Applied Data Systems Bitsy Plus, User Manual, Page: 48 / 68

Bitsy Plus User’s Manual
Page 38 ADS document # 110114-1001A
The supercaps discharge linearly from the constant-current drain during sleep according to the
equation
t =
Eff * C * 0.2) - V - (V
f i
sleep
I
where
t is the duration the system can sleep, in seconds;
V
i
is the initial charge voltage of the capacitor;
V
f
is the supercap voltage at which onboard systems will fail (assume 3.2 V);
C is the capacitance of the supercaps, in Farads;
Eff is the efficiency of power delivery; 85-90% is a safe value to use;
I
sleep
is the amount of current the system consumes while in sleep mode.
For example, a system with fully charged 1.65 F supercaps and a sleep current of 4 mA can expect
to run for up to ten minutes after a power failure. Consult the electrical specifications of section
6.2.4 and power consumption specifications of 6.2.5 for the values to use in your calculations.
5.3.6 Backlight Power
The Bitsy Plus provides software control of Backlight Intensity and On/Off using the ADSmartIO
controller. Power for the backlight is not routed through the board, and must be supplied to the
backlight separately from the Bitsy Plus. This provides the greater flexibility when selecting
backlight inverters for an application. See section 4.6.6 for further details about backlight control.
5.3.7 Battery Trickle Charger (factory option)
The Bitsy Plus includes a trickle charger for basic charging of external batteries. The following
diagram illustrates the charging circuit and a standard means of combining it with DC line power.
Bitsy Plus
VBatt_Pos
Ground
VBatt_Neg
DCIn_Pos
DC "Line"
power
Charge
Ground
The Charge signal comes from the ADSmartIO controller (port PB0) and is also available on J3
pin 22 for external use. Writing a logic "1" to PB0 turns on the trickle charging. It is up to the
application to manage battery charging.