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19-3498; Rev 0; 11/04
KIT ATION EVALU ABLE AVAIL
Simplified Multichemistry SMBus Battery Charger
General Description Features
Over 2A Charge Current Intel SMBus 2-Wire Serial Interface 0.6% Charge Voltage Accuracy 11-Bit Charge Voltage Resolution 6-Bit Charge Current Resolution Adjustable Switching Frequency +8V to +28V Input Voltage Range Cycle-By-Cycle Current Limit Charges Any Battery Chemistry (Li+, NiCd, NiMH, Lead Acid, etc.) Small 24-Pin TQFN
MAX8713
The MAX8713 multichemistry battery charger simplifies construction of smart chargers with a minimum number of external components. It uses the Intel System Management Bus (SMBusTM) to control the charge voltage and charge current. High efficiency is achieved through the use of a constant off-time step-down topology with synchronous rectification. The MAX8713 charges one to four lithium-ion (Li+) cells in series and delivers over 2A charge current--scalable with the sense resistor. The MAX8713 drives n-channel MOSFETs for improved efficiency and reduced cost. A low-offset charge-current-sense amplifier provides highaccuracy charge current with small sense resistors. The MAX8713 is available in a space-saving 24-pin 4mm x 4mm thin QFN package and operates over the extended (-40C to +85C) temperature range. An evaluation kit is available to reduce design time.
Applications
Handset Car Kits Digital Cameras PDAs and Tablet Computers Notebook Computers Portable Equipment with Rechargeable Batteries
PART MAX8713ETG
Ordering Information
TEMP RANGE -40C to +85C PIN-PACKAGE 24 Thin QFN 4mm x 4mm
Typical Operating Circuit
EXTERNAL LOAD OPTIONAL
SMBus is a trademark of Intel Corp.
Pin Configuration
DCSNS DCIN LDO BST DHI LX
DCIN DCSNS
DHI LX
N
REF 19 DAC 18 17 DLOV DLO PGND CSIP IC3 CSIN FREQ HOST SCL SDA VDD SCL SDA VDD
DLO
N
24 REF IC1 CCI CCV DAC VDD 1 2 3 4 5 6
23
22
21
20
MAX8713 BST
CSIP CSIN BATT
BATTERY
MAX8713
16 15 14
DLOV LDO GND PGND CCI CCV
*EXPOSED PADDLE 7 SDA 8 SCL 9 IC2 10 FREQ 11 GND 12 BATT
13
THIN QFN (4mm x 4mm)
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Simplified Multichemistry SMBus Battery Charger MAX8713
ABSOLUTE MAXIMUM RATINGS
VDCSNS, VDCIN to GND ..........................................-0.3V to +30V VBST to GND ..........................................................-0.3V to +36V VBST to LX ................................................................-0.3V to +6V VDHI to LX..................................................-0.3V to (VBST + 0.3V) VLX to GND................................................................-6V to +30V VDHI to GND ..............................................................-6V to +36V VBATT, VCSIN to GND .............................................-0.3V to +20V VCSIP to VCSIN .......................................................-0.3V to +0.3V PGND to GND .......................................................-0.3V to +0.3V VCCI, VCCV, VDAC, VREF to GND ..............-0.3V to (VLDO + 0.3V) VDLOV, VLDO, VDD, VSCL, VSDA, VFREQ to GND ......-0.3V to +6V VDLO to PGND ........................................-0.3V to (VDLOV + 0.3V) LDO Short-Circuit Current...................................................25mA Continuous Power Dissipation (TA = +70C) 24-Pin Thin QFN 4mm x 4mm (derate 20.8mW/C above +70C).............................................................1667mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER CHARGE VOLTAGE REGULATION ChargingVoltage() = 0x20D0 Battery Regulation Voltage Accuracy ChargingVoltage() = 0x1060 ChargingVoltage() = 0x41A0 and 0x3130 ChargingVoltage() = 0x41A0, VDCIN = 19V Battery Full Charge Voltage ChargingVoltage() = 0x3130, VDCIN = 19V ChargingVoltage() = 0x20D0, VDCIN = 12V ChargingVoltage() = 0x1060, VDCIN = 12V CHARGE CURRENT REGULATION CSIP to CSIN Full-Scale Current-Sense Voltage Compliance Current Accuracy VBATT = 8.4V, VDCIN = 12V ChargingCurrent() = 0x07e0 ChargingCurrent() = 0x03e0 ChargingCurrent() = 0x07e0 Battery Charge Current-Sense Voltage ChargingCurrent() = 0x03e0 ChargingCurrent() = 0x0180 ChargingCurrent() = 0x0020 BATT/CSIP/CSIN Input Voltage Range CSIP/CSIN Input Current SUPPLY AND LINEAR REGULATOR DCIN Input Voltage Range DCSNS Input Voltage Range 7.5 7.5 28.0 28.0 V V VDCIN = 0 or charger not switching VCSIP = VCSIN = 19V 0 0.1 78.22 -3 -5 78.22 37.68 13.82 80.64 39.68 15.36 1.28 19 1 700 V A A 80.64 88.05 +3 +5 83.05 41.68 16.88 mV mV % -0.6 -1.0 -0.8 16.668 12.491 8.439 4.150 16.8 8.4 4.192 +0.6 +1.0 +0.8 16.934 8.442 4.234 V 12.592 12.693 % CONDITIONS MIN TYP MAX UNITS
2
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Simplified Multichemistry SMBus Battery Charger
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DCIN Undervoltage-Lockout Trip Point DCIN Quiescent Current DCSNS Quiescent Current BATT Input Current LDO Output Voltage LDO Load Regulation LDO Undervoltage-Lockout Trip Point VDD Range VDD UVLO Rising VDD UVLO Hysteresis VDD Quiescent Current REFERENCE REF Output Voltage REF Undervoltage-Lockout Trip Point TRIP POINTS BATT POWER_FAIL Threshold BATT POWER_FAIL Threshold Hysteresis SWITCHING REGULATOR VBATT = 8.4V Off-Time VBST - VLX = 4.5V VBATT = 11V DLOV Supply Current BST Supply Current BST Input Quiescent Current LX Input Bias Current Maximum Discontinuous-Mode Peak Current DHI On-Resistance High DHI On-Resistance Low DLO On-Resistance High DLO On-Resistance Low ERROR AMPLIFIERS GMV Amplifier Transconductance ChargingVoltage() = 0x20d0, VBATT = 8.400V 0.0625 0.125 0.2500 mA/V VBST =12.9V, VBATT = 8.4V, VDCSNS = 12, DHI = VLX; IDHI = -10mA VBST =12.9V, VBATT = 8.4V, VCSNS = 12, DHI = VBST; IDHI = +100mA VDLOV = 4.5V, IDLO = -10mA VDLOV = 4.5V, IDLO = +100mA Charger not switching DHI high VDCIN = 0V, VBST = 23.5V, VBATT = VLX = 19V VDCIN = 28V, VBATT = VLX = 19V RFREQ = 100k RFREQ = 400k RFREQ = 100k RFREQ = 400k 675 2700 370 1476 750 3000 410 1640 5 6 0.3 150 0.125 7 2 7 2 14 4 14 4 825 3300 450 1804 10 15 1 500 A A A A A ns VDCSNS falling 50 50 100 200 150 400 mV mV 0 < IREF < 500A REF falling 4.067 4.096 3.1 4.125 3.9 V V VDCIN < 6V, VDD = 5.5V, VSCL = VSDA = 5.5V DCIN falling DCIN rising 7.5V < VDCIN < 28V 7.5V < VDCSNS < 28V VBATT = 19V, VDCIN = 0 or charger not switching VBATT = 2V to 19V, VDCIN > VBATT + 0.3V 7.5V < VDCIN < 28V, no load 0 < ILDO < 5mA VDCIN = 7.5V 3.20 2.7 2.5 100 27 5.25 CONDITIONS MIN 6.5 TYP 7 7 2.7 200 0.1 200 5.4 34 4 7.5 6 300 1 500 5.55 100 5.15 5.5 2.7 MAX UNITS V mA A A V mV V V V mV A
MAX8713
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Simplified Multichemistry SMBus Battery Charger MAX8713
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER GMI Amplifier Transconductance CCI/CCV Clamp Voltage SDA/SCL Input Low Voltage SDA/SCL Input High Voltage SDA/SCL Input Bias Current SDA, Output Sink Current CONDITIONS ChargingCurrent() = 0x03e0, VCSIP - VCSIN = 39.68mV 0.25V < VCCV/I < 2.0V VDD = 2.7V to 5.5V VDD = 2.7V to 5.5V VDD = 2.7V to 5.5V V(SDA) = 0.4V 2.1 -1 6 +1 MIN 0.5 150 TYP 1 300 MAX 2.0 600 0.8 UNITS mA/V mV V V A mA
SMBus INTERFACE LEVEL SPECIFICATIONS
TIMING CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER SMBus Frequency Bus Free Time Start Condition Hold Time from SCL Start Condition Setup Time from SCL Stop Condition Setup Time from SCL SDA Hold Time from SCL SDA Setup Time from SCL SCL Low Timeout SCL Low Period SCL High Period Cumulative Clock Low Extend Time SYMBOL fSMB tBUF tHD:STA tSU:STA tSU:STO tHD:DAT tSU:DAT tTIMEOUT tLOW tHIGH tLOW:SEXT (Note 2) (Note 1) CONDITIONS MIN 10 4.7 4 4.7 4 300 250 25 4.7 4 25 35 TYP MAX 100 UNITS kHz s s s s ns ns ms s s ms SMBus TIMING SPECIFICATION (VDD = 2.7V TO 5.5V) (Figures 6 and 7)
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Simplified Multichemistry SMBus Battery Charger
ELECTRICAL CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER CHARGE VOLTAGE REGULATION ChargingVoltage() = 0x20D0 Battery Regulation Voltage Accuracy ChargingVoltage() = 0x1060 ChargingVoltage() = 0x41A0 and 0x3130 ChargingVoltage() = 0x41A0, VDCIN = 19V Battery Full Charge Voltage ChargingVoltage() = 0x3130, VDCIN = 19V ChargingVoltage() = 0x20D0, VDCIN = 12V ChargingVoltage() = 0x1060, VDCIN = 12V CHARGE CURRENT REGULATION CSIP to CSIN Full-Scale Current-Sense Voltage Compliance Current Accuracy VBATT = 8.4V, VDCIN = 12V ChargingCurrent() = 0x07e0 ChargingCurrent() = 0x03e0 ChargingCurrent() = 0x07e0 Battery Charge Current-Sense Voltage BATT/CSIP/CSIN Input Voltage Range CSIP/CSIN Input Current SUPPLY AND LINEAR REGULATOR DCIN Input Voltage Range DCSNS Input Voltage Range DCIN Undervoltage-Lockout Trip Point DCIN Quiescent Current DCSNS Quiescent Current BATT Input Current LDO Output Voltage LDO Load Regulation LDO Undervoltage-Lockout Trip Point VDD Range VDD UVLO Rising VDD Quiescent Current REFERENCE REF Output Voltage REF Undervoltage-Lockout Trip Point 0 < IREF < 500A REF falling 4.053 4.133 3.9 V V VDCIN < 6V, VDD = 5.5V, VSCL = VSDA = 5.5V DCIN falling DCIN rising 7.5V < VDCIN < 28V 7.5V < VDCSNS < 28V VBATT = 19V, VDCIN = 0 or charger not switching VBATT = 2V to 19V, VDCIN > VBATT + 0.3V 7.5V < VDCIN < 28V, no load 0 < ILDO < 5mA VDCIN = 7.5V 3.20 2.7 5.25 7.5 7.5 6.5 7.5 6 300 1 500 5.55 100 5.15 5.5 2.7 27 28.0 28.0 V V V mA A A V mV V V V A VDCIN = 0 or charger not switching VCSIP = VCSIN = 19V ChargingCurrent() = 0x03e0 ChargingCurrent() = 0x0180 78.22 -3 -5 78.22 37.68 13.056 0 83.05 +3 +5 83.05 41.68 17.664 19 1 700 V A A mV mV % -1.0 -1.5 -1.2 16.598 12.441 8.312 4.124 +1.0 +1.5 +1.2 17.002 12.743 8.484 4.253 V % CONDITIONS MIN TYP MAX UNITS
MAX8713
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Simplified Multichemistry SMBus Battery Charger MAX8713
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER TRIP POINTS BATT POWER_FAIL Threshold BATT POWER_FAIL Threshold Hysteresis SWITCHING REGULATOR VBATT = 8.4V Off-Time VBST - VLX = 4.5V VBATT = 11V DLOV Supply Current BST Supply Current BST Input Quiescent Current LX Input Bias Current DHI On-Resistance High DHI On-Resistance Low DLO On-Resistance High DLO On-Resistance Low ERROR AMPLIFIERS GMV Amplifier Transconductance GMI Amplifier Transconductance CCI/CCV Clamp Voltage SDA/SCL Input Low Voltage SDA/SCL Input High Voltage SDA/SCL Input Bias Current SDA, Output Sink Current ChargingVoltage() = 0x20d0, VBATT = 8.384V ChargingCurrent() = 0x03e0, VCSIP - VCSIN = 39.68mV 0.25V < VCCV/I < 2.0V VDD = 2.7V to 5.5V VDD = 2.7V to 5.5V VDD = 2.7V to 5.5V V(SDA) = 0.4V 2.2 -1 6 +1 0.0625 0.5 130 0.2500 2.0 600 0.8 mA/V mA/V mV V V A mA Charger not switching DHI high VDCIN = 0V, VBST = 23.5V, VBATT = VLX = 19V VDCIN = 28V, VBATT = VLX = 19V VBST =12.9V, VBATT = 8.4V, VDCSNS = 12, DHI= VLX; IDHI = -10mA VBST =12.9V, VBATT = 8.4V, VCSNS = 12, DHI = VBST; IDHI = +100mA VDLOV = 4.5V, IDLO = -10mA VDLOV = 4.5V, IDLO = +100mA RFREQ = 100k RFREQ = 400k RFREQ = 100k RFREQ = 400k 637 2550 350 1394 862 3450 470 1866 10 15 1 500 14 4 14 4 A A A A ns VDCSNS falling 50 50 150 400 mV mV CONDITIONS MIN TYP MAX UNITS
SMBus INTERFACE LEVEL SPECIFICATIONS
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Simplified Multichemistry SMBus Battery Charger
TIMING CHARACTERISTICS
(VDCIN = VDCSNS = 12V, VBATT = VCSIP = VCSIN = VBST = VLX = 8.4V, GND = PGND = 0, LDO = DLOV, CREF = CLDO = CDLOV = 1F, CDAC = 0.1F , VDD = 3.3V. Pins CCI and CCV are compensated per Figure 1. TA = -40C to +85C, unless otherwise noted.) (Note 3)
PARAMETER SMBus Frequency Bus Free Time Start Condition Hold Time from SCL Start Condition Setup Time from SCL Stop Condition Setup Time from SCL SDA Hold Time from SCL SDA Setup Time from SCL SCL Low Timeout SCL Low Period SCL High Period Cumulative Clock Low Extend Time SYMBOL fSMB tBUF tHD:STA tSU:STA tSU:STO tHD:DAT tSU:DAT tTIMEOUT tLOW tHIGH tLOW:SEXT (Note 2) (Note 1) CONDITIONS MIN 10 4.7 4 4.7 4 300 250 25 4.7 4 25 35 TYP MAX 100 UNITS kHz s s s s ns ns ms s s ms SMBus TIMING SPECIFICATION (VDD = 2.7V TO 5.5V) (Figures 6 and 7)
MAX8713
Note 1: Devices participating in a transfer timeout when any clock low exceeds the tTIMEOUT:MIN value of 25ms. Devices that have detected a timeout condition must reset the communication no later than tTIMEOUT:MAX of 35ms. The maximum value specified must be adhered to by both a master and a slave as it incorporates the cumulative stretch limit for both a master (10ms) and a slave (25ms). Note 2: tLOW:SEXT is the cumulative time a slave device is allowed to extend the clock cycles in one message from the initial start to the stop. If a slave device exceeds this time, it is expected to release both its clock and data lines and reset itself. Note 3: Specifications to -40C are guaranteed by design and not production tested.
__________________________________________Typical Operating Characteristics
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25C, unless otherwise noted.)
LDO LOAD REGULATION
MAX8713 toc01
LDO LINE REGULATION
MAX8713 toc02
REFERENCE LOAD REGULATION
MAX8713 toc03
5.44 5.42 5.40 VLDO (V)
5.360 5.355 5.350 3.345 VLDO (V) CHARGER SWITCHING
4.0980 4.0975 4.0970 VREF (V) 4.0965 4.0960 4.0955
5.38 CHARGER NOT SWITCHING 5.36 5.34 5.32 5.30 0 5 10 15 20 25 30 35 40 45 50 ILDO (mA)
3.340 3.335 5.330 5.325 5.320 5.315 8 10 12 14 16 18 20 22 24 26 28 INPUT VOLTAGE (V)
4.0950 0 100 200 300 400 500 600 700 800 900 1000 IREF (A)
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Simplified Multichemistry SMBus Battery Charger MAX8713
____________________________Typical Operating Characteristics (continued)
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25C, unless otherwise noted.)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX8713 toc04
EFFICIENCY vs. CHARGE CURRENT
MAX8713 toc05
FREQUENCY vs. RFREQ
600 FREQUENCY (kHz) 500 400 300 200 100 0
MAX8713 toc06
4.100 4.098 REFERENCE VOLTAGE (V) 4.096 4.094 4.092 4.090 4.088 4.086 4.084 4.082 4.080 -40 -20 0 20 40 60 80 TEMPERATURE (C)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 VBATT = 4.2V VBATT = 12.6V VBATT = 16.8V VBATT = 8.4V
700
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 CHARGE CURRENT (A)
0
100
200
300
400
500
RFREQ (k)
FREQUENCY vs. VIN
MAX8713 toc07
CHARGE-CURRENT ERROR vs. BATTERY VOLTAGE
MAX8713 toc08
CHARGE-CURRENT ERROR vs. CHARGE-CURRENT SETTING
4 CHARGE-CURRENT ERROR (%) 3 2 1 0 -1 -2 -3 -4 -5
MAX8713 toc09
450 400 350 FREQUENCY (kHz) 300 250 200 150 100 50 0 8 VBATT = 8.4V VBATT = 12.6V VBATT = 16.8V VBATT = 4.2V
10 8 CHARGE-CURRENT ERROR (%) 6 4 2 0 -2 -4 -6 -8 -10 2 4 6 8 10 12 14 16 18 CHARGECURRENT() = 2A CHARGECURRENT() = 0.992A
5
10 12 14 16 18 20 22 24 26 28 INPUT VOLTAGE (V)
20
0
0.5
1.0
1.5
2.0
2.5
VBATT (V)
CHARGE-CURRENT SETTING (A)
ADAPTER CURRENT vs. ADAPTER VOLTAGE
MAX8713 toc10
BATTERY CURRENT vs. BATTERY VOLTAGE
MAX8713 toc11
5.0 4.5 ADAPTER CURRENT (mA) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 5 10 15 20 CHARGER NOT SWITCHING CHARGER SWITCHING, NO LOAD
6 5 BATTERY CURRENT (A) 4 ADAPTER ABSENT 3 2 1 0 ADAPTER PRESENT
25
0
2
4
6
8
10 12 14 16 18 20
ADAPTER VOLTAGE (V)
BATTERY VOLTAGE (V)
8
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Simplified Multichemistry SMBus Battery Charger MAX8713
____________________________Typical Operating Characteristics (continued)
(VDCIN = VDCSNS = 20V, Circuit of Figure 1, TA = +25C, unless otherwise noted.)
BATTERY-VOLTAGE ERROR vs. CHARGE VOLTAGE SETTING
MAX8713 toc12
BATTERY-VOLTAGE ERROR vs. LOAD
-5 BATTERY-VOLTAGE ERROR (mV) -10 -15 -20 -25 -30 -35 -40 -45
MAX8713 toc13
20 BATTERY-VOLTAGE ERROR (mV) 0 -20 -40 -60 -80 -100 0 5 10 15
0
-50 20 0 0.5 1.0 LOAD CURRENT (A) 1.5 2.0 CHARGE VOLTAGE SETTING (V)
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 NAME REF IC1 CCI CCV DAC VDD SDA SCL IC2 FREQ GND BATT CSIN IC3 CSIP PGND DLO DLOV FUNCTION 4.096V Voltage Reference. Bypass REF with a 1F capacitor to GND. Internally Connected. Connect to the exposed paddle for improved layout. Output Current-Regulation Loop Compensation Point. Connect 0.01F to GND. Voltage-Regulation Loop Compensation Point. Connect 10k in series with 0.01F to GND. DAC Voltage Output. Bypass with a 0.1F capacitor to GND. Logic Circuitry Supply Voltage Input. Bypass with a 0.1F capacitor to GND. SMBus Data IO. Open-drain output. Connect the external pullup resistor according to SMBus specifications. SMBus Clock Input. Connect the external pullup resistor according to SMBus specifications. Internally Connected. Connect to the exposed paddle for improved layout. tOFF Frequency Adjust Input. Connect a 100k to 400k resistor between FREQ and GND to set the PWM frequency. Analog Ground Battery Voltage Sense Input Output Current-Sense Negative Input Internally Connected. Connect to the exposed paddle for improved layout. Output Current-Sense Positive Input. Connect a current-sense resistor from CSIP to CSIN. Power Ground Low-Side Power MOSFET Driver Output. Connect to the low-side n-channel MOSFET gate. Low-Side Driver Supply. Bypass DLOV with a 1F capacitor to PGND. Connect a 33 resistor from LDO to DLOV for filtering.
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Simplified Multichemistry SMBus Battery Charger MAX8713
Pin Description (continued)
PIN 19 20 21 22 23 24 NAME LX DHI BST DCSNS LDO DCIN FUNCTION High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1F capacitor from BST to LX. High-Side Power MOSFET Driver Output. Connect to the high-side n-channel MOSFET gate. High-Side Power MOSFET Driver Power-Supply Connection. Connect a 0.1F capacitor from BST to LX. DC Supply-Voltage Sense Input. Charging is disabled for VDCSNS < VCSIN + 100mV. DCSNS is also used to calculate the switching regulator's off-time. Device Power Supply. LDO is the output of the 5.4V linear regulator supplied from DCIN. Bypass LDO with a 1F ceramic capacitor from LDO to GND. Charger Bias Supply Input. Bypass DCIN with a 0.1F ceramic capacitor to PGND.
D1 ADAPTER D2 24 C1 0.1F 1 C3 1F 2 C4 0.1F HOST SCL SDA VDD 8 SCL 7 SDA 6 VDD REF DCIN 22 DCSNS C2 22F DHI LX DLO 20 19 17 M2 M1 L1 22H
EXTERNAL LOAD
MAX8713 BST 21
DAC 15 CSIP 13 CSIN 12 BATT
RS 40m
C6 0.1F
D3
BATTERY C5 10F
C7 0.1F
DLOV
18 R6 33 C11 1F C12 1F R5 10k
LDO
23
GND
11
PGND 16 10 FREQ CCI 3 CCV C8 0.01F 4
R3 100k
C9 0.01F
BATT+ BATTERY SCL SDA BATT-
Figure 1. Typical Application Circuit
10
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Simplified Multichemistry SMBus Battery Charger MAX8713
150mV (188mA FOR 40m)
2V (2.5A FOR 40m) BST
CSI
HIGHSIDE DRIVER IZX CCMP LVC IMIN 0.1V DC-DC CONVERTER IMAX LEVEL SHIFT
DHI LX DLOV
LOWSIDE DRIVER
DLO PGND FREQ DCSNS DCIN
LOWEST VOLTAGE CLAMP
CCV CCI
OFF-TIME GENERATOR 5.4V LINEAR REGULATOR
GMI
GMV
LDO
MAX8713
4.096V REFERENCE REF
CURRENTSENSE AMPLIFIER
11-BIT DAC
ChargingVoltage() SMBus LOGIC
SCL
A = 20V/V 6-BIT DAC
ChargingVoltage()
SDA
CSIN
CSIP
BATT
DAC
GND
Figure 2. Functional Diagram
Detailed Description
The MAX8713 includes all of the functions necessary to charge Li+, NiMH, and NiCd smart batteries. A highefficiency, synchronous-rectified, step-down DC-DC converter is used to implement a precision constantcurrent, constant-voltage charger. The DC-DC converter drives a high-side n-channel MOSFET and provides synchronous rectification with a low-side n-channel MOSFET. The charge current-sense amplifier has a low input offset error, allowing the use of small-valued sense resistors. The MAX8713 features a voltage-regu-
lation loop (CCV) and a current-regulation loop (CCI). CCI and CCV operate independently of each other. The CCV voltage-regulation loop monitors BATT to ensure that its voltage never exceeds the voltage set by the ChargeVoltage() command. The CCI battery currentregulation loop monitors current delivered to BATT to ensure that it never exceeds the current limit set by the ChargeCurrent() command. The charge current-regulation loop is in control as long as the BATT voltage is below the set point. When the BATT voltage reaches its set point, the voltage-regulation loop takes control and maintains the battery voltage at the set point.
11
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Simplified Multichemistry SMBus Battery Charger MAX8713
The circuit shown in Figure 1 demonstrates a typical application for smart-battery systems. A functional diagram is shown in Figure 2. the sense resistor. All codes requesting charge current between 1mA to 32mA result in a current setting of 32mA. To stop charging, set ChargeCurrent() to 0. Upon initial power-up, the ChargeVoltage() and ChargeCurrent() values are cleared and the charger remains shut down. To start the charger, send valid ChargeVoltage() and ChargeCurrent() commands. The ChargeCurrent() command uses the Write-Word protocol (Figure 5). The command code for ChargeCurrent() is 0x14 (0b00010100). Table 2 shows the format of the ChargeCurrent() register. Figure 4 shows the mapping between the charge-current set point and the ChargeCurrent() code. The default charge current setting at power-up is 0mA.
Setting Charge Voltage
To set the output voltage of the MAX8713, use the SMBus to write a 16-bit ChargeVoltage() command. This 16-bit command translates to a 1mV LSB and a 65.535V full-scale voltage. The MAX8713 ignores the first 4 LSBs and uses the next 11 bits to set the voltage DAC. The charge voltage range of the MAX8713 is 0 to 19.200V. All codes requesting charge voltage greater than 19.200V result in a voltage setting of 19.200V. All codes requesting charge voltage below 1.024V result in a voltage set point of zero, which terminates charging. Upon reset, the ChargeVoltage() and ChargeCurrent() values are cleared and the charger remains shut down until a ChargeVoltage() and ChargeCurrent() command is sent. The ChargeVoltage() command uses the Write-Word protocol (Figure 5). The command code for ChargeVoltage() is 0x15 (0b00010101). The 16-bit binary number formed by D15-D0 represents the charge-voltage set point in mV. However, the resolution of the MAX8713 is 16mV in setting the charge voltage because the D0-D3 bits are ignored as shown in Table 1. The D15 bit is also ignored because it is not needed to span the 0 to 19.2V range. Figure 3 shows the mapping between the charge-voltage set point and the ChargeVoltage() code. All codes requesting charge voltage greater than 19.200V result in a 19.200V setting. All codes requesting charge voltage below 1024mV result in a voltage set point of zero, which terminates charging. Upon initial power-up, ChargingVoltage() is reset to zero and a ChargingVoltage() command must be sent to initiate charging.
LDO Regulator
An integrated low-dropout (LDO) linear regulator provides a 5.4V supply derived from DCIN, and delivers over 5mA of load current. The LDO powers the gate drivers of the n-channel MOSFETs in the DC-DC converter. See the MOSFET Drivers section. The LDO also biases the 4.096V reference and most of the control circuitry. Bypass LDO to GND with a 1F ceramic capacitor.
VDD Supply
The VDD input provides power to the SMBus interface. Connect VDD to LDO, or apply an external supply to VDD to keep the SMBus interface active while the supply to DCIN is removed. When VDD is biased, the internal registers are maintained. Bypass VDD to GND with a 0.1F ceramic capacitor.
Operating Conditions
Table 3 is a summary of operating states of the MAX8713. * Adapter Present. When DCIN is greater than 7.5V, the adapter is considered to be present. In this condition, both the LDO and REF function properly and battery charging is allowed. * Power Fail. When DCIN is less than BATT + 0.3V, the MAX8713 is in the power-fail state, since the DC-DC converter is in dropout. The charger will not attempt to charge when in the power-fail state. VDD Undervoltage. When VDD is less than 2.5V, the VDD supply is considered to be in an undervoltage state. The SMBus interface does not respond to commands. When coming out of the undervoltage condition, the part is in its power-on reset state. No charging occurs when VDD is in the undervoltage state. When VDD is greater than 2.5V, SMBus registers are preserved.
Setting Charge Current
To set the charge current for the MAX8713, use the SMBus interface to write a 16-bit ChargeCurrent() command. This 16-bit command translates to a 1mA per LSB and a 65.535A full-scale current using a 40m current-sense resistor (RS in Figure 1). Equivalently, the ChargeCurrent() value sets the voltage across the CSIP and CSIN inputs in 40V increments. The MAX8713 ignores the lowest 5 LSBs and uses the next 6 bits to set the current DAC. The charge current range is 0 to 2.016A using a 40m current-sense resistor. All codes requesting charge current above 2.016A result in a setting of 2.016A. For larger current settings, scale down
*
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Simplified Multichemistry SMBus Battery Charger
Table 1. ChargeVoltage()
BIT 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 BIT NAME -- -- -- -- Charge Voltage, DACV 0 Charge Voltage, DACV 1 Charge Voltage, DACV 2 Charge Voltage, DACV 3 Charge Voltage, DACV 4 Charge Voltage, DACV 5 Charge Voltage, DACV 6 Charge Voltage, DACV 7 Charge Voltage, DACV 8 Charge Voltage, DACV 9 Charge Voltage, DACV 10 -- Not used. Normally a 1mV weight. Not used. Normally a 2mV weight. Not used. Normally a 4mV weight. Not used. Normally an 8mV weight. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 16mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 32mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 64mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 128mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 256mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance, 1024mV (min). 1 = Adds 512mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance. 1 = Adds 1024mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance. 1 = Adds 2048mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance. 1 = Adds 4096mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance. 1 = Adds 8192mV of charge-voltage compliance. 0 = Adds 0mV of charge-voltage compliance. 1 = Adds 16,384mV of charge-voltage compliance, 19,200mV (max). Not used. Normally a 32,768mV weight. DESCRIPTION
MAX8713
Command: 0x15
SMBus Interface
The MAX8713 receives control inputs from the SMBus interface. The serial interface complies with the SMBus protocols as documented in the System Management Bus Specification V1.1, which can be downloaded from www.smbus.org. The MAX8713 uses the SMBus ReadWord and Write-Word protocols (Figure 5) to communicate with the smart battery. The MAX8713 is an SMBus slave device and does not initiate communication on the bus. It responds to the 7-bit address 0b0001001_ (0x12). In addition, the MAX8713 has two identification
(ID) registers: a 16-bit device ID register and a 16-bit manufacturer ID register. The data (SDA) and clock (SCL) pins have Schmitt-trigger inputs that can accommodate slow edges. Choose pullup resistors for SDA and SCL to achieve rise times according to the SMBus specifications. Communication starts when the master signals a START condition, which is a high-to-low transition on SDA, while SCL is high. When the master has finished communicating, the master issues a STOP condition, which is a low-to-high transition on SDA, while SCL is high.
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Simplified Multichemistry SMBus Battery Charger MAX8713
Table 2. ChargeCurrent()
BIT 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 BIT NAME -- -- -- -- -- Charge Current DAC, bit 0 Charge Current DAC, bit 1 Charge Current DAC, bit 2 Charge Current DAC, bit 3 Charge Current DAC, bit 4 Charge Current DAC, bit 5 -- -- -- -- -- DESCRIPTION Not used. Normally a 1mA weight. Not used. Normally a 2mA weight. Not used. Normally a 4mA weight. Not used. Normally an 8mA weight. Not used. Normally a 16mA weight. 0 = Adds 0mA of charger current compliance. 1 = Adds 32mA of charger current compliance. 0 = Adds 0mA of charger current compliance. 1 = Adds 64mA of charger current compliance. 0 = Adds 0mA of charger current compliance. 1 = Adds 128mA of charger current compliance. 0 = Adds 0mA of charger current compliance. 1 = Adds 256mA of charger current compliance. 0 = Adds 0mA of charger current compliance. 1 = Adds 512mA of charger current compliance. 0 = Adds 0mA of charger current compliance. 1 = Adds 1024mA of charger current compliance. 2016mA (max). Not used. Normally a 2048mA weight. Not used. Normally a 4096mA weight. Not used. Normally a 8192mA weight. Not used. Normally a 16,384mA weight. Not used. Normally a 32,768mA weight.
Command: 0x14
The bus is then free for another transmission. Figures 6 and 7 show the timing diagram for signals on the SMBus interface. The address-byte, command-byte, and data-bytes are transmitted between the START and STOP conditions. The SDA state is allowed to change only while SCL is low, except for the START and STOP conditions. Data is transmitted in 8-bit bytes and is sampled on the rising edge of SCL. Nine clock cycles are required to transfer each byte in or out of the MAX8713 because either the master or the slave acknowledges the receipt of the correct byte during the ninth clock. The MAX8713 supports the charger commands as described in Tables 2-4.
Battery Charger Commands
The MAX8713 supports four battery-charger commands that use either Write-Word or Read-Word protocols, as summarized in Table 2. ManufacturerID() and DeviceID() can be used to identify the MAX8713. On the MAX8713, ManufacturerID() always returns 0x004D and DeviceID() always returns 0x0007.
DC-DC Converter
The MAX8713 employs a pseudo-fixed-frequency, current-mode control scheme with cycle-by-cycle current limit. The controller's constant off-time (tOFF) is calculated based on VDCIN, VBATT, and RFREQ, and has a minimum value of 300ns. The operation of the DC-DC controller is determined by the following four comparators as shown in the functional diagram (Figure 2):
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Simplified Multichemistry SMBus Battery Charger MAX8713
19200 2016
16800
CHARGE-CURRENT SET POINT (mA)
CHARGE-VOLTAGE SET POINT (mV)
8400
1024
4200
512
1024 0x0400 0x1060 0x20D0 0x41A0 0x4B00 0xFFFF
32 0x0020 0x0200 0x0400 CHARGECURRENT() CODE 0x07E0 0xFFFF
CHARGEVOLTAGE() CODE
Figure 3. ChargeVoltage() Code to Charge-Voltage Set-Point Mapping
Figure 4. ChargeCurrent() Code to Charge-Current Set Point Mapping (R2 = 40m)
Table 3. Summary of Operating States
INPUT CONDITIONS DCIN BATT VDD OPERATING STATES ADAPTER PRESENT VDCIN > 7.5V X X POWER FAIL VDCIN < VBATT + 0.1V VBATT > VDCIN - 0.1V X VDD UNDERVOLTAGE X X VDD < 2.5V
X = Don't care.
The IMIN comparator sets the peak inductor current in discontinuous mode. IMIN compares the control signal (LVC) against 100mV (typ). When LVC voltage is less than 100mV, DHI and DLO are both low. The CCMP comparator is used for current-mode regulation in continuous-conduction mode. CCMP compares LVC against the charging-current feedback signal (CSI). The comparator output is high and the high-side MOSFET on-time is terminated when the CSI voltage is higher than LVC. The IMAX comparator provides a cycle-by-cycle current limit. IMAX compares CSI to 2V (corresponding to 2.5A when RS = 40m). The comparator output is high and the high-side MOSFET on-time is terminated when the current-sense signal exceeds 2.5A. A new cycle cannot start until the IMAX comparator output goes low. The ZCMP comparator provides zero-crossing detection during discontinuous conduction. ZCMP compares the current-sense feedback signal to 188mA (RS = 40m). When the inductor current is lower than the
188mA threshold, the comparator output is high and DLO is turned off.
Setting the Switching Frequency
The MAX8713 features an adjustable switching frequency. To set the switching frequency, choose RFREQ according to the following equation: RFREQ = 100kHz x 400k fSWITCH
Higher switching frequencies are typically preferred to minimize inductor and capacitor requirements. See the Typical Operating Characteristics. The switching frequency has a minor dependence on VDCIN and VBATT because of voltage losses along the high current path and other 2nd-order effects not accounted in the MAX8713's off-time calculation. These can be accounted for by observing the curves in the Typical Operating Characteristics.
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Simplified Multichemistry SMBus Battery Charger MAX8713
a) WRITE-WORD FORMAT S SLAVE W ADDRESS 7 BITS 1b MSB LSB 0 PRESET to 0b0001001 ACK 1b 0 COMMAND LOW DATA ACK ACK BYTE BYTE 8 BITS 1b 8 BITS 1b MSB LSB 0 MSB LSB 0 ChargingCurrent() = 0x14 D7 D0 ChargerVoltage() = 0x15 HIGH DATA ACK P BYTE 8 BITS 1b MSB LSB 0 D15 D8
b) READ-WORD FORMAT S SLAVE W ADDRESS 7 BITS 1b MSB LSB 0 PRESET to 0b0001001 ACK 1b 0 COMMAND BYTE 8 BITS MSB LSB DeviceID() = 0xFF ManufacturerID() = 0xFE ACK 1b 0 S SLAVE ADDRESS 7 BITS MSB LSB PRESET to 0b0001001 R 1b 1 ACK 1b 0 LOW DATA ACK BYTE 8 BITS 1b MSB LSB 0 D7 D0 HIGH DATA NACK P BYTE 8 BITS 1b MSB LSB 1 D15 D8
LEGEND S = START CONDITION OR REPEATED START CONDITION ACK = ACKNOWLEDGE (LOGIC LOW) W = WRITE BIT (LOGIC LOW) MASTER TO SLAVE SLAVE TO MASTER
P = STOP CONDITION NACK = NOT ACKNOWLEDGE (LOGIC HIGH) R = READ BIT (LOGIC HIGH)
Figure 5. SMBus Write-Word and Read-Word Protocols
CCV, CCI, and LVC Control Blocks
The MAX8713 controls charge current (CCI control loop) or charge voltage (CCV control loop), depending on the operating condition. The two control loops CCV and CCI are brought together internally at the LVC (lowest voltage clamp) amplifier. The output of the LVC amplifier is the feedback control signal for the DC-DC controller. The minimum voltage of CCV and CCI appears at the output of the LVC amplifier and clamps the remaining control loop to within 0.3V above the control point. Clamping the other control loop close to the lowest control loop ensures fast transition with minimal overshoot when switching between different regulation modes (see the Compensation section).
Continuous-Conduction Mode
With sufficient charge current, the MAX8713's inductor current never crosses zero, which is defined as continuous-conduction mode. The regulator switches at 400kHz (RFREQ = 100k) if it is not in dropout (VBATT < 0.88 x VDCIN). The controller starts a new cycle by turning on the high-side MOSFET and turning off the lowside MOSFET. When the charge-current feedback signal (CSI) is greater than the control point (LVC), the CCMP comparator output goes high and the controller
initiates the off-time by turning off the high-side MOSFET and turning on the low-side MOSFET. The operating frequency is governed by the off-time and is dependent upon VDCIN, VBATT, and RFREQ. See the Setting the Switching Frequency section for more information. At the end of the fixed off-time, the controller initiates a new cycle if the control point (LVC) is greater than 100mV, and the peak charge current is less than the cycle-by-cycle current limit. Restated another way, IMIN must be high and IMAX must be low for the controller to initiate a new cycle. If the peak inductor current exceeds the IMAX comparator threshold, then the on-time is terminated. The cycle-by-cycle current limit effectively protects against overcurrent and short-circuit faults. There is a 0.3s minimum off-time when the (VDCSNS VBATT) differential becomes too small. If VBATT 0.88 x V DCSNS, then the threshold for minimum off-time is reached and the off-time is fixed at 0.3s. The switching frequency in this mode varies according to the equation: f= VIN - VOUT 0.3s x VIN
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Simplified Multichemistry SMBus Battery Charger MAX8713
A tLOW B tHIGH C D E F G H I J K L M
SMBCLK
SMBDATA
tSU:STA
tHD:STA
tSU:DAT
tHD:DAT
tHD:DAT
tSU:STO tBUF J = ACKNOWLEDGE CLOCKED INTO MASTER K = ACKNOWLEDGE CLOCK PULSE L = STOP CONDITION, DATA EXECUTED BY SLAVE M = NEW START CONDITION
A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE E = SLAVE PULLS SMBDATA LINE LOW
F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO SLAVE H = LSB OF DATA CLOCKED INTO SLAVE I = SLAVE PULLS SMBDATA LINE LOW
Figure 6. SMBUs Write Timing
A tLOW
B tHIGH
C
D
E
F
G
H
I
J
K
SMBCLK
SMBDATA
tSU:STA tHD:STA A = START CONDITION B = MSB OF ADDRESS CLOCKED INTO SLAVE C = LSB OF ADDRESS CLOCKED INTO SLAVE D = R/W BIT CLOCKED INTO SLAVE
tSU:DAT
tHD:DAT E = SLAVE PULLS SMBDATA LINE LOW F = ACKNOWLEDGE BIT CLOCKED INTO MASTER G = MSB OF DATA CLOCKED INTO MASTER H = LSB OF DATA CLOCKED INTO MASTER
tSU:DAT
tSU:STO
tBUF
I = ACKNOWLEDGE CLOCK PULSE J = STOP CONDITION K = NEW START CONDITION
Figure 7. SMBus Read Timing
Table 4. Battery-Charger Command Summary
COMMAND 0x14 0x15 0xFE 0xFF COMMAND NAME ChargeCurrent() ChargeVoltage() ManufacturerID() DeviceID() READ/WRITE Write Only Write Only Read Only Read Only DESCRIPTION 6-Bit Charge Current Setting 11-Bit Charge Voltage Setting Manufacturer ID Device ID POR STATE 0x0000 0x0000 0x004D 0x0007
Discontinuous Conduction The MAX8713 can also operate in discontinuous-conduction mode to ensure that the inductor current is always positive. The MAX8713 enters discontinuous-
conduction mode when the output of the LVC control point falls below 100mV. For RS = 40m, this corresponds to 62.5mA.
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Simplified Multichemistry SMBus Battery Charger MAX8713
100mV = 62.5mA 20 x RS ch arg e current for RS = 40m IDIS = 0.5 x In discontinuous mode, a new cycle is not started until the LVC voltage rises above 100mV. Discontinuousmode operation can occur during conditioning charge of overdischarged battery packs or when the charger is in constant voltage mode as the charge current drops to zero. RCV is much higher impedance than CCV and dominates the series combination of RCV and CCV, so: ROGMV x (1+ sCCV x RCV ) RCV (1+ sCCV x ROGMV ) C OUT is also much lower impedance than RL near crossover, so the parallel impedance is mostly capacitive and: RL (1+ sCOUT x RL ) 1 sCOUT
Compensation
The charge voltage and charge current-regulation loops are compensated separately and independently at CCV and CCI. CCV Loop Compensation The simplified schematic in Figure 9 is sufficient to describe the operation of the MAX8713 when the voltage loop (CCV) is in control. The required compensation network is a pole-zero pair formed with CCV and RCV. The pole is necessary to roll off the voltage loop's response at low frequency. The zero is necessary to compensate the pole formed by the output capacitor and the load. RESR is the equivalent series resistance (ESR) of the charger output capacitor (COUT). RL is the equivalent charger output load, where RL = VBATT / ICHG. The equivalent output impedance of the GMV amplifier, ROGMV, is greater than 10M. The voltage amplifier transconductance, GMV = 0.125A/mV. The DC-DC converter transconductance is dependent upon the charge current-sense resistor RS: GMOUT = 1 A CSI x RS
If RESR is small enough, its associated output zero has a negligible effect near crossover and the loop-transfer function can be simplified as follows: LTF = GMOUT x RCV x GMV sCOUT
Setting LTF = 1 to solve for the unity-gain frequency yields: fCO_CV = GMOUT x GMV x RCV 2 x COUT
where ACSI = 20 and RS = 0.04 in the typical application circuits, so GMOUT = 1.25A/V. The loop-transfer function is given by: LTF = GMOUT x RL x GMV x ROGMV x (1+ sCOUT x RESR )(1+ sCCV x RCV ) (1+ sCCV x ROGMV )(1+ sCOUT x RL ) The poles and zeros of the voltage loop-transfer function are listed from lowest frequency to highest frequency in Table 5. Near crossover, CCV is much lower impedance than ROGMV. Since CCV is in parallel with ROGMV, CCV dominates the parallel impedance near crossover. Additionally
For stability, choose a crossover frequency less than 1/10 of the switching frequency. For example, choosing a crossover frequency of 25kHz and solving for RCV using the component values listed in Figure 1 yields: RCV = 10k. VBATT= 8.4V GMV = 0.125mA/mV ICHG = 2A GMOUT = 1.25A/V fOSC = 400kHz COUT = 10F RL = 0.2 fCO_CV = 25kHz RCV = 2 x COUT x fCO_CV GMV x GMOUT 10k
To ensure that the compensation zero adequately cancels the output pole, select fZ_CV fP_OUT. CCV (RL / RCV) x COUT C CV 200pF (assuming 2 cells and 2A maximum charge current). Figure 10 shows the Bode plot of the voltage loop frequency response using the values calculated above.
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Simplified Multichemistry SMBus Battery Charger MAX8713
CSI IMAX 2V R Q TO DH DRIVER
fCO_CI =
GMI 2 CCI
CCMP LVC
IMIN 100mV
R
Q
TO DL DRIVER
ZCMP 150mV DCIN BATT OFF-TIME COMPUTE OFF-TIME ONE-SHOT
For stability, choose a crossover frequency lower than 1/10 of the switching frequency. CCI > 10 x GMI / (2 fOSC) = 4nF, for a 400kHz switching frequency (RFREQ = 100k). Values for CCI greater than ten times the minimum value may slow down the current-loop response. Choosing CCI=10nF yields a crossover frequency of 15.9kHz. Figure 12 shows the Bode plot of the current-loop frequency response using the values calculated above.
MOSFET Drivers
The DHI and DLO outputs are optimized for driving moderate-sized power MOSFETs. The MOSFET drive capability is the same for both the low-side and highside switches. This is consistent with the variable duty factor that occurs in the notebook computer environment where the battery voltage changes over a wide range. There must be a low-resistance, low-inductance path from the DLO driver to the MOSFET gate to prevent shoot-through. Otherwise, the sense circuitry in the MAX8713 will interpret the MOSFET gate as "off" while there is still charge left on the gate. Use very short, wide traces measuring 10 to 20 squares or less (1.25mm to 2.5mm wide if the MOSFET is 25mm from the device). Unlike the DLO output, the DHI output uses a 50ns (typ) delay time to prevent the low-side MOSFET from turning on until DHI is fully off. The same considerations should be used for routing the DHI signal to the high-side MOSFET.
Figure 8. DC-DC Converter Block Diagram
CCI Loop Compensation The simplified schematic in Figure 11 is sufficient to describe the operation of the MAX8713 when the battery current loop (CCI) is in control. Since the output capacitor's impedance has little effect on the response of the current loop, only a simple single pole is required to compensate this loop. ACSI is the internal gain of the current-sense amplifier. RS is the charge current-sense resistor (40m). ROGMI is the equivalent output impedance of the GMI amplifier, which is greater than 10M. GMI is the charge-current amplifier transconductance = 1A/mV. GMOUT is the DC-DC converter transconductance = 1.25A/V. The loop-transfer function is given by: LTF = GMOUT x A CSI x RS x GMI ROGMI , 1+ sROGMI x CCI
BATT GMOUT RESR COUT GMV RCV CCV ROGMV REF RL
which describes a single-pole system. Since GMOUT = 1 , A CSI x RS
CCV
the loop-transfer function simplifies to: ROGMI LTF = GMI 1+ sROGMI x CCI The crossover frequency is given by:
Figure 9. CCV Loop Diagram
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Simplified Multichemistry SMBus Battery Charger MAX8713
Table 5. CCV Loop Poles and Zeros
NAME CCV Pole EQUATION DESCRIPTION Lowest Frequency Pole Created by CCV and GMV's Finite Output Resistance. Since ROGMV is very large and not well controlled, the exact value for the pole frequency is also not well controlled (ROGMV > 10M). Voltage Loop-Compensation Zero. If this zero is at the same frequency or lower than the output pole fP_OUT, then the loop-transfer function approximates a single-pole response near the crossover frequency. Choose CCV to place this zero at least 1 decade below crossover to ensure adequate phase margin. Output Pole Formed with the Effective Load Resistance (RL) and the Output Capacitance (COUT). RL influences the DC gain but does not affect the stability of the system or the crossover frequency. Output ESR Zero. This zero can keep the loop from crossing unity gain if fZ_OUT is less than the desired crossover frequency; therefore, choose a capacitor with an ESR zero greater than the crossover frequency.
fP_CV =
1 2 ROGMV x CCV
CCV Zero
1 fZ_CV = 2 RCV x CCV 1 2 RL x COUT 1 2 RESR x COUT
Output Pole
fP_OUT =
Output Zero
fZ_OUT =
80 60 MAGNITUDE (dB) 40 20 0 -20 -40 0 1 10 100 1k 10k 100k 1M FREQUENCY (Hz) MAGNITUDE PHASE
0 CSIP GMOUT RS2 -45 PHASE (DEGREES) CSIN
CSI
-90
CCI GMI -135 CCI ROGMI ICTL
Figure 10. CCV Loop Response
Figure 11. CCI Loop Diagram
The high-side driver (DHI) swings from LX to 5V above LX (BST) and has a typical impedance of 7 sourcing and 2 sinking. The low-side driver (DLO) swings from DLOV to ground and has a typical impedance of 2 sinking and 7 sourcing. This helps prevent DLO from being pulled up when the high-side switch turns on, due to capacitive coupling from the drain to the gate of the low-side MOSFET. This places some restrictions on the MOSFETs that can be used. Using a low-side MOSFET with smaller gate-to-drain capacitance can prevent these problems.
Design Procedure
MOSFET Selection
Choose the n-channel MOSFETs according to the maximum-required charge current. Low-current applications usually require less attention. The high-side MOSFET (M1) must be able to dissipate the resistive losses plus the switching losses at both V DCIN(MIN) and VDCIN(MAX). Calculate both of these sums. Ideally, the losses at V DCIN(MIN) should be roughly equal to the losses at VDCIN(MAX), with lower losses in between. If the losses at VDCIN(MIN) are significantly
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Simplified Multichemistry SMBus Battery Charger MAX8713
60 50 40 30 20 10 0 -10 -20 100 1k 10k FREQUENCY (Hz) 100k 1M -90 -45 PHASE (DEGREES) MAGNITUDE (dB) MAGNITUDE PHASE RIPPLE CURRENT (A) 0 0.40 VADAPTER = 12V 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 0 2 4 6 8 10 12 BATTERY VOLTAGE (V)
Figure 12. CCI Loop Response
Figure 13. Ripple Current vs. Battery Voltage
higher than the losses at VDCIN(MAX), consider increasing the size of M1. Conversely, if the losses at VDCIN(MAX) are significantly higher than the losses at VIN(MIN), consider reducing the size of M1. If DCIN does not vary over a wide range, the minimum power dissipation occurs where the resistive losses equal the switching losses. Choose a low-side MOSFET that has the lowest-possible on-resistance (RDS(ON)), comes in a moderate-sized package (i.e., one or two 8-pin SO, DPAK, or D2 PAK), and is reasonably priced. Make sure that the DLO gate driver can supply sufficient current to support the gate charge and the current injected into the parasitic gate-to-drain capacitor caused by the high-side MOSFET turning on; otherwise, cross-conduction problems can occur. Select devices that have short turn-off times, and make sure that M2(tDOFF(MAX)) - M1(t DON(MIN) ) < 30ns, and M1(t DOFF(MAX) ) M2(tDON(MIN)) < 30ns. Failure to do so may result in efficiency-killing shoot-through currents.
MOSFET can be. The optimum occurs when the switching (AC) losses equal the conduction (RDS(ON)) losses. Switching losses in the high-side MOSFET can become an insidious heat problem when maximum AC adapter voltages are applied, due to the squared term in the CV2f switching-loss equation. If the high-side MOSFET that was chosen for adequate RDS(ON) at low supply voltages becomes extraordinarily hot when subjected to VIN(MAX), then choose a MOSFET with lower losses. Calculating the power dissipation in M1 due to switching losses is difficult since it must allow for difficult quantifying factors that influence the turn-on and turnoff times. These factors include the internal gate resistance, gate charge, threshold voltage, source inductance, and PC board layout characteristics. The following switching-loss calculation provides only a very rough estimate and is no substitute for breadboard evaluation, preferably including a verification using a thermocouple mounted on M1:
PD(HS_SWITCHING) = VDCIN(MAX)2 x CRSS x fSW x ILOAD 2 x IGATE
MOSFET Power Dissipation
Worst-case conduction losses occur at the duty-factor extremes. For the high-side MOSFET, the worst-case power dissipation (PD) due to resistance occurs at the minimum supply voltage:
2 V I PD(HIGH-SIDE) = BATT LOAD x RDS(ON) VDCIN 2
where CRSS is the reverse transfer capacitance of M1, and IGATE is the peak gate-drive source/sink current (0.7A sourcing and 2.5A sinking). For the low-side MOSFET (M2), the worst-case power dissipation always occurs at maximum input voltage:
2 V I PD(LOW-SIDE) = 1- BATT LOAD x RDS(ON) VDCIN 2
Generally, a small high-side MOSFET is desired to reduce switching losses at high input voltages. However, the RDS(ON) required to stay within package power-dissipation limits often limits how small the
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Simplified Multichemistry SMBus Battery Charger MAX8713
Inductor Selection
The charge current, ripple, and operating frequency (off-time) determine the inductor characteristics. For optimum efficiency, choose the inductance according to the following equation: L = VBATT x tOFF / (0.3 x ICHG) This sets the ripple current to 1/3 of the charge current and results in a good balance between inductor size and efficiency. Higher inductor values decrease the ripple current. Smaller inductor values require high saturation current capabilities and degrade efficiency. Inductor L1 must have a saturation current rating of at least the maximum charge current plus 1/2 of the ripple current (IL): ISAT = ICHG + (1/2) IL The ripple current is determined by: IL = VBATT x tOFF / L where tOFF = 2.5s (VDCIN - VBATT) / VDCIN for VBATT < 0.88 VDCIN, or: tOFF = 0.3s for VBATT > 0.88 VDCIN. Figure 13 illustrates the variation of the ripple current vs. battery voltage when the circuit is charging at 2A with a fixed input voltage of 19V. the battery when it is initially plugged into the charger. As such, both capacitance and ESR are important parameters in specifying the output capacitor as a filter and to ensure the stability of the DC-DC converter (see the Compensation section). Beyond the stability requirements, it is often sufficient to make sure that the output capacitor's ESR is simply much lower than the battery's ESR. Either tantalum or ceramic capacitors can be used on the output. Ceramic devices are preferable because of their good voltage ratings and resilience to surge currents.
Applications Information
Layout and Bypassing
Bypass DCIN with a 0.1F ceramic to ground (Figure 1). D1 and D2 protect the MAX8713 when the DC power source input is reversed. A signal diode for D2 is adequate because DCIN only powers the LDO and the internal reference. Bypass V DD , DCIN, LDO, DHIV, DLOV, SRC, DAC, and REF as shown in Figure 1. Good PC board layout is required to achieve specified noise immunity, efficiency, and stable performance. The PC board layout artist must be given explicit instructions--preferably, a sketch showing the placement of the power switching components and high-current routing. Refer to the PC board layout in the MAX8713 evaluation kit for examples. A ground plane is essential for optimum performance. In most applications, the circuit is located on a multilayer board, and full use of the four or more copper layers is recommended. Use the top layer for high-current connections, the bottom layer for quiet connections, and the inner layers for uninterrupted ground planes. Use the following step-by-step guide: 1) Place the high-power connections first, with their grounds adjacent: * Minimize the current-sense resistor trace lengths, and ensure accurate current sensing with Kelvin connections. Minimize ground trace lengths in the high-current paths. Minimize other trace lengths in the high-current paths. Use >5mm-wide traces in the high-current paths. Connect C1 and C2 to the high-side MOSFET (10mm max length). Minimize the LX node (MOSFETs, rectifier cathode, inductor (15mm max length)). Keep LX on one side of the PC board to reduce EMI radiation.
Input Capacitor Selection
The input capacitor must meet the ripple-current requirement (IRMS) imposed by the switching currents. Nontantalum chemistries (ceramic, aluminum, or OS-CON) are preferred due to their resilience to powerup surge currents. IRMS = ICHG VBATT (VDCIN - VBATT ) VDCIN The input capacitors should be sized so that the temperature rise due to ripple current in continuous conduction does not exceed approximately +10C. The maximum ripple current occurs at 50% duty factor or VDCIN = 2 x VBATT, which equates to 0.5 x ICHG. If the application of interest does not achieve the maximum value, size the input capacitors according to the worstcase conditions.

* * * * *
Output Capacitor Selection
The output capacitor absorbs the inductor ripple current and must tolerate the surge current delivered from
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Simplified Multichemistry SMBus Battery Charger
Ideally, surface-mount power components are flush against one another with their ground terminals almost touching. These high-current grounds are then connected to each other with a wide, filled zone of top-layer copper, so they do not go through vias. The resulting top-layer subground plane is connected to the normal inner-layer ground plane at the paddle. Other high-current paths should also be minimized, but focusing primarily on short ground and current-sense connections eliminates about 90% of all PC board layout problems. 2) Place the IC and signal components. Keep the main switching node (LX node) away from sensitive analog components (current-sense traces and REF capacitor). Note: The IC must be no further than 10mm from the current-sense resistors. Quiet connections to REF, VMAX, IMAX, CCV, CCI, ACIN, and DCIN should be returned to a separate ground (GND) island. The appropriate traces are marked on the schematic with the () ground symbol. There is very little current flowing in these traces, so the ground island need not be very large. When placed on an inner layer, a sizable ground island can help simplify the layout because the low-current connections can be made through vias. The ground pad on the backside of the package should also be connected to this quiet ground island. 3) Keep the gate-drive traces (DHI and DLO) as short as possible (L < 20mm), and route them away from the current-sense lines and REF. These traces should also be relatively wide (W > 1.25mm). 4) Place ceramic bypass capacitors close to the IC. The bulk capacitors can be placed further away. Place the current-sense input filter capacitors under the part, connected directly to the GND pin. 5) Use a single-point star ground placed directly below the part at the PGND pin. Connect the power ground (ground plane) and the quiet ground island at this location.
MAX8713
Chip Information
TRANSISTOR COUNT: 8400 PROCESS: BiCMOS
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Simplified Multichemistry SMBus Battery Charger MAX8713
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 24L QFN THIN.EPS
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
1
2
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Simplified Multichemistry SMBus Battery Charger
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX8713
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
2
2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 25 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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