Datasheet
19
4009fd
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
I
mV R µA
V R
C
MAX
PROG
PROG
10
400 11 67
1 2085
=
( )
– • .
. –
•• .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.
Figure 9. Digital C/10 Indicator
Figure 10. Microprocessor Status Interface
17
8
INTV
DD
CHRG
Q1
TP0610T
Q2
2N7002
100k
LTC4009
4009 F09
100k
V
LOGIC
100k
C/10
CHRG
100k
0.1µF
Q3
2N7002
33k
200k
4009 F10
V
DD
3.3V
µP
IN
OUT
LTC4009
CHRG
8
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