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FEATURES
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LT1505 Constant-Current/Voltage High Efficiency Battery Charger DESCRIPTIO
The LT(R)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. Maximum 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 operation of the equipment and fast battery charging without overloading 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 10A sleep mode when the wall adapter is unplugged. 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 10A 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* VIN (FROM ADAPTER) TO SYSTEM POWER RS4 0.025 C1 1F CIN 47F 35V VCC BOOST BOOSTC GBIAS CLN CLP INFET UV R6 4k SYNC SHDN FLAG *BODY DIODE POLARITY MUST BE AS SHOWN C6 0.1F CAP COMP1 R1 1k C7 0.68F BAT2 BAT SENSE LT1505 TGATE SW BGATE VC PROG 3 CELL VFB 4.2V 4.1V AGND PGND SPIN 300 CPROG 1F RPROG 4.93k 1% RX4 3k 0.33F RS2 200 1% RS3 200 1% 5 C3 D2 2.2F MMSD4148T1 M1 Si4412 M2 Si4412 D4 MBRS140 C4 0.1F D3 MMSD4148T1 C2 0.68F L1 15H RS1 0.025 VBAT COUT 22F 25V x2 12.6V BATTERY
R7 500 100k R5 4k
NOTE: DBODY IS THE BODY DIODE OF M3 CIN: SANYO OS-CON L1: SUMIDA CDRH127-150 (CAN BE FROM 10H TO 30H)
1505 F01
Figure 1. Low Dropout 4A Lithium-Ion Battery Charger
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1
LT1505
ABSOLUTE MAXIMUM RATINGS (Note 1)
VCC, CLP, CLN, INFET, UV, 3CELL, FLAG................ 27V SW Voltage with Respect to GND ........................... - 2V BOOST, BOOSTC Voltage with Respect to VCC ....... 10V GBIAS ..................................................................... 10V SYNC, BAT2, BAT, SENSE, SPIN ............................ 20V VC, PROG, VFB, 4.1V, 4.2V ........................................ 7V CAP, SHDN .......................................................... 3mA TGATE, BGATE Current Continuous ....................... 0.2A TGATE, BGATE Output Energy (per cycle) ............... 2J Maximum Operating VCC ......................................... 24V Operating Ambient Temperature Range ....... 0C to 70C Operating Junction Temperature Range .... 0C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
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 VCC 23 BAT 22 SPIN 21 SENSE 20 BAT2 19 PROG 18 VC 17 VFB 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
TJMAX = 125C, JA = 100C/ W
Consult factory for Industrial and Military grade parts.
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any outputs unless otherwise noted.
PARAMETER Overall Supply Current Sense Amplifier CA1 Gain and Input Offset Voltage (With RS2 = 200, RS3 = 200) (Measured across RS1, Figure 1) (Note 2) BOOST Pin Current VCC 24V 11V VCC 24V , 0V VBAT 20V RPROG = 4.93k RPROG = 4.93k RPROG = 49.3k VBOOST = VSW + 8V, 0V VSW 20V TGATE High TGATE Low VBOOSTC = VCC + 8V RPROG = 4.93k, Measured at VFB with VA Supplying IPROG and Switching Off 11V VCC 24V
q q
ELECTRICAL CHARACTERISTICS
CONDITIONS
BOOSTC Pin Current Reference Reference Voltage (Note 3) Reference Voltage Tolerance
2
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W
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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 VCC 23 BAT 22 SPIN 21 SENSE 20 BAT2 19 PROG 18 VC 17 VFB 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
TJMAX = 125C, JA = 100C/ 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
LT1505
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (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 VCC is Connected SHDN Pin Current Supply Current in Shutdown (VSHDN is Low, VCC is Connected) Minimum IPROG for Switching "On" Minimum IPROG for Switching "Off" at VPROG 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 (fNOM) Switching Frequency Tolerance SYNC Pin Input Current Synchronization Pulse Threshold on SYNC Pin Synchronization Frequency Maximum Duty Cycle VBOOST Threshold to Turn TGATE Off (Comparator A2) (Note 4) Maximum Duty Cycle of Natural Frequency 200kHz (Note 5) Current Amplifier CA2 Transconductance Maximum VC for Switch Off IVC Current (Out of Pin) VC at Shutdown VC 0.6V VC < 0.45V VSHDN = Low (Shutdown) VC = 1V, IVC = 1A
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ELECTRICAL CHARACTERISTICS
CONDITIONS Measured at BAT2 Pin (VBAT + 0.3V) VCC 24V VBAT2 = VPRESET - 1V
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MIN
TYP 0.5
MAX
UNITS %
-1 - 40
1 6 40 6.7 7.15 5 10 30 2 8 15 20 - 22
% A % V A A V A mA A mA
Measured at UV Pin 0V VUV 8V VBAT 20V, VUV 0.4V, VCC = VSW = Battery Voltage
q q
6.3 -1
q
1
0V VSHDN 3V VCC 24V -1 -1
-4 - 2.4 - 50
VSHDN = High VSHDN = Low (Shutdown)
q q q
- 120 - 10 VCC - 0.3 2 10
A A V V mA A kHz kHz mA A V kHz
- 0.25
VSHDN = High, VSPIN 2V (Note 8) VSHDN = Low (Shutdown)
q
180 170 VSYNC = 0V VSYNC = 2V 0.9 240
200 200
220 230 - 0.5 - 30
1.2
2.0 280
Measured at (VBOOST - VSW) Low to High Hysteresis
q q
6.8 85
7.1 0.25 90
7.3
V V %
150
200
300 0.6 50 3 0.35
mho V A mA V
3
LT1505
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 18V, VBAT = 12.6V, VCLN = VCC (LT1505), no load on any outputs unless otherwise noted.
PARAMETER Voltage Amplifier VA Transconductance (Note 3) Output Source Current VFB Input Bias Current CONDITIONS Output Current from 50A to 500A VFB = VPROG = VREF + 10mV At 0.5mA VA Output Current, TA = 25C At 0.5mA VA Output Current, TA = 70C (3 CELL, 4.1V, 4.2V Are Not Connected, VBAT2 = 0V) 0.5mA Output Current Output Current from 50A to 500A 0.5mA Output Current 0.5mA Output Current VCC 11V VINFET = VCC - 6V VCC Not Connected, IINFET < - 2A VCC Not Connected, (VCC - VINFET) 2V Measured at VRS1, VCAP = 2V (Note 7) Low to High Threshold High to Low Threshold VSHDN = Low (Shutdown) VCAP = 4V, I FLAG < 1mA VCAP = 0.6V 11V < VCC < 24V, IGBIAS 15mA VSHDN = Low (Shutdown) ITGATE 20mA, VBOOST = VGBIAS - 0.5V IBGATE 20mA ITGATE 50mA IBGATE 50mA 10nF Load 1nF Load VSHDN = Low (Shutdown) ITGATE = IBGATE = 10A
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ELECTRICAL CHARACTERISTICS
MIN 0.21 1.1
TYP 0.6 3
MAX 1.0 10 25
UNITS mho mA nA nA
- 10
Current Limit Amplifier CL1 Turn-On Threshold Transconductance CLP Input Current CLN Input Current Input P-Channel FET Driver (INFET) INFET "On" Clamping Voltage (VCC - VINFET) INFET "On" Driver Current INFET "Off" Clamping Voltage (VCC - VINFET) INFET "Off" Drive Current Charging Completion Flag (Comparator E6) Charging Completion Threshold (Note 6) Threshold On CAP Pin VCAP at Shutdown FLAG (Open Collector) Output Low FLAG Pin Leakage Current Gate Drivers (TGATE, BGATE) VGBIAS VTGATE High (VTGATE - VSW) VBGATE High VTGATE Low (VTGATE - VSW) VBGATE Low Peak Gate Drive Current Gate Drive Rise and Fall Time VTGATE, VBGATE at Shutdown
87 0.5
92 1 1 0.8
97 3 3 2 9 1.4
mV mho A mA V mA V mA mV V V V V A V V V V
6.5 8
7.8 20 - 2.5
14 0.6
20 3.3 0.13
28 4.2 0.3 0.3 3
8.4 5.6 6.2
8.9 1 6.6 7.2
9.3 3
0.8 0.8 1 25 1
V V A ns V
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 VCC 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 VBOOST 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 0.2s at 200kHz to charge up C2. Comparator A2 senses VBOOST and switches to the normal PWM mode when VBOOST 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: ISPIN keeps switching on to keep VBAT regulated when battery is not present to avoid high surge current from COUT when battery is inserted. Note 9: Above undervoltage threshold switching is enabled. Note 10: Do not connect VCC directly to VIN (see Figure 1). This connection will cause the internal diode between VBAT and VCC to be forward-biased and may cause high current to flow from VIN. When the adapter is removed, VCC will be held up by the body diode of M1.
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LT1505 TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency of Figure 1 Circuit
105 VIN = 19V VBAT = 12.6V 100 9.2 9.1 9.0 8.9
EFFICIENCY (%)
VGBIAS (V)
8.7 8.6 8.5
125C
VREF (V)
95
90
85
80 0 1 2 IBAT (A)
1505 G01
3
VFB vs IVA (Voltage Amplifier)
4
3
THRESHOLD (mV)
VFB (mV)
2 125C 1 25C 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 IVA (mA)
1505 G04
92
ICC (mA)
PROG Pin Characteristics
6 CURRENT FEEDBACK AMPLIFIER OPEN LOOP -1.2 -1.0 -0.8 125C -0.6 -0.4
REFERENCE VOLTAGE (V)
IPROG (mA)
IVC (mA)
0
-6 0 1 2 3 VPROG (V) 4 5
1505 G07
UW
4 5 25C
VGBIAS vs IGBIAS
0.003 0.002
0C 25C
VREF Line Regulation
0C TJ 125C
0.001 0
8.8
ALL TEMPERATURES
-0.001 -0.002 -0.003
0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 IGBIAS (mA)
1505 G02
8.4 8.3 8.1
0
5
10
15 VCC (V)
20
25
30
1505 G03
Current Limit Amplifier CL1 Threshold
98
15
ICC vs VCC
96
14
94
13
12
0C 25C 125C
90
11
88
0
25
50 75 100 TEMPERATURE (C)
125
1505 G05
10 10 13 16 19 VCC (V) 22 25
1505 G06
VC 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 VC (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
5
LT1505
PIN FUNCTIONS
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, VBOOST is powered from an internally generated 8.6V regulator VGBIAS, VBOOST VCC + 8.9V 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 VSW + 6.6V. A series resistor of 5 to 10 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 VCC 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 currents of CA1 will be off. Note that input current of about 4A keeps the device in shutdown unless an external pull-up signal is applied. The voltage range on this pin is 0V to VCC. AGND (Pin 6): Low Current Analog Ground. UV (Pin 7): Undervoltage Lockout Input. The rising threshold 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 reversebattery current will be approximately 200A instead of 10A. Do not leave the UV pin floating. If it is connected to VIN with no resistor divider, the built-in 6.7V undervoltage lockout will be effective. Maximum voltage allowed on this pin is VCC. INFET (Pin 8): For very low dropout applications, an external P-channel MOSFET can be used to connect the input supply to VCC. This pin provides the gate drive for the PFET. The gate drive is clamped to 8V below VCC. The gate is driven on (low) when VCC > (VBAT + 0.2V) and VUV > 6.7V. The gate is off (high) when VCC < (VBAT + 0.2V). The body diode of the PFET is used to pull up VCC 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 VCC (to the VCC bypass capacitor for less noise). Maximum voltage allowed on both CLP and CLN is VCC + 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 0.1F 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 VCC. 4.1V (Pin 14), 4.2V (Pin 15), 3CELL (Pin 16), VFB (Pin 17): These four pins are used to select the battery voltage using the preset internal resistor network. The VFB pin is
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LT1505
PIN FUNCTIONS
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 VFB pin at the reference voltage (2.465V). Input bias current for VA is approximately 3nA. The LT1505 incorporates 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 VFB pin. For four cells the 3CELL pin is not connected. For 4.1V cells the 4.1V pin is connected to the VFB pin and the 4.2V pin is not connected. For 4.2V cells the 4.2V pin is connected to VFB and the 4.1V pin is not connected. See the table below.
PRESET BATTERY VOLTAGE 12.3V (3 x 4.1V Cell) 16.4V (4 x 4.1V Cell) 12.6V (3 x 4.2V Cell) 16.8V (4 x 4.2V Cell) PIN SELECTION 4.1V, VFB, 3CELL Short Together 4.1V, VFB, Short Together, 3CELL Floats 4.2V, VFB, 3CELL Short Together 4.2V, VFB, 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 VFB pin will float high and inhibit switching if it is left open. VC (Pin 18): This is the control signal of the inner loop of the current mode PWM. Switching starts at 0.9V, higher VC corresponds to higher charging current in normal operation and reaches 1.1V at full charging current. A capacitor of at least 0.33F to GND filters out noise and controls the rate of soft start. Pulling this pin low will stop switching. Typical output current is 60A. PROG (Pin 19): This pin is for programming the charge current and for system loop compensation. During normal operation, VPROG 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 program charging current, it must be capable of sinking current at a compliance up to 2.465V.
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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 disconnected. 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 - 50A. 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 - 50A. VCC (Pin 24): Input Supply. For good bypass, a low ESR capacitor of 10F or higher is required. Keep the lead length to a minimum. VCC should be between 11V and 24V. Do not force VCC below VBAT 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. VCC can be as low as only 0.4V above the battery voltage. A diode and a capacitor are needed to get the voltage from VBOOST. If low dropout is not needed and VCC is always 3V or higher than VBAT, this pin can be left floating or tied to VCC. Do not force this pin to a voltage lower than VCC. Typical input current is 1mA. GBIAS (Pin 26): This is the output of the internal 8.6V regulator to power the drivers and control circuits. This pin must be bypassed to a ground plane with a minimum of 2.2F ceramic capacitor. Switching will stop when VGBIAS 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.
7
LT1505
BLOCK DIAGRAM
E2
+
6.7V
+
6.7V
E3
BAT 0.2V VCC 24 GBIAS
E5 VIN SW E7 5 4U BGATE A4
7V
+
1.3V S R A7 ONE SHOT OSC 200k VRS1
SYNC 4
+
0.02V IVA 4 CAP 12 PWM IPROG
Q1 SLOPE COMP
CA1
IPROG A11
FLAG 13
E6
C1
B1 R2
+
3.3V
R1 1k R3 R4 50.55k 16 R5 21k IVA VA VREF 2.465V 3CELL
CA2
R6 0.33k 15 R7 12.3k
CL1* 10 CLN
6
AGND
18
VC CPROG
19
PROG RPROG
11
COMP1
8
-
+
+
R8 75k
VREF 92mV
+
*LT1505 ONLY. SEE PIN FUNCTIONS FOR LT1505-1 CONNECTIONS
-
+
-
+
-
+
-
+
-
+
-
+
-
-
+
+
-
SHDN
+
4V E4
+
2.5V A6
A5 A8 A9 50k A10 28 PGND 27 BGATE M2
A12
Q3
Q2 22 21 IPROG 23
+
-
+
-
+
+
+
E1
SHUTDOWN
-
7
+
-
UV
+
VCC
W
(LT1505)
VIN VCC
8
INFET
VCC E8 7.8V
A13 SHUTDOWN
Q4 VCC 1 BOOST C2 1F A2 TGATE A1 50k 3 SW 2 M1
+ +
7V
- + -
-
A3
+
8.9V
26
GBIAS C3 4.7F
L1 10H IBAT
+
VRS1 RS1
- +
12.6V BATTERY
25
BOOSTC
SPIN SENSE RS3
BAT
RS2
20
BAT2
17
VFB
14 4.1V 4.2V VIN 9 CLP RS VCC SYSTEM LOAD
1505 BD
LT1505
TEST CIRCUITS
Test Circuit 1
LT1505 SPIN SENSE RS3 200 RS2 200 RS1 10
+
CA1 1k VREF
VC 0.047F 75k
CA2
+
1k LT1006
+
-
0.65V 20k
IPROG
0.47F
RPROG
2.465V
Test Circuit 3
LT1505 CAP 0.047F IVA 4 FLAG 2V E6 CA1
+
1k
IPROG
+
3.3V VA IVA PROG
-
0.033F LT1013
+
20k 10k
0.47F
4.93k
+
2.465V
+
-
+
+
-
-
+
- +
1F 300 RPROG PROG 2k PROG
-
BAT
+
VBAT
1505 TC01
Test Circuit 2
LT1505 VFB OR BAT2
+
VA
-
VREF
2nF LT1013
1505 TC02
+ -
IPROG
SENSE
RS3 200 RS2 VRS1 200 -
+
10
BAT
+
VBAT VFB
+ -
VREF
10k
LT1013
1505 TC03
9
LT1505
OPERATION
The LT1505 is a synchronous current mode PWM stepdown (buck) switcher. The battery DC charge current is programmed by a resistor RPROG (or a DAC output current) at the PROG pin and the ratio of sense resistors RS2 over RS1 (see Block Diagram). Amplifier CA1 converts the charge current through RS1 to a much lower current IPROG (IPROG = IBAT * RS1/RS2) fed into the PROG pin. Amplifier CA2 compares 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 CPROG. Note that IPROG has both AC and DC components. IPROG 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 8.6V VGBIAS to power drives and VBOOSTC. BOOSTC pin supplies the current amplifier CA1 with a voltage higher than VCC for low dropout application. For batteries like lithium that require both constantcurrent 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/RS). At input current limit, CL1 will supply the programming current IPROG, 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 RS1) to allow for inductor discontinuous mode operation. Therefore sometimes even in continuous 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, VCC will be held up by the body diode of the topside MOSFET. The LT1505 goes into a low current, 10A typical, sleep mode as VCC drops below the battery voltage. To shut down the charger simply pull the VC pin or SHDN pin low with a transistor.
APPLICATIONS INFORMATION
Input and Output Capacitors In the 4A Lithium Battery Charger (Figure 1), the input capacitor (CIN) 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 capacitors 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 manufacturer before use. Alternatives include new high capacity ceramic (at least 20F) from Tokin or United Chemi-Con/ Marcon, et al. The output capacitor (COUT) is also assumed to absorb output switching current ripple. The general formula for capacitor current is: V 0.29 (VBAT) 1 - BAT VCC IRMS = (L1)(f)
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(
)
For example, VCC = 19V, VBAT = 12.6V, L1 = 15H, and f = 200kHz, IRMS = 0.4A.
LT1505
APPLICATIONS INFORMATION
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 between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. If the ESR of COUT is 0.2 and the battery impedance is raised to 4 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 0.33F capacitor on the VC pin. On start-up, the VC pin voltage will rise quickly to 0.5V, then ramp up at a rate set by the internal 45A pullup current and the external capacitor. Battery charge current starts ramping up when VC voltage reaches 0.7V and full current is achieved with VC at 1.1V. With a 0.33F 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 1F 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 computer 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 regulators 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.
92mV
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CL1
+
CLP 1F
-
CLN
500 AC ADAPTER OUTPUT VIN
VCC
RS4*
+
LT1505 UV *RS4 = 92mV ADAPTER CURRENT LIMIT R6
1505 F02
CIN
R5
Figure 2. Adapter Current Limiting
A resistor divider is used to set the desired VCC lockout voltage as shown in Figure 2. A typical value for R6 is 5k and R5 is found from: R5 = R6(VIN - VUV ) VUV
VUV = Rising lockout threshold on the UV pin VIN = Charger input voltage that will sustain full load power Example: With R6 = 5k, VUV = 6.7V and setting VIN 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 VCC pin to prevent battery drain with no adapter voltage. If the UV pin is not used, connect it to the adapter output (not VCC) and connect a resistor no greater than 5k to ground. Floating the pin will cause reverse battery current to increase from 10A to 200A. 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. Additionally, batteries will automatically be charged at the maximum possible rate of which the adapter is capable.
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LT1505
APPLICATIONS INFORMATION
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 RS4, 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/RS4. A lowpass filter formed by 500 and 1F 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 VCC. Charge Current Programming The basic formula for charge current is (see Block Diagram):
IBAT = IPROG
( )(
RS2 2.465V = RS1 RPROG
)( )
RS2 RS1
where RPROG is the total resistance from PROG pin to ground. For the sense amplifier CA1 biasing purpose, RS3 should have the same value as RS2 and SPIN should be connected directly to the sense resistor (RS1) as shown in the Block Diagram. For example, 4A charging current is needed. For low power dissipation on RS1 and enough signal to drive the amplifier CA1, let RS1 = 100mV/4A = 0.025. This limits RS1 power to 0.4W. Let RPROG = 5k, then:
LT1505 PROG RPROG 4.7k 5V 0V Q1 VN2222 PWM
1505 F03
CPROG 1F
IBAT = (DC)(4A)
Figure 3. PWM Current Programming
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)(R ) (I )(R RS2 = RS3 = BAT PROG S1 2.465V (4A)(5k)(0.025) = = 200 2.465V
Charge current can also be programmed by pulse width modulating IPROG with a switch Q1 to RPROG 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. Lithium-Ion Charging The 4A Lithium Battery Charger (Figure 1) charges lithiumion 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. 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 voltages, 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 4) is set at 15A . The input current to the VFB pin is 3nA and the error can be neglected.
LT1505
APPLICATIONS INFORMATION
With divider current set at 15A, R4 = 2.465/15A = 162k and,
R3 =
(R4)(VBAT - 2.465) = 162k (8.4 - 2.465)
2.465 2.465
= 390k
Li-Ion batteries typically require float voltage accuracy of 1% to 2%. Accuracy of the LT1505 VFB voltage is 0.5% at 25C 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 50C 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.
LT1505 VFB R3 390k 0.25% R4 162k 0.25%
1505 F04
+
8.4V
VBAT
Figure 4. External Resistor Divider
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 manufacturers 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 (VRS1). The comparator E6 in the Block Diagram compares the charge current sample IPROG to the output current IVA voltage amplifier VA. When the charge current drops to 20% of full current, IPROG will be equal to 0.25 IVA and the open-collector output VFLAG will go low and can be used to start an external timer. When this feature is used, a capacitor of at least 0.1F is required at the CAP pin to filter out the switching noise and a pull-up
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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 VCC 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 VCC sometimes requires a duty factor greater then 99% and TGATE stays on for many switching cycles. While TGATE stays on, the voltage VBOOST across the capacitor C2 drops down because TGATE control circuits require 2mA DC current. C2 needs to be recharged before VBOOST drops too low to keep the topside switch on. A unique design allows the LT1505 to operate under these conditions; the comparator A2 monitors VBOOST and when it drops from 8.9V to 6.9V, TGATE will be turned off for about 0.2s to recharge C2. Note that the LT1505 gets started the same way when power turns on and there is no initial VBOOST. It is important to use 0.56F or greater value for C2 to hold VBOOST up for a sufficient amount of time. When minimum operating VCC is less than 2.5V above the battery voltage, D3 and C4 (see Figure 1) are also needed to bootstrap VBOOSTC higher than VCC to bias the current amplifier CA1. They are not needed if VCC is at least 2.5V higher than VBAT. The PFET M3 is optional and can be replaced with a diode if VIN is at least 3V higher than VBAT. The gate control pin INFET turns on M3 when VIN gets up above the undervoltage lockout level set by R5 and R6 and is clamped internally to 8V below VCC. In sleep mode when VIN is removed, INFET will clamp M3 VSG to 0.2V. Shutdown When adapter power is removed, VCC will drift down and be held by the body diode of the topside NFET switch. As soon as VCC goes down to 0.2V above VBAT, the LT1505 will go into sleep mode drawing only 10A from the battery. There are two ways to stop switching: pulling the SHDN pin low or pulling the VC pin low. Pulling the SHDN pin low will also turn off VGBIAS and CA1 input currents. Pulling the VC pin low will only stop switching and VGBIAS stays high. Make sure there is a pull-up resistor on the SHDN pin even
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LT1505
APPLICATIONS INFORMATION
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 VCC is 24V. For short transients the LT1505 can be operated as high as 27V. For VCC higher than 24V it is preferred to use the VC pin to shut down. If the SHDN pin has to be used to shut down at VCC higher than 24V, the Figure 5 pull-up circuit must be used to slow down the VGBIAS ramp-up rate when the SHDN pin is released. Otherwise, high surge current charging the bypass capacitor might damage the LT1505. For VCC less than 24V, only a 100k resistor and no capacitor is needed at SHDN pin to VIN 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 6). 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 7). For 2A full current, the current sense resistor (RS1) should be increased to 0.05 so that enough signal (10mV) will be across RS1 at 0.2A trickle charge to keep charging current accurate. For a 2-level charger, R1 and R2 are found from:
R1 =
24V VCC < 27V VIN 3M LT1505 SHDN OPEN DRAIN 3.3F
1505 F05
(2.465)(4000)
ILOW
R2 =
(2.465)(4000 )
IHI - ILOW
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.
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Figure 5
5V TO 20V 5k SYNC VN2222 PULSE WIDTH > 200ns
1505 F06
LT1505
Figure 6
LT1505 PROG CPROG 1F R1 49.3k Q1
1505 F07
R2 5.49k
Figure 7. 2-Level Charging
The charge current is then reduced to a much lower value and maintained as a constant trickle charge. An intermediate "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 approached 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, constant trickle charge may not be recommended.
LT1505
APPLICATIONS INFORMATION
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 4 should be calculated according to the procedure described in the Lithium-Ion Charging section. The VFB pin should be grounded if not used. Charger Crowbar Protection If the VIN 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 8), 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 VBAT is grounded. If VBAT 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 9) from the SHDN pin to VBAT will shut down switching and protect the charger. Note that M4 and/or D5 are needed only if the charger system can be potentially crowbarred. 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
M3 VIN M4 TPO610 LT1505 INFET RS4 VCC
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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1505 F08
Figure 8. VIN Crowbar Protection
VIN 100k SHDN D5 1N4148 VBAT
1505 F09
LT1505
Figure 9. VBAT Crowbar Protection
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 dissipating device in the charging system. The resistance on a 4A, 15H inductor, can be 0.03 . 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 (1F ceramic) should be placed very close the chip. The demo board DC219 should be used for layout reference.
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LT1505
PACKAGE DESCRIPTION
0.205 - 0.212** (5.20 - 5.38)
0.005 - 0.009 (0.13 - 0.22)
0.022 - 0.037 (0.55 - 0.95)
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSIONS DO NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
RELATED PARTS
PART NUMBER LTC 1325 LT1372/LT1377 LT1376 LT1510 LT1511 LT1512 LT1513 LTC1759 LT1769
(R)
DESCRIPTION Microprocessor-Controlled Battery Management System 1.5A, 500kHz/1MHz Step-Up Switching Regulators 1.5A, 500kHz Step-Down Switching Regulator Constant-Voltage/Constant-Current Battery Charger 3A Constant-Voltage/Constant-Current Battery Charger SEPIC CC/CV Battery Charger SEPIC CC/CV Battery Charger SMBus Controlled Smart Battery Charger 2A Constant-Voltage/Constant-Current Battery Charger
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com
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Dimensions in inches (millimeters) unless otherwise noted. G Package 28-Lead Plastic SSOP (0.209)
(LTC DWG # 05-08-1640)
0.397 - 0.407* (10.07 - 10.33) 28 27 26 25 24 23 22 21 20 19 18 17 16 15
0.301 - 0.311 (7.65 - 7.90)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 0.068 - 0.078 (1.73 - 1.99)
0 - 8
0.0256 (0.65) BSC
0.010 - 0.015 (0.25 - 0.38)
0.002 - 0.008 (0.05 - 0.21)
G28 SSOP 0694
COMMENTS Can Charge, Discharge and Gas Gauge NiCd and Lead-Acid Batteries with Software Charging Profiles High Frequency, Small Inductor, High Efficiency Switchers, SO-8 High Frequency, Small Inductor, High Efficiency Switcher, SO-8 Up to 1.5A Charge Current, Small SO-8 Footprint Charges Lithium, NiCd and NiMH Batteries, 28-Lead SO Package VIN Can Be Higher or Lower Than Battery Voltage, 2A Internal Switch VIN Can Be Higher or Lower Than Battery Voltage, 3A Internal Switch LT1505 Charger Functionality with SMBus Control Charges Lithium, NiCd and NiMH Batteries, 28-Lead SSOP
1505fa LT/TP 0400 2K REV A * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1999

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