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LTC1980 Combination Battery Charger and DC/DC Converter
FEATURES

DESCRIPTIO

Single Controller IC Includes Battery Charger Plus DC/DC Converter Wall Adapter Voltage May be Above or Below Battery Voltage LDO Controller Allows Simultaneous Charging and Regulating from Wall Adapter Input Standalone Li-Ion Battery Charger Including Charge Termination, Overvoltage Protection, Shorted-Cell Detection and Battery Recharge Selectable 4.1V, 4.2V, 8.2V and 8.4V Float Voltages Simple NiMH and NiCd Battery Charger Pin Programmable Regulator Burst Mode(R) Operation and Shutdown for High Efficiency High Efficiency Current Mode 300kHz PWM Reduced Component Architecture Undervoltage Protection and Soft-Start Ensures Start-Up with Current Limited Wall Adapter Small 24-Pin SSOP Package
The LTC(R)1980 integrates PWM power control for charging a battery and converting the battery voltage to a regulated output or simultaneously charging the battery while powering a system load from an unregulated AC wall adapter. Combining these features into a single IC produces a smaller area and lower cost solution compared to presently available multi-IC solutions. The LTC1980 shares the discrete components for both the battery charger and the DC/DC converter thus minimizing size and cost relative to dual controller solutions. Both the battery charger and DC/DC converter use a current mode flyback topology for high efficiency and excellent transient response. Optional Burst Mode operation and power-down mode allow power density, efficiency and output ripple to be tailored to the application. The LTC1980 provides a complete Li-Ion battery charger with charge termination timer, preset Li-Ion battery voltages, overvoltage and undervoltage protection, and userprogrammable constant-current charging. Automatic battery recharging, shorted-cell detection, and open-drain C/10 and wall plug detect outputs are also provided. User programming allows NiMH and NiCd battery chemistries to be charged as well.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. Patents Pending.
APPLICATIO S

Digital Cameras Handheld Computers Personal Digital Assistants 1W to 10W Uninterruptable Power Supplies
TYPICAL APPLICATIO
POWER FLOW CHARGING BATTERY OPERATION Li-Ion BATTERY
Li-Ion Charger and DC/DC Converter Using One IC
3.3V Regulator Efficiency vs Load Current
90
*
SYSTEM POWER BAT-FET
UNREGULATED WALL ADAPTER INPUT (3V TO 10V)
85
EFFICIENCY (%)
80 75 70 65 60 VBAT = 3.6V TA = 25C FIGURE 5 10 100 LOAD CURRENT (mA) 1000
1980 G04
*
REG-FET LDO/ SWITCH
SYSTEM LOAD DC/DC CONVERTERS LTC1980
1980 TA01
3.3V 1.8V 1.5V
U
1980f
U
U
1
LTC1980
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW PROG PROGT REGFB VC LDOFB LDODRV VREG WA BATT1 1 2 3 4 5 6 7 8 9 24 SS 23 OVP 22 CAOUT 21 ISENSE 20 GND 19 VBIAS2 18 VBAT 17 TIMER 16 MODE 15 REG 14 BGTDR 13 VBIAS1
VREG to GND ............................................. -0.5V to 12V VBAT to GND ............................................. -0.5V to 12V PROG, ISENSE .............................................. -0.5V to 5V PROGT, REGFB, VC, BATT1, BATT2 TIMER, SS ............................................ -0.5V to VBIAS2 LDOFB, LDODRV .................................... -0.5V to VREG WA, VBIAS1, REG ....................................... -0.5V to 12V MODE ................................................... -0.5V to VBIAS1 VBIAS2 ......................................................... -0.5V to 5V OVP ............................................................ -0.5V to 5V PGND to GND .................................... Connect Together Operating Ambient Temperature Range (Note 2) ................................................. - 40C to 85C Storage Temperature Range ................. - 65C to 125C Lead Temperature (Soldering, 10 sec)................ 300C
ORDER PART NUMBER LTC1980EGN
BATT2 10 RGTDR 11 PGND 12
GN PACKAGE 24-LEAD NARROW PLASTIC SSOP TJMAX = 125C, JA = 85C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL VBAT VREG VFB VPROGT IBURST IHIGH ISHDN VUVL VUVHYS ISS VFLOAT0 VFLOAT1 VFLOAT2 VFLOAT3 VFLOAT4 VRCHG0 VRCHG1 PARAMETER Positive Supply Voltage, VBAT Positive Supply Voltage, VREG Feedback Voltage Voltage on PROGT Pin Burst Mode Operation Supply Current, Quiescent, VREG Supply Current, Quiescent, VREG Supply Current in Shutdown Mode, VREG Positive-Going Undervoltage Lockout Voltage Undervoltage Lockout Hysteresis Soft-Start Ramp Current Output Float Voltage in Constant Voltage Mode Output Float Voltage in Constant Voltage Mode Output Float Voltage in Constant Voltage Mode Output Float Voltage in Constant Voltage Mode Output Float Voltage in Constant Voltage Mode Recharge Threshold, Delta Voltage with Respect to Float Voltage Recharge Threshold, Delta Voltage with Respect to Float Voltage REGFB Tied to VC PROGT Tied to VC Regulator Mode, REGFB = 1.5V Regulator Mode, REGFB = 0V Mode = 0V From Either VBAT or VREG From Either VBAT or VREG BATT1 = 0, BATT2 = 0, Charger Mode BATT1 = 0, BATT2 = 0 BATT1 = 1, BATT2 = 0 BATT1 = 0, BATT2 = 1 (Note 3) BATT1 = 1, BATT2 = 1 (Note 3) BATT1 = Open, BATT2 = Don't Care Measured from OVP Input BATT2 = 0, BATT1 = 0 or 1 BATT2 = 1, BATT1 = 0 or 1

ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN 2.85 2.85 1.194 1.194
TYP
MAX 10 10
UNITS V V V V mA
1.225 1.225 0.75 2
1.256 1.256
4.3 15 2.85
2.45
2.7 100 10
4.059 4.158 8.118 8.316 1.207
4.1 4.2 8.2 8.4 1.225 200 400
4.141 4.242 8.282 8.484 1.243
2
U
mA A V mV A V V V V V mV mV
1980f
W
U
U
WW
W
LTC1980
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL VRCHG2 VLT0 VLT1 IBLDO gmldo VOLLDO VOHLDO IOUTLDO AVOL IBEA VOLEA VOHEA IOUT gmflt IBFLT VOS1 IBIS AVCA RPROG IPROG fS tr, tf tBREAK fTIMER ITIMER1 ITIMER2 RREG IREGPD IREGLK VVTHREG VIL1 VIH1 VIL2 VIH2 PARAMETER Recharge Threshold, Delta Voltage with Respect to Float Voltage, Measured at OVP Charger Shorted Cell Threshold Charger Shorted Cell Threshold Input Bias Current, Low Dropout Regulator Transconductance, Low Dropout Regulator Output Low Voltage, Low Dropout Regulator Output High Voltage, Low Dropout Regulator Low Dropout Regulator Output Current, Source/Sink Error Amplifier Open-Loop Voltage Gain Error Amplifier Input Bias Current Error Amplifier Output Low Voltage Error Amplifier Output High Voltage Error Amplifier Output Source Current Error Amplifier Output Sink Current Float Voltage Error Amplifier Transconductance Float Voltage Error Amplifier Input Current (Measured at OVP Input) Current Amplifier Offset Voltage Input Bias Current, ISENSE Input Current Amplifier Voltage Gain PROG Pin On Resistance PROG Pin Leakage Current Switching Frequency Driver Output Transition Times Driver Output Break Times Timer Frequency TIMER Pin Source Current TIMER Pin Sink Current REG On Resistance REG Pull-Down Current REG Leakage Current REG Logic Threshold Digital Input Low Voltage, Negative-Going, Wall Adapter (WA) Digital Input High Voltage, Positive-Going, Wall Adapter (WA) Digital Input Low Voltage, BATT1 Digital Input High Voltage, BATT1 VBIAS2 -100 VREG = 5V VREG = 5V 0.3 1.185 1.195 1.221 1.226 2 CL = 15pF VBAT = VREG = 10V C = 1000pF
ELECTRICAL CHARACTERISTICS
CONDITIONS BATT 1 = Open BATT2 = 0 BATT2 = 1 Measured at LDOFB Pin Measured from LDOFB to LDODRV
MIN
TYP 60
MAX
UNITS mV
2.55 5.2
2.7 5.4 1.0 350
2.8 5.65
V V A mhos
0.1 VREG - 0.1 20 From REGFB to VC -0.1 0 SS = Open 1.4 0.5 -1.2 Measured from OVP to SS, Charger Mode, BATT1 = Open -0.1 -6 -100 Measured from ISENSE to CAOUT Pin 2.3 2.44 400 100 260 300 10 100 4.5 -4 4 68 5 60 1.3 1.247 1.257 100 9 340 2.55 65 0.1 6 60 0.1 0.5 2
V V A dB A V V mA mA mhos A mV A V/V nA kHz ns ns kHz A A A nA V V V mV V
1980f
3
LTC1980
The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C.VBAT = 2.4V, VREG = 5V, VBAT unloaded.
SYMBOL VP2 VIL3 VIH3 II1 II2 II3 PARAMETER Digital Input Pull-Up Voltage, BATT1 Digital Input Low Voltage, BATT2 Digital Input High Voltage, BATT2 Digital Input Current, WA Digital Input Current, BATT1 Digital Input Current, BATT2 2 -5 -10 -1 5 10 1 CONDITIONS BATT1 Input Floating MIN TYP 1.6 0.3 MAX UNITS V V V A A A
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1980E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the -40C to 85C operating
temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: TA = 0C to 70C.
TYPICAL PERFOR A CE CHARACTERISTICS
Feedback Reference Voltage vs Temperature
1.2240
FEEDBACK REFERENCE VOLTAGE (V)
1.5 1.0
1.2235 1.2230 1.2225 1.2220 1.2215 1.2210 1.2205 -40
FREQUENCY VARIANCE (%)
0 -0.5 -1.0 -1.5 -40
VREG (%)
-15
10 35 TEMPERATURE (C)
3.3V Regulator Efficiency vs Load Current
90 85
EFFICIENCY (%)
EFFICIENCY (%)
80 75 70 65 60 VBAT = 3.6V TA = 25C FIGURE 5 10 100 LOAD CURRENT (mA) 1000
1980 G04
4
UW
60
1980 G01
Switching Frequency Variance vs Temperature
0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2
Regulator Load Regulation
VBAT = 4.2V VREG 3.3V TA = 25C FIGURE 5
0.5
85
-15
10 35 TEMPERATURE (C)
60
85
1980 G02
0
100
200 300 400 LOAD CURRENT (mA)
500
1980 G03
5V Regulator Efficiency vs Load Current
90 85 80 75 70 65 60 VBAT = 3.6V TA = 25C R8 = 309k FIGURE 5 10 100 LOAD CURRENT (mA) 1000
1980 G05
Regulator Load Step Response
VREG 50mV/DIV
IL 500mA/DIV VBAT = 3.6V 100s/DIV VREG 3.3V IL = 100mA TO 500mA TA = 25C FIGURE 5
1980 G06
1980f
LTC1980 TYPICAL PERFOR A CE CHARACTERISTICS
Typical BGTDR and RGTDR Waveforms Typical ISENSE Waveforms, Regulator
VREG 50mV/DIV
ISENSE 20mV/DIV PIN 21 FIGURE 5
BGTDR 1V/DIV
RGTDR 1V/DIV
VBAT = 3.6V VREG = 3.3V TA = 25C IL = 500mA
1s/DIV
Burst Mode Circuit Operation
VREG 50mV/DIV
BGTDR 2V/DIV
VBAT = 3.6V VREG = 3.3V IL = 10mA TA = 25C FIGURE 5
200s/DIV
Mode Pin Input Current vs VIN
1.5
MODE PIN INPUT CURRENT (A)
VBAT = 2.4V VREG = 5V 1.0 TA = 25C 0.5 0 -0.5 -1.0 -1.5
1980 G14
0
0.5
UW
Typical Operation with Burst Mode Operation Disabled
ISENSE 50mV/DIV
1980 G07
VBAT = 3.6V VREG = 3.3V IL = 500mA TA = 25C FIGURE 5
1s/DIV
1980 G08
VBAT = 3.6V VREG 3.3V IL = 500mA MODE = VBIAS1 TA = 25C FIGURE 5
1s/DIV
1980 G09
Regulator Output Transient Response--Wall Adapter Removal
Regulator Output Transient Response--Wall Adapter "Hot Plugged"
VREG 1V/DIV
VREG 1V/DIV
VLDO 0.1V/DIV
VLDO 0.5V/DIV
1980 G10
VBAT = 3.6V 500s/DIV VREG = 3.3V VLDO = 3.1V ILDO = 200mA VWALL ADAPTER = 6V TO 0V TA = 25C FIGURE 5
1980 G11
VBAT = 3.6V 500s/DIV VREG = 3.3V VLDO = 3.1V ILDO = 200mA VWALL ADAPTER = 0V TO 6V TA = 25C FIGURE 5
1980 G12
Typical CTIMER Waveform
TIMER 100mV/DIV PIN 17
CTIMER = 0.24F TA = 25C
1.0 1.5 2.0 MODE PIN VIN (V) 2.5 3.0
1980 G13
5ms/DIV
1980f
5
LTC1980
PI FU CTIO S
PROG (Pin 1): Charge Current Ratio Programming Pin. Programs the full charge current when the charger is in the constant current mode. A resistor placed between the PROG pin and the PROGT pin (Pin 2) determines the charge current. The PROG pin connects to an open drain MOSFET which turns on for full current and is off when trickle charging. PROGT (Pin 2): Trickle Charge Programming Pin. Programs the trickle charge current for a deeply discharged battery. Two resistors are used, one between the PROGT pin and CAOUT (Pin 22) and another from PROGT to ground. A capacitor between the PROGT pin and VC (Pin 4) provides compensation for the constant current feedback loop. REGFB (Pin 3): DC/DC Converter Feedback Pin. This pin is used to program the DC/DC converter output voltage when the LTC1980 is in the DC/DC (regulator) converter mode. An external resistor divider from VREG to REGFB to ground programs the output voltage. The virtual reference voltage (VREF) on this pin is 1.225V. A series RC from the REGFB pin to VC (Pin 4) provides pole-zero compensation for the regulator outer loop. VC (Pin 4): Control Signal of the Inner Loop of the Current Mode PWM. A common current mode loop is used by the battery charger and voltage regulator functions. Minimum duty factor (measured on BGTDR (Pin 14) in regulator mode and RGTDR (Pin 11) in charger mode) occurs at approximately 1V. Duty factor increases as VC increases. This part includes slope compensation, so there is some variation in VC for minimum and maximum duty factor as VREG or VBAT is varied. LDOFB (Pin 5): Low Dropout Regulator Feedback Pin. This pin is used to program the low dropout linear regulator output voltage. An external resistor divider from the output of the LDO regulator (drain of the external MOSFET) to LDOFB to ground programs the output voltage. The virtual reference voltage on this pin is 1.225V. LDODRV (Pin 6): Low Dropout Error Amplifier Output. This pin drives the gate of an external PMOS pass transistor. This pin is pulled up to VREG (shutting off the pass transistor) if MODE (Pin 16) is grounded or if undervoltage occurs. VREG (Pin 7): Connection Point to the DC/DC Converter Side of the Combo Charger/Converter Circuit. WA (Pin 8): Wall Adapter Comparator Input. An external resistor divider from the wall adapter output to WA to ground sets the threshold which determines if charging can occur. If the wall adapter is below this threshold, the LTC1980 assumes the wall adapter is not present and the charger shuts down. Wall adapter sense threshold is set higher than the DC/DC converter output voltage to insure correct operation. BATT1 (Pin 9): Logic Input Pin for Selecting Preprogrammed Li-Ion Charge Voltage. See Truth Table logic settings. BATT2 (Pin 10): Logic Input Pin for Selecting Preprogrammed Li-Ion Charge Voltage. The following combinations of BATT1 and BATT2 select the correct LiIon charge voltage. See Truth Table.
BATT2 0 0 1 1 Don't Care BATT1 0 1 0 1 Open FLOAT VOLTAGE 4.1V 4.2V 8.2V 8.4V Externally Set Via OVP
6
U
U
U
Logic 1 = VBIAS2 (Pin 19), Logic 0 = GND
RGTDR (Pin 11): DC/DC Converter (Regulator) Side Gate Drive Pin. This pin provides gate drive to the external MOSFET (REG-FET) that connects to VREG via the transformer. PGND (Pin 12): Power Ground. Refer to the Applications Information section for proper use of ground and power ground connections. VBIAS1 (Pin 13): Internally Generated Power Bus. Bypass this pin with a 1F or larger ceramic capacitor (or other low ESR capacitor) to PGND (Pin 12). Do not connect any load to this pin. BGTDR (Pin 14): DC/DC Converter (Battery) Side Gate Drive Pin. This pin provides gate drive to the external MOSFET (BAT-FET) that connects to VBAT via the transformer.
1980f
LTC1980
PI FU CTIO S
REG (Pin 15): Bidirectional Regulator Mode Control Pin. A pull-up resistor is required between this pin and VBIAS2. This pin is open when charging normally, has a weak pulldown (approximately 5A) when conditioning the battery and a strong pull-down when in regulator mode. Pulling this pin low forces the IC into regulator mode. MODE (Pin 16): Selects different operating modes in both charger and DC/DC converter configurations. Also enables and disables Burst Mode operation. See Mode Pin Operation table in Application section. TIMER (Pin 17): A timing capacitor on this pin determines the normal charge time for charge termination. C(F) = 0.25 * Time (Hours) VBAT (Pin 18): This pin connects to the positive terminal of the battery and the battery side of the power converter. VBIAS2 (Pin 19): Internally Generated Voltage. Bypass this pin with a 1F or larger ceramic capacitor (or other low ESR capacitor). Do not connect any load to this pin. GND (Pin 20): Signal Ground. This pin should Kelvinconnect to the current sense resistor (RSENSE). ISENSE (Pin 21): Current Sense Input Pin. Connects internally to a current amplifier and zero current comparator. This pin should Kelvin-connect to the current sense resistor (RSENSE) . CAOUT (Pin 22): Current Amplifier Output. A program resistor connects between this pin and PROGT (Pin 2) to set the charge current (in constant-current mode). OVP (Pin 23): Overvoltage Protection. This pin connects to the tap on an optional external voltage divider connected across the battery. This allows nonstandard float voltages to be used for the battery charger. Overvoltage, restart and undervoltage thresholds will also be affected by the external voltage division ratio. To use this pin, BATT1 (Pin 9) must float. SS (Pin 24): Soft-Start. A capacitor between this pin and ground sets the battery charge ramp rate. Battery charge current is very low the moment after the converter switches from DC/DC converter (regulator) mode to battery charger mode then ramps up to final battery charge current from there. This insures that the wall adapter is not loaded down with a large inrush current that could prevent correct battery charger operation. The same capacitor, which sets the soft-start ramp rate, also sets the compensation for the battery float voltage control loop.
U
U
U
1980f
7
LTC1980
BLOCK DIAGRA
VBIAS1 13
VBAT 18
VMAX VREF
VBIAS2 19 L H
-
DIS MODE VREF DUMP XFMR
VREF
MODE 16
H = BURST MODE OPERATION OFF OPEN = BURST MODE OPERATION ON L = DISABLE VC 4 AC 2 3
OSC
RAMP VREG VBAT
+
PWM COMP
PROGT REGFB
-
VREF
+
EA
VREF
- +
BURST WAKE
AC SLEEP
-
BATT1 9 VREF OVP 23
+
CONDITION BATTERY
-
BATT2 10
VREF
+
RECHARGE START
-
TIMEOUT TIMER SHORT CYCLE
VREF
+ -
5A 1 PROG
WA 8 REG 15 VREF
+
GM
-
GND 20 REG 24 SS
1980 BD
8
+ -
+ -
VREG
7
VDD REG
W
LDOFB 5 REF_UVL LDODRV 6 CAOUT 22 21 ISENSE GM VREF VREF REFERENCE
+ - + +
I=O COMP
-
-
+
UVL VREF SR_EN VM S Q R 14 BGTDR 12 PGND 11 RGTDR
17 TIMER
1980f
LTC1980
OPERATIO
The LTC1980 is an IC designed to provide a regulated voltage to a system load from an unregulated or regulated wall adapter, or from a battery and also charge a battery, thereby providing an uninterruptable power source for the system. When the wall adapter is present it provides power to the system load and, if needed, a portion of the power can be used to simultaneously charge the battery. If the wall adapter is removed, the LTC1980 uses the battery as a power source to continue providing a regulated output voltage to power the system. Combining these two functions into a single IC reduces circuit area compared to presently available solutions
CHARGE TERMINATION
BATTERY CHARGER POWER ROUTING PWM REGULATOR LOW DROPOUT REGULATOR
Li-Ion BATTERY
BAT-FET
ISENSE
LTC1980
1980 F02a
(a) Battery Charger Mode
U
(Figure 1). The unique bidirectional power converter topology (Figure 2) accounts for much of the area savings. A transformer based design allows the wall adapter voltage to be less than or greater than the battery voltage. The LTC1980 includes a 300kHz DC/DC PWM converter that operates in two modes. The first mode is when the wall adapter is present and the LTC1980 is used to charge the battery using a constant-current/constant-voltage charge scheme. The second mode is when the wall adapter is removed and the battery powers the LTC1980 and the DC/DC converter generates a regulated output voltage.
Existing Methods Using the LTC1980
FROM WALL ADAPTER LTC1980-BASED POWER DESIGN TO SYSTEM LOAD DC/DC CONVERTERS
1980 F01
FROM WALL ADAPTER TO SYSTEM LOAD DC/DC CONVERTERS
Figure 1. Portable Power Systems
T1
*
REG-FET
WALL ADAPTER
Li-Ion BATTERY
T1
*
BAT-FET
*
*
REG-FET SYSTEM LOAD DC/DC CONVERTERS
RS
SYSTEM LOAD DC/DC CONVERTERS ISENSE
RS
LTC1980
1980 F02a
(b) DC/DC Converter Mode (Wall Adapter Removed)
Figure 2. LTC1980 Bidirectional Power Conversion
1980f
9
LTC1980
OPERATIO
Lithium-Ion Battery Charger Operation With the wall adapter power applied, the LTC1980 operates as a constant-current/constant-voltage PWM battery charger, with a portion of the adapter current used for charging and the rest flowing to the system load through an optional low dropout regulator. A charge cycle begins when the voltage at VREG exceeds the undervoltage lockout threshold level and the IC is enabled via the MODE pin. If the battery has been deeply discharged and the battery voltage is less than 2.7V, the charger will begin with the programmed trickle charge current. When the battery exceeds 2.7V, the charger begins the constant-current portion of the charge cycle with the charge current equal to the programmed level. As the battery accepts charge, the voltage increases. When the battery voltage reaches the recharge threshold, the programmable timer begins. Constant-current charging continues until the battery approaches the programmed charge voltage of 4.1V or 4.2V/cell at which time the charge current will begin to drop, signaling the beginning of the constant-voltage portion of the charge cycle. The charger
U1 VOLTAGE SELECTION VBAT T1 VREG SN2 SNUBBER NETWORK
+
DIRECTION SENSE VREF CURRENT AMPLIFIER U7 OSC VREF R13
TYPICAL WAVEFORM
+
R4
R5
+
U6
+
U8
U5 ZC
-
-
SW1 R7 R9 SW3 R8 SW2 C4 U10 EA R6 C3
-
PWM
U12 U11 REFERENCE
Figure 3. Simplified Diagram--Power Converter
1980f
10
+
C5
-
-
+
+
-
-
+
U
will maintain the programmed preset float voltage across the battery until the timer terminates the charge cycle. During trickle charging, if the battery voltage remains below 2.7V for 1/4 of the total programmed charge time, the battery may be defective and the charge cycle ends. Also, if a battery open circuit is detected, the charge cycle ends immediately. The charger can be shut down by pulling the REG pin low, although the timer will continue until it times out. Power Converter Operation from Battery When the AC adapter is removed, the LTC1980 operates as a DC/DC PWM converter using the battery for input power to provide a regulated output voltage for the system load. The LTC1980 is a current mode switcher. This means that the switch duty cycle is directly controlled by switch current rather than by output voltage or current. Battery charger operation will be described for the simplified diagram (Figure 3). At the start of the oscillator cycle, latch U9 is set causing M2 to turn on. When switch current reaches a predetermined level M2 turns off and M1 turns on. This level is set by the control voltage at the output of error amplifier U10.
B1 C1 SN1 SNUBBER NETWORK C2 R1 U2 WALL ADAPTER
- +
R12 C6 TO SYSTEM LOAD
U4 DRIVERS
BDRIVE
M1 M2
RDRIVE
R2
S R
U9
Q
R10
R11 VREF
1980 F03
LTC1980
OPERATIO
Transformer current is sensed across RS, gained up via U6 and sampled through switch SW1. The current in R7 is a scaled-down replica of the battery charging current pulses from the transformer. During battery charging, switch SW2 is in the down position connecting R7, R8, R9 and C4 to the inverting input of amplifier U10 forming an integrator which closes the outer loop of the converter and establishes constant current charging. U12 is a gm amplifier that clamps U10 as the battery float voltage is reached. R10 and R11 set the float voltage and C5 compensates this loop and provides a soft-start function.
APPLICATIO S I FOR ATIO
Setting Battery Charge Current
Referring to the simplified schematic in Figure 4, the average current through R7 must equal the current through RTRKL with switch SW3 open. This leads to the equation for setting the trickle charge current:
RTRKL =
VREF * R7 ITRICKLE * RS * A V
Normal charge current is set via the parallel combination of RTRKL and RCHRG which leads to the following equation for RCHRG
RCHRG = VREF * R7
(INORMAL - ITRICKLE) * RS * A V
ISENSE 21
I
+
U6 AV = 2.44
SW1 22 CAOUT
RS 20 GND
-
Figure 4. Battery Charger Current Control Loop
1980f
U
W
UU
U
DC/DC Converter Operation When the LTC1980 is operating as a DC/DC converter, M1 turns on at the start of the oscillator cycle. When transformer current reaches a predetermined level set by U10's output voltage, M1 turns off and M2 turns on. SW2 is in the up position forming an integrator with zero, which compares the output voltage (via R1 and R2 to reference U11 establishing the output voltage. where AV = 2.44 and VREF = 1.225V. The suggested value for R7 is 10k. Setting the Float Voltage Pin selectable 4.1V, 4.2V, 8.2V, and 8.4V Li-Ion float voltages are available. Other float voltages may be set via external resistors. The following combinations of logic inputs BATT1 and BATT2 determine the float voltage.
BATT2 0 0 1 1 Don't Care BATT1 0 1 0 1 Open FLOAT VOLTAGE 4.1V 4.2V 8.2V 8.4V Externally Set via OVP where logic 0 = GND and logic 1 = VBIAS2 (Pin 19)
VREF 1.225V R7 10k 2 RTRKL RCHRG PROG 1 SW3 20
1980 F04
C4
+
U10 4
VC
PROGT
-
11
LTC1980
APPLICATIO S I FOR ATIO
An external resistor divider (Figure 3) can be used to program other float voltages. Resistor values are found using the following equation: R10 = R11 * (VFLOAT - VREF)/VREF where VREF = 1.225V. The suggested value for R11 is 100k. Use 1% or better resistors. Setting DC/DC Converter Output Voltage From Figure 5, select the following resistors based on output voltage VREG: R8 = R14 * (VREG - VREF)/VREF where VREF = 1.225V, suggested value for R14 is 100k, 1%. LDO Operation The LTC1980 provides an uninterrupted power supply for the system load. When a wall adapter is connected and operating, power is taken from the wall adapter to charge the batteries and supply power to the system. In applications where an unregulated wall adapter is used but a regulated voltage is needed by the system, an external Pchannel MOSFET pass transistor may be added to the LTC1980 to create a low dropout linear regulator. From Figure 5, select the following resistors based on the output voltage VLDO: R5 = R6 * (VLDO - VREF)/VREF where VREF = 1.225V, suggested value for R6 is 100k, 1%. This is the voltage that will be seen when operating from a higher voltage wall adapter. When operating from the batteries (as a regulator), the load will see either this voltage or the voltage set by the PWM regulator, whichever is less, minus any drops in the pass transistor. Placing a large-valued capacitor from the drain of this MOSFET to ground creates output compensation. Wall Adapter Comparator Threshold From Figure 5, select the following resistors based on the wall adapter comparator threshold VWATH: R15 = R7(VWATH - VIH1)/VIH1
12
U
where VIH1= 1.226V, suggested value for R7 is 100k. Use 1% resistors. MODE Pin Operation The following truth table describes MODE pin operation. Burst Mode operation is disabled during battery charging to reduce broadband noise inherent in Burst Mode operation. (Refer to the LT1307 data sheet for details).
POWER FLOW Battery Charger Battery Charger Battery Charger DC/DC converter DC/DC converter DC/DC converter MODE PIN 0 Open 1 0 Open 1 OPERATING MODE Disabled Enabled Continuous Enabled Continuous Disabled Enabled Burst Mode Operation Enabled Continuous Logic 1 = VBIAS1 (Pin 13) Logic 0 = GND
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The MODE pin should be decoupled with 200pF to ground when left open. Snubber Design The values given in the applications schematics have been found to work quite well for most applications. Care should be taken in selecting other values for your application since efficiency may be impacted by a poor choice. For a detailed look at snubber design, Application Note 19 is very helpful. Frequency Compensation Load step testing can be used to empirically determine compensation. Application Note 25 provides information on the technique. To adjust the compensation for the DC/ DC converter, adjust C12 and R13 (in Figure 5). Battery charger current loop compensation is set by C11 and battery charger float voltage compensation is set by C8. Component Selection Basics The application circuits work well for most 1- and 2-cell Li-Ion, 0.5A to 1A output current designs. The next section highlights the component selection process. More information is available in Application Note 19.
1980f
LTC1980
APPLICATIO S I FOR ATIO
Current Sense Resistor Voltage drop in the current sense resistor should be limited to approximately 100mV with respect to ground at max load currents in all modes. This value strikes a reasonable balance between providing an adequate low current signal, while keeping the losses from this resistor low. For applications where the inputs and output voltages may be low, a somewhat lower drop can be used (in order to reduce conduction losses slightly). The LTC1980 has several features, such as leading-edge blanking, which make application of this part easier to use. However for best charge current accuracy, the current sense resistor should be Kelvin sensed. MOSFETs The LTC1980 uses low side MOSFET switches. There are two very important advantages. First, N-channel MOSFETs are used--this generally means that efficiency will be higher than a comparable on-resistance P-channel device (because less gate charge is required). Second, low VT (`logic-level') MOSFETs with relatively low absolute maximum VGS ratings can be used, even in higher voltage applications. Refer to Application Note 19 for information on determining MOSFET voltage and current ratings. Transformer Turns ratio affects the duty factor of the power converter which impacts current and voltage stress on the power MOSFETs, input and output capacitor RMS currents and transformer utilization (size vs power). Using a 50% duty factor under nominal operating conditions usually gives reasonable results. For a 50% duty factor, the turns ratio is: N = VREG/VBAT N should be calculated for the design operating as a DC/DC converter and as a battery charger. The final turns ratio should be chosen so that it is approximately equal to the average of the two calculated values for N. In addition choose a turns ratio which can be made from the ratio of small integers. This allows bifilar windings to be used in
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the transformer which can reduce the leakage inductance, reduce the need for aggressive snubber design and for this reason improve efficiency.
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Avoid transformer saturation under all operating conditions and combinations (usually the biggest problems occur at high output currents and extreme duty cycles. Also check these conditions for battery charging and regulation modes.
Finally, in low voltage applications, select a transformer with low winding resistance. This will improve efficiency at heavier loads. Capacitors Check the RMS current rating on your capacitors on both sides of your circuit. Low ESR and ESL is recommended for lowest ripple. OS-CON capacitors (from Sanyo) work very well in this application. Diodes In low voltage applications, Schottky diodes should be placed in parallel with the drain and source of the MOSFETs in the PWM supply. This prevents body diode turn on and improves efficiency by eliminating loss from reverse recovery in these diodes. It also reduces conduction loss during the RGTDR/BGTDR break interval. The LTC1980 can operate to voltages as low as 2.8V. Suitable Schottky diodes include the ZHCS1000 (VF = 420mV at IF = 1A) and SL22/23 (VF = 440mV at IF = 2A) for most 500mA to 1A output current applications.
Vendor List
VENDOR BH Electronics Coiltronics/Cooper Electronic Fairchild Semiconductor COMPONENTS Transformers Transformers MOSFETs Schottky Rectifiers TELEPHONE 952-894-9590 561-752-5000 800-341-0392 631-847-3000 408-749-9714 847-956-0666 408-988-8000
Vishay (General Semiconductor) MOSFETs Schottky Rectifiers Sanyo Sumida Electric USA Vishay (Siliconix) OS-CON Capacitors Transformers MOSFETs
1980f
13
LTC1980
TYPICAL APPLICATIO
VBAT BH511-1014
VREG 5.1 1nF
+
4.1V Li-Ion BATTERY
+
C1 5.1 68F 1nF
1/2 FDC6401N
50m RSENSE
14 12 BGTDR PGND 18 V 23 BAT OVP 3 REGFB 22 CAOUT PROG R9 10k 1 R10 110k PROGT 2
20 GND
ISENSE
VC C11 1nF 4
R11 1M
R13 806k
1980 F05
Figure 5. 4.1V/1A Li-Ion Battery Charger and 3.3V DC/DC Converter
14
U
3.3V D1* IN5819 DCOUT WALL ADAPTER OPTIONAL PASS TRANSISTOR FOR LDO FDC636P ACIN
+
C4 68F
VLDO 3.1V C6 470F SYSTEM LOAD DC/DC CONVERTERS VOUT
1/2 FDC6401N
R5 154k
21
11 RGTDR
7 VREG
6 5 LDODRV LDQFB
8 WA 15 REG 16 MODE 9 BATT1 10 BATT2
R6 100k
R15 300k
LTC1980
200pF
TIMER 17 C7 0.27F
SS 24 C8 0.1F
VBIAS1 13 C9 1F
VBIAS2 19 C10 1F R12 100k
R8 169k
R7 100k
R14 100k *OPTIONAL DIODE FOR SHORTED WALL ADAPTER TERMINAL PROTECTION
C12 82pF
1980f
LTC1980
PACKAGE DESCRIPTIO
.254 MIN
.0165 .0015 RECOMMENDED SOLDER PAD LAYOUT
.015 .004 x 45 (0.38 0.10) .007 - .0098 (0.178 - 0.249) .016 - .050 (0.406 - 1.270)
NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *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 - 8 TYP
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.
U
GN Package 24-Lead Plastic SSOP (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1641)
.337 - .344* (8.560 - 8.738) 24 23 22 21 20 19 18 17 16 15 1413
.045 .005 .033 (0.838) REF
.229 - .244 (5.817 - 6.198)
.150 - .165
.150 - .157** (3.810 - 3.988)
1
.0250 TYP
23
4
56
7
8
9 10 11 12
.053 - .068 (1.351 - 1.727)
.004 - .0098 (0.102 - 0.249)
.008 - .012 (0.203 - 0.305)
.0250 (0.635) BSC
GN24 (SSOP) 0502
1980f
15
LTC1980
RELATED PARTS
PART NUMBER LT1571 LTC1729 LTC1731 LTC1732 LTC1733 LTC1734 LTC1734L LTC1760 LTC1960 LTC4002 LTC4007 LTC4050 LTC4052 LTC4411 LTC4412 DESCRIPTION 200kHz/500kHz Switching Battery Charger Lithium-Ion Linear Battery Charger Controller Lithium-Ion Linear Battery Charger Controller Monolithic Lithium-Ion Linear Battery Charger Lithium-Ion Linear Battery Charger in ThinSOTTM Lithium-Ion Linear Battery Charger Controller Dual Battery Charger/Selector with SPI Wide VIN Range Li-Ion Battery Charger 4A Standalone Multiple Cell Li-Ion Battery Charger Lithium-Ion Linear Battery Charger Controller Lithium-Ion Linear Battery Pulse Charger 2.6A Low Loss Ideal Diode in ThinSOT Ideal Diode or PowerPathTM COMMENTS Isolated Flyback Mode Up to 1.5A Charge Current; Preset and Adjustable Battery Voltages Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication Standalone Charger with Programmable Timer, Up to 1.5A Charge Current Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed 50mA to 180mA, No Blocking Diode, No Sense Resistor Needed Complete Dual-Battery Charger/Selector System, Easy Interface with Microcontroller, Extends Run Time by 10%, reduces Charge Time by 50% 1-, 2-Cell Batteries, Switch Mode Charger, Up to A Charge Current, 4.7V VIN 22V 6V VIN 28V, 3- or 4-Cell, Up to 96% Efficiency Simple Charger uses External FET, Thermistor Input for Battery Temperature Sensing Fully Integrated, Standalone Pulse Charger, Minimal Heat Dissipation, Overcurrent Protection Very Low Loss Replacement for Power Supply ORing Diodes, 2.6V to 5.5V Supply Voltage, ThinSOT Package Very Low Loss Replacement for Power Supply ORing Diodes, Enternal Pass Element, 3V to 28V Supply Voltage,ThinSOT Package LT1170/LT1171/LT1172 5A/3A/1.25A Flyback Regulators
Lithium-Ion Battery Charger Termination Controllers Time or Charge Current Termination, Preconditioning 8-Lead MSOP
Dual Battery Charger/Selector with SMBus Interface Complete SMBus Charger/Selector for Two Smart Batteries
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
1980f
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
LT/TP 0604 1K * PRINTED IN USA
FAX: (408) 434-0507 www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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