Datasheet
27
LTC1759
Figure 14. Kelvin Sensing of Charging Current
TO R
S1
AND R
S2
1759 F14
DIRECTION OF CHARGING CURRENT
R
SENSE
APPLICATIONS INFORMATION
WUU
U
Charging Indication
When a CHARGECURRENT() command with a value of
zero is sent to the LTC1759, current stops flowing into the
battery. However, the command does not cause the CHGEN
pin to pull low. This prevents use of the CHGEN pin as a
charge termination indication. Figure 16 shows a circuit
that reliably indicates when the battery is receiving a
charge current.
The circuit shown, except for the optional 555 timer IC,
filters out the I
SET
DAC 80kHz output into a smooth signal.
Q1 and R5 partially isolate the capacitance of C1 from
effecting the I
SET
pin of the LTC1759. Q1 is configured as
1759 F15
V
BAT
L1
V
IN
HIGH
FREQUENCY
CIRCULATING
PATH
BAT
SWITCH NODE
C
IN
C
OUT
D1
Figure 15. High Speed Switching Path
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
a crude voltage level detector looking for voltage going
below approximately one volt on the emitter. The RC
circuit consisting of R4 and C1 filters low pulses from the
I
SET
pin. Q2 buffers the RC filter circuit allowing a more
logic level type interface. The circuit is powered from the
logic output driver of the CHGEN pin of the LTC1759. The
circuit does not need any capacitive supply bypassing to
function and draws little current. When the CHGEN pin
goes low, the current consumption of the circuit is elimi-
nated. Note that some resistor values must change de-
pending on the supply voltage connected to the V
DD
pin of
the LTC1759. An optional low power 555 timer can be
added to to give a blinking LED charge indication.
UV
V
DD
SYNC
SDB
CHGEN
V
LIMIT
I
LIMIT
DGND
I
SET
PROG
V
C
COMP1
AGND
RNR
THERM
SDA
SCL
INTB
22
21
8
32
33
9
10
2
3
35
1
34
30
29
31
23
26
36
U2
LTC1759
7
16
4
5
12
25
24
18
17
28
27
11
6
20
19
14
15
13
DCIN
DCDIV
INFET
V
CC
BOOSTC
CLP
CLN
TGATE
SW
BGATE
BOOST
GBIAS
SPIN
SENSE
BAT1
BAT2
V
SET
PGND
GROUND
TRIGGER
OUTPUT
RESET
8
7
6
5
LMC555
(OPTIONAL, SEE TEXT)
R1
R1
3.3V = 240Ω
5V = 510Ω
CHARGE
CHARGE (H)
1
2
3
4
V
CC
DISCHARGE
THRESHOLD
CONTROL
VOLTAGE
1759 F16
R2
4.7k
R3
2.7M
C3
0.1µF
V
DD
V
DD
C1
0.1µF
C2
0.1µF
R4
4.7M
R5
10k
R6
R6
3.3V = 330k
5V = 680k
Q1
MMBT3904
D
Q2, 2N7002
G
S
R7
330k
Figure 16. Battery Charge Indicator Circuit