Datasheet

NXP Semiconductors

UM11121

LPCXpresso51U68

UM11121

All information provided in this document is subject to legal disclaimers.

User manual

Rev 1.1 — 27 April 27, 2018

12 of 22

The LPC51U68 Target VDD selection of 1.8V or 3.3V is made at JP9, with 3.3V set as

the default.

Fig 4. Board power diagram

5.1 LPCXpresso51U68 current measurement

The LPC51U68 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 LPC51U68 LQFP 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

LPC51U68 IO pins must be configured according to how the software has configured the

shield board to ensure there is no extra current from the LPC51U68 IO ports that have

external pull-up or pull-down resistors enabled. JS17 should be opened to ensure no

leakage through the tri-color LED and +3.3V supply, and JP3 installed to avoid leakage

to the Link2 via the I2C and SPI connections between it and the LPC51U68.