Operation - Linear Technology 789 Quick Start Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789

OPERATION

Demonstration circuit 789 allows three methods of
charge termination which are selected using jumper
JP1. In the lower "TIMER" position, the charge cy-
cle terminates at the end of the timer period as set
by capacitor C2. The 3 hour timer is sufficient time
to fully charge a depleted battery when charging at
a current level ranging from C/2 to 1C.
The upper "ITERM" position selects minimum
charge current termination (I DETECT ). This method
Table 2. Jumper Positions for Charge Current and Termination Current.
ICHG-1
(JP3)
HIGH
LOW
The CHRG LED always indicates the presence of
charge current that is greater than the I DETECT cur-
rent level that is selected by the IDET jumper (JP4).
The LED is on for charge current greater than IDET,
regardless of the termination method used as set by
jumper JP1.
When minimum charge
(I DETECT ) is used, the charge cycle ends when the
Charge current drops below the I DETECT level. The
CHRG LED also goes off.
The CURRENT MONITOR terminal can be used to
indicate charge current level at all times during the
charge cycle with 1 Volt indicating 100% of the
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
ICHG-2 Charge Current
(JP2)
C 1A
C / 5 200mA
C 500mA
C/5 100mA
current termination
terminates the charge cycle when the charge cur-
rent drops to a programmed threshold level after
the battery has reached the constant voltage portion
of the charge cycle. Placing the jumper (JP1) in the
middle position defeats the on board termination
thus allowing external user termination.
The charge current and the termination current are
selected using a combination of jumpers JP2, JP3
and JP4. (See table 2)
IDET JUMPER (JP4)
100MA
Idetect Current
100mA
100mA
100mA
100mA
programmed current. This terminal can also be
used to program other charge currents by removing
jumper JP3 and connecting an external program-
ming resistor from the CURRENT MONITOR termi-
nal to ground.
The COMP IN terminal is connected to the com-
parator's non-inverting input when selected using
the COMP jumper (JP5 upper position) and COMP
OUT is the open drain comparator output. The
comparator output also drives the COMP LED. The
comparator monitors the battery voltage when
jumper (JP5) is in the BAT (lower) position. See
data sheet for details.
C / 10
Charge Current Idetect Current
500mA
100mA
250mA
50mA
50mA
50mA
25mA
25mA
2