Rainbow Electronics DS2770 - Manual (Page 7)

DS2770
7 of 27
After initiation and clearing of the above conditions, fast charging begins with the CC pin driven low.
During fast charging, CC remains low, except for periodic testing of premature charge source removal in
which CC is driven high for approximately 27
ms every 55ms. As long as the charge source remains
connected and the temperature remains in the valid range, charging will proceed per the method selected
by the CTYPE bit. If the charge source is removed or the Stop Charge command [BEh] is issued, CC is
driven high and charging must be reinitiated by one of the two charge initiation methods described
previously. Charging will also be stopped if the DQ line is low for >2s and the CINI bit is set to 0.
Assuming any previous charge status has been cleared, a “charge in progress” status is indicated during
fast charging with (0, 1) values, respectively, in the CSTAT1 and CSTAT0 bits of the Status Register.
Upon charge completion according to the method selected with the CTYPE bit, or completion due to
either of the secondary methods, pin CC will return to the high state, and a charge done condition will be
flagged with (1, 1) values in the CSTAT1 and CSTAT0 bits of the Status Register. Note that the charge
done status is latched and must be cleared by a write of any value to the Status Register. Once charging
has been completed or aborted, the DS2770 may either enter the Sleep Mode or remain active, depending
on the state of the PMOD bit described previously in the Power Modes section.
RECHARGEABLE LITHIUM CHARGER OPERATION
Fast charging of lithium cell types is performed in two distinct regions. The bulk charge region delivers
most of the charge to the cell by gating current from the charge source while the battery voltage is below
the charge voltage threshold, V
CV
. The CC pin remains low, driving a PNP or P-channel MOSFET
switch. When the battery voltage reaches V
CV
, the pulse region begins in which a pulse-charge technique
is employed that allows CC to remain low for a delay period of t
VCV
(875ms) after which CC is driven
high. When the battery voltage decays below V
CV
, CC is again driven low and the cycle is repeated. The
pulse region of charge continues with the CC duty cycle slowly changing. Eventually, the battery voltage
decay time, and thus the CC high time, becomes longer than 13.125s, and charge is terminated. The
charge decay time limit, t
CD
, includes one 875ms period of CC low and 15 periods high for a total time of
14s. The average charge rate at termination is 1/16 of the rate set by the charge source. See Figure 3 for
an illustration of the t
CD
decay method. See the Secondary Charge Termination section for the secondary
termination means based on time or temperature included for increased safety.