1
LT1505
1505fc
TYPICAL APPLICATION
U
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
Constant-Current/Voltage
High Efficiency Battery Charger
Figure 1. Low Dropout 4A Lithium-Ion Battery Charger
■
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
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.
■
Notebook Computers
■
Portable Instruments
■
Chargers for Li-Ion, NiMH, NiCd and Lead Acid
Rechargeable Batteries
, LTC and LT are registered trademarks of Linear Technology Corporation.
5Ω
CPROG
1µF
300Ω
C7
0.68µF
C6
0.1µF
C3
2.2µF
COUT
22µF
25V
×2
C2
0.68µF
VBAT
12.6V
BATTERY
* DBODY IS THE BODY DIODE OF M3
CIN: SANYO OS-CON
L1: SUMIDA CDRH127-150
(CAN BE FROM 10µH TO 30µH)
M1
Si4412
M2
Si4412 D4
MBRS140
D2
MMSD4148T1
D3
MMSD4148T1
R7
500Ω
100k
R5
4k
R1
1k
R6
4k
*BODY DIODE
POLARITY MUST
BE AS SHOWN
RS4
0.025Ω
M3
Si4435
DBODY*
TO
SYSTEM POWER
VIN
(FROM
ADAPTER)
RS1
0.025Ω
L1
15µH
1505 F01
RPROG
4.93k
1%
0.33µF
RX4
3k
RS2
200Ω
1%
RS3
200Ω
1%
CIN
47µF
35V
C1
1µF
C4
0.1µF
BAT2 BAT SENSE
LT1505
VCC BOOST BOOSTC
SPIN
PGND
AGND
4.1V
4.2V
VFB
3 CELL
PROG
VC
BGATE
COMP1
CAP
FLAG
SHDN
SYNC
UV
INFET
SW
TGATE
GBIAS
CLP
CLN
*US Patent No. 5,723,970
2
LT1505
1505fc
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
ABSOLUTE MAXIMUM RATINGS
W
WW
U
(Note 1)
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
ORDER PART
NUMBER
LT1505CG LT1505CG-1
ORDER PART
NUMBER
T
JMAX
= 125°C, θ
JA
= 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TOP VIEW
G PACKAGE
28-LEAD PLASTIC SSOP
28
27
26
25
24
23
22
21
20
19
18
17
16
15
BOOST
TGATE
SW
SYNC
SHDN
AGND
UV
INFET
CLP
CLN
COMP1
CAP
FLAG
4.1V
PGND
BGATE
GBIAS
BOOSTC
V
CC
BAT
SPIN
SENSE
BAT2
PROG
V
C
V
FB
3CELL
4.2V
T
JMAX
= 125°C, θ
JA
= 100°C/W
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TOP VIEW
G PACKAGE
28-LEAD PLASTIC SSOP
28
27
26
25
24
23
22
21
20
19
18
17
16
15
BOOST
TGATE
SW
SYNC
SHDN
AGND
UV
INFET
NC
NC
GND
CAP
FLAG
4.1V
PGND
BGATE
GBIAS
BOOSTC
V
CC
BAT
SPIN
SENSE
BAT2
PROG
V
C
V
FB
3CELL
4.2V
NOTE: LT1505CG-1 DOES NOT
HAVE INPUT CURRENT
LIMITING FUNCTION.
ELECTRICAL CHARACTERISTICS
PACKAGE/ORDER INFORMATION
W
UU
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any
outputs unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Overall
Supply Current V
CC
≤ 24V ●12 15 mA
Sense Amplifier CA1 Gain and Input Offset Voltage 11V ≤ V
CC
≤ 24V , 0V ≤ V
BAT
≤ 20V
(With R
S2
= 200Ω, R
S3
= 200Ω)R
PROG
= 4.93k 95 100 105 mV
(Measured across R
S1
, Figure 1) (Note 2) R
PROG
= 4.93k ●92 108 mV
R
PROG
= 49.3k 7 10 13 mV
BOOST Pin Current V
BOOST
= V
SW
+ 8V, 0V ≤ V
SW
≤ 20V
TGATE High 2 3 mA
TGATE Low 2 3 mA
BOOSTC Pin Current V
BOOSTC
= V
CC
+ 8V 1 mA
Reference
Reference Voltage (Note 3) R
PROG
= 4.93k, Measured at V
FB
with V
A
2.453 2.465 2.477 V
Supplying I
PROG
and Switching Off
Reference Voltage Tolerance 11V ≤ V
CC
≤ 24V ●2.441 2.489 V
3
LT1505
1505fc
PARAMETER CONDITIONS MIN TYP MAX UNITS
Preset Battery Voltage (12.3V, 16.4V, 12.6V, 16.8V)
All Preset Battery Voltages Measured at BAT2 Pin 0.5 %
Preset Battery Voltage Tolerance (V
BAT
+ 0.3V) ≤ V
CC
≤ 24V ●–1 1 %
BAT2 Pin Input Current V
BAT2
= V
PRESET
– 1V ●6µA
Voltage Setting Resistors Tolerance (R4, R5, R6, R7) –40 40 %
Shutdown
Undervoltage Lockout (TGATE and BGATE “Off”) Measured at UV Pin ●6.3 6.7 7.25 V
Threshold (Note 9)
UV Pin Input Current 0V ≤ V
UV
≤ 8V ●–1 5 µA
Reverse Current from Battery in Micropower V
BAT
≤ 20V, V
UV
≤ 0.4V, 10 50 µA
Shutdown (Note 10) V
CC
= V
SW
= Battery Voltage
Shutdown Threshold at SHDN Pin When V
CC
●12V
is Connected
SHDN Pin Current 0V ≤ V
SHDN
≤ 3V 8 µA
Supply Current in Shutdown V
CC
≤ 24V 15 20 mA
(V
SHDN
is Low, V
CC
is Connected)
Minimum I
PROG
for Switching “On” –1 –4 –22 µA
Minimum I
PROG
for Switching “Off” at V
PROG
≤ 1V ●–1 –2.4 mA
Current Sense Amplifier CA1 Inputs (SENSE, BAT)
Input Bias Current (SENSE, BAT) V
SHDN
= High ●–50 –120 µA
V
SHDN
= Low (Shutdown) –10 µA
Input Common Mode Low ●–0.25 V
Input Common Mode High ●V
CC
– 0.3 V
SPIN Input Current V
SHDN
= High, V
SPIN
≥ 2V (Note 8) ●2mA
V
SHDN
= Low (Shutdown) 10 µA
Oscillator
Switching Frequency (f
NOM
)180 200 220 kHz
Switching Frequency Tolerance ●170 200 230 kHz
SYNC Pin Input Current V
SYNC
= 0V –0.5 mA
V
SYNC
= 2V –30 µA
Synchronization Pulse Threshold on SYNC Pin 0.9 1.2 2.0 V
Synchronization Frequency ●240 280 kHz
Maximum Duty Cycle
V
BOOST
Threshold to Turn TGATE Off Measured at (V
BOOST
– V
SW
)
(Comparator A2) (Note 4) Low to High ●6.8 7.3 7.6 V
Hysteresis 0.25 V
Maximum Duty Cycle of Natural Frequency 200kHz ●85 90 %
(Note 5)
Current Amplifier CA2
Transconductance V
C
= 1V, I
VC
= ±1µA 150 200 300 µmho
Maximum V
C
for Switch Off ●0.6 V
I
VC
Current (Out of Pin) V
C
≥ 0.6V ●50 µA
V
C
< 0.45V ●3mA
V
C
at Shutdown V
SHDN
= Low (Shutdown) ●0.35 V
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any
outputs unless otherwise noted.
4
LT1505
1505fc
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.
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.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any
outputs unless otherwise noted.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Voltage Amplifier VA
Transconductance (Note 3) Output Current from 50µA to 500µA 0.21 0.6 1.0 mho
Output Source Current V
FB
= V
PROG
= V
REF
+ 10mV 1.1 mA
V
FB
Input Bias Current At 0.5mA VA Output Current, T
A
< 70°C –10 25 nA
(3 CELL, 4.1V, 4.2V Are Not Connected, V
BAT2
= 0V)
Current Limit Amplifier CL1
Turn-On Threshold 0.5mA Output Current 87 92 97 mV
Transconductance Output Current from 50µA to 500µA 0.5 1 3 mho
CLP Input Current 0.5mA Output Current 1 3 µA
CLN Input Current 0.5mA Output Current 0.8 2 mA
Input P-Channel FET Driver (INFET)
INFET “On” Clamping Voltage (V
CC
– V
INFET
)V
CC
≥ 11V ●6.5 7.8 9 V
INFET “On” Driver Current V
INFET
= V
CC
– 6V ●820 mA
INFET “Off” Clamping Voltage (V
CC
– V
INFET
)V
CC
Not Connected, I
INFET
< –2µA 1.4 V
INFET “Off” Drive Current V
CC
Not Connected, (V
CC
– V
INFET
) ≥ 2V –2.5 mA
Charging Completion Flag (Comparator E6)
Charging Completion Threshold (Note 6) Measured at V
RS1
, V
CAP
= 2V (Note 7) 14 20 28 mV
Threshold On CAP Pin Low to High Threshold ●3.3 4.2 V
High to Low Threshold ●0.6 V
V
CAP
at Shutdown V
SHDN
= Low (Shutdown) ●0.13 0.3 V
FLAG (Open Collector) Output Low V
CAP
= 4V, I
FLAG
< 1mA ●0.3 V
FLAG Pin Leakage Current V
CAP
= 0.6V ●3µA
Gate Drivers (TGATE, BGATE)
V
GBIAS
11V < V
CC
< 24V, I
GBIAS
≤ 15mA ●8.4 9.1 9.6 V
V
SHDN
= Low (Shutdown) ●13 V
V
TGATE
High (V
TGATE
– V
SW
)I
TGATE
≤ 20mA, V
BOOST
= V
GBIAS
– 0.5V ●5.6 6.6 V
V
BGATE
High I
BGATE
≤ 20mA ●6.2 7.2 V
V
TGATE
Low (V
TGATE
– V
SW
)I
TGATE
≤ 50mA ●0.8 V
V
BGATE
Low I
BGATE
≤ 50mA ●0.8 V
Peak Gate Drive Current 10nF Load 1 A
Gate Drive Rise and Fall Time 1nF Load 25 ns
V
TGATE
, V
BGATE
at Shutdown V
SHDN
= Low (Shutdown) ●1V
I
TGATE
= I
BGATE
= 10µA
5
LT1505
1505fc
TYPICAL PERFORMANCE CHARACTERISTICS
UW
I
BAT
(A)
0
EFFICIENCY (%)
105
100
95
90
85
80 4
1505 G01
1235
V
IN
= 19V
V
BAT
= 12.6V
Efficiency of Figure 1 Circuit
I
VA
(mA)
0
∆V
FB
(mV)
4
3
2
1
00.8
1505 G04
0.20.1 0.3 0.5 0.7 0.9
0.4 0.6 1.0
125°C
25°C
V
CC
(V)
15
14
13
12
11
10
I
CC
(mA)
1505 G06
10 13 16 19 22 25
0°C
25°C
125°C
I
GBIAS
(mA)
9.2
9.1
9.0
8.9
8.8
8.7
8.6
8.5
8.4
8.3
8.1
V
GBIAS
(V)
1505 G02
0 –2–4–6–8 –10 –12 –14 –16 –18 –20
0°C
25°C
125°C
VGBIAS vs IGBIAS
∆VFB vs IVA (Voltage Amplifier)
TEMPERATURE (°C)
0 255075100
THRESHOLD (mV)
125
1505 G05
98
96
94
92
90
88
Current Limit Amplifier
CL1 Threshold ICC vs VCC
JUNCTION TEMPERATURE (°C)
0
REFERENCE VOLTAGE (V)
2.470
2.468
2.466
2.464
2.462
2.460
2.458 25 50 75 100
1505 G09
125 150
Reference Voltage vs Temperature
V
PROG
(V)
0123 54
I
PROG
(mA)
6
0
–6
1505 G07
125°C
CURRENT FEEDBACK
AMPLIFIER OPEN LOOP
25°C
PROG Pin Characteristics
V
C
(V)
–1.2
–1.0
–0.8
–0.6
–0.4
–0.2
0
0.2
0.4
0.6
0.8
1.0
I
VC
(mA)
1505 G08
0 0.4 0.60.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0
VC Pin Characteristics
VREF Line Regulation
V
CC
(V)
0
∆V
REF
(V)
0.003
0.002
0.001
0
–0.001
–0.002
–0.003 510 15 20
1505 G03
25 30
ALL TEMPERATURES
0°C ≤ T
J
≤ 125°C
6
LT1505
1505fc
PIN FUNCTIONS
UUU
BOOST (Pin 1): This pin is used to bootstrap and supply
power for the topside power switch gate drive and control
circuity. In normal operation, V
BOOST
is powered from an
internally generated 8.6V regulator V
GBIAS
, V
BOOST
≈ V
CC
+ 9.1V when TGATE is high. Do not force an external
voltage on BOOST pin.
TGATE (Pin 2): This pin provides gate drive to the topside
power FET. When TGATE is driven on, the gate voltage will
be approximately equal to V
SW
+ 6.6V. A series resistor of
5Ω to 10Ω should be used from this pin to the gate of the
topside FET.
SW (Pin 3): This pin is the reference point for the floating
topside gate drive circuitry. It is the common connection
for the top and bottom side switches and the output
inductor. This pin switches between ground and V
CC
with
very high dv/dt rates. Care needs to be taken in the PC
layout to keep this node from coupling to other sensitive
nodes. A 1A Schottky clamp diode should be placed from
this pin to the ground pin, using very short traces to
prevent the chip substrate diode from turning on. See
Applications Information for more details.
SYNC (Pin 4): Synchronization Input. The LT1505 can be
synchronized to an external clock with pulses that have
duty cycles between 10% and 95%. An internal one shot
that is triggered on the rising edge of the sync pulse makes
this input insensitive to the duty cycle of the sync pulse.
The input voltage range on this pin is 0V to 20V. This pin
can float if not used.
SHDN (Pin 5): Shutdown. When this pin is pulled below 1V,
switching will stop, GBIAS will go low and the input cur-
rents of CA1 will be off. Note that input current of about 4µA
keeps the device in shutdown unless an external pull-up
signal is applied. The voltage range on this pin is 0V to V
CC
.
AGND (Pin 6): Low Current Analog Ground.
UV (Pin 7): Undervoltage Lockout Input. The rising thresh-
old is 6.7V with a hysteresis of 0.5V. Switching stops in
undervoltage lockout. When the input supply (normally
the wall adapter output) to the chip is removed, the UV pin
must be pulled down to below 0.7V (a 5k resistor from
adapter output to GND is required), otherwise the reverse-
battery current will be approximately 200µA instead of
10µA. Do not leave the UV pin floating. If it is connected
to V
IN
with no resistor divider, the built-in 6.7V undervoltage
lockout will be effective. Maximum voltage allowed on this
pin is V
CC
.
INFET (Pin 8): For very low dropout applications, an
external P-channel MOSFET can be used to connect the
input supply to V
CC
. This pin provides the gate drive for the
PFET. The gate drive is clamped to 8V below V
CC
. The gate
is driven on (low) when V
CC
>(V
BAT
+ 0.2V) and
V
UV
> 6.7V. The gate is off (high) when V
CC
< (V
BAT
+ 0.2V).
The body diode of the PFET is used to pull up V
CC
to turn
on the LT1505.
CLP (Pin 9): LT1505: Positive Input to the Input Current
Limit Amplifier CL1. The threshold is set at 92mV. When
used to limit input current, a filter is needed to filter out the
200kHz switching noise. (LT1505-1: No Connection.)
CLN (Pin 10): LT1505: Negative Input to the Input Current
Limit Amplifier CL1. When used, both CLP and CLN should
be connected to a voltage higher than 6V and normally
V
CC
(to the V
CC
bypass capacitor for less noise). Maximum
voltage allowed on both CLP and CLN is V
CC
+ 1V.
(LT1505-1: No Connection.)
COMP1 (Pin 11): LT1505: Compensation Node for the
Input Current Limit Amplifier CL1. At input adapter current
limit, this pin rises to 1V. By forcing COMP1 low with an
external transistor, amplifier CL1 will be disabled (no
adapter current limit). Output current is less than 0.2mA.
See the Figure 1 circuit for the required resistor and
capacitor values. (LT1505-1: connect to GND.)
CAP (Pin 12): A 0.1µF capacitor from CAP to ground is
needed to filter the sampled charging current signal. This
filtered signal is used to set the FLAG pin when the
charging current drops below 20% of the programmed
maximum charging current.
FLAG (Pin 13): This pin is an open-collector output that is
used to indicate the end of charge. The FLAG pin is driven
low when the charge current drops below 20% of the
programmed charge current. A pull-up resistor is
required if this function is used. This pin is capable of
sinking at least 1mA. Maximum voltage on this pin is V
CC
.
4.1V (Pin 14), 4.2V (Pin 15), 3CELL (Pin 16), V
FB
(Pin
17): These four pins are used to select the battery voltage
using the preset internal resistor network. The V
FB
pin is
7
LT1505
1505fc
the noninverting input to the amplifier, VA in the Block
Diagram, that controls the charging current when the
device operates in constant voltage mode. The amplifier
VA controls the charging current to maintain the voltage
on the V
FB
pin at the reference voltage (2.465V). Input bias
current for VA is approximately 3nA. The LT1505 incorpo-
rates a resistor divider that can be used to select the
correct voltage for either three or four 4.1V or 4.2V
lithium-ion cells. For three cells the 3CELL pin is shorted
to the V
FB
pin. For four cells the 3CELL pin is not con-
nected. For 4.1V cells the 4.1V pin is connected to the V
FB
pin and the 4.2V pin is not connected. For 4.2V cells the
4.2V pin is connected to V
FB
and the 4.1V pin is not
connected. See the table below.
PRESET BATTERY VOLTAGE PIN SELECTION
12.3V (3 × 4.1V Cell) 4.1V, V
FB
, 3CELL Short Together
16.4V (4 × 4.1V Cell) 4.1V, V
FB
, Short Together, 3CELL Floats
12.6V (3 × 4.2V Cell) 4.2V, V
FB
, 3CELL Short Together
16.8V (4 × 4.2V Cell) 4.2V, V
FB
, Short Together, 3CELL Floats
For battery voltages other than the preset values, an
external resistor divider can be used. If an external divider
is used then the 4.1V, 4.2V and 3CELL pins should not be
connected and BAT2 pin should be grounded. To maintain
the tight voltage tolerance, the external resistors should
have better than 0.25% tolerance. Note that the V
FB
pin will
float high and inhibit switching if it is left open.
V
C
(Pin 18): This is the control signal of the inner loop of
the current mode PWM. Switching starts at 0.9V, higher
V
C
corresponds to higher charging current in normal
operation and reaches 1.1V at full charging current. A
capacitor of at least 0.33µF to GND filters out noise and
controls the rate of soft start. Pulling this pin low will stop
switching. Typical output current is 60µA.
PROG (Pin 19): This pin is for programming the charge
current and for system loop compensation. During normal
operation, V
PROG
stays at 2.465V. If it is shorted to GND or
more than 1mA is drawn out of the pin, switching will stop.
When a microprocessor controlled DAC is used to pro-
gram charging current, it must be capable of sinking
current at a compliance up to 2.465V.
PIN FUNCTIONS
UUU
BAT2 (Pin 20): This pin is used to connect the battery to
the internal preset voltage setting resistor. An internal
switch disconnects the internal divider from the battery
when the device is in shutdown or when power is discon-
nected. This disconnect function eliminates the current
drain due to the resistor divider. This pin should be
connected to the positive node of the battery if the internal
preset divider is used. This pin should be grounded if an
external divider is used. Maximum input voltage on this
pin is 20V.
SENSE (Pin 21): This pin is the noninverting input to the
current amplifier CA1 in the Block Diagram. Typical bias
current is –50µA.
SPIN (Pin 22): This pin is for the internal amplifier CA1
bias. It must be connected as shown in the application
circuit.
BAT (Pin 23): Current Amplifier CA1 Inverting Input.
Typical bias current is –50µA.
V
CC
(Pin 24): Input Supply. For good bypass, a low ESR
capacitor of 10µF or higher is required. Keep the lead
length to a minimum. V
CC
should be between 11V and 24V.
Do not force V
CC
below V
BAT
by more than 1V with the
battery present.
BOOSTC (Pin 25): This pin is used to bootstrap and supply
the current sense amplifier CA1 for very low dropout
condition. V
CC
can be as low as only 0.4V above the battery
voltage. A diode and a capacitor are needed to get the
voltage from V
BOOST
. If low dropout is not needed and V
CC
is always 3V or higher than V
BAT
, this pin can be left
floating or tied to V
CC
. Do not force this pin to a voltage
lower than V
CC
. Typical input current is 1mA.
GBIAS (Pin 26): This is the output of the internal 9.1V
regulator to power the drivers and control circuits. This pin
must be bypassed to a ground plane with a minimum of
2.2µF ceramic capacitor. Switching will stop when V
GBIAS
drops below 7V.
BGATE (Pin 27): Low Side Power MOSFET Drive.
PGND (Pin 28): MOSFET Driver Power Ground. A solid
system ground plane is very important. See the LT1505
Demo Manual for further information.
8
LT1505
1505fc
BLOCK DIAGRAM
W
–
+
–
+
A2
A3
7V
A1 2
50k
C3
4.7µF
L1
10µHRS1
VRS1
+–
TGATE
VCC
3SW
1BOOST
M1
M2
+
2.5V
BGATE
+
9.1V 12.6V
BATTERY
++
–
+
A4
A6
4V
SW
+
–
+
–
+
A12
0.02V
PWM SLOPE COMP
Q2
Q1 CA1
–
+
–+
–
+
A11
IPROG
VRS1
+
–
+
E4
1.3V
4U
+
50k
A5
A9
A7
A8
26 GBIAS
27 BGATE
28 PGND
22 SPIN
RS3
21 SENSE
23 BAT
20 BAT2
16 3CELL
17 VFB
14 4.1V
R4
50.55k
R5
21k
15 4.2V
R6
0.33k
R7
12.3k
RPROG
CPROG
VREF
2.465V
VIN
VCC
R1
1k
R2
R3
R8
75k
25 BOOSTC
C2
1µF
SR
SHUTDOWN
A10
IVA
VREF
IPROG
B1
–
+
E6
–
+
CA2
C1
RS2
IBAT
–
+
–
+
CL1*
*LT1505 ONLY. SEE PIN FUNCTIONS
FOR LT1505-1 CONNECTIONS
COMP1 1505 BD
PROG
VC
9CLP
92mV
10
111918
CLN
SYSTEM
LOAD
AGND
6
Q3
VA
OSC
200k
ONE
SHOT
SYNC 4
FLAG 13
5
SHDN
–
+
E5
7V +
GBIAS
BAT
3.3V
IPROG
+
–
+
E1
SHUTDOWN
VCC
VIN
24
UV
VCC
7
8
–
+
E2
6.7V +
+
–
+
E8
6.7V
0.2V
+
E3
A13 Q4
7.8V
VCC
INFET
VCC
VIN
CAP 12
E7
+RS
IVA
4
(LT1505)
9
LT1505
1505fc
TEST CIRCUITS
–
+
–
+
CA1
–
+
–
+
–+
VA
V
REF
I
VA
R
S3
200Ω
10k
10k
4.93k
I
PROG
I
PROG
SENSE
BAT
PROG
LT1505
1505 TC03
0.047µF
0.47µF
0.033µF
3.3V
2.465V
LT1013
FLAG
+
V
BAT
V
RS1
+
–
+
+
2V 1k
+
V
FB
CAP
20k
R
S2
200Ω10Ω
E6
LT1013
I
VA
4
Test Circuit 1
Test Circuit 3
Test Circuit 2
V
REF
2.465V
–
+
–
+
VA
+
2k 2nF
V
FB
OR BAT2
1505 TC02
I
PROG
R
PROG
LT1505
PROG
LT1013
0.47µF
–
+
VREF
≈ 0.65V
VBAT
VCCA2
–
+
–
+
CA1
+
300Ω
20k
1k
1k
RS1
10Ω
BAT
SENSE
SPIN
1505 TC01
PROG
RPROG
0.047µF
LT1505
1µF
75k
LT1006
+
RS2
200Ω
RS3
200Ω
10
LT1505
1505fc
The LT1505 is a synchronous current mode PWM step-
down (buck) switcher. The battery DC charge current is pro-
grammed by a resistor R
PROG
(or a DAC output current) at
the PROG pin and the ratio of sense resistors R
S2
over R
S1
(see Block Diagram). Amplifier CA1 converts the charge cur-
rent through R
S1
to a much lower current I
PROG
(I
PROG
=
I
BAT
• RS1/RS2) fed into the PROG pin. Amplifier CA2 com-
pares the output of CA1 with the programmed current and
drives the PWM loop to force them to be equal. High DC
accuracy is achieved with averaging capacitor C
PROG
. Note
that I
PROG
has both AC and DC components. I
PROG
goes
through R1 and generates a ramp signal that is fed to the
PWM control comparator C1 through buffer B1 and level
shift resistors R2 and R3, forming the current mode inner
loop. The BOOST pin supplies the topside power switch gate
drive. The LT1505 generates an 9.1V V
GBIAS
to power drives
and V
BOOSTC
. BOOSTC pin supplies the current amplifier
CA1 with a voltage higher than V
CC
for low dropout appli-
cation. For batteries like lithium that require both constant-
current and constant-voltage charging, the 0.5% 2.465V
reference and the amplifier VA reduce the charge current
when battery voltage reaches the preset level. For NiMH and
NiCd, VA can be used for overvoltage protection.
The amplifier CL1 monitors and limits the input current,
normally from the AC adapter, to a preset level (92mV/R
S
).
At input current limit, CL1 will supply the programming
current I
PROG
, thus reducing battery charging current.
To prevent current shoot-through between topside and
lowside switches, comparators A3 and A4 assure that one
switch turns off before the other is allowed to turn on.
Comparator A12 monitors charge current level and turns
lowside switch off if it drops below 20% of the programmed
value (20mV across R
S1
) to allow for inductor discontinu-
ous mode operation. Therefore sometimes even in con-
tinuous mode operation with light current level the lowside
switch stays off.
Comparator E6 monitors the charge current and signals
through the FLAG pin when the charger is in voltage mode
and the charge current level is reduced to 20%. This charge
complete signal can be used to start a timer for charge
termination.
The INFET pin drives an external P-channel FET for low
dropout application.
When input voltage is removed, V
CC
will be held up by the
body diode of the topside MOSFET. The LT1505 goes into
a low current, 10µA typical, sleep mode as V
CC
drops
below the battery voltage. To shut down the charger
simply pull the V
C
pin or SHDN pin low with a transistor.
OPERATION
U
APPLICATIONS INFORMATION
WUUU
Input and Output Capacitors
In the 4A Lithium Battery Charger (Figure 1), the input
capacitor (C
IN
) is assumed to absorb all input switching
ripple current in the converter, so it must have adequate
ripple current rating. Worst-case RMS ripple current will
be equal to one half of output charging current. Actual
capacitance value is not critical. Solid tantalum capacitors
such as the AVX TPS and Sprague 593D series have high
ripple current rating in a relatively small surface mount
package, but
caution must be used when tantalum capaci-
tors are used for input bypass
. High input surge currents
can be created when the adapter is hot-plugged to the
charger and solid tantalum capacitors have a known
failure mechanism when subjected to very high turn-on
surge currents. Highest possible voltage rating on the
capacitor will minimize problems. Consult the manufac-
turer before use. Alternatives include new high capacity
ceramic (at least 20µF) from Tokin or United Chemi-Con/
Marcon, et al.
The output capacitor (C
OUT
) is also assumed to absorb
output switching current ripple. The general formula for
capacitor current is:
IRMS =
(L1)(f)
VBAT
VCC
()
0.29 (VBAT) 1 –
For example, V
CC
= 19V, V
BAT
= 12.6V, L1 = 15µH,
and f = 200kHz, I
RMS
= 0.4A.
11
LT1505
1505fc
APPLICATIONS INFORMATION
WUUU
EMI considerations usually make it desirable to minimize
ripple current in the battery leads. Beads or inductors may
be added to increase battery impedance at the 200kHz
switching frequency. Switching ripple current splits be-
tween the battery and the output capacitor depending on
the ESR of the output capacitor and the battery imped-
ance. If the ESR of C
OUT
is 0.2Ω and the battery impedance
is raised to 4Ω with a bead or inductor, only 5% of the
ripple current will flow in the battery.
Soft Start and Undervoltage Lockout
The LT1505 is soft started by the 0.33µF capacitor on the
V
C
pin. On start-up, the V
C
pin voltage will rise quickly to
0.5V, then ramp up at a rate set by the internal 45µA pull-
up current and the external capacitor. Battery charge
current starts ramping up when V
C
voltage reaches 0.7V
and full current is achieved with V
C
at 1.1V. With a 0.33µF
capacitor, time to reach full charge current is about 10ms
and it is assumed that input voltage to the charger will
reach full value in less than 10ms. The capacitor can be
increased up to 1µF if longer input start-up times are
needed.
In any switching regulator, conventional timer-based soft
starting can be defeated if the input voltage rises much
slower than the time out period. This happens because the
switching regulators in the battery charger and the com-
puter power supply are typically supplying a fixed amount
of power to the load. If input voltage comes up slowly
compared to the soft start time, the regulators will try to
deliver full power to the load when the input voltage is still
well below its final value. If the adapter is current limited,
it cannot deliver full power at reduced output voltages and
the possibility exists for a quasi “latch” state where the
adapter output stays in a current limited state at reduced
output voltage. For instance, if maximum charger plus
computer load power is 30W, a 15V adapter might be
current limited at 2.5A. If adapter voltage is less than
(30W/2.5A = 12V) when full power is drawn, the adapter
voltage will be pulled down by the constant 30W load until
it reaches a lower stable state where the switching regu-
lators can no longer supply full load. This situation can be
prevented by setting
undervoltage lockout
higher than the
minimum adapter voltage where full power can be achieved.
Figure 2. Adapter Current Limiting
92mV
–
+
500Ω
CLP
CLN
V
CC
UV
1505 F02
R5
LT1505
R6
1µF
+
R
S4
*
C
IN
V
IN
CL1
AC ADAPTER
OUTPUT
*R
S4
= 92mV
ADAPTER CURRENT LIMIT
+
A resistor divider is used to set the desired V
CC
lockout
voltage as shown in Figure 2. A typical value for R6 is 5k
and R5 is found from:
R5 = R6(V – V )
V
UV
UV
IN
V
UV
= Rising lockout threshold on the UV pin
V
IN
= Charger input voltage that will sustain full load power
Example: With R6 = 5k, V
UV
= 6.7V and setting V
IN
at 16V;
R5 = 5k (16V – 6.7V)/6.7V = 6.9k
The resistor divider should be connected directly to the
adapter output as shown, not to the V
CC
pin to prevent
battery drain with no adapter voltage. If the UV pin is not
used, connect it to the adapter output (not V
CC
) and
connect a resistor no greater than 5k to ground. Floating
the pin will cause reverse battery current to increase from
10µA to 200µA.
Adapter Current Limiting
(Not Applicable for the LT1505-1)
An important feature of the LT1505 is the ability to
automatically adjust charge current to a level which avoids
overloading the wall adapter. This allows the product to
operate at the same time batteries are being charged
without complex load management algorithms. Addition-
ally, batteries will automatically be charged at the maximum
possible rate of which the adapter is capable.
12
LT1505
1505fc
APPLICATIONS INFORMATION
WUUU
This is accomplished by sensing total adapter output
current and adjusting charge current downward if a preset
adapter current limit is exceeded. True analog control is
used, with closed loop feedback ensuring that adapter load
current remains within limits. Amplifier CL1 in Figure 2
senses the voltage across R
S4
, connected between the
CLP and CLN pins. When this voltage exceeds 92mV, the
amplifier will override programmed charge current to limit
adapter current to 92mV/R
S4
. A lowpass filter formed by
500Ω and 1µF is required to eliminate switching noise. If
the current limit is not used, then the R7 /C1 filter and the
COMP1 (R1/C7) compensation networks are not needed,
and both CLP and CLN pins should be connected to V
CC
.
Charge Current Programming
The basic formula for charge current is (see Block
Diagram):
IBAT = IPROG = 2.465V
RPROG
RS2
RS1
()()
RS2
RS1
()
where R
PROG
is the total resistance from PROG pin to ground.
For the sense amplifier CA1 biasing purpose, R
S3
should
have the same value as R
S2
and SPIN should be connected
directly to the sense resistor (R
S1
) as shown in the Block
Diagram.
For example, 4A charging current is needed. For low power
dissipation on R
S1
and enough signal to drive the amplifier
CA1, let R
S1
= 100mV/4A = 0.025Ω. This limits R
S1
power
to 0.4W. Let R
PROG
= 5k, then:
R
S2
= R
S3
=
= = 200Ω
(I
BAT
)(R
PROG
)(R
S1
)
2.465V
(4A)(5k)(0.025)
2.465V
Charge current can also be programmed by pulse width
modulating I
PROG
with a switch Q1 to R
PROG
at a frequency
higher than a few kHz (Figure 3). Charge current will be
proportional to the duty cycle of the switch with full current
at 100% duty cycle.
When a microprocessor DAC output is used to control
charge current, it must be capable of sinking current at a
compliance up to 2.5V if connected directly to the PROG
pin.
Note that for charge current accuracy and noise immu-
nity, 100mV full scale level across the sense resistor RS1
is required. Consequently, both RS2 and RS3 should be
200Ω.
It is critical to have a good Kelvin connection on the
current sense resistor RS1 to minimize stray resistive
and inductive pickup. RS1 should have low parasitic
inductance (typical 3nH or less, as exhibited by Dale or
IRC sense resistors). The layout path from RS2 and RS3
to RS1 should be kept away from the fast switching SW
node. Under low charge current conditions, a low quality
sense resistor with high ESL (4nH or higher) coupled
with a very noisy current sense path might false trip
comparator A12 and turn on BGATE at the wrong time,
potentially damaging the bottom power FET. In this case,
an RC filter of 10Ω and 10nF should be used across RS1
to filter out the noise (see Figure 4).
PWM
R
PROG
4.7k
PROG
C
PROG
1µF
Q1
VN2222
5V
0V
LT1505
1505 F03
I
BAT
= (DC)(4A)
Figure 3. PWM Current Programming
Figure 4. Reducing Current Sensing Noise
1505 F04
LT1505
SPIN
SENSE
BAT
BAT2
+
–
L1 RS1
RS2
RS3
10Ω
10nF
+ VRS1 –
BATTERY
Lithium-Ion Charging
The 4A Lithium Battery Charger (Figure 1) charges lithium-
ion batteries at a constant 4A until battery voltage reaches
the preset value. The charger will then automatically go
into a constant-voltage mode with current decreasing to
near zero over time as the battery reaches full charge.
13
LT1505
1505fc
Preset Battery Voltage Settings
The LT1505 provides four preset battery voltages: 12.3V,
12.6V, 16.4V and 16.8V. See the Pin Functions section for
pin setting voltage selection. An internal switch connects
the resistor dividers to the battery sense pin, BAT2. When
shutting down the LT1505 by removing adaptor power or
by pulling the SHDN pin low, the resistor dividers will be
disconnected and will not drain the battery. The BAT2 pin
should be connected to the battery when any of the preset
battery voltages are used.
External Battery Voltage Setting Resistors
When an external divider is used for other battery volt-
ages, BAT2 should be grounded. Pins 4.1V, 4.2V and
3CELL should be left floating. To minimize battery drain
when the charger is off, current through the R3/R4 divider
(Figure 5) is set at 15µA . The input current to the V
FB
pin
is 3nA and the error can be neglected.
With divider current set at 15µA, R4 = 2.465/15µA = 162k
and,
R3 R4 V 2.465
2.465
162k 8.4 2.465
2.465
390k
BAT
=
()
−
()
=−
()
=
APPLICATIONS INFORMATION
WUUU
Lithium-Ion Charging Completion
Some battery manufacturers recommend termination of
constant-voltage float mode after charge current has
dropped below a specified level (typically around 20% of
the full current) and a further time-out period of 30
minutes to 90 minutes has elapsed. Check with manufac-
turers for details. The LT1505 provides a signal at the
FLAG pin when charging is in voltage mode and current is
reduced to 20% of full current, assuming full charge
current is programmed to have 100mV across the current
sense resistor (V
RS1
). The comparator E6 in the Block
Diagram compares the charge current sample I
PROG
to the
output current I
VA
voltage amplifier VA. When the charge
current drops to 20% of full current, I
PROG
will be equal to
0.25 I
VA
and the open-collector output V
FLAG
will go low
and can be used to start an external timer. When this
feature is used, a capacitor of at least 0.1µF is required at
the CAP pin to filter out the switching noise and a pull-up
resistor is also needed at the FLAG pin. If this feature is not
used, C6 is not needed.
Very Low Dropout Operation
The LT1505 can charge the battery even when V
CC
goes
as low as 0.5V above the combined voltages of the
battery and the drops on the sense resistor as well as
parasitic wiring. This low V
CC
sometimes requires a duty
factor greater then 99% and TGATE stays on for many
switching cycles. While TGATE stays on, the voltage
V
BOOST
across the capacitor C2 drops down because
TGATE control circuits require 2mA DC current. C2 needs
to be recharged before V
BOOST
drops too low to keep the
topside switch on. A unique design allows the LT1505 to
operate under these conditions; the comparator A2 moni-
tors V
BOOST
and when it drops from 9.1V to 6.9V, TGATE
will be turned off for about 0.2µs to recharge C2. Note that
the LT1505 gets started the same way when power turns
on and there is no initial V
BOOST
.
It is important to use 0.56µF or greater value for C2 to hold
V
BOOST
up for a sufficient amount of time.
When minimum operating V
CC
is less than 2.5V above the
battery voltage, D3 and C4 (see Figure 1) are also needed
to bootstrap V
BOOSTC
higher than V
CC
to bias the current
V
BAT
1505 F04
8.4V
R3
390k
0.25%
R4
162k
0.25%
+
V
FB
LT1505
Figure 5. External Resistor Divider
Li-Ion batteries typically require float voltage accuracy of
1% to 2%. Accuracy of the LT1505 V
FB
voltage is ±0.5%
at 25°C and ±1% over the full temperature range. This
leads to the possibility that very accurate (0.1%) resistors
might be needed for R3 and R4. Actually, the temperature
of the LT1505 will rarely exceed 50°C in float mode
because charging currents have tapered off to a low level,
so 0.25% resistors will normally provide the required level
of overall accuracy.
14
LT1505
1505fc
Nickel-Cadmium and Nickel-Metal-Hydride Charging
The circuit in the 4A Lithium Battery Charger (Figure 1) can
be modified to charge NiCd or NiMH batteries. For
example, 2-level charging is needed; 2A when Q1 is on,
and 200mA when Q1 is off (Figure 8).
APPLICATIONS INFORMATION
WUUU
Figure 6. High Input Voltage Shudown
Figure 7. Synchronizing with External Clock
R2
5.49k
R1
49.3k
PROG
C
PROG
1µF
Q1
LT1505
1505 F07
5V TO 20V
VN2222
PULSE WIDTH > 200ns
5k
SYNC
1505 F06
LT1505
Figure 8. 2-Level Charging
SHDN
1505 F05
3M
V
IN
24V ≤ V
CC
< 27V
OPEN DRAIN
3.3µF
LT1505
amplifier CA1. They are not needed if V
CC
is at least 2.5V
higher than V
BAT
. The PFET M3 is optional and can be
replaced with a diode if V
IN
is at least 3V higher than V
BAT
.
The gate control pin INFET turns on M3 when V
IN
gets up
above the undervoltage lockout level set by R5 and R6 and
is clamped internally to 8V below V
CC
. In sleep mode when
V
IN
is removed, INFET will clamp M3 V
SG
to 0.2V.
Shutdown
When adapter power is removed, V
CC
will drift down and
be held by the body diode of the topside NFET switch. As
soon as V
CC
goes down to 0.2V above V
BAT
, the LT1505 will
go into sleep mode drawing only 10µA from the battery.
There are two ways to stop switching: pulling the SHDN
pin low or pulling the V
C
pin low. Pulling the SHDN pin low
will also turn off V
GBIAS
and CA1 input currents. Pulling the
V
C
pin low will only stop switching and V
GBIAS
stays high.
Make sure there is a pull-up resistor on the SHDN pin even
if the SHDN pin is not used, otherwise internal pull-down
current will keep the SHDN pin low and switching off when
power turns on.
Each TGATE and BGATE pin has a 50k pull-down resistor
to keep the external power FETs off when shut down or
power is off.
Note that maximum operating V
CC
is 24V. For short
transients the LT1505 can be operated as high as 27V. For
V
CC
higher than 24V it is preferred to use the V
C
pin to shut
down. If the SHDN pin has to be used to shut down at V
CC
higher than 24V, the Figure 6 pull-up circuit must be used
to slow down the V
GBIAS
ramp-up rate when the SHDN pin
is released. Otherwise, high surge current charging the
bypass capacitor might damage the LT1505. For V
CC
less
than 24V, only a 100k resistor and no capacitor is needed
at SHDN pin to V
IN
for pull-up.
Synchronization
The LT1505 can be synchronized to a frequency range
from 240kHz to 280kHz. With a 200ns one-shot timer on
chip, the LT1505 provides flexibility on the synchronizing
pulse width. Sync pulse threshold is about 1.2V (Figure 7).
For 2A full current, the current sense resistor (R
S1
) should
be increased to 0.05Ω so that enough signal (10mV) will
be across R
S1
at 0.2A trickle charge to keep charging
current accurate.
For a 2-level charger, R1 and R2 are found from:
R1 2.465 4000
I R2 2.465 4000
II
LOW HI LOW
=
()()
=
()()
−
15
LT1505
1505fc
APPLICATIONS INFORMATION
WUUU
Note that M4 and/or D5 are needed only if the charger
system can be potentially crowbarred.
Figure 10. VBAT Crowbar Protection
1505 F09
SHDN
LT1505
D5
1N4148
100k
VBAT
VIN
M3
1505 F08
M4
TPO610
R
S4
INFET
LT1505
V
CC
V
IN
Figure 9. VIN Crowbar Protection
All battery chargers with fast charge rates require some
means to detect full charge state in the battery to terminate
the high charge current. NiCd batteries are typically charged
at high current until temperature rise or battery voltage
decrease is detected as an indication of near full charge.
The charge current is then reduced to a much lower value
and maintained as a constant trickle charge. An interme-
diate “top off” current may be used for a fixed time period
to reduce 100% charge time.
NiMH batteries are similar in chemistry to NiCd but have
two differences related to charging. First, the inflection
characteristic in battery voltage as full charge is ap-
proached is not nearly as pronounced. This makes it
more difficult to use –∆V as an indicator of full charge,
and an increase in temperature is more often used with a
temperature sensor in the battery pack. Secondly, con-
stant trickle charge may not be recommended.
Instead, a moderate level of current is used on a pulse
basis (≈1% to 5% duty cycle) with the time-averaged
value substituting for a constant low trickle. Please
contact the Linear Technology Applications department
about charge termination circuits.
If overvoltage protection is needed, R3 and R4 in Figure 5
should be calculated according to the procedure described
in the Lithium-Ion Charging section. The V
FB
pin should be
grounded if not used.
Charger Crowbar Protection
If the V
IN
connector of Figure 1 can be instantaneously
shorted (crowbarred) to ground, then a small P-channel FET
M4 should be used to quickly turn off the input
P-channel FET M3 (see Figure 9), otherwise, high reverse
surge current might damage M3. M3 can also be replaced
by a diode if dropout voltage and heat dissipation are not
problems.
Note that the LT1505 will operate even when V
BAT
is
grounded. If V
BAT
of Figure 1 charger gets shorted to
ground very quickly (crowbarred) from a high battery
voltage, slow loop response may allow charge current to
build up and damage the topside N-channel FET M1. A
small diode D5 (see Figure 10) from the SHDN pin to V
BAT
will shut down switching and protect the charger.
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.
Layout Considerations
Switch rise and fall times are under 20ns for maximum
efficiency. To prevent radiation, the power MOSFETs, the
SW pin and input bypass capacitor leads should be kept as
short as possible. A Schottky diode (D4 in Figure 1) rated
for at least 1A is necessary to clamp the SW pin and should
be placed close to the low side MOSFET. A ground plane
should be used under the switching circuitry to prevent
interplane coupling and to act as a thermal spreading path.
Note that the inductor is probably the most heat dissipat-
ing device in the charging system. The resistance on a 4A,
15µH inductor, can be 0.03Ω . With DC and AC losses, the
power dissipation can go as high as 0.8W. Expanded
traces should be used for the inductor leads for low
thermal resistance.
The fast switching high current ground path including the
MOSFETs, D4 and input bypass capacitor should be kept
very short. Another smaller input bypass (1µF ceramic)
should be placed very close the chip. The demo board
DC219 should be used for layout reference.
16
LT1505
1505fc
G Package
28-Lead Plastic SSOP (5.3mm)
(Reference LTC DWG # 05-08-1640)
LT/TP 1101 1.5K REV C • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
PACKAGE DESCRIPTION
U
PART NUMBER DESCRIPTION COMMENTS
LT1372/LT1377 1.5A, 500kHz/1MHz Step-Up Switching Regulators High Frequency, Small Inductor, High Efficiency Switchers, SO-8
LT1376 1.5A, 500kHz Step-Down Switching Regulator High Frequency, Small Inductor, High Efficiency Switcher, SO-8
LT1510 Constant-Voltage/Constant-Current Battery Charger Up to 1.5A Charge Current, Small SO-8 Footprint
LT1511 3A Constant-Voltage/Constant-Current Battery Charger Charges Lithium, NiCd and NiMH Batteries, 28-Lead SO Package
LT1512 SEPIC CC/CV Battery Charger V
IN
Can Be Higher or Lower Than Battery Voltage, 2A Internal Switch
LT1513 SEPIC CC/CV Battery Charger V
IN
Can Be Higher or Lower Than Battery Voltage, 3A Internal Switch
LT1571 Constant-Voltage/Constant-Current Battery Charger 1.5A Charge Current, Preset Voltage for 1 or 2 Li-Ion Cells, C/10 Flag
LTC1731 Linear Charger Controller Programmable Timer; 8-Pin MSOP; C/10 Flag
LTC1732 Linear Charger Controller AC Adapter Present Flag; Programmable Timer; 10-Pin MSOP; C/10 Flag
LTC1733 Linear Charger with Integrated FET 1.5A Charge Current, Programmable Timer,
10-Pin Thermally Enhanced MSOP Package
LTC1734 Linear Charger Controller Inexpensive Constant-Voltage/Constant-Current Li-Ion Charger,
5-Pin SOT-23 Package
LTC1759 SMBus Controlled Smart Battery Charger LT1505 Charger Functionality with SMBus Control
LT1769 2A Constant-Voltage/Constant-Current Battery Charger Charges Lithium, NiCd and NiMH Batteries, 20-Lead Exposed Pad TSSOP
LTC1960 Dual Battery Charger and Selector with SPI Interface I
CHARGE
up to 6A, Fast Charge, Longer Battery Life, Crisis Management
RELATED PARTS
LINEAR TECHNOLOGY CORP ORATION 1999
G28 SSOP 0501
.13 – .22
(.005 – .009)
0° – 8°
.55 – .95
(.022 – .037)
5.20 – 5.38**
(.205 – .212)
7.65 – 7.90
(.301 – .311)
12345678 9 10 11 12 1413
10.07 – 10.33*
(.397 – .407)
2526 22 21 20 19 18 17 16 1523242728
1.73 – 1.99
(.068 – .078)
.05 – .21
(.002 – .008)
.65
(.0256)
BSC .25 – .38
(.010 – .015)
MILLIMETERS
(INCHES)
DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED .152mm (.006") PER SIDE
DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED .254mm (.010") PER SIDE
*
**
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN
3. DRAWING NOT TO SCALE
