Data Sheet

LC840PA
Datasheet
https://www.lairdconnect.com
39
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6 HARDWARE INTEGRATION SUGGESTIONS
6.1 Circuit
The LC840PA is easy to integrate, requiring no external components on your board apart from those which you require for
development and in your end application.
The following are suggestions for your design for the best performance and functionality.
Checklist (for Schematic):
▪ LC840PA power supply options:
Option 1 – Normal voltage power supply mode entered when the external supply voltage is connected to both the VDD and
VDDH pins (so that VDD equals VDD_HV). Connect external supply within range 3.0V to 3.6V range to LC840PA VDD and
VDD_HV pins.
OR
Option 2 – High voltage mode power supply mode (using LC840PA VDD_HV pin) entered when the external supply
voltage in ONLY connected to the VDDH pin and the VDD pin is not connected to any external voltage supply. Connect
external supply within range 3.0V to 5.5V range to LC840PA VDD_HV pin. LC840PA VDD pin left unconnected.
For either option, if you use USB interface then the LC840PA VBUS pin must be connected to external supply within the
range 4.35V to 5.5V. When using the LC840PA VBUS pin, you MUST externally fit a 4.7uF to ground.
External power source should be within the operating range, rise time and noise/ripple specification of the LC840PA. Add
decoupling capacitors for filtering the external source. Power-on reset circuitry within LC840PA module incorporates brown-
out detector, thus simplifying your power supply design. Upon application of power, the internal power-on reset ensures that
the module starts correctly.
▪ VDD and coin-cell operation
With a built-in DCDC (operating range 3.0V to 3.6V) that reduces the peak current required from a coin cell battery, making
it easier to use with a coin cell. The coin cell battery MUST be able to service the peak and average current requirements
of the customer application.
▪ AIN (ADC) and SIO pin IO voltage levels
LC840PA SIO voltage levels are at VDD. Ensure input voltage levels into SIO pins are at VDD also (if VDD source is a
battery whose voltage will drop). Ensure ADC pin maximum input voltage for damage is not violated.
▪ AIN (ADC) impedance and external voltage divider setup
If you need to measure with ADC a voltage higher than 3.6V, you can connect a high impedance voltage divider to lower
the voltage to the ADC input pin.
▪ JTAG
This is REQUIRED as Nordic SDK applications can only be loaded using the JTAG (smartBASIC firmware can be loaded
using the JTAG as well as the UART).
Laird recommends you use JTAG (2-wire interface) to handle future LC840PA module firmware upgrades. You MUST wire
out the JTAG (2-wire interface) on your host design (see Figure 7, where four lines should be wired out, namely SWDIO,
SWDCLK, GND and VCC). Firmware upgrades can still be performed over the LC840PA UART interface, but this is slower
(60 seconds using UART vs. 10 seconds when using JTAG) than using the LC840PA JTAG (2-wire interface).
JTAG may be used if you intend to use Flash Cloning during production to load smartBASIC scripts.
▪ UART
Required for loading your smartBASIC application script during development (or for subsequent firmware upgrades (except
JTAG for FW upgrades and/or Flash Cloning of the smartBASIC application script). Add connector to allow interfacing with
UART via PC (UART–RS232 or UART-USB). UART is required for IEEE802.15.4 ProFLEX application for host
interface and optional debug interface.
▪ UART_RX and UART_CTS
SIO_08 (alternative function UART_RX) is an input, set with internal weak pull-up (in firmware). The pull-up prevents the
module from going into deep sleep when UART_RX line is idling.
SIO_07 (alternative function UART_CTS) is an input, set with internal weak pull-down (in firmware). This pull-down
ensures the default state of the UART_CTS will be asserted which means can send data out of the UART_TX line. Laird
recommends that UART_CTS be connected.
▪ nAutoRUN pin and operating mode selection (smartBASIC only)
nAutoRUN pin needs to be externally held high or low to select between the two LC840PA operating modes at power-up:
– Self-contained Run mode (nAutoRUN pin held at 0V).