LTC1759 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1759' PDF : 28 Pages View PDF
LTC1759
APPLICATIONS INFORMATION
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 ISET DAC 80kHz output into a smooth signal.
Q1 and R5 partially isolate the capacitance of C1 from
effecting the ISET pin of the LTC1759. Q1 is configured as
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
ISET 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 VDD pin of
the LTC1759. An optional low power 555 timer can be
added to to give a blinking LED charge indication.
DIRECTION OF CHARGING CURRENT
RSENSE
1759 F14
TO RS1 AND RS2
Figure 14. Kelvin Sensing of Charging Current
SWITCH NODE
HIGH
VIN
CIN
FREQUENCY
CIRCULATING
PATH
L1
VBAT
D1
COUT
BAT
1759 F15
Figure 15. High Speed Switching Path
VDD
CHARGE
R1
R1
3.3V = 240Ω
5V = 510Ω
LMC555
1
8
GROUND
VCC
2
7
TRIGGER DISCHARGE
3
6
OUTPUT THRESHOLD
4
RESET
5
CONTROL
VOLTAGE
(OPTIONAL, SEE TEXT)
C1
0.1µF
R6
3.3V = 330k
5V = 680k
R4
4.7M
D
G
Q2, 2N7002
R6
R5
10k
S
Q1
MMBT3904
R7
330k
R2
4.7k
R3
2.7M
C3
0.1µF
C2
0.1µF
U2
LTC1759
7
UV
22
DCIN
16
VDD
VDD
21
DCDIV
4
SYNC
8
INFET
5 SDB
12
CHGEN
32
VCC
33
BOOSTC
25
VLIMIT
9
CLP
24
ILIMIT
10
CLN
18
DGND
2
TGATE
17
ISET
3
SW
28
PROG
35
BGATE
27
VC
1
BOOST
11
34
COMP1 GBIAS
6
AGND
30
SPIN
20 RNR
29
SENSE
19
THERM
31
BAT1
14
SDA
23
BAT2
15
SCL
13 INTB
26
VSET
36
PGND
1759 F16
Figure 16. Battery Charge Indicator Circuit
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.
27
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