View LT1512_150276.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

LT1512 SEPIC Constant-Current/ Constant-Voltage Battery Charger
FEATURES
s s s
DESCRIPTION
The LT (R)1512 is a 500kHz current mode switching regulator specially configured to create a constant-current/ constant-voltage battery charger. In addition to the usual voltage feedback node, it has a current sense feedback circuit for accurately controlling output current of a flyback or SEPIC (Single-Ended Primary Inductance Converter) topology charger. These topologies allow the current sense circuit to be ground referred and completely separated from the battery itself, simplifying battery switching and system grounding problems. In addition, these topologies allow charging even when the input voltage is lower than the battery voltage. Maximum switch current on the LT1512 is 1.5A. This allows battery charging currents up to 1A for a single lithium-ion cell. Accuracy of 1% in constant-voltage mode is perfect for lithium battery applications. Charging current can be easily programmed for all battery types.
, LTC and LT are registered trademarks of Linear Technology Corporation.
s s s
s
Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage Charges Any Number of Cells Up to 30V* 1% Voltage Accuracy for Rechargeable Lithium Batteries 100mV Current Sense Voltage for High Efficiency Battery Can Be Directly Grounded 500kHz Switching Frequency Minimizes Inductor Size Charging Current Easily Programmable or Shut Down
APPLICATIONS
s s s s
Battery Charging of NiCd, NiMH, Lead-Acid or Lithium Rechargeable Cells Precision Current Limited Power Supply Constant-Voltage/Constant-Current Supply Transducer Excitation
*Maximum Input Voltage = 40V - VBAT
TYPICAL APPLICATION
1.0
Maximum Charging Current
SINGLE LITHIUM CELL (4.1V)
WALL ADAPTER INPUT CHARGE
*
L1 A* C2** D1 2.2F MBRS130LT3
CURRENT (A)
0.8
+
C3 22F 25V
VIN LT1512 S/S GND GND S VC
VSW L1 B* FB IFB C5 0.1F R5 1k C4 0.22F R3 0.2 * R4 24 R2 R1
0.5A
0.6
SYNC AND/OR SHUTDOWN SHUTDOWN
0.4
+
C1 22F 25V
0.2
0
0
*L1 A, L1 B ARE TWO 33H WINDINGS ON A SINGLE INDUCTOR: COILTRONICS CTX33-3 **TOKIN CERAMIC 1E225ZY5U-C203-F
1512 F01
Figure 1. SEPIC Charger with 0.5A Output Current
ACTUAL PROGRAMMED CHARGING CURRENT WILL BE INDEPENDENT OF INPUT VOLTAGE AND BATTERY VOLTAGE IF IT DOES NOT EXCEED THE VALUES SHOWN. THESE ARE ELECTRICAL LIMITATIONS BASED ON MAXIMUM SWITCH CURRENT. PACKAGE THERMAL LIMITATIONS MAY REDUCE MAXIMUM CHARGING CURRENT. SEE APPLICATIONS INFORMATION.
U
U
U
DOUBLE LITHIUM CELL (8.2V) 6V BATTERY 12V BATTERY INDUCTOR = 33H 5 15 10 INPUT VOLTAGE (V) 20 25
1512 TA02
1
LT1512 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW VC 1 FB 2 IFB 3 S/S 4 N8 PACKAGE 8-LEAD PDIP 8 7 6 5 VSW GND GND S VIN
Input Voltage .......................................................... 30V Switch Voltage ........................................................ 40V S/S Pin Voltage ....................................................... 30V FB Pin Voltage (Transient, 10ms) ......................... 10V VFB Pin Current .................................................... 10mA IFB Pin Voltage (Transient, 10ms) ......................... 10V Storage Temperature Range ................ - 65C to 150C Ambient Temperature Range LT1512C (Note 3) .................................... 0C to 70C LT1512I .............................................. - 40C to 85C Operating Junction Temperature Range LT1512C (Note 3) ............................ - 20C to 125C LT1512I ............................................ - 40C to 125C Short Circuit ......................................... 0C to 150C Lead Temperature (Soldering, 10 sec)................. 300C
ORDER PART NUMBER LT1512CN8 LT1512CS8 LT1512IN8 LT1512IS8 S8 PART MARKING 1512 1512I
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 125C, JA = 100C/ W (N) TJMAX = 125C, JA = 130C/ W (S) NOTE: CONTACT FACTORY CONCERNING 16-LEAD FUSED-LEAD GN PACKAGE WITH LOWER THERMAL RESISTANCE
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 5V, VC = 0.6V, VFB = VREF, IFB = 0V, VSW and S/S pins open, unless otherwise noted.
SYMBOL VREF PARAMETER VFB Reference Voltage FB Input Current FB Reference Voltage Line Regulation VIREF IFB Reference Voltage IFB Input Current IFB Reference Voltage Line Regulation gm Error Amplifier Transconductance Error Amplifier Source Current Error Amplifier Sink Current Error Amplifier Clamp Voltage AV f Error Amplifier Voltage Gain VC Pin Threshold Switching Frequency Duty Cycle = 0% 2.7V VIN 25V 0C TJ 125C - 40C TJ < 0C (LT1512I)
q q
CONDITIONS Measured at FB Pin VC = 0.8V VFB = VREF
q q
MIN 1.233 1.228
TYP 1.245 1.245 300
MAX 1.257 1.262 550 600 0.03 - 93 - 90 35 0.05 1900 2300 350 2400 2.30 0.52 1.25 550 580 580 260
UNITS V V nA nA %/V mV mV A %/V mho mho A A V V V/ V V kHz kHz kHz % ns V V
2.7V VIN 25V, VC = 0.8V Measured at IFB Pin VFB = 0V, VC = 0.8V VIFB = VIREF (Note 2) 2.7V VIN 25V, VC = 0.8V IC = 25A
q q q q q
0.01 - 107 -110 10 1100 700 120 1.70 0.25 0.8 450 430 400 88 40 35 - 100 - 100 25 0.01 1500 200 1400 1.95 0.40 500 1 500 500 95 130 47
VFB = VREF - 150mV, VC = 1.5V VFB = VREF + 150mV, VC = 1.5V High Clamp, VFB = 1V Low Clamp, VFB = 1.5V
q q
Maximum Switch Duty Cycle Switch Current Limit Blanking Time BV Output Switch Breakdown Voltage 0C TJ 125C - 40C TJ < 20C (LT1512I)
q
2
U
W
U
U
WW
W
LT1512
ELECTRICAL CHARACTERISTICS
VIN = 5V, VC = 0.6V, VFB = VREF, IFB = 0V, VSW and S/S pins open, unless otherwise noted.
SYMBOL VSAT ILIM IIN ISW PARAMETER Output Switch ON Resistance Switch Current Limit Supply Current Increase During Switch ON Time Control Voltage to Switch Current Transconductance Minimum Input Voltage IQ Supply Current Shutdown Supply Current 2.7V VIN 25V 2.7V VIN 25V, VS/S 0.6V 0C TJ 125C - 40C TJ 0C (LT1512I) 2.7V VIN 25V 0V VS/S 5V
q q q q q q q
CONDITIONS ISW = 2A Duty Cycle = 50% Duty Cycle = 80% (Note 1)
q q q
MIN 1.5 1.3
TYP 0.5 1.9 1.7 15 2 2.4 4 12
MAX 0.8 2.7 2.5 25
UNITS A A mA/A A/V
2.7 5.5 30 50 2 25 15 800
V mA A A V s A kHz
Shutdown Threshold Shutdown Delay S/S Pin Input Current Synchronization Frequency Range
0.6 5 - 10 600
1.3 12
The q denotes specifications which apply over the full operating temperature range. Note 1: For duty cycles (DC) between 50% and 85%, minimum guaranteed switch current is given by ILIM = 0.667 (2.75 - DC). Note 2: The IFB pin is servoed to its regulating state with VC = 0.8V. Note 3: Commercial devices are guaranteed over 0C to 125C junction temperature range and 0C to 70C ambient temperature range. These parts are also designed, characterized and expected to operate over the - 20C to 85C extended ambient temperature range, but are not tested at - 20C or 85C. Devices with full guaranteed electrical specifications over
the ambient temperature range - 40C to 85C are available as industrial parts with an "I" suffix. Maximum allowable ambient temperature may be limited by power dissipation. Parts may not necessarily be operated simultaneously at maximum power dissipation and maximum ambient temperature. Temperature rise calculations must be done as shown in the Applications Information section to ensure that maximum junction temperature does not exceed 125C limit. With high power dissipation, maximum ambient temperature may be less than 70C.
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage vs Switch Current
1.0
SWITCH SATURATION VOLTAGE (V)
0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
150C 100C
SWITCH CURRENT LIMIT (A)
2.0 -55C 1.5 1.0 0.5 0
INPUT VOLTAGE (V)
-55C
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A)
1512 G01
UW
25C
Switch Current Limit vs Duty Cycle
3.0 2.5 25C AND 125C
3.0 2.8 2.6 2.4 2.2 2.0
Minimum Input Voltage vs Temperature
0
10 20 30 40 50 60 70 80 90 100 DUTY CYCLE (%)
1512 G02
1.8 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
1512 G03
3
LT1512 TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Peak-to-Peak Synchronization Voltage vs Temp
MINIMUM SYNCHRONIZATION VOLTAGE (VP-P)
fSYNC = 700kHz
FEEDBACK INPUT CURRENT (nA)
2.5 2.0 1.5 1.0 0.5 0 -50 -25
700 600 500 400 300 200 100
VFB = VREF
NEGATIVE FEEDBACK INPUT CURRENT (A)
3.0
0
25 50 75 100 125 150 TEMPERATURE (C)
1512 G04
PIN FUNCTIONS
VC: The compensation pin is primarily used for frequency compensation, but it can also be used for soft starting and current limiting. It is the output of the error amplifier and the input of the current comparator. Peak switch current increases from 0A to 1.8A as the VC voltage varies from 1V to 1.9V. Current out of the VC pin is about 200A when the pin is externally clamped below the internal 1.9V clamp level. Loop frequency compensation is performed with a capacitor or series RC network from the VC pin directly to the ground pin (avoid ground loops). FB: The feedback pin is used for positive output voltage sensing. This pin is the inverting input to the voltage error amplifier. The R1/R2 voltage divider connected to FB defines Li-Ion float voltage at full charge, or acts as a voltage limiter for NiCd or NiMH applications. Input bias current is typically 300nA, so divider current is normally set to 100A to swamp out any output voltage errors due to bias current. The noninverting input of this amplifier is tied internally to a 1.245V reference. The grounded end of the output voltage divider should be connected directly to the LT1512 ground pin (avoid ground loops). IFB: The current feedback pin is used to sense charging current. It is the input to a current sense amplifier that controls charging current when the battery voltage is below the programmed voltage. During constant-current operation, the IFB pin regulates at - 100mV. Input resistance of this pin is 5k, so filter resistance (R4, Figure 1) should be less than 50. The 24, 0.22F filter shown in Figure 1 is used to convert the pulsating current in the sense resistor to a smooth DC current feedback signal. S/S: This pin can be used for shutdown and/or synchronization. It is logic level compatible, but can be tied to VIN if desired. It defaults to a high ON state when floated. A logic low state will shut down the charger to a micropower state. Driving the S/S pin with a continuous logic signal of 600kHz to 800kHz will synchronize switching frequency to the external signal. Shutdown is avoided in this mode with an internal timer. VIN: The input supply pin should be bypassed with a low ESR capacitor located right next to the IC chip. The grounded end of the capacitor must be connected directly to the ground plane to which the GND pin is connected. GND S, GND: The LT1512 uses separate ground pins for switch current (GND) and the control circuitry (GND S). This isolates the control ground from any induced voltage created by fast switch currents. Both pins should be tied directly to the ground plane, but the external control circuit components such as the voltage divider, frequency compensation network and IFB bypass capacitor should
4
UW
Feedback Input Current vs Temperature
800
0
Negative Feedback Input Current vs Temperature
-10
-20
-30
-40
0 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
1512 G05
-50 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
1512 G06
U
U
U
LT1512
PIN FUNCTIONS
be connected directly to the GND S pin or to the ground plane close to the point where the GND S pin is connected. VSW: The switch pin is the collector of the power switch, carrying up to 1.5A of current with fast rise and fall times. Keep the traces on this pin as short as possible to minimize radiation and voltage spikes. In particular, the path in Figure 1 which includes SW to C2, D1, C1 and around to the LT1512 ground pin should be as short as possible to minimize voltage spikes at switch turn-off.
BLOCK DIAGRAM
S/S
5k IFB 62k
FB
1.245V REF
GND S
OPERATION
The LT1512 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage or current. Referring to the Block Diagram, the switch is turned "on" at the start of each oscillator cycle. It is turned "off" when switch current reaches a predetermined level. Control of output voltage and current is obtained by using the output of a dual feedback voltage sensing error amplifier to set switch current trip level. This technique has the advantage of simplified loop frequency compensation. A low dropout internal regulator provides a 2.3V supply for all internal circuitry on the LT1512. This low dropout design allows input voltage to vary from 2.7V to 25V. A 500kHz oscillator is the basic clock for all internal timing. It turns "on" the output switch via the logic and driver circuitry. Special adaptive antisat circuitry detects onset of saturation in the power switch and adjusts driver current instantaneously to limit switch saturation. This minimizes driver dissipation and provides very rapid turn-off of the switch. A unique error amplifier design has two inverting inputs which allow for sensing both output voltage and current. A 1.245V bandgap reference biases the noninverting input. The first inverting input of the error amplifier is brought out for positive output voltage sensing. The second inverting input is driven by a "current" amplifier which is sensing output current via an external current sense resistor. The
+ - -
W
U
U
U
U
VIN SHUTDOWN DELAY AND RESET 500kHz OSC LOW DROPOUT 2.3V REG
SW
ANTI-SAT
SYNC
LOGIC
DRIVER
SWITCH
+
IFBA
-
COMP
+
EA VC AV 6 IA 0.08
-
GND
1512 F02
Figure 2
5
LT1512
OPERATION
current amplifier is set to a fixed gain of - 12.5 which provides a - 100mV current limit sense voltage. The error signal developed at the amplifier output is brought out externally and is used for frequency compensation. During normal regulator operation this pin sits at a voltage between 1V (low output current) and 1.9V (high output current). Switch duty cycle goes to zero if the VC pin is pulled below the VC pin threshold, placing the LT1512 in an idle mode.
APPLICATIONS INFORMATION
The LT1512 is an IC battery charger chip specifically optimized to use the SEPIC converter topology. The SEPIC topology has unique advantages for battery charging. It will operate with input voltages above, equal to or below the battery voltage, has no path for battery discharge when turned off and eliminates the snubber losses of flyback designs. It also has a current sense point that is ground referred and need not be connected directly to the battery. The two inductors shown are actually just two identical windings on one inductor core, although two separate inductors can be used. A current sense voltage is generated with respect to ground across R3 in Figure 1. The average current through R3 is always identical to the current delivered to the battery. The LT1512 current limit loop will servo the voltage across R3 to - 100mV when the battery voltage is below the voltage limit set by the output divider R1/R2. Constant current charging is therefore set at 100mV/R3. R4 and C4 filter the current signal to deliver a smooth feedback voltage to the IFB pin. R1 and R2 form a divider for battery voltage sensing and set the battery float voltage. The suggested value for R2 is 12.4k. R1 is calculated from: tional uncorrectable error to the constant voltage float mode of about 0.5% as calculated by:
VBAT Error = 0.15A(R1)(R2) 1.245(R1+ R2)
R1 =
R2(VBAT - 1.245) 1.245 + R2(0.3A)
VBAT = battery float voltage 0.3A = typical FB pin bias current A value of 12.4k for R2 sets divider current at 100A. This is a constant drain on the battery when power to the charger is off. If this drain is too high, R2 can be increased to 41.2k, reducing divider current to 30A. This introduces an addi-
6
U
W
U
U
U
0.15A = expected variation in FB bias current around the nominal 0.3A typical value. With R2 = 41.2k and R1 = 228k, (VBAT = 8.2V), the error due to variations in bias current would be 0.42%. A second option is to disconnect the voltage divider with a small NMOS transistor as shown in Figure 3. To ensure adequate drive to the transistor (even when the VIN voltage is at its lowest operating point of 2.4V), the FET gate is driven wth a peak detected voltage via D2. Note that there are two connections for D2. The L1 A connection must be used if the voltage divider is set for less than 3.5V (fully charged battery). Gate drive is equal to battery voltage plus input voltage. The disadvantage of this connection is that Q1 will still be "on" if the VIN voltage is active and the charger is shut down via the S/S pin. The L1 B connection allows Q1 to turn off when VIN is off or when shutdown is initiated, but the reduced gate drive (=VBAT) is not adequate to ensure a Q1 on-state for fully charged battery voltages less than 3.5V. Do not substitute for Q1 unless the new device has adequate VGS maximum rating, especially if D2 is connected to L1A. C6 filters the gate drive and R5 pulls the gate low when switching stops. Disconnecting the divider leaves only D1 diode leakage as a battery drain. See Diode Selection for a discussion of diode leakage.
LT1512
APPLICATIONS INFORMATION
CONNECT D2 ANODE HERE FOR FULLY CHARGED BATTERY VOLTAGE LESS THAN 3.5V. Q1 WILL NOT BE TURNED OFF IN SHUTDOWN IF VIN IS PRESENT * L1 A D2 1N4148 C2 VIN VSW R1 SHUTDOWN S/S LT1512 L1 B Q1 2N7002 GND FB R3 R2 D1 C6 470pF R5 470k CONNECT D2 ANODE HERE IF FULLY CHARGED BATTERY VOLTAGE IS GREATER THAN 3.5V AND Q1 MUST BE TURNED OFF IN SHUTDOWN WITH VIN STILL ACTIVE
Figure 3. Eliminating Divider Current
Maximum Input Voltage Maximum input voltage for the circuit in Figure 1 is partly determined by battery voltage. A SEPIC converter has a maximum switch voltage equal to input voltage plus output voltage. The LT1512 has a maximum input voltage of 30V and a maximum switch voltage of 40V, so this limits maximum input voltage to 30V, or 40V - VBAT, whichever is less. Maximum VBAT = 40V - VIN. Shutdown and Synchronization The dual function S/S pin provides easy shutdown and synchronization. It is logic level compatible and can be pulled high or left floating for normal operation. A logic low on the S/S pin activates shutdown, reducing input supply current to 12A. To synchronize switching, drive the S/S pin between 600kHz and 800kHz. Inductor Selection L1A and L1B are normally just two identical windings on one core, although two separate inductors can be used. A typical value is 33H, which gives about 0.25A peak-to-peak inductor current. Lower values will give higher ripple current, which reduces maximum charging current. 15H can be used if charging currents are at least 20% lower than the values shown in the maximum charging current graph. Higher inductance values give slightly higher maximum charging current, but are larger and more expensive. A low
U
W
U
U
+
1512 F03
loss toroid core such as KoolM(R), Molypermalloy or Metglas(R) is recommended. Series resistance should be less than 0.1 for each winding. "Open core" inductors, such as rods or barrels are not recommended because they generate large magnetic fields which may interfere with other electronics close to the charger. Input Capacitor The SEPIC topology has relatively low input ripple current compared to other topologies and higher harmonics are especially low. RMS ripple current in the input capacitor is less than 0.1A with L = 33H and less than 0.2A with L = 15H. A low ESR 22F, 25V solid tantalum capacitor (AVX type TPS or Sprague type 593D) is adequate for most applications with the following caveat. Solid tantalum capacitors can be destroyed with a very high turn-on surge current such as would be generated if a low impedance input source were "hot switched" to the charger input. If this condition can occur, the input capacitor should have the highest possible voltage rating, at least twice the surge input voltage if possible. Consult with the capacitor manufacturer before a final choice is made. A 2.2F ceramic capacitor such as the one used for the coupling capacitor can also be used. These capacitors do not have a turn-on surge limitation. The input capacitor must be connected directly to the VIN pin and the ground plane close to the LT1512.
KoolM is a registered trademark of Magnetics, Inc. Metglas is a registered trademark of AlliedSignal Inc.
7
LT1512
APPLICATIONS INFORMATION
Output Capacitor It is assumed as a worst case that all the switching output ripple current from the battery charger could flow in the output capacitor. This is a desirable situation if it is necessary to have very low switching ripple current in the battery itself. Ferrite beads or line chokes are often inserted in series with the battery leads to eliminate high frequency currents that could create EMI problems. This forces all the ripple current into the output capacitor. Total RMS current into the capacitor has a maximum value of about 0.5A, and this is handled with a 22F, 25V capacitor shown in Figure 1. This is an AVX type TPS or Sprague type 593D surface mount solid tantalum unit intended for switching applications. Do not substitute other types without ensuring that they have adequate ripple current ratings. See Input Capacitor section for details of surge limitation on solid tantalum capacitors if the battery may be "hot switched" to the output of the charger. Coupling Capacitor C2 in Figure 1 is the coupling capacitor that allows a SEPIC converter topology to work with input voltages either higher or lower than the battery voltage. DC bias on the capacitor is
VIN 1 4 R4 R1 L1A 2 WINDING INDUCTOR L1B R3 C4 R2 2 3
C3 C2B C2A S/S
D1
R5
C5
VC VSW GND
IFB GND S
GND
GND
1512 F04a
R1 R2
FB
S/S
R5
VIN
U1
C1
a. Double-Sided (Vias Connect to the Backside of Ground Plane. Dash Lines Indicate Interconnects on Backside. Demo Board Uses This Layout, Except that R5 Has Been Added to Increase Phase Margin)
Figure 4. LT1512 Suggested Layouts for Critical Thermal and Electrical Paths
8
U
W
U
U
equal to input voltage. RMS ripple current in the coupling capacitor has a maximum value of about 0.5A at full charging current. A conservative formula to calculate this is:
I (V + V )(1.1) ICOUP(RMS) = CHRG IN BAT 2(VIN ) (1.1 is a fudge factor to account for inductor ripple current and other losses)
With ICHRG = 0.5A, VIN = 15V and VBAT = 8.2V, ICOUP = 0.43A The recommended capacitor is a 2.2F ceramic type from Marcon or Tokin. These capacitors have extremely low ESR and high ripple current ratings in a small package. Solid tantalum units can be substituted if their ripple current rating is adequate, but typical values will increase to 22F or more to meet the ripple current requirements. Diode Selection The switching diode should be a Schottky type to minimize both forward and reverse recovery losses. Average diode current is the same as output charging current , so this will be under 1A. A 1A diode is recommended for most applications, although smaller devices could be used at reduced
GND +VIN
4
L1B
3
D1
C2 1
L1A
2
VBATT
+
VBATT
C1
C3
+
C5
R3 C4
R4
S/S
1512 F04b
b. Single-Sided Altenative Layout
LT1512
APPLICATIONS INFORMATION
charging current. Maximum diode reverse voltage will be equal to input voltage plus battery voltage. Diode reverse leakage current will be of some concern during charger shutdown. This leakage current is a direct drain on the battery when the charger is not powered. High current Schottky diodes have relatively high leakage currents (2A to 200A) even at room temperature. The latest very-low-forward devices have especially high leakage currents. It has been noted that surface mount versions of some Schottky diodes have as much as ten times the leakage of their through-hole counterparts. This may be because a low forward voltage process is used to reduce power dissipation in the surface mount package. In any case, check leakage specifications carefully before making a final choice for the switching diode. Be aware that diode manufacturers want to specify a maximum leakage current that is ten times higher than the typical leakage. It is very difficult to get them to specify a low leakage current in high volume production. This is an on going problem for all battery charger circuits and most customers have to settle for a diode whose typical leakage is adequate, but theoretically has a worst-case condition of higher than desired battery drain. Thermal Considerations Care should be taken to ensure that worst-case conditions do not cause excessive die temperatures. Typical thermal resistance is 130C/W for the S8 package but this number will vary depending on the mounting technique (copper area, air flow, etc). Average supply current (including driver current) is: For VIN = 10V, VBAT = 8.2V, ICHRG = 0.5A, RSW = 0.65 IIN = 4mA + 10mA = 14mA PSW = 0.24W PD = (0.014)(10) + 0.24 = 0.38W The S8 package has a thermal resistance of 130C/W. (Contact factory concerning 16-lead fused-lead package with footprint approximately same as S8 package and with lower thermal resistance.) Die temperature rise will be (0.38W)(130C/W) = 49C. A maximum ambient temperature of 60C will give a die temperature of 60C + 49C = 109C. This is only slightly less than the maximum junction temperature of 125C, illustrating the importance of doing these calculations! Programmed Charging Current LT1512 charging current can be programmed with a PWM signal from a processor as shown in Figure 5. C6 and D2 form a peak detector that converts a positive logic signal to a negative signal. The average negative signal at the input to R5 is equal to the processor VCC level multiplied by the inverse PWM ratio. This assumes that the PWM signal is a CMOS output that swings rail-to-rail with a source resistance less than a few hundred ohms. The negative voltage is converted to a current by R5 and R6 and filtered by C7. This current multiplied by R4 generates a voltage that subtracts from the 100mV sense voltage of the LT1512. This is not a high precision technique because of the errors in VCC and the diode voltage, but it can typically be used to adjust charging current over a 20% to 100% range with good repeatability (full charging current accuracy is not affected). To reduce the load on the logic signal, R4 has been increased
IIN = 4mA +
(VBAT )(ICHRG )(0.024) VIN
Switch power dissipation is given by:
(I )2 (RSW )(VBAT + VIN )(VBAT) PSW = CHRG (VIN )2
RSW = output switch ON resistance Total power dissipation of the die is equal to supply current times supply voltage, plus switch power: PD(TOTAL) = (IIN)(VIN) + PSW
+
PWM INPUT 1kHz
U
W
U
U
LT1512 IFB C6 1F R5 4.02k D2 R6 4.02k C7 10F R4 200 C4 0.22F L1B
+
R3
1512 F05
Figure 5. Programming Charge Current
9
LT1512
APPLICATIONS INFORMATION
from 24 to 200. This causes a known increase in fullscale charging current (PWM = 0) of 3% due to the 5k input resistance of the IFB pin. Note that 100% duty cycle gives full charging current and that very low duty cycles (especially zero!) will not operate correctly. Very low duty cycle (<10%) is a problem because the peak detector requires a finite up-time to reset C6. More Help Linear Technology Field Application Engineers have a CAD spreadsheet program for detailed calculations of circuit operating conditions, and our Applications Department is always ready to lend a helping hand. For additional information refer to the LT1372 data sheet. This part is identical to the LT1512 except for the current amplifier circuitry.
PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package 8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400* (10.160) MAX 8 7 6 5
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
10
U
U
W
U
U
0.255 0.015* (6.477 0.381)
1
2
3
4 0.130 0.005 (3.302 0.127)
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.005 (0.127) MIN 0.100 0.010 (2.540 0.254) 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076) 0.015 (0.380) MIN
N8 0695
LT1512
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0695
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.
11
LT1512
TYPICAL APPLICATION
The circuit in Figure 6 will provide adapter current limiting to ensure that the battery charger never overloads the adapter. In addition, it adjusts charging current to a lower value if other system power increases to the point where the adapter would be overloaded. This allows the LT1512
R6 0.2 R5 1k 2 7 3
WALL ADAPTER INPUT
-
LM301 4 6
Q1 2N3904 R7 12k
*L1 A, L1 B ARE TWO 33H WINDINGS ON A COMMON CORE: COILTRONICS CTX33-3 **TOKIN CERAMIC 1E225ZY5U-C203-F
RELATED PARTS
PART NUMBER DESCRIPTION LT1239 LTC(R)1325 LT1510 LT1511 LT1513 Backup Battery Management System Microprocessor Controlled Battery Management System 1.5A Constant-Current/Constant-Voltage Battery Charger 3.0A Constant-Current/Constant-Voltage Battery Charger with Input Current Limiting COMMENTS Charges Backup Battery and Regulates Backup Battery Output when Main Battery Removed Can Charge, Discharge and Gas Gauge NiCd, NiMH and Pb-Acid Batteries with Software Charging Profiles Step-Down Charger for Li-Ion, NiCd and NiMH Step-Down Charger that Allows Charging During Computer Operation and Prevents Wall-Adapter Overload
SEPIC Constant-Current/Constant-Voltage Battery Charger Step-Up/Step-Down Charger for Up to 2A Current
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
U
to charge the battery at the maximum possible rate without concern about varying system power levels. The LM301 op amp used here is unusual in that it can operate with its inputs at a voltage equal to the positive supply voltage.
SYSTEM POWER *
L1 A*
+ +
8 D2 1N4148
C3 22F 25V
5 VIN VSW 8
C2** D1 2.2F MBRS130LT3 0.5A L1 B* FB IFB 3 2 R4 24 C4 0.22F R3 0.2 * R2 R1
1 30pF LT1512 SYNC 4 AND/OR S/S SHUTDOWN GND GND S VC 7 TO FB PIN 6 1
+
C1 22F 25V
C5 0.1F
1512 F06
Figure 6. Adding Adapter Current Limiting
LT/GP 1096 7K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1996

▲Up To Search▲

Price & Availability of LT1512

	To Download LT1512 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .