LTC4009-2_15 Datasheet, PDF (19/28 Pages) Linear Technology – High Efficiency, Multi-Chemistry Battery Charger

LTC4009
LTC4009-1/LTC4009-2
Applications Information
If R_PROG is greater than 26.7k, the actual level at which
low charge current is detected will be less than C/10. The
highest value of R_PROG that can be used while reliably
indicating low charge current before reaching final V_BAT
is 30.1k. R_PROG can safely be set to values higher than
this, but low current indication will be lost.
If R_PROG is less than 26.7k, low charge current detection
occurs at a level higher than C/10. More importantly, the
LTC4009 becomes increasingly sensitive to reverse cur-
rent. The lowest value of R_PROG that can be used without
the risk of erroneous boost operation detection at end of
charge is 26.1k. Values of R_PROG less than this should not
be used. See the Operation section for more information
about reverse current.
The nominal fractional value of I_MAX at which C/10 indica-
tion occurs is given by:
( ) I_C10
( ) ^I_MAX
=
400mV – R_PROG • 11.67µA
1.2085V – R_PROG • 11.67µA
Direct digital monitoring of C/10 indication is possible with
an external application circuit like the one shown in Figure 9.
The LTC4009 initially indicates C/10 until the PWM has
started and the actual charge current can be determined
(PROG pin voltage). The 0.1µF capacitor from CHRG to
GND is used to filter this initial pulse, which is typically
less than 2ms when starting toward a final charge current
that is actually greater than C/10. If external circuitry is
insensitive to, or can ignore, this momentary C/10 indica-
tion at start-up, the capacitor can be omitted.
By using two different value pull-up resistors, a micro-
processor can detect three states from this pin (charging,
C/10 and not charging). See Figure 10. When a digital
output port (OUT) from the microprocessor drives one
of the resistors and a second digital input port polls the
network, the charge state can be determined as shown
in Table 5.
3.3V
LTC4009
CHRG 8
200k
33k
V_DD
µP
OUT
IN
4009 F10
Figure 10. Microprocessor Status Interface
Table 5. Digital Read Back State (IN, Figure 10)
LTC4009
CHARGER STATE
OUT STATE
Hi-Z
1
Off
1
1
C/10 Charge
0
1
Bulk Charge
0
0
INTV_DD 17
LTC4009
CHRG 8
V_LOGIC
100k
Q1
TP0610T
0.1µF
100k
100k 100k
Q2
2N7002
C/10
CHRG
Q3
2N7002
4009 F09
Figure 9. Digital C/10 Indicator
4009fd
19