Embedded Planet, Inc.
Agora | Product User Manual
Document Version: 1.0.0 | 11 Feb 22
Embedded Planet, Inc. | 31225 Bainbridge Rd Suite N, Solon, OH 44139 | 216-245-4180 | www.embeddedplanet.com |
Page 21 of 47
11.1.
Power | Battery
The Agora board is designed to operate with power from a battery connected to its JST connector. The
battery must be a secondary, 1SxP lithium battery. A 3.7 VDC nominal lithium-ion/lithium-polymer battery is
the suggested battery choice for Agora. The battery should be chosen with the consideration that the
minimum required voltage is 3.2V and the charge termination voltage is 4.2V. The capacity of the battery
may vary based on the needs of the end application. The battery charger has a charge current limit of
500mA which should be taken into consideration when the capacity and maximum allowable charge current
of the battery are determined. Configurations of Agora that include a LiPo battery conform to the suggested
specifications. The current default LiPo battery model provided with Agora is a 3.7V model with a 4400 mAh
capacity. If a battery is not available, the operator may apply a DC voltage (such as from a bench power
supply) within the battery operating voltage range specification (3.2V-4.2V, nominally 3.7V).
11.2.
Power | Battery Charging
The Agora board (PCBA) does not support LiPo charging. Configurations of Agora that include the
custom plastic housing & LiPo battery, however, include a LiPo charging circuit. The LiPo charging interface in
the Agora module configuration is a Micro-B USB port on the underside of the plastics module that can connect
to standard USB host devices. The charging port features two LEDs: one red LED, and one green LED.
The
red
LED illuminates to indicate the battery is
charging
.
The
green
LED illuminates to indicate the battery is
fully charged
(
trickle charge state
)
The battery charging process begins with a preconditioning charge. The charger then moves to a
constant-current quick charge for the bulk of the charge process. A constant-voltage trickle charge completes
the charge cycle and keeps the battery voltage topped-up while the voltage source of the charger (USB cable)
remains connected. The maximum charge current is 500mA.
11.3.
Power | Battery Monitor
Agora supports an integrated battery voltage monitor feature so that the system can react to changes to or
threshold levels of the battery voltage. The battery voltage monitor output that goes to the nRF52840’s analog
input (ADC) is set to one-half of the battery voltage. The battery voltage monitor is controlled by a GPIO on the
nRF52840 so that it can be disconnected from the battery if needed. Since the battery voltage may be as high as
4.2V, the ADC reference must be set for at least 2.4V. With the battery voltage monitor characterized as a high
impedance circuit, the ADC sample time must be set to the maximum setting.
