DS1672U-3 datasheet(4/13 Pages) DALLAS

4 / 13 page

DS1672

4 of 13

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 3 volt is applied to VCC and a super cap is

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

between VCC and VBACKUP. The maximum current Imax would therefore be calculated as follows:

Imax = (3.0V – diode drop) / R2

~ (3.0V – 0.7V) / 2 k

Ω

~ 1.2 mA

Obviously, as the super cap changes, the voltage drop between VCC and VBACKUP will decrease and

therefore the charge current will decrease.

DS1672 PROGRAMMABLE TRICKLE CHARGER Figure 3

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

100Ω

Ω

TRICKLE CHARGE REGISTER

TCS = TRICKLE CHARGER SELECT

DS = DIODE SELECT

RS = RESISTOR SELECT

VCC

VBACKUP

2kΩ

4kΩ

DS1672U-3 Datasheet(PDF) 4 Page - Dallas Semiconductor