 19
5. Board power connections & measurement
The LPCXpresso4367 board re5V input to power the on-board voltage regulators
which in turn power the Link2 debug probe and other +3.3V circuits, the Target MCU and
the A5V and +3.3V power rails. When the main external power source is from
the Link2 side USB micro B-type connector (J5), both the Link side and Target MCU
sections of the board are powered. When the main external power is from the Target
side USB micro B-type connector (J4) or FTDI header (P4) only the Target MCU section
of the board is powered.
When the Target MCU is to be debugged from an external debug probe, instead of the
on-board Link2 debug probe, the Link USB connector (J5) must be disconnected.
5.1 Target MCU current measurement
The Target MCU current can be determined by measuring the voltage across a sense
resistor in series with the supply, using a current meter or using the built-in power
measurement circuitry with the LPCXpresso IDE tools. Each of these methods will be
described in subsections below. There is no current monitoring of the Link section
circuits on the board.
5.1.1 Target MCU current measurement using voltage sense resistor
The voltage across a series 200m
Ω resistor with the Target MCU Core VDD can be
manually measured at P2 on the PCB. The voltmeter positive probe is applied to P2 pin
1 (square pad) and negative probe to P2
pin 2. Use Ohm’s law to calculate the current
(Target MCU current = measured voltage / 0.2).
The voltage ac
ross a series 3Ω resistor with the Target MCU I/O VDD can be manually
measured at P3 on the PCB. The voltmeter positive probe is applied to P3 pin 1 (square
pad) and negative probe to P3
pin 2. Use Ohm’s law to calculate the current (Target
MCU current = measured voltage / 3).
5.1.2 Target MCU VDD and VDD I/O current measurement using a current meter
A current meter may be installed across JP5 to measure the Target MCU VDD input
current. The 0Ω resistor at JS11 must be removed and the current meter connected at
the positive input at JP5 pin 1 (square pad) and negative input at JP5 pin 2
.
A current meter may be installed across JP7 to measure the Target MCU I/O VDD input
current. The 0Ω resistor at JS14 must be removed and the current meter connected at
the positive input at JP7 pin 1 (square pad) and negative input at JP7 pin 2
.
5.1.3 Built-in current measurement
The LPCXpresso4367 includes an on-board current measurement system consisting of a
pair of amplifiers and a fast, 2 channel ADC, which is controlled by the on-board Link2
debug probe. Each amplifier measures the voltage drop across of two series resistors,
one pair of resistors being in line with the Target MCU supply and one in line with the I/O
supply. By default, one of the series resistors in each of these circuits is shorted by (JP7
for Target supply, JP9 for I/O supply) in order to allow the ADC to measure up to 235mA
(Target supply) / 32mA (I/O supply) without the ADC input saturating. JP7 can be
removed to make more accurate measurements when the Target MCU is consuming
52mA or less, and/or JP9 can be removed if the I/O supply current is 32mA or less. Note
that the current measurement system will not be damaged if the amplifier outputs
saturate.