FEATURES
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LT1505
Constant-Current/Voltage
High Efficiency Battery Charger
DESCRIPTIO
The LT
®
1505 PWM battery charger controller fast charges
multiple battery chemistries including lithium-ion (Li-Ion),
nickel-metal-hydride (NiMH) and nickel-cadmium (NiCd)
using constant-current or constant-voltage control. Maxi-
mum current can be easily programmed by resistors or a
DAC. The constant-voltage output can be selected for 3 or 4
series Li-Ion cells with 0.5% accuracy.
A third control loop limits the current drawn from the AC
adapter during charging*. This allows simultaneous opera-
tion of the equipment and fast battery charging without over-
loading the AC adapter.
The LT1505 can charge batteries ranging from 2.5V to 20V
with dropout voltage as low as 0.5V. Synchronous
N-channel FETs switching at 200kHz give high efficiency
and allow small inductor size. A diode is not required in
series with the battery because the charger automatically
enters a 10µA sleep mode when the wall adapter is un-
plugged. A logic output indicates Li-Ion full charge when
current drops to 20% of the programmed value.
The LT1505 is available in a 28-pin SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*US Patent No. 5,723,970
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Simple Charging of Li-Ion, NiMH and NiCd Batteries
Very High Efficiency: Up to 97%
Precision 0.5% Charging Voltage Accuracy
Preset Battery Voltages: 12.3V, 12.6V,
16.4V and 16.8V
5% Charging Current Accuracy
Charging Current Programmed by Resistor or DAC
0.5V Dropout Voltage, Duty Cycle > 99.5%
AC Adapter Current Limit* Maximizes Charging Rate
Flag Indicates Li-Ion Charge Completion
Auto Shutdown with Adapter Removal
Only 10µA Battery Drain When Idle
Synchronizable Up to 280kHz
APPLICATIO S
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Notebook Computers
Portable Instruments
Chargers for Li-Ion, NiMH, NiCd and Lead Acid
Rechargeable Batteries
TYPICAL APPLICATION
M3
Si4435
DBODY*
V
IN
(FROM
ADAPTER)
TO
SYSTEM POWER
R
S4
0.025Ω
C1
1µF
C
IN
47µF
35V
V
CC
BOOST
BOOSTC
GBIAS
CLN
CLP
INFET
UV
R6
4k
SYNC
SHDN
FLAG
*BODY DIODE
POLARITY MUST
BE AS SHOWN
C6
0.1µF
CAP
COMP1
R1
1k
C7
0.68µF
BAT2 BAT
SENSE
LT1505
TGATE
SW
BGATE
V
C
PROG
3 CELL
V
FB
4.2V
4.1V
AGND
PGND
SPIN
300Ω
C
PROG
1µF
R
PROG
4.93k
1%
R
X4
3k
0.33µF
R
S2
200Ω
1%
R
S3
200Ω
1%
5Ω
C3
D2
2.2µF MMSD4148T1
M1
Si4412
M2
Si4412
D4
MBRS140
C4
0.1µF
D3
MMSD4148T1
C2
0.68µF
L1
15µH
R
S1
0.025Ω
V
BAT
C
OUT
22µF
25V
×
2
12.6V
BATTERY
R7
500Ω
100k
R5
4k
* DBODY IS THE BODY DIODE OF M3
C
IN
: SANYO OS-CON
L1: SUMIDA CDRH127-150
(CAN BE FROM 10µH TO 30µH)
1505 F01
Figure 1. Low Dropout 4A Lithium-Ion Battery Charger
1505fc
U
U
U
1
LT1505
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
V
CC
, CLP, CLN, INFET, UV, 3CELL, FLAG................ 27V
SW Voltage with Respect to GND ........................... – 2V
BOOST, BOOSTC Voltage with Respect to V
CC
....... 10V
GBIAS ..................................................................... 10V
SYNC, BAT2, BAT, SENSE, SPIN ............................ 20V
V
C
, PROG, V
FB
, 4.1V, 4.2V ........................................ 7V
CAP, SHDN ..........................................................
±3mA
TGATE, BGATE Current Continuous ....................... 0.2A
TGATE, BGATE Output Energy (per cycle) ............... 2µJ
Maximum Operating V
CC
......................................... 24V
Operating Ambient Temperature Range ....... 0°C to 70°C
Operating Junction Temperature Range .... 0°C to 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
BOOST
TGATE
SW
SYNC
SHDN
AGND
UV
INFET
CLP
1
2
3
4
5
6
7
8
9
28 PGND
27 BGATE
26 GBIAS
25 BOOSTC
24 V
CC
23 BAT
22 SPIN
21 SENSE
20 BAT2
19 PROG
18 V
C
17 V
FB
16 3CELL
15 4.2V
ORDER PART
NUMBER
LT1505CG
CLN 10
COMP1 11
CAP 12
FLAG 13
4.1V 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 100°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 18V, V
BAT
= 12.6V, V
CLN
= V
CC
(LT1505), no load on any
outputs unless otherwise noted.
PARAMETER
Overall
Supply Current
Sense Amplifier CA1 Gain and Input Offset Voltage
(With R
S2
= 200Ω, R
S3
= 200Ω)
(Measured across R
S1
, Figure 1) (Note 2)
BOOST Pin Current
V
CC
≤
24V
11V
≤
V
CC
≤
24V , 0V
≤
V
BAT
≤
20V
R
PROG
= 4.93k
R
PROG
= 4.93k
R
PROG
= 49.3k
V
BOOST
= V
SW
+ 8V, 0V
≤
V
SW
≤
20V
TGATE High
TGATE Low
V
BOOSTC
= V
CC
+ 8V
R
PROG
= 4.93k, Measured at V
FB
with V
A
Supplying I
PROG
and Switching Off
11V
≤
V
CC
≤
24V
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
BOOSTC Pin Current
Reference
Reference Voltage (Note 3)
Reference Voltage Tolerance
2
U
U
W
W W
U
W
TOP VIEW
BOOST
TGATE
SW
SYNC
SHDN
AGND
UV
INFET
NC
1
2
3
4
5
6
7
8
9
28 PGND
27 BGATE
26 GBIAS
25 BOOSTC
24 V
CC
23 BAT
22 SPIN
21 SENSE
20 BAT2
19 PROG
18 V
C
17 V
FB
16 3CELL
15 4.2V
ORDER PART
NUMBER
LT1505CG-1
NC 10
GND 11
CAP 12
FLAG 13
4.1V 14
G PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 100°C/ W
NOTE:
LT1505CG-1 DOES NOT
HAVE INPUT CURRENT
LIMITING FUNCTION.
MIN
TYP
12
MAX
15
105
108
13
3
3
UNITS
mA
mV
mV
mV
mA
mA
mA
q
95
92
7
100
10
2
2
1
2.453
2.441
2.465
2.477
2.489
V
V
1505fc
LT1505
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 18V, V
BAT
= 12.6V, V
CLN
= V
CC
(LT1505), no load on any
outputs unless otherwise noted.
PARAMETER
Preset Battery Voltage (12.3V, 16.4V, 12.6V, 16.8V)
All Preset Battery Voltages
Preset Battery Voltage Tolerance
BAT2 Pin Input Current
Voltage Setting Resistors Tolerance (R4, R5, R6, R7)
Shutdown
Undervoltage Lockout (TGATE and BGATE “Off”)
Threshold (Note 9)
UV Pin Input Current
Reverse Current from Battery in Micropower
Shutdown (Note 10)
Shutdown Threshold at SHDN Pin When V
CC
is Connected
SHDN Pin Current
Supply Current in Shutdown
(V
SHDN
is Low, V
CC
is Connected)
Minimum I
PROG
for Switching “On”
Minimum I
PROG
for Switching “Off” at V
PROG
≤
1V
Current Sense Amplifier CA1 Inputs (SENSE, BAT)
Input Bias Current (SENSE, BAT)
Input Common Mode Low
Input Common Mode High
SPIN Input Current
Oscillator
Switching Frequency (f
NOM
)
Switching Frequency Tolerance
SYNC Pin Input Current
Synchronization Pulse Threshold on SYNC Pin
Synchronization Frequency
Maximum Duty Cycle
V
BOOST
Threshold to Turn TGATE Off
(Comparator A2) (Note 4)
Maximum Duty Cycle of Natural Frequency 200kHz
(Note 5)
Current Amplifier CA2
Transconductance
Maximum V
C
for Switch Off
I
VC
Current (Out of Pin)
V
C
at Shutdown
V
C
≥
0.6V
V
C
< 0.45V
V
SHDN
= Low (Shutdown)
V
C
= 1V, I
VC
=
±1µA
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
Measured at BAT2 Pin
(V
BAT
+ 0.3V)
≤
V
CC
≤
24V
V
BAT2
= V
PRESET
– 1V
q
q
MIN
TYP
0.5
MAX
UNITS
%
–1
– 40
1
6
40
6.7
7.25
5
10
50
2
8
15
20
– 22
%
µA
%
V
µA
µA
V
µA
mA
µA
mA
Measured at UV Pin
0V
≤
V
UV
≤
8V
V
BAT
≤
20V, V
UV
≤
0.4V,
V
CC
= V
SW
= Battery Voltage
q
q
6.3
–1
q
1
0V
≤
V
SHDN
≤
3V
V
CC
≤
24V
–1
–1
–4
– 2.4
– 50
V
SHDN
= High
V
SHDN
= Low (Shutdown)
q
q
q
– 120
– 10
V
CC
– 0.3
2
10
µA
µA
V
V
mA
µA
kHz
kHz
mA
µA
V
kHz
– 0.25
V
SHDN
= High, V
SPIN
≥
2V (Note 8)
V
SHDN
= Low (Shutdown)
q
180
170
V
SYNC
= 0V
V
SYNC
= 2V
0.9
240
200
200
220
230
– 0.5
– 30
1.2
2.0
280
Measured at (V
BOOST
– V
SW
)
Low to High
Hysteresis
q
q
6.8
85
7.3
0.25
90
7.6
V
V
%
150
200
300
0.6
50
3
0.35
µmho
V
µA
mA
V
1505fc
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LT1505
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 18V, V
BAT
= 12.6V, V
CLN
= V
CC
(LT1505), no load on any
outputs unless otherwise noted.
PARAMETER
Voltage Amplifier VA
Transconductance (Note 3)
Output Source Current
V
FB
Input Bias Current
Current Limit Amplifier CL1
Turn-On Threshold
Transconductance
CLP Input Current
CLN Input Current
Input P-Channel FET Driver (INFET)
INFET “On” Clamping Voltage (V
CC
– V
INFET
)
INFET “On” Driver Current
INFET “Off” Clamping Voltage (V
CC
– V
INFET
)
INFET “Off” Drive Current
Charging Completion Flag (Comparator E6)
Charging Completion Threshold (Note 6)
Threshold On CAP Pin
V
CAP
at Shutdown
FLAG (Open Collector) Output Low
FLAG Pin Leakage Current
Gate Drivers (TGATE, BGATE)
V
GBIAS
V
TGATE
High (V
TGATE
– V
SW
)
V
BGATE
High
V
TGATE
Low (V
TGATE
– V
SW
)
V
BGATE
Low
Peak Gate Drive Current
Gate Drive Rise and Fall Time
V
TGATE
, V
BGATE
at Shutdown
0.5mA Output Current
Output Current from 50µA to 500µA
0.5mA Output Current
0.5mA Output Current
V
CC
≥
11V
V
INFET
= V
CC
– 6V
V
CC
Not Connected, I
INFET
< – 2µA
V
CC
Not Connected, (V
CC
– V
INFET
)
≥
2V
Measured at V
RS1
, V
CAP
= 2V (Note 7)
Low to High Threshold
High to Low Threshold
V
SHDN
= Low (Shutdown)
V
CAP
= 4V, I
FLAG
< 1mA
V
CAP
= 0.6V
11V < V
CC
< 24V, I
GBIAS
≤
15mA
V
SHDN
= Low (Shutdown)
I
TGATE
≤
20mA, V
BOOST
= V
GBIAS
– 0.5V
I
BGATE
≤
20mA
I
TGATE
≤
50mA
I
BGATE
≤
50mA
10nF Load
1nF Load
V
SHDN
= Low (Shutdown)
I
TGATE
= I
BGATE
= 10µA
14
q
q
q
q
q
q
q
q
q
q
q
q
q
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
0.21
1.1
– 10
TYP
0.6
MAX
1.0
25
UNITS
mho
mA
nA
Output Current from 50µA to 500µA
V
FB
= V
PROG
= V
REF
+ 10mV
At 0.5mA VA Output Current, T
A
< 70°C
(3 CELL, 4.1V, 4.2V Are Not Connected, V
BAT2
= 0V)
87
0.5
92
1
1
0.8
97
3
3
2
9
1.4
mV
mho
µA
mA
V
mA
V
mA
6.5
8
7.8
20
– 2.5
20
3.3
0.13
28
4.2
0.3
0.3
3
0.6
mV
V
V
V
V
µA
V
V
V
V
V
V
A
ns
V
8.4
5.6
6.2
9.1
1
6.6
7.2
9.6
3
0.8
0.8
1
25
q
1
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Tested with Test Circuit 1.
Note 3:
Tested with Test Circuit 2.
Note 4:
When V
CC
and battery voltage differential is low, high duty factor
is required. The LT1505 achieves a duty factor greater than 99% by
skipping cycles. Only when V
BOOST
drops below the comparator A2
threshold will TGATE be turned off. See Applications Information.
Note 5:
When the system starts, C2 (boost cap) has to be charged up to
drive TGATE and to start the system. The LT1505 will keep TGATE off and
turn BGATE on for 0.2µs at 200kHz to charge up C2. Comparator A2
senses V
BOOST
and switches to the normal PWM mode when V
BOOST
is
above the threshold.
Note 6:
See “Lithium-Ion Charging Completion” in the Applications
Information Section.
Note 7:
Tested with Test Circuit 3.
Note 8:
I
SPIN
keeps switching on to keep V
BAT
regulated when battery is
not present to avoid high surge current from C
OUT
when battery is
inserted.
Note 9:
Above undervoltage threshold switching is enabled.
Note 10:
Do not connect V
CC
directly to V
IN
(see Figure 1). This connection
will cause the internal diode between V
BAT
and V
CC
to be forward-biased
and may cause high current to flow from V
IN
. When the adapter is
removed, V
CC
will be held up by the body diode of M1.
1505fc
4
LT1505
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency of Figure 1 Circuit
105
V
IN
= 19V
V
BAT
= 12.6V
100
9.2
9.1
9.0
8.9
125°C
25°C
EFFICIENCY (%)
V
GBIAS
(V)
∆V
REF
(V)
95
90
85
80
0
1
2
I
BAT
(A)
1505 G01
3
∆V
FB
vs I
VA
(Voltage Amplifier)
4
3
THRESHOLD (mV)
∆V
FB
(mV)
2
125°C
1
25°C
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
I
VA
(mA)
1505 G04
92
I
CC
(mA)
PROG Pin Characteristics
6
CURRENT FEEDBACK
AMPLIFIER OPEN LOOP
–1.2
–1.0
–0.8
125°C
–0.6
–0.4
REFERENCE VOLTAGE (V)
I
PROG
(mA)
I
VC
(mA)
0
–6
0
1
2
3
V
PROG
(V)
4
5
1505 G07
U W
4
5
25°C
V
GBIAS
vs I
GBIAS
0°C
V
REF
Line Regulation
0.003
0°C
≤
T
J
≤
125°C
0.002
0.001
0
8.8
8.7
8.6
8.5
8.4
8.3
8.1
0
–2 –4 –6 –8 –10 –12 –14 –16 –18 –20
I
GBIAS
(mA)
1505 G02
ALL TEMPERATURES
–0.001
–0.002
–0.003
0
5
10
15
V
CC
(V)
20
25
30
1505 G03
Current Limit Amplifier
CL1 Threshold
98
15
I
CC
vs V
CC
96
14
94
13
12
0°C
25°C
125°C
90
11
88
0
25
50
75
100
TEMPERATURE (°C)
125
1505 G05
10
10
13
16
19
V
CC
(V)
22
25
1505 G06
V
C
Pin Characteristics
2.470
2.468
2.466
2.464
2.462
2.460
2.458
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
V
C
(V)
1505 G08
Reference Voltage vs Temperature
–0.2
0
0.2
0.4
0.6
0.8
1.0
0
125
50
75
100
25
JUNCTION TEMPERATURE (°C)
150
1505 G09
1505fc
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