Figure 5. programmable trickle charger, And a super cap is connected to v, And v – Rainbow Electronics DS1672 User Manual

Page 9: Maximum current i, Would, therefore, be calculated as follows: i

DS1672

9 of 12

Diode and resistor selection is determined by the user according to the maximum current desired for
battery or super cap charging. The maximum charging current can be calculated as illustrated in the
following example. Assume that a system power supply of 3V is applied to V

and a super cap is

connected to V

BACKUP

. Also assume that the trickle charger has been enabled with a diode and resistor R2

between V

and V

BACKUP

. The

maximum current I

MAX

would, therefore, be calculated as follows:

MAX

= (5.0V - diode drop) / R1

» (5.0V - 0.7V) / 2kW » 2.2mA

As the super cap changes, the voltage drop between V

and V

BACKUP

will decrease and, therefore, the

charge current will decrease.

Figure 5. Programmable Trickle Charger

1 OF 16 SELECT

NOTE: ONLY 1010 ENABLES

1 OF 2

SELECT

1 OF 3

SELECT

TCS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

250

TRICKLE CHARGE REGISTER

TCS = TRICKLE CHARGER SELECT
DS = DIODE SELECT
RS = RESISTOR SELECT

BACKUP