NXP Semiconductors LPC86 Series Guide

LPC86XHDG

LPC86x Hardware Design Guide

Rev. 0 — 8 May 2023 User guide

Document Information

Information Content

Keywords LPC86x, hardware design, LPC86x power circuit

Abstract This document provides guide for LPC86x hardware design, including power system, clock, pin

status, and PCB layout.

NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

1 Introduction

The LPC86x is introduced to market by NXP. It is an Arm Cortex-M0+ based, low-cost 32-bit MCU supporting up

to 64 kB of flash memory and 8 kB of SRAM.

This document provides guide for LPC86x hardware design, including power system, clock, pin status, and PCB

layout. This guide is expected to help customers to avoid any board bring-up problems.

2 Power system

2.1 Power supply configurations

LPC86x has several power supplies: VDD/VSS, VDDA/VSSA, and VREFP/VREFN. Table 1 describes the

configuration of these power supplies.

Package - Pin number

Pin name Description Operating voltage LQFP64 HVQFN48 HVQFN32

7 29 19

26 — —VDD Supply voltage for the I/O pad,

and core voltage regulator 1.8 V – 3.6 V

39 — —

8 30 33

25 — —VSS Ground GND

40 — —

VDDA[1] Analog supply voltage VDD 52 40 —

VSSA[2] Analog ground GND 53 41 —

VREFP[3] ADC positive reference voltage ≤ VDD 42 32 21

VREFN[2] ADC negative reference voltage GND 41 31 20

Table 1. LPC86x - Power supply configurations

[1] All VDD and VDDA pins must be shortened and connected externally together to a common reference on the PCB. A decoupling capacitor must be used

per each supply pin and a local Bulk capacitor just for the VDD and VDDA domains.

[2] VSSA and VREFN must be shortened to GND at package level.

[3] VREFP must be equal or less than VDD and VDDA.

2.2 Bulk and decoupling capacitors

In application design, to improve design stability, bulk, and decoupling capacitors are normally used. Bulk

capacitance is used to help supply a power rail with instantaneous power that exceeds the ability of the power

supply feedback loop to react to. These capacitors tend to be large as they are not meant to perform any high

frequency power decoupling.

Bypass/decoupling capacitors are needed to allow for local high-frequency interference to instantaneous power

requirements of a device.

Figure 1 to Figure 3 provide circuit design references for applying Bulk and decoupling capacitors on different

package of LPC86x.

•Figure 1 is for LPC86x LQFP64 package.

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

Figure 1. Bulk and decoupling capacitors for LPC86x LQFP64

•Figure 2 is for LPC86x HVQFN48 package.

Figure 2. Bulk and decoupling capacitors for LPC86x HVQFN48

•Figure 3 is for LPC86x HVQFN32 package.

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

Figure 3. Bulk and decoupling capacitors for LPC86x HVQFN32

2.3 Power measurement

For LPC86x chip power consumption measurement, the measurement circuits is as shown in Figure 4. Only the

current into LPC86x VDD should be measured. P1 is designed for the measurement of LPC86x total current

here using multi-meter's voltage mode, by measuring the voltage on R24, then calculate the current by dividing

by the resistance value of R24. JP2 is designed for the measurement of LPC86x total current here using multi-

meter's current mode, by removing R51. The user can choose either of these two methods to measure the

LPC86x chip power consumption. The default method is using P1.

Figure 4. Power consumption measurement for LPC86x

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

2.4 Board design for VREFP and VREFN

To improve ADC conversion accuracy, ADC module provide VREFP and VREFN inputs as accurate external

reference voltage.

For best performance, normally select VREFP and VREFN at the same voltage levels as VDD and VSS.

When selecting VREFP and VREFN different from VDD and VSS, ensure that the voltage midpoints are the

same (required by design specification):

(1)

For LPC86x ADC external reference voltage board connection design, see VREFP/VREFN design circuit shown

in Figure 5.

P2 is used as VREFP/VREFN select.

•When P2 is not installed, VREFP connects to 3.3 V and VREFN connects to GND.

•When P2 is installed and R53 and R54 are changed to B side, VREFP connects to P2-1 external V+ and

VREFN connects to P2-3 external V-.

Figure 5. Board design for VREFP/VREFN

3 Clock circuit

LPC86x provides the interface for a crystal or an external clock to control the internal clock generator circuit.

XTALIN is the input to the crystal oscillator amplifier. XTALOUT is the output of the crystal oscillator amplifier.

XTALIN and XTALOUT pins require pins with special characteristics and cannot be moved to other physical

pins. These functions are mapped to a fixed port pin in Switch Matrix. XTALIN and XTALOUT function is

associated with 10, 11 bits in the PINENABLE0 register.

Pin number

Pin name Description LQFP64 HVQFN48 HVQFN32

XTALIN

Input to the oscillator circuit and internal clock

generator circuits. Input voltage must not exceed

1.95 V in slave mode

34 26 18

XTALOUT Output from the oscillator circuit 33 25 17

Table 2. XTALIN and XTALOUT pins

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

3.1 XTAL oscillator mode

In the XTAL oscillator circuit, only the crystal (XTAL) and the capacitances CX1 and CX2 must be connected

externally to XTALIN and XTALOUT, as shown in Figure 6.

Figure 6. XTAL oscillator operation circuit

In user application design, when user selected the proper crystal, the external load capacitor CX1 and CX2

values can also be generally determined by the following expression:

(2)

Where:

•CL: Crystal load capacitance

•CPad: Pad capacitance of the XTALIN and XTALOUT pins (~3 pF).

•CParasitic: Parasitic or stray capacitance of external circuit.

Although CParasitic can be ignored in general, the actual board layout and placement of external components

influences the optimal values of external load capacitors. Therefore, it is recommended to fine-tune the values

of external load capacitors on actual hardware board to get the accurate clock frequency.

3.2 Slave mode (External clock input mode)

In slave mode, the input clock signal should be coupled with a capacitor of 100 pF, as shown in Figure 7, with

an amplitude between 200 mV (RMS) and 1000 mV (RMS). It corresponds to a square wave signal with a signal

swing of between 280 mV and 1.4 V.

The XTALOUT pin in this configuration can be left unconnected.

To limit the input voltage to the specified range, choose an additional capacitor to ground Cg which attenuates

the input voltage by a factor Ci/(Ci + Cg).

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

Figure 7. Slave mode operation of the on-chip oscillator

4 I3C circuit

LPC86x provides the MIPI Alliance Improved Inter-Integrated Circuit (MIPI I3C). It brings major improvements

in use and power over I2C and provides an alternative to SPI for mid-speed applications with bus capable of 12

MHz clock speeds.

4.1 Pin description

I3C comes with three pins for the function:

•For clock

•For data

•For pullup resistor control

The three pins all are movable functions pins and can be assigned to any GPIO pins through Switch Matrix.

Pin name Description Type Pin assignment

I3C0_SCL Clock for I3C master or slave function I/O Movable functions pin

I3C0_SDA Data for I3C master or slave function I/O Movable functions pin

I3C0_PUR Pullup resistor control for I3C master function O Movable functions pin

Table 3. I3C pins description

4.2 Design I3C circuit compatible with I2C

The I3C circuit design requires to be compatible with I2C. Figure 8 shows an I3C circuit reference design.

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

This design has the default function of I3C connection. When the I2C connection is required, remove R56 and

install R58 and R59.

Figure 8. A sample design for I3C circuit compatible with I2C

5 Pin state and unused pins termination

The unused pins must be connected externally to get a stable condition and configured correctly by software to

minimize the overall power consumption of the part. Unused pins with GPIO function should be configured as

outputs set to LOW with their internal pullup disabled.

Table 4 describes the LPC86x pins state and terminations for the unused pins.

Pin name Reset state Recommended termination of unused pins

RESET Tri-status

Without internal pullup

Can be left unconnected if the application does not use it. (In this

case, during Power On Reset, the chip uses internal reset signal)

GPIO Tri-status

Without internal pullup

Can be left unconnected if driven LOW and configured as GPIO

output with pull-up disabled by software

XTALIN — Connect to ground. When grounded, the main oscillator is disabled

XTALOUT — Can be left unconnected

VDDA — Tie to VDD

VSSA — Tie to VSS

VREFP — Tie to VDD

VREFN — Tie to VSS

Table 4. LPC86x pins state and terminations for the unused pins

For ISP select pin (PIO0_12)，because the reset state is Tri-status without internal pullup, an external pullup

resistor is needed, otherwise, after reset, the LPC86x enters the ISP state as default.

For WAKEUP pin (PIO0_4), if the LPC86x must wake up from deep power-down mode via the WAKEUP pin,

do not assign any movable function to this pin and must be externally pulled HIGH before entering deep power-

down mode. A LOW-going pulse as short as 50 ns causes the chip to exit deep power-down mode and wakes

up the part. The WAKEUP pin can be left unconnected or be used as a GPIO or for any movable function if an

external WAKEUP function is not needed.

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LPC86x Hardware Design Guide

6 General PCB layout guide

6.1 PCB layout suggestions for crystal oscillator circuit

The crystal oscillator is an analog circuit and must be designed carefully according to the analog-board layout

rules:

•Signal traces to the XTAL/EXTAL pins, the crystal and the external capacitors must be as short as possible,

these traces pins should only be connected to required oscillator components and must not be connected to

any other devices or components. The connection between the MCU and the external oscillator should not

have vias on the trace.

•Do not lay out other signal lines under crystal unit for multi-layered PCB. The crystal oscillator is sensitive to

stray capacitance and noise from other signals. It should be placed away from high-frequency devices and

traces in order to avoid the capacitive coupling between the XTAL and EXTAL pins and their PCB traces.

•Connect the crystal and external load capacitors on the PCB as close as possible to the oscillator input

and output pins of the chip. Ensure that the load capacitors CXTAL, CEXTAL, have a common ground plane

(GROUND plane first layer).

•Loops must be made as small as possible to minimize the noise coupled in through the PCB and to keep the

parasitics as small as possible.

•Lay out the ground pattern under crystal unit (GROUND second layer).

Figure 9 shows the recommended placement and routing for the oscillator layout.

Figure 9. Recommended placement and routing for the crystal oscillator PCB layout

6.2 Motor control pin arrangement in board design

LPC86x provides Flextime with PWM channels which can be designed for motor control signals from AT to

CB. See Table 5. There are three selections for PWM channel assigned to different pins. User can design with

Switch Matrix to choose different selection for FTMx_CHy.

Function name Type Selection 0 Selection 1 Selection 2 Selection 3

FTM0_EXTCLK I P0_24 P0_30 — Not connected

FTM0_CH0 I/O P0_17 P1_1 — Not connected

FTM0_CH1 I/O P0_18 P1_2 P0_16 Not connected

Table 5. Flextime PWM channels pin assignment

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NXP Semiconductors LPC86XHDG

LPC86x Hardware Design Guide

Function name Type Selection 0 Selection 1 Selection 2 Selection 3

FTM0_CH2 I/O P0_19 P1_3 P1_2 Not connected

FTM0_CH3 I/O P0_20 P1_4 P0_27 Not connected

FTM0_CH4 I/O P0_21 P1_5 P0_25 Not connected

FTM0_CH5 I/O P0_22 P1_6 P0_24 Not connected

FTM0_FAULT0 I P0_10 P1_7 P0_28 Not connected

FTM0_FAULT1 I P0_11 P1_12 P1_3 Not connected

FTM0_FAULT2 I P0_13 P1_13 — Not connected

FTM0_FAULT3 I P0_23 P1_14 — Not connected

FTM1_EXTCLK I P0_25 P0_29 — Not connected

FTM1_CH0 I/O P0_15 P1_8 — Not connected

FTM1_CH1 I/O P0_16 P1_9 — Not connected

FTM1_CH2 I/O P0_26 P0_31 — Not connected

FTM1_CH3 I/O P0_27 P1_0 — Not connected

FTM1_QD_PHA I P0_24 P0_29 — Not connected

FTM1_QD_PHB I P0_25 P0_30 — Not connected

Table 5. Flextime PWM channels pin assignment...continued

Motor control design requires that the PWM channels must be consistent, AT~CB correspond to PWM channels

0~5 or 5~0 respectively and prefer to 0~5.

During PCB layout, designer should consider arranging the PWM channels in same order with the AT~CB pins,

this way can avoid across wires on the board which results more difficulties for PCB routing.

Motor control AT-CB Flextimer PWM channels

PWM_AT FTM0_CH0

PWM_AB FTM0_CH1

PWM_BT FTM0_CH2

PWM_BB FTM0_CH3

PWM_CT FTM0_CH4

PWM_CB FTM0_CH5

Table 6. PCB layout pins sequence for PWM channels and AT~CB pins

6.3 EMI/EMC and ESD considerations for layout

In application design, the main purposes for EMC/EMI consideration are:

•The radiated and conducted EMI from the board should be lower than the allowed levels by the standards you

are following (EMI).

•The ability of the board to operate successfully counteracting the radiated and conducted electromagnetic

energy from other systems around it (EMC).

Every board or system is different as far as EMI/EMC and ESD issues are concerned, requiring its own solution.

However, the common guides to reduce an unwanted generation of electromagnetic energy are as shown

below:

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