19-4041; Rev 0; 2/08 KIT ATION EVALU E L B AVAILA 1.2MHz Low-Cost, High-Performance Chargers The MAX17005/MAX17006/MAX17015 are high-frequency multichemistry battery chargers. These circuits feature a new high-frequency current-mode architecture that significantly reduces component size and cost*. The charger uses a high-side MOSFET with n-channel synchronous rectifier. Widely adjustable charge current, charge voltage, and input current limit simplify the construction of highly accurate and efficient chargers. The charge voltage and charge current are set with analog control inputs. The charge current setting can also be adjusted with a PWM input. High-accuracy current-sense amplifiers provide fast cycle-by-cycle current-mode control to protect against short circuits to the battery and respond quickly to system load transients. In addition, the charger provides a high-accuracy analog output that is proportional to the adapter current. In the MAX17015, this current monitor remains active when the adapter is absent to monitor battery discharge current. The MAX17005 charges three or four Li+ series cells, and the MAX17006 charges two or three Li+ series cells. The MAX17015 adjusts the charge voltage setting and the number of cells through a feedback resistordivider from the output. All variants of the charger can provide at least 4A of charge current with a 10mΩ sense resistor. The charger utilizes a charge pump to control an n-channel adapter selection switch. The charge pump remains active even when the charger is off. When the adapter is absent, a p-channel MOSFET selects the battery. The MAX17005/MAX17006/MAX17015 are available in a small, 4mm x 4mm x 0.8mm 20-pin, lead-free TQFN package. An evaluation kit is available to reduce design time. Applications Notebook Computers Features ♦ High Switching Frequency (1.2MHz) ♦ Controlled Inductor Current-Ripple Architecture Reduced BOM Cost Small Inductor and Output Capacitors ♦ ±0.4% Accurate Charge Voltage ♦ ±2.5% Accurate Input-Current Limiting ♦ ±3% Accurate Charge Current ♦ Single-Point Compensation ♦ Monitor Outputs for ±2.5% Accurate Input Current Limit ±2.5% Battery Discharge Current (MAX17015 only) AC Adapter Detection ♦ Analog/PWM Adjustable Charge-Current Setting ♦ Battery Voltage Adjustable for 3 and 4 Cells (MAX17005) or 2 and 3 Cells (MAX17006) ♦ Adjustable Battery Voltage (4.2V to 4.4V/Cell) ♦ Cycle-by-Cycle Current Limit Battery Short-Circuit Protection Fast Response for Pulse Charging Fast System-Load-Transient Response ♦ Programmable Charge Current < 5A ♦ Automatic System Power Source Selection with n-Channel MOSFET ♦ Internal Boost Diode ♦ +8V to +26V Input Voltage Range Ordering Information PART TEMP RANGE PINPACKAGE MAX17005ETP+ -40°C to +85°C 20 Thin QFN (4mm x 4mm) T2044-3 MAX17006ETP+ -40°C to +85°C 20 Thin QFN (4mm x 4mm) T2044-3 MAX17015ETP+ -40°C to +85°C 20 Thin QFN (4mm x 4mm) T2044-3 Tablet PCs Portable Equipment with Rechargeable Batteries PKG CODE +Denotes a lead-free package. *Patent pending. Pin Configuration and Minimal Operating Circuit appear at end of data sheet. ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX17005/MAX17006/MAX17015 General Description MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers ABSOLUTE MAXIMUM RATINGS DCIN, CSSP, CSSN, BATT, CSIN, CSIP, ACOK, LX to AGND .......................................................-0.3V to +30V BST to LDO.............................................................-0.3V to +30V CSIP to CSIN, CSSP to CSSN .............................. -0.3V to +0.3V IINP, FB, ACIN to AGND.............................-0.3V to (VAA + 0.3V) VAA, LDO, ISET, VCTL, CC to AGND .......................-0.3V to +6V DHI to LX ....................................................-0.3V to (BST + 0.3V) BST to LX..................................................................-0.3V to +6V DLO to PGND ............................................-0.3V to (LDO + 0.3V) PGND to AGND .................................................... -0.3V to +0.3V Continuous Power Dissipation (TA = +70°C) 16-Pin TQFN (derate 16.9mW/°C above +70°C)....1349.1mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-60°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX 8.40 8.4336 UNITS CHARGE-VOLTAGE REGULATION Battery Regulation-Voltage Accuracy 2 cells, V VCTL = GND (for MAX17006) 8.3664 3 cells, VVCTL = VAA (for MAX17005 and MAX17006) 12.549 12.60 12.651 4 cells, V VCTL = GND (for MAX17005) 16.733 16.80 16.867 FB accuracy using FB divider (for MAX17015) (Note 1) 2.0916 FB Input Bias Curent 2 cells (for MAX17006), 4 cells (for MAX17005) 2.1 V 2.1084 -1 +1 0.0 VAA/2 -0.2 VAA/2 +0.2 VAA VCTL Range μA V 3 cells (for MAX17005 and MAX17006) VCTL Gain VCELL/VVCTL VCTL Input Bias Current VVCTL = GND and VCTL = VAA 5.85 6 -1 6.15 V/V +1 μA VAA/2 V CHARGE-CURRENT REGULATION ISET Range ISET Full-Scale Setting 0.0 ISET = 1.4V 80 ISET = 99.9% duty cycle 60 Full-Charge Current Accuracy (CSIP to CSIN) VBATT = 1V to 16.8V Trickle Charge-Current Accuracy VISET = VAA/4 or ISET = 99.9% duty cycle 58.2 VISET = VAA/6 or ISET = 66.7% duty cycle 38.2 VISET = VAA/80 or ISET = 5% duty cycle 1.4 60 -3 40 -4.5 3 mV 61.8 mV +3 % 41.8 mV +4.5 % 4.6 mV -52 +52 % Charge-Current Gain Error Based on VISET = VVAA/4 and VISET = V VAA/80 -2 +2 % Charge-Current Offset Error Based on VISET = VVAA/4 and VISET = V VAA/80 -1.4 +1.4 mV 24 V BATT/CSIP/CSIN Input Voltage Range ISET Power-Down Mode Threshold 2 0 ISET falling 21 26 31 ISET rising 33 40 47 _______________________________________________________________________________________ mV 1.2MHz Low-Cost, High-Performance Chargers (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER ISET Input Bias Current ISET PWM Threshold CONDITIONS MIN TYP -0.2 +0.2 CSSN = BATT, VISET = 5V Rising -0.2 +0.2 Falling 0.8 ISET Frequency 2.4 0.128 ISET Effective Resolution MAX VISET = 3V f PWM = 3.2MHz 500 8 UNITS μA V kHz Bits INPUT-CURRENT REGULATION Input Current-Limit Threshold VCSSP - VCSSN CSSN Input Bias Current Adapter present 58.5 CSSP/CSSN Input-Voltage Range IINP Transconductance IINP Accuracy 60 61.5 mV -2.5 +2.5 % -0.1 +0.1 μA 8.0 26.0 V 2.94 μA/mV VCSSP - VCSSN = 60mV 2.66 VCSSP - VCSSN = 60mV, VIINP = 0V to 4.5V -2.5 2.8 +2.5 VCSSP - VCSSN = 35mV -2.5 +2.5 DCIN falling 7.9 % SUPPLY AND LINEAR REGULATOR DCIN Input Voltage Range DCIN Undervoltage-Lockout (UVLO) Trip-Point DCIN + CSSP + CSSN Quiescent Current BATT + CSIP + CSIN + LX Input Current 8 DCIN rising 26 8.1 8.7 8.9 V V Adapter present (Note 2) 3 6 mA Adapter absent (Note 2) 30 50 μA Adapter absent (Note 2) 10 20 Charger shutdown (Note 2) 10 20 VBATT = 16.8V VBATT = 2V to 19V, adapter present (Note 2) μA 200 500 5.35 5.55 V 100 200 mV 3.2 4.1 5.0 V 4.18 4.20 4.22 V 3.1 3.9 V 2.058 2.1 2.142 V ACIN Threshold Hysteresis 10 20 30 mV ACIN Input Bias Current -1 +1 μA LDO Output Voltage 8.0V < VDCIN < 26V, no load LDO Load Regulation 0 < ILDO < 40mA LDO UVLO Threshold 5.15 REFERENCES VAA Output Voltage I VAA = 50μA VAA UVLO Threshold VAA falling ACIN ACIN Threshold ACOK ACOK Sink Current V ACOK = 0.4V, VACIN = 1.5V ACOK Leakage Current V ACOK = 5.5V, VACIN = 2.5V 6 mA 1 μA _______________________________________________________________________________________ 3 MAX17005/MAX17006/MAX17015 ELECTRICAL CHARACTERISTICS (continued) MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.029 0.030 0.041 μs/V SWITCHING REGULATOR DHI Off-Time K Factor VDCIN = 19V, VBATT = 10V Sense Voltage for Minimum Discontinuous Mode Ripple Current VCSIP - VCSIN Zero-Crossing Comparator Threshold VCSIP - VCSIN Cycle-by-Cycle Current-Limit Sense Voltage VCSIP - VCSIN DHI Resistance High 10 mV 10 105 mV 110 115 mV IDLO = 10mA 1.5 3 DHI Resistance Low IDLO = -10mA 0.8 1.75 DLO Resistance High IDLO = 10mA 3 6 DLO Resistance Low IDLO = -10mA 3 7 ADAPTER DETECTION Adapter Absence-Detect Threshold VDCIN - VBATT, VDCIN falling +70 +120 +170 mV Adapter Detect Threshold VDCIN - VBATT, VDCIN rising +360 +420 +580 mV Hz Adapter Switch Charge-Pump Frequency Adapter Switch Charge-Pump Refresh Pulse Charger Shutdown 180 200 220 DLO 0.04 0.1 0.20 DHI 0.07 0.15 0.30 μs ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS CHARGE-VOLTAGE REGULATION 2 cells, V VCTL = GND (for MAX17006) Battery Regulation-Voltage Accuracy 8.366 8.433 12.549 12.651 4 cells, V VCTL = GND (for MAX17005) 16.73 16.86 FB accuracy using FB divider (for MAX17015) (Note 1) 2.091 2.108 0.0 VAA/2 - 0.2 VAA/2 + 0.2 VAA 5.85 6.15 3 cells, V VCTL = VAA (for MAX17005 and MAX17006) 2 cells (for MAX17006), 4 cells (for MAX17005) VCTL Range V 3 cells (for MAX17005 and MAX17006) VCTL Gain 4 V VCELL/VVCTL _______________________________________________________________________________________ V/V 1.2MHz Low-Cost, High-Performance Chargers (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS CHARGE-CURRENT REGULATION ISET Range Full Charge-Current Accuracy (CSIP to CSIN) 0.0 VAA/2 V 57.5 62.5 mV -4.2 +4.2 % 38 42 mV -5 +5 % 1.4 4.6 mV -52 +52 % -2 +2 % -1.4 +1.4 mV 0 24 V ISET falling 21 31 ISET rising 33 47 VISET = VAA/4 or ISET = 99.9% duty cycle V = VAA/6 or VBATT = 1V to 16.8V ISET ISET = 66.7% duty cycle VISET = VAA/80 or ISET = 5% duty cycle Trickle Charge-Current Accuracy Charge-Current Gain Error Charge-Current Offset Error Based on VISET = VVAA/4 and VISET = V VAA/80 Based on VISET = VVAA/4 and VISET = V VAA/80 BATT/CSIP/CSIN Input Voltage Range ISET Power-Down Mode Threshold ISET PWM Threshold Rising 2.4 Falling 0.8 ISET Frequency mV V 0.128 500 kHz 58.2 61.8 mV -3 +3 % -2 +2 μA 8.0 26.0 V μA/mV INPUT-CURRENT REGULATION Input Current-Limit Threshold VCSSP - VCSSN CSSN Input Bias Current Adapter present CSSP/CSSN Input-Voltage Range IINP Transconductance IINP Accuracy VCSSP - VCSSN = 60mV 2.66 2.94 VCSSP - VCSSN = 60mV, VIINP = 0V to 4.5V -2.5 +2.5 VCSSP - VCSSN = 35mV -2.5 +2.5 8 26 % SUPPLY AND LINEAR REGULATOR DCIN Input-Voltage Range DCIN UVLO Trip-Point DCIN + CSSP + CSSN Quiescent Current BATT + CSIP + CSIN + LX Input Current DCIN falling 7.9 DCIN rising 8.9 V Adapter present (Note 2) 6 mA Adapter absent (Note 2) 50 μA VBATT = 16.8V Adapter absent (Note 2) 20 Charger shutdown (Note 2) 20 VBATT = 2V to 19V, adapter present (Note 2) LDO Output Voltage 8.0V < VDCIN < 26V, no load LDO Load Regulation 0 < ILDO < 40mA LDO UVLO Threshold V μA 500 5.15 3.2 5.55 V 200 mV 5.0 V _______________________________________________________________________________________ 5 MAX17005/MAX17006/MAX17015 ELECTRICAL CHARACTERISTICS (continued) MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VDCIN = VCSSP = VCSSN = 19V, VBATT = VCSIP = VCSIN = 16.8V, VVCTL = VAA, VISET = 1V, TA = -40°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 4.22 V 3.9 V 2.058 2.142 V 10 30 mV REFERENCES VAA Output Voltage I VAA = 50μA VAA UVLO Threshold VAA falling 4.18 ACIN ACIN Threshold ACIN Threshold Hysteresis ACOK ACOK Sink Current V ACOK = 0.4V, VACIN = 1.5V 6 mA SWITCHING REGULATOR DHI Off-Time K Factor VDCIN = 19V, VBATT = 10V Cycle-by-Cycle Current-Limit Sense Voltage DHI Resistance High VCSIP - VCSIN IDLO = 10mA 0.029 0.041 μs/V 105 115 mV DHI Resistance Low IDLO = -10mA 1.75 3 DLO Resistance High IDLO = 10mA 6 DLO Resistance Low IDLO = -10mA 7 ADAPTER DETECTION Adapter Absence-Detect Threshold VDCIN - VBATT, VDCIN falling +70 +170 mV Adapter Detect Threshold VDCIN - VBATT, VDCIN rising +320 +620 mV 180 220 Hz DLO 0.04 0.2 DHI 0.07 0.3 Adapter Switch Charge-Pump Frequency Adapter Switch Charge-Pump Refresh Pulse Note 1: Accuracy does not include errors due to external resistance tolerances. Note 2: Adapter present conditions are tested at VDCIN = 19V and VBATT = 16.8V. Adapter absent conditions are tested at VDCIN = 16V, VBATT = 16.8V. 6 _______________________________________________________________________________________ μs 1.2MHz Low-Cost, High-Performance Chargers IINP ERROR vs. SYSTEM CURRENT 4 6 2 0 -2 4 VBATT = 16.8V 2 0 -2 -4 -4 -6 -6 -8 -8 2.5 2.0 1.5 1.0 0.5 -10 -10 2 3 4 0 0 5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 SYSTEM CURRENT (A) ISET PWM DUTY-CYCLE CHANGE 2.5 2.0 1.5 1.0 BATTERY VOLTAGE-SETTING ERROR MAX17005 toc05 3.0 CHARGE-CURRENT ERROR (%) 3.0 DUTY CYCLE ISET PWM FREQUENCY SWEEP MAX17005 toc04 3.5 2.5 2.0 DUTY CYCLE = 75% 1.5 DUTY CYCLE = 25% 1.0 0 0 -0.2 -0.3 -0.4 -0.6 0 10 20 30 40 50 60 70 80 90 100 -0.1 -0.5 0.5 0.5 0 0 100 200 300 400 500 600 700 800 DUTY CYCLE 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VCTL (V) FREQUENCY (kHz) EFFICIENCY vs. CHARGE CURRENT SYSTEM LOAD TRANSIENT MAX17005 toc07 95 SYSTEM CURRENT 5A/div CHARGING CURRENT 5A/div INDUCTOR CURRENT 5A/div MAX17005 toc08 100 90 EFFICIENCY (%) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 SYSTEM CURRENT (A) MAX17005 toc06 1 BATTERY VOLTAGE ERROR (%) 0 CHARGE CURRENT (A) VBATT = 8.4V VBATT = 12.6V 3.0 MAX17005 toc03 8 IINP ERROR (%) IINP ERROR (%) 6 MAX17005 toc02 8 ISET PWM DUTY-CYCLE CHANGE 10 MAX17005 toc01 10 CHARGE-CURRENT ERROR (%) IINP DC ERROR vs. SYSTEM CURRENT 2 CELLS 85 3 CELLS 80 4 CELLS 75 70 65 60 200μs/div 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 CHARGE CURRENT (A) _______________________________________________________________________________________ 7 MAX17005/MAX17006/MAX17015 Typical Operating Characteristics (Circuit of Figure 1, adapter = 19V, battery = 10V, ISET = 1.05V, VCTL = GND, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (Circuit of Figure 1, adapter = 19V, battery = 10V, ISET = 1.05V, VCTL = GND, TA = +25°C, unless otherwise noted.) 4.205 MAX17005 toc10 MAX17005 toc09 4.204 4.203 5.40 VAA VOLTAGE (V) 5.45 LDO VOLTAGE (V) 5.45 LDO VOLTAGE (V) VAA LOAD REGULATION LDO LINE REGULATION 5.50 MAX17005 toc11 LDO LOAD REGULATION 5.50 5.40 4.202 4.201 4.200 4.199 4.198 5.35 5.35 5.30 5.30 4.197 4.196 5 10 15 20 25 30 35 40 4.195 8 10 12 LDO CURRENT (mA) 14 16 18 20 22 24 0 26 0.4 1.4 4.1995 VAA (V) 4.1990 4.1985 4.1980 4.1975 5 SWITCHING FREQUENCY 4 1.0 3 0.8 0.6 2 HIGH-SIDE MOSFET OFF-TIME 0.4 1 0 -20 0 20 40 60 80 0 100 2 4 ADAPTER CURRENT vs. ADAPTER VOLTAGE 1.0 0.8 0.6 0.4 0.2 10 12 14 16 0 18 MAX17005 toc16 MAX17005 toc15 400 BATTERY LEAKAGE CURRENT (μA) 1.2 8 ADAPTER REMOVAL BATTERY LEAKAGE MAX17005 toc14 1.4 6 BATTERY VOLTAGE (V) TEMPERATURE (°C) 1.6 350 300 250 200 5.00V 5.00V 150 5.00V 100 50 0 0 0 5 10 15 ADAPTER VOLTAGE (V) 20 1.0 6 1.2 0.2 4.1970 -40 0.8 VIN = 20V SWITCHING FREQUENCY (MHz) 4.2000 MAX17005 toc13 1.6 MAX17005 toc12 4.2005 4.1965 -60 0.6 LOAD CURRENT (mA) HIGH-SIDE MOSFET OFF-TIME AND SWITCHING FREQUENCY vs. BATTERY VOLTAGE VAA vs. TEMPERATURE 8 0.2 INPUT VOLTAGE (V) HIGH-SIDE MOSFTE OFF-TIME (μs) 0 ADAPTER CURRENT (mA) MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers 0 2 4 6 8 10 12 14 16 18 20 200ms/div BATTERY VOLTAGE (V) _______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers PIN NAME 1 DCIN Charger Bias Supply Input. Bypass DCIN with a 1μF capacitor to PGND. FUNCTION 2 AGND Analog Ground 3 CSIP Output Current-Sense Positive Input. Connect a current-sense resistor from CSIP to CSIN. 4 CSIN Output Current-Sense Negative Input 5 IINP Input Current-Monitor Output. IINP sources the current proportional to the current sensed across CSSP and CSSN. The transconductance from (CSSP - CSSN) to IINP is 2.8μA/mV. See the Analog Input Current-Monitor Output section to configure the current monitor for a particular gain setting. 6 BATT Battery Voltage Feedback Input 7 ACOK AC Detect Output. This open-drain output is high impedance when ACIN is lower than VAA/2. Connect a 10k pullup resistor from LDO to ACOK. 8 CSSP Input Current Sense for Positive Input. Connect a current-sense resistor from CSSP to CSSN. 9 CSSN Input Current-Sense Negative Input Dual Mode™ Input for Setting Maximum Charge Current. ISET can be configured either with a resistor voltage-divider or with a PWM signal from 128Hz to 500kHz. If there is no clock edge within 20ms, ISET defaults to analog input mode. Pull ISET to GND to shut down the charger. 10 ISET In the MAX17015, when the adapter is absent, drive ISET above 1V to enable IINP during battery discharge. When the adapter is reinserted, ISET must be released to the correct control level within 300ms. 11 PGND 12 DLO Power Ground Connection for MOSFET Drivers Low-Side Power-MOSFET Driver Output. Connect to low-side n-channel MOSFET gate. 13 LDO Linear Regulator Output. LDO provides the power to the MOSFET drivers. LDO is the output of the 5.4V linear regulator supplied from DCIN. Bypass LDO with a 4.7μF ceramic capacitor from LDO to PGND. 14 BST High-Side Driver Supply. Connect a 0.68μF capacitor from BST to LX. 15 DHI High-Side Power-MOSFET Driver Output. Connect to high-side n-channel MOSFET gate. 16 LX 17 ACIN High-Side Driver Source Connection. Connect a 0.68μF capacitor from BST to LX. 18 VAA 4.2V Voltage Reference and Device Power-Supply Input. Bypass VAA with a 1μF capacitor to GND. 19 CC Voltage Regulation Loop-Compensation Point. Connect 3k and 0.01μF capacitor in series from CC to GND. 20 VCTL Battery Voltage Adjust Input. VCTL sets the number of cells and adjusts the voltage per cell. The adjustment range is 4.2V to 4.4V per cell. See the Setting Charge Voltage section. — BP AC Adapter Detect Input. ACIN is the input to an uncommitted comparator. Backside Paddle. Connect the backside paddle to analog ground. Dual Mode is a trademark of Maxim Integrated Products, Inc. _______________________________________________________________________________________ 9 MAX17005/MAX17006/MAX17015 Pin Description MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers SYSTEM LOAD RS1 15mΩ Q1a Q1b ADAPTER N3 R9 2MΩ C7 0.1μF C6 1μF CIN R4 200kΩ RACIN1 ADAPTER N4 R6 200kΩ D1 DCIN BATT CSSP CSSN BST C4 0.68μF ACIN LDO 10kΩ DHI N1 ACOK CIN = 2 x 4.7μF COUT = 4.7μF L1 = 2μH LX RACIN2 IINP N2 DLO C2 0.1μF R1 22.6kΩ L1 PGND CSIP VAA C3 1μF R2 GND MAX17005 MAX17006 MAX17015 RS2 10mΩ CSIN COUT R3 VCTL BATTERY BATT R5 3kΩ ISET PWM SIGNAL CC R7 R8 C5 0.01μF LDO C1 4.7μF ONLY FOR MAX17015 Figure 1. Typical Operating Circuit Detailed Description The MAX17005/MAX17006/MAX17015 include all the functions necessary to charge Li+, NiMH, and NiCd batteries. An all n-channel synchronous-rectified stepdown DC-DC converter is used to implement a precision constant-current, constant-voltage charger. The charge current and input current-limit sense amplifiers have low-input offset errors (250μV typ), allowing the use of small-valued sense resistors. 10 The MAX17005/MAX17006/MAX17015 use a new thermally optimized high-frequency architecture. With this new architecture, the switching frequency is adjusted to control the power dissipation in the high-side MOSFET. Benefits of the new architecture include: reduced output capacitance and inductance, resulting in smaller printed-circuit board (PCB) area and lower cost. ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers ACOK CSSP LDO CSA A = 17.5V/V Gm = 2.8μA/mV CSSN DCIN BATT VAA/2 4.2V REFERENCE GMS VAA VCTL + 100mV 60mV GND BDIV POWER FAIL CC BATT CELL SELECT LOGIC 10mV LDO OVP BDIV GMV 5.4V LINEAR REGULATOR IMIN LOWEST VOLTAGE CLAMP BST DC-DC CONVERTER VCTL LEVEL SHIFT HIGH-SIDE DRIVER DHI LX CCMP CSI VAA LDO CSIP CSA A = 17.5V/V 110mV GMI CSIN PWM FILTER LOW-SIDE DRIVER IMAX IZX DLO PGND 26mV CHARGER 10mV SHUTDOWN ISET MAX17005 MAX17006 MAX17015 Figure 2. Functional Diagram The MAX17005/MAX17006/MAX17015 feature a voltage-regulation loop (CCV) and two current-regulation loops (CCI and CCS). The loops operate independently of each other. The CCV voltage-regulation loop monitors BATT to ensure that its voltage never exceeds the voltage set by VCTL. The CCI battery charge currentregulation loop monitors current delivered to BATT to ensure that it never exceeds the current limit set by ISET. The charge current-regulation loop is in control as long as the battery voltage is below the set point. When the battery voltage reaches its set point, the voltage- regulation loop takes control and maintains the battery voltage at the set point. A third loop (CCS) takes control and reduces the charge current when the adapter current exceeds the input current limit. The MAX17005/MAX17006/MAX17015 have singlepoint compensation. The two current loops are internally compensated while the voltage loop is compensated with a series RC network at CC pin. See the CC Loop Compensation section for the resistor and capacitor selection. A functional diagram is shown in Figure 2. ______________________________________________________________________________________ 11 MAX17005/MAX17006/MAX17015 IINP ACIN MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers Setting Charge Voltage The VCTL input adjusts the battery-output voltage, VBATT, and determines the number of cells. For 3- and 4-cell applications, use the MAX17005; for 2- and 3-cell applications, use the MAX17006. Use the MAX17015 to adjust the cell number and set the cell voltage with a resistive voltage-divider from the output. Based on the version of the part, the number of cells and the level of VCTL should be set as in Table 1: Setting Charge Current Table 1. Cell Configuration VERSION NO. OF CELLS LEVEL MAX17005 3 2.4V < VCTL < 4.2V MAX17005 4 0V < VCTL < 1.8V MAX17006 2 0V < VCTL < 1.8V MAX17006 3 2.4V < VCTL < 4.2V MAX17015 Sets FB VCTL = GND or VCTL = VAA The MAX17005 and MAX17006 support from 4.2V/cell to 4.4V/cell, whereas the MAX17015 supports minimum 2.1V. The maximum voltage is determined with the dropout performance of IC. When the required voltage falls outside the range available with the MAX17005 or MAX17006, the MAX17015 should be used. The charge-voltage regulation for the MAX17005 and MAX17006 is calculated with the following equations: VCELL = 4.2V + There are two constraints in choosing R7 and R8. The resistors cannot be too small since they discharge the battery, and they cannot be too large because FB pin consumes less than 1μA of input bias current. Pick R8 to be approximately 10kΩ and then calculate R7. FB regulation error (±0.5% max) and the tolerance of R7 and R8 both contribute to the error on the battery voltage. Use 0.1% feedback resistors for best accuracy. 4.2V − VVCTL 6 The voltage at ISET determines the voltage across current-sense resistor RS2. ISET can accept either analog or digital inputs. The full-scale differential voltage between CSIP and CSIN is 80mV (8A for RS2 = 10mΩ) for the analog input, and 60mV (6A for RS2 = 10mΩ) for the digital PWM input. When the MAX17005/MAX17006/MAX17015 power up and the charger is ready, if there is no clock edge within 20ms, the circuit assumes ISET is an analog input, and disables the PWM filter block. To configure the charge current, force the voltage on ISET according to the following equation: ICHG = 240mV VISET × RS2 VAA The input range for ISET is from 0 to VAA/2. To shut down the charger, pull ISET below 26mV. If there is a clock edge on ISET within 20ms, the PWM filter is enabled and ISET accepts digital PWM input. The PWM filter has a DAC with 8-bit resolution that corresponds to equivalent VCSIP-CSIN steps. for 3-cell selection of MAX17005 and MAX17006, 4.2V > VCTL > 2.4V: V VCELL = 4.2V + VCTL 6 CSIN for 2- or 4-cell selection of MAX17006 or MAX17005, respectively, 0V < VCTL < 1.8V. Connect VCTL to GND or to VAA for default 4.2V/cell battery-voltage setting. For the MAX17015, connect VCTL to GND to set the FB regulation point to 2.1V. The charge-voltage regulation is calculated with the following equation: COUT MAX17015 R7 BATTERY FB R8 VCHG _ REG = VFB _ SETPOINT × R8 + R7 R8 Figure 3. MAX17015 Charge-Voltage Regulation Feedback Network 12 ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers Setting Input-Current Limit The total input current, from a wall adapter or other DC source, is the sum of the system supply current and the current required by the charger. When the input current exceeds the set input-current limit, the controller decreases the charge current to provide priority to system load current. System current normally fluctuates as portions of the system are powered up or down. The input-current-limit circuit reduces the power requirement of the AC wall adapter, which reduces adapter cost. As the system supply rises, the available charge current drops linearly to zero. Thereafter, the total input current can increase without limit. The total input current is the sum of the device supply current, the charger input current, and the system load current. The total input current can be estimated as follows: I × VBATTERY IINPUT = ILOAD + CHARGE VIN × η where η is the efficiency of the DC-to-DC converter (typically 85% to 95%). In the MAX17005/MAX17006/MAX17015, the voltage across CSSP and CSSN is constant at 60mV. Choose the current-sense resistor, RS1, to set the input current limit. For example, for 4A input current limit, choose RS1 = 15mΩ. For the input current-limit settings, which cannot be achievable with standard sense resistor values, use a resistive voltage-divider between CSSP and CSSN to tune the setting (Figure 4). RS1 Rb Ra CSSP IINPUT _ LIMIT = 60mV Rb × (1 + ) RS1 Ra To minimize power dissipation, first choose RS1 according to the closest available value. For convenience, choose Ra = 6kΩ and calculate Rb from the above equation. Choose a current-sense resistor (RS1) to have a sufficient power rating to handle the full system current. The current-sense resistor can be reduced to improve efficiency, but this degrades accuracy due to the currentsense amplifier’s input offset (0.15mV typ). See Typical Operating Characteristics to estimate the input currentlimit accuracy at various set points. Automatic Power-Source Selection The MAX17005/MAX17006/MAX17015 use an external charge pump to drive the gate of an n-channel adapter selection switch (N3 and Q1a). In Figure 1, when the adapter is present, BST is biased 5V above VADAPTER so that N3 and Q1a are on, and Q1b is off. As long as the adapter is present, even though the charger is off, the power stage forces a refresh pulse to the BST charge pump every 5ms. When the adapter voltage is removed, the charger stops generating BST refresh pulses and N4 forces N2 off, Q1b turns on and supplies power to the system from the battery. In Figure 1, D1 must have low forward-voltage drop and low reverse-leakage current to ensure sufficient gate drive at N3 and Q1a. A 100mA, low reverse-leakage Schottky diode is the right choice. Analog Input Current-Monitor Output Use IINP to monitor the system-input current, which is sensed across CSSP and CSSN. The voltage at IINP is proportional to the input current: IINPUT = VIINP RS1 × GIINP × RIINP where I INPUT is the DC current supplied by the AC adapter, GIINP is the transconductance of the sense amplifier (2.8 mA/V typ), and RIINP is the resistor connected between IINP and ground. Typically, IINP has a 0V to 3.5V output voltage range. Leave IINP unconnected when not used. CSSN MAX17005/MAX17006/MAX17015 Figure 4. Input Current-Limit Fine Tuning ______________________________________________________________________________________ 13 MAX17005/MAX17006/MAX17015 The PWM filter accepts the digital signal with a frequency from 128Hz to 500kHz. Zero duty cycle shuts down the MAX17005/MAX17006/MAX17015, and 99.5% duty cycle corresponds to full scale (60mV) across CSIP and CSIN. Choose a current-sense resistor (RS2) to have a sufficient power-dissipation rating to handle the full-charge current. The current-sense voltage can be reduced to minimize the power-dissipation period. However, this can degrade accuracy due to the current-sense amplifier’s input offset (0.25mV typ). See Typical Operating Characteristics to estimate the charge-current accuracy at various set points. MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers Operating Conditions RS1 15mΩ Q1a The MAX17005/MAX17006/MAX17015 have the following operating states: SYSTEM LOAD • CIN C7 10nF ADAPTER Q1b R6 50kΩ a) Charging: The total MAX17005/MAX17006/ MAX17015 quiescent current when charging is 3mA (max) plus the current required to drive the MOSFETs. BATTERY D1 CSSP CSSN b) Not Charging: To disable charging drive ISET below 26mV. When the adapter is present and charging is disabled, the total adapter quiescent current is less than 1.5mA and the total battery quiescent current is less than 60μA. The charge pump still operates. BST C4 0.1μF MAX17015 DHI N1 LX • Figure 5. Current-Monitoring Design Battery Discharge IINP can also be used to monitor battery discharge current (see Figure 5). In the MAX17015, when the adapter is absent, drive ISET above 1V to enable IINP during battery discharge. When the adapter is reinserted, ISET must be released to the correct control level within 300ms. AC Adapter Detection The MAX17005/MAX17006/MAX17015 include a hysteretic comparator that detects the presence of an AC power adapter. When ACIN is lower than 2.1V, the open-drain ACOK output becomes high impedance. Connect a 10kΩ pullup resistance between LDO and ACOK. Use a resistive voltage-divider from the adapter’s output to the ACIN pin to set the appropriate detection threshold. Select the resistive voltage-divider so that the voltage on ACIN does not to exceed its absolute maximum rating (6V). LDO Regulator and VAA An integrated low-dropout (LDO) linear regulator provides a 5.4V supply derived from DCIN, and delivers over 40mA of load current. Do not use the LDO to external loads greater than 10mA. The LDO powers the gate drivers of the n-channel MOSFETs. See the MOSFET Drivers section. Bypass LDO to PGND with a 4.7μF ceramic capacitor. VAA is 4.2V reference supplied by DCIN. VAA biases most of the control circuitry, and should be bypassed to GND with a 1μF or greater ceramic capacitor. 14 Adapter Present: When DCIN is greater than 8.7V, the controller detects the adapter. In this condition, both the LDO and VAA turn on and battery charging is allowed: Adapter Absent (Power Fail): When VDCIN is less than VCSIN + 120mV, the DC-DC converter is in dropout. The charger detects the dropout condition and shuts down. The MAX17005/MAX17006/MAX17015 allow charging under the following conditions: • DCIN > 7.5V, LDO > 4V, VAA > 3.1V • VDCIN > VCSIN + 420mV (300mV falling hysteresis) • VISET > 45mV or PWM detected ____________________DC-DC Converter The MAX17005/MAX17006/MAX17015 employ a synchronous step-down DC-DC converter with an n-channel high-side MOSFET switch and an n-channel low-side synchronous rectifier. The charger features a controlled inductor current-ripple architecture, currentmode control scheme with cycle-by-cycle current limit. The controller’s off-time (tOFF) is adjusted to keep the high-side MOSFET junction temperature constant. In this way, the controller switches faster when the highside MOSFET has available thermal capacity. This allows the inductor current ripple and the output-voltage ripple to decrease so that smaller and cheaper components can be used. The controller can also operate in discontinuous conduction mode for improved light-load efficiency. ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers MAX17005/MAX17006/MAX17015 BDIV OVP SET POINT + 100mV CSI IMAX 11A Q R DH DRIVER CCMP LVC IMIN S Q DL DRIVER 1A ZCMP 1A CSSP CSIN OFF-TIME ONE SHOT OFF-TIME COMPUTE Figure 6. DC-DC Converter Functional Diagram The operation of the DC-to-DC controller is determined by the following five comparators as shown in the functional diagram in Figures 2 and 6: • The IMIN comparator triggers a pulse in discontinuous mode when the accumulated error is too high. IMIN compares the control signal (LVC) against 10mV (referred at VCSIP - VCSIN). When LVC is less than this threshold, DHI and DLO are both forced low. Indirectly, IMIN sets the peak inductor current in discontinuous mode. • The ZCMP comparator provides zero-crossing detection during discontinuous conduction. ZCMP compares the current-sense feedback signal to 1A (RS2 = 10mΩ). When the inductor current is lower than the 1A threshold, the comparator output is high, and DLO is turned off. • The CCMP comparator is used for current-mode regulation in continuous-conduction mode. CCMP compares LVC against the inductor current. The high-side MOSFET on-time is terminated when the CSI voltage is higher than LVC. • • The IMAX comparator provides a secondary cycleby-cycle current limit. IMAX compares CSI to 110mV (corresponding to 11A when RS2 = 10mΩ). The high-side MOSFET on-time is terminated when the current-sense signal exceeds 11A. A new cycle cannot start until the IMAX comparator’s output goes low. The OVP comparator is used to prevent overvoltage at the output due to battery removal. OVP compares BATT against the VCTL. When BATT is 100mV/cell above the set value, the OVP comparator output goes high, and the high-side MOSFET on-time is terminated. DHI and DLO remain off until the OVP condition is removed. ______________________________________________________________________________________ 15 MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers CC, CCI, CCS, and LVC Control Blocks The MAX17005/MAX17006/MAX17015 control input current (CCS control loop), charge current (CCI control loop), or charge voltage (CC control loop), depending on the operating condition. The three control loops, CC, CCI, and CCS are brought together internally at the lowest voltage clamp (LVC) amplifier. The output of the LVC amplifier is the feedback control signal for the DC-DC controller. The minimum voltage at the CC, CCI, or CCS appears at the output of the LVC amplifier and clamps the other control loops to within 0.3V above the control point. Clamping the other two control loops close to the lowest control loop ensures fast transition with minimal overshoot when switching between different control loops (see the Compensation section). The CCS and CCI loops are compensated internally, and the CC loop is compensated externally. Continuous-Conduction Mode With sufficiently large charge current, the MAX17005/ MAX17006/MAX17015s’ inductor current never crosses zero, which is defined as continuous-conduction mode. The controller starts a new cycle by turning on the highside MOSFET and turning off the low-side 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 VCSIN and VDCIN. The on-time can be determined using the following equation: L × IRIPPLE tON = VDCIN − VBATT where: V ×t IRIPPLE = BATT OFF L The switching frequency can then be calculated: fSW = 16 At the end of the computed off-time, the controller initiates a new cycle if the control point (LVC) is greater than 10mV (VCSIP - VCSIN referred), and the charge current is less than the cycle-by-cycle current limit. Restated another way, IMIN must be high, IMAX must be low, and OVP must be low for the controller to initiate a new cycle. If the peak inductor current exceeds IMAX comparator threshold or the output voltage exceeds the OVP threshold, then the on-time is terminated. The cycle-by-cycle current limit effectively protects against overcurrent and short-circuit faults. If during the off-time the inductor current goes to zero, the ZCMP comparator output pulls high, turning off the low-side MOSFET. Both the high- and low-side MOSFETs are turned off until another cycle is ready to begin. ZCOMP causes the MAX17005/MAX17006/ MAX17015 to enter into the discontinuous conduction mode (see the Discontinuous Conduction section). Discontinuous Conduction The MAX17005/MAX17006/MAX17015 can also operate in discontinuous conduction mode to ensure that the inductor current is always positive. The MAX17005/ MAX17006/MAX17015 enter discontinuous conduction mode when the output of the LVC control point falls below 10mV (referred at VCSIP - VCSIN). For RS2 = 10mΩ, this corresponds to a peak inductor current of 1A. In discontinuous mode, a new cycle is not started until the LVC voltage rises above IMIN. Discontinuous mode operation can occur during conditioning charge of overdischarged battery packs, when the charge current has been reduced sufficiently by the CCS control loop, or when the charger is in constant-voltage mode with a nearly full battery pack. Compensation The charge voltage, charge current, and input currentlimit regulation loops are compensated separately. The charge current and input current-limit loops, CCI and CCS, are compensated internally, whereas the charge voltage loop is compensated externally at CC. 1 tON + tOFF ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers BATT GMOUT RESR RL COUT GMOUT = 1 ACSI × RS2 where ACSI = 20, and RS2 = 10mΩ in the typical application circuits, so GMOUT = 5A/V. The loop transfer function is given by: LTF = GMOUT × RL × GMV × ROGMV × (1 + sCOUT × RESR )(1 + sCCC × RCC ) (1 + sCCC × ROGMV )(1 + sCOUT × RL ) The poles and zeros of the voltage-loop transfer function are listed from lowest frequency to highest frequency in Table 2. Near crossover, CCC is much lower impedance than ROGMV. Since CCC is in parallel with ROGMV, CCC dominates the parallel impedance near crossover. Additionally, RCC is much higher impedance than CCC and dominates the series combination of RCC and CCC, so: ROGMV × (1 + sCCC × RCC ) ≅ RCC (1 + sCCC × ROGMV ) C OUT is also much lower impedance than R L near crossover so the parallel impedance is mostly capacitive and: CC GMV RCC ROGMV CCC VCTL RL 1 ≅ (1 + sCOUT × RL ) sCOUT Figure 7. CC Loop Diagram Table 2. CC Loop Poles and Zeros NAME CCV Pole EQUATION fP _ CV = 1 2πROGMV × CCC 1 CCV Zero fZ _ CV = Output Pole fP _ OUT = Output Zero fZ _ OUT = 2πRCC × CCC 1 2πRL × COUT 1 2πRESR × COUT DESCRIPTION Lowest frequency pole created by CCV and GMV’s finite output resistance. Voltage-loop compensation zero. If this zero is at the same frequency or lower than output pole f P_OUT, the loop-transfer function approximates a single-pole response near the crossover frequency. Choose CCV to place this zero at least one decade below crossover to ensure adequate phase margin. Output pole formed with the effective load resistance RL and the output capacitance C OUT. 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 f Z_OUT is less than the desired crossover frequency; therefore, choose a capacitor with an ESR zero greater than the crossover frequency. ______________________________________________________________________________________ 17 MAX17005/MAX17006/MAX17015 CC Loop Compensation The simplified schematic in Figure 7 is sufficient to describe the operation of the controller’s voltage loop, CC. The required compensation network is a pole-zero pair formed with CCC and RCC. 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 = ΔVBATT/ ΔICHG. The equivalent output impedance of the GMV amplifier, ROGMV, is greater than 10MΩ. The voltageamplifier transconductance, GMV = 0.125μA/mV. The DC-DC converter transconductance is dependent upon charge current-sense resistor RS2: If RESR is small enough, its associated output zero has a negligible effect near crossover and the loop-transferfunction can be simplified as follows: LTF = GMOUT × RCC G sCOUT MV Setting LTF = 1 to solve for the unity-gain frequency yields: RCC fCO _ CV = GMOUT × GMV × 2π × COUT For stability, choose a crossover frequency lower than 1/10 the switching frequency (f OSC) . For example, choose a crossover frequency of 50kHz and solve for RCC using the component values listed in Figure 1 to yield RCC = 3kΩ: RCC = 2π × COUT × fCO _ CV GMV × GMOUT ≅ 3kΩ GMV = 0.125μA/mV GMOUT = 5A/V COUT = 4.7μF fOSC_CV = 600kHz RL = 0.2Ω fCO_CV = 50kHz To ensure that the compensation zero adequately cancels the output pole, select fZ_CV ≤ fP_OUT: CCC ≥ (RL/RCC) x COUT C CC ≥ 300pF (assuming 2 cells and 2A maximum charge current). Figure 8 shows the Bode plot of the voltage-loopfrequency 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 highsides 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 MAX17005/MAX17006 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 fewer (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. The high-side driver (DHI) swings from LX to 5V above LX (BST) and has a typical impedance of 1.5Ω sourcing and 0.8Ω sinking. The strong high-side MOSFET driver eliminates most of the power dissipation due to switching losses. The low-side driver (DLO) swings from LDO to ground and has a typical impedance of 3Ω sinking and 3Ω 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 80 0 MOSFET Selection -45 40 20 -90 0 -20 -40 1 10 Choose the n-channel MOSFETs according to the maximum required charge current. The MOSFETs must be able to dissipate the resistive losses plus the switching losses at both VDCIN(MIN) and VDCIN(MAX). For the high-side MOSFET, the worst-case resistive power losses occur at the maximum battery voltage and minimum supply voltage: PDCOND (HighSide) = MAG PHASE 0.1 PHASE (DEGREES) 60 MAGNITUDE (dB) MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers 100 1k 10k 100k VBATT(MAX) VDCIN(MIN) × ICHG2 × RDS(ON) -135 1M FREQUENCY (Hz) Figure 8. CC Loop Response 18 ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers 1 PDSW (HS) = × t TRANS × VCSSP × ICHG × fSW 2 where tTRANS is the drivers transition time and can be calculated as follows: ⎛ 1 1 ⎞ t TRANS = ⎜ + × ( QGD + QGS ) ⎝ IGSRC IGSNK ⎟⎠ IGSRC and IGSNK are the peak gate-drive source/sink current (3Ω sourcing and 0.8Ω sinking, typically). The MAX17005/MAX17006/MAX17015 control the switching frequency as shown in the Typical Operating Characteristics. The following is the power dissipated due to high-side n-channel MOSFET’s output capacitance (CRSS): PDCRSS (HS) ≈ V 2CSSP × CRSS × fSW 2 The following high-side MOSFET’s loss is due to the reverse-recovery charge of the low-side MOSFET’s body diode: PDQRR (HS) = QRR2 × VCSSP × fSW 2 Ignore PDQRR(HighSide) if a Schottky diode is used parallel to a low-side MOSFET. The total high-side MOSFET power dissipation is: Switching losses in the high-side MOSFET can become an insidious heat problem when maximum AC adapter voltages are applied. If the high-side MOSFET chosen for adequate RDS(ON) at low-battery voltages becomes hot when biased from VDCIN(MAX), consider choosing another MOSFET with lower parasitic capacitance. For the low-side MOSFET (N2), the worst-case power dissipation always occurs at maximum input voltage: ⎛ VBATT(MIN) ⎞ 2 PDCOND (LS) = ⎜ 1 − ⎟ × ICHG × RDS(ON) ⎝ VCSSP(MAX) ⎠ The following additional loss occurs in the low-side MOSFET due to the body diode conduction losses: PDBDY (LS) = 0.05 × IPEAK × 0.4V The total power low-side MOSFET dissipation is: PDTOTAL (LS) ≈ PDCOND (LS) + PDBDY (LS) These calculations provide an estimate and are not a substitute for breadboard evaluation, preferably including a verification using a thermocouple mounted on the MOSFET. Inductor Selection The selection of the inductor has multiple trade-offs between efficiency, transient response, size, and cost. Small inductance is cheap and small, and has a better transient response due to higher slew rate; however, the efficiency is lower because of higher RMS current. High inductance results in lower ripple so that the need of the output capacitors for output voltage ripple goes low. The MAX17005/MAX17006/MAX17015 combine all the inductor trade-offs in an optimum way by controlling switching frequency. High-frequency operation permits the use of a smaller and cheaper inductor, and consequently results in smaller output ripple and better transient response. 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= k × VIN2 4 × ICHG × LIRMAX where k = 35ns/V. PDTOTAL (HS) ≈ PDCOND (HS) + PDSW (HS) + PDCRSS (HS) + PDQRR (HS) ______________________________________________________________________________________ 19 MAX17005/MAX17006/MAX17015 Generally, a low gate charge high-side MOSFET is preferred to minimize switching losses. However, the RDS(ON) required to stay within package power dissipation often limits how small the MOSFET can be. The optimum occurs when the switching losses equal the conduction losses. High-side switching losses do not usually become an issue until the input is greater than approximately 15V. Calculating the power dissipation in N1 due to switching losses is difficult since it must allow for difficult quantifying factors that influence the turn-on and turn-off times. These factors include the internal gate resistance, gate charge, threshold voltage, source inductance, and PCB 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 N1: MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers For optimum size and inductor current ripple, choose LIRMAX = 0.4, which sets the ripple current to 40% the charge current and results in a good balance between inductor size and efficiency. Higher inductor values decrease the ripple current. Smaller inductor values save cost but require higher saturation current capabilities and degrade efficiency. Inductor L1 must have a saturation current rating of at least the maximum charge current plus 1/2 the ripple current (ΔIL): ISAT = ICHG + (1/2) ΔIL The ripple current is determined by: ΔIL = k × VIN2 4L 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 and surge currents: ⎛ V ⎞ BATT × ( VDCIN − VBATT ) ⎟ IRMS = ICHG × ⎜ VDCIN ⎜⎝ ⎟⎠ The input capacitors should be sized so that the temperature rise due to ripple current in continuous conduction does not exceed approximately 10°C. 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 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-to-DC converter (see the Compensation section.) Beyond the stability requirements, it is often sufficient to make sure that the output capacitor’s ESR is 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. Choose the output capacitor based on: COUT = 20 IRIPPLE × kCAP − BIAS fSW × 8 × ΔVBATT Choose kCAP-BIAS is a derating factor of 2 for typical 25Vrated ceramic capacitors. For fSW = 800kHz, IRIPPLE = 1A, and to get ΔVBATT = 70mV, choose COUT as 4.7μF. If the internal resistance of battery is close to the ESR of the output capacitor, the voltage ripple is shared with the battery and is less than calculated. Applications Information Setting Input Current Limit The input current limit should be set based on the current capability of the AC adapter and the tolerance of the input current limit. The upper limit of the input current threshold should never exceed the adapter’s minimum available output current. For example, if the adapter’s output current rating is 5A ±10%, the input current limit should be selected so that its upper limit is less than 5A × 0.9 = 4.5A. Since the input current-limit accuracy of the MAX17005/MAX17006/MAX17015 is ±3%, the typical value of the input current limit should be set at 4.5A/1.03 ≈ 4.36A. The lower limit for input current must also be considered. For chargers at the low end of the spec, the input current limit for this example could be 4.36A × 0.95 or approximately 4.14A. Layout and Bypassing Bypass DCIN with a 0.1μF ceramic to ground (Figure 1). N1 and N2 protect the MAX17005/MAX17006/ MAX17015 when the DC power source input is reversed. Bypass VAA, CSSP, and LDO as shown in Figure 1. Good PCB layout is required to achieve specified noise immunity, efficiency, and stable performance. The PCB layout designer must be given explicit instructions— preferably, a sketch showing the placement of the power switching components and high current routing. Refer to the PCB layout in the MAX17005/MAX17006/ MAX17015 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 an uninterrupted ground plane. Use the following step-by-step guide: 1) Place the high-power connections first, with their grounds adjacent: a) Minimize the current-sense resistor trace lengths, and ensure accurate current sensing with Kelvin connections. b) Minimize ground trace lengths in the high-current paths. ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers d) Use > 5mm wide traces in the high-current paths. e) Connect CIN to high-side MOSFET (10mm max length). f) Minimize the LX node (MOSFETs, rectifier cathode, inductor (15mm max length)). Keep LX on one side of the PCB to reduce EMI radiation. 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 PCB 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 VAA capacitor). Important: the IC must be no further than 10mm from the current-sense resistors. Quiet connections to VAA and CC should be returned to a separate ground (GND) island. 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 V AA . 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. ______________________________________________________________________________________ 21 MAX17005/MAX17006/MAX17015 c) Minimize other trace lengths in the high-current paths. 1.2MHz Low-Cost, High-Performance Chargers MAX17005/MAX17006/MAX17015 Minimal Operating Circuit SYSTEM ADAPTER ADAPTER DCIN CSSP CSSN BST BATT DHI LDO LX DLO VAA PGND GND IINP MAX17005 MAX17006 MAX17015 CSIP CSIN VCTL BATTERY BATT CC ISET ACOK BST LDO DLO PGND TOP VIEW DHI Pin Configuration 15 14 13 12 11 10 ISET ACIN 17 9 CSSN 8 CSSP 7 ACOK 6 BATT MAX17005 MAX17006 MAX17015 CC 19 2 3 4 5 CSIP CSIN IINP DCIN 1 AGND EXPOSED PADDLE VCTL 20 Chip Information TRANSISTOR COUNT: 12,990 PROCESS: BiCMOS LX 16 VAA 18 ACIN THIN QFN 4mm x 4mm 22 ______________________________________________________________________________________ 1.2MHz Low-Cost, High-Performance Chargers 24L QFN THIN.EPS ______________________________________________________________________________________ 23 MAX17005/MAX17006/MAX17015 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.) MAX17005/MAX17006/MAX17015 1.2MHz Low-Cost, High-Performance Chargers 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.) 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. 24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.