NXP Semiconductors
UM11192
User Manual for LPCXpresso54S018M Development Board
UM11192
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2019. All rights reserved.
User manual
Rev. 1.0
— 13th February 2019
19 of 34
be inadvertently selected. In these situations, try removing power for several second,
then hold down ISP0 reconnecting power to the board.
7. Board power connections & measurement
The LPCXpresso54S018M board re5V input to power the on-board voltage
regulators which in turn power the Link2 Debug Probe and other +3.3V circuits, the
LPC54S018J4M target and other +1.8V circuits, and the A5V and +3.3V power
rails. When the main external power source is from the Link2 side USB micro B-type
connector (J8), both the Link side and LPC54S018J4M Target sections of the board are
powered. When the main external power is from the power only USB micro B-type
connector (J1), or one of more of the USB device ports (USB0 at J3 or USB1 at J2), only
the LPC54S018J4M target and supporting devices and peripherals are powered.
7.1 LPCXpresso54S018M current measurement
The LPC54S018J4M current can be measured by measuring the voltage across a sense
resistor in series with the supply, a current meter or using the on board current
measurement circuit. Each of these methods will be described in subsections below.
There is no current monitoring of the Link2 section circuits on the board. The Target side
power going to LEDs and support ICs is not monitored by the current measurement
circuit. The LPC54S018J4M BGA package has the core and IO power both sourced
from the same VDD pins.
When a shield board is attached, attempting to measure the lowest possible power the
LPC54S018J4M IO pins must be configured according to how the software has
configured the shield board to ensure there is no extra current from the LPC54S018J4M
IO ports that have external pull-up or pull-down resistors enabled.
There are several leakage paths through the various devices on the
LPCXpresso54S018M board, so this board may not be suitable for accurately measuring
the lowest possible leakage current achievable in a target application.
7.1.1 LPC54S018J4M Vsense resistor current measurement
The voltage across a pair of 1
Ω resistors in series with the target LPC54S018J4M VDD
can be manually measured at JP4 across pins 1 and 4 on the PCB. For a higher range of
current a jumper should be installed between pins 3 and 4 of JP4 to short out on of these
resistors. The voltmeter positive probe is applied to JP4 pin 1 (see silkscreen labelling)
and pin 4
. Use Ohm’s law to calculate the current (LPC54S018J4M current = measured
voltage / 2
Ω). As an example, if the measured voltage is 20 mV, then 20e-3 / 2 Ω = 10
mA.
Note: The input current to the MAX9634 used in the on-board current measurement will
be included in the voltage measured across this resistor.
7.1.2 LPC54S018J4M VDD current measurement using a current meter
A current meter may be inserted at JP4 between pins 5 and 6 to measure the
LPC54S018J4M VDD input current. Note that a jumper needs to be installed in the 5-6
position when an ammeter is not present so power can reach the LPC54S018J4M target.