19-3450; Rev 1; 5/05 KIT ATION EVALU LE B A IL A AV Complete Backup-Management ICs for Lithium and NiMH Batteries The MAX8568A/MAX8568B backup-battery-management ICs are complete charging and backup switchover control solutions for PDAs, Smart Phones, and other smart portable devices. They charge both NiMH and rechargeable lithium battery types and feature programmable charge current and termination voltage. Separate optimized charge algorithms for both lithium and NiMH cells are included on-chip. The MAX8568A/MAX8568B also manage backup switchover from a primary power source. An accurate onchip voltage detector monitors the main supply and backs up two system supplies (typically I/O and memory) when main power falls. On-chip drivers switch external MOSFETs to disconnect the main supply from the system loads so the backup source is not drained. Low-voltage backup cells can be stepped up by an onchip synchronous-rectified, low-quiescent-current boost converter. Additionally, a low-quiescent-current LDO generates a second backup voltage. The MAX8568A LDO is preset to 2.5V while the MAX8568B LDO is preset to 1.8V. Both devices are supplied in 16-pin 3mm x 3mm thin QFN packages rated for -40°C to +85°C operation. Features ♦ Automatically Manage All Backup Switchover Functions ♦ Charge Both NiMH and Rechargeable Lithium Backup Batteries ♦ On-Chip Battery Boost Converter for 1-Cell NiMH ♦ Two Backup Output Voltages ♦ Programmable Charge Current ♦ Programmable Charge Voltage Limit ♦ Low 17µA Operating Current in Backup Mode ♦ Eliminate Many Discrete Components ♦ Tiny 3mm x 3mm Thin QFN Package Ordering Information PART TEMP RANGE PINPACKAGE MAX8568AETE -40°C to +85°C 16 Thin QFN 3mm x 3mm (T1633-4) ACK MAX8568BETE -40°C to +85°C 16 Thin QFN 3mm x 3mm (T1633-4) ACL Applications PDAs and PDA Phones Smart Phones TOP MARK DSCs and DVCs Palmtops and Wireless Handhelds Typical Operating Circuit Internet Appliances and Web-Books MAIN BATTERY 2.8V TO 5.5V INOK BKV NI/LI TOP VIEW CHGI Pin Configuration 12 11 10 9 GND 13 8 OD2 STRTV 14 7 OD1 6 LDO 5 BKSU TERMV 15 REF 16 BK MAX8568A MAX8568B TERMV I/O OUT 3.3V, 50mA MAX8568A MAX8568B REF IN BACKUP BATTERY LX STRTV BKSU IN I/O IN MEM OUT 1.8V OR 2.5V, 10mA PGND GND BKV INOK OD1 CHGI 2 3 4 PGND LX IN 1 BK LDO THIN QFN MEM IN NI OD2 NI/LI LI ________________________________________________________________ Maxim Integrated Products 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. 1 MAX8568A/MAX8568B General Description MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries ABSOLUTE MAXIMUM RATINGS IN, BK, BKSU, OD1, OD2 to GND.........................-0.3V to +6.0V BKV, LDO, NI/LI to GND.........................-0.3V to (VBKSU + 0.3V) REF, CHGI, INOK, TERMV, STRTV to GND...-0.3V to (VIN + 0.3V) PGND to GND ......................................................-0.3V to + 0.3V LX Current ......................................................................0.9ARMS Continuous Power Dissipation (TA = +70°C) 16-Pin 3mm x 3mm Thin QFN (derate 15.6mW/°C above +70°C) .............................1250mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°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 7, VIN = VINOK = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, VBKV = GND = PGND = 0V, VSTRTV = VTERMV = 1.2V, R5 = 250kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN IN Voltage Range IN Operating Current Charger off, VINOK = 1.5V TA = +25°C 3 TA = +85°C 3 Charger on, not including charge current CHGI Current Limit RCHGI = 169kΩ, VBK = 1.3V 8 CHGI Bias Voltage CHGI Resistor Range BK Charge Voltage Limit TYP 2.8 MAX UNITS 5.5 V 5 µA 50 90 10 12 600 VBK = 1.3V 50 mA mV 1800 VIN = 5.5V, VNI/LI = 0V 4.116 4.2 4.284 VIN = 3.8V, VNI/LI = 0V, VTERMV = 1V 3.42 3.5 3.58 VIN = VNI/LI = 3.6V 1.746 1.8 1.854 TA = +25°C 0.01 0.5 TA = +85°C 0.1 kΩ V BK Reverse Leakage Current to IN VIN = 0V NiMH Mode BK High Threshold Voltage, VBK(NIHI) VTERMV = 1.2V 1.37 1.4 1.43 V NiMH Mode BK Low Threshold Voltage, VBK(NILO) VSTRTV = 1.2V 1.17 1.2 1.23 V TERMV Input Current VTERMV = 1.1V TA = +25°C 0.001 0.05 TA = +85°C 0.01 STRTV Input Current VSTRTV = 1.1V TA = +25°C 0.001 TA = +85°C 0.01 REF Output Voltage IREF = 1µA REF Load Regulation IREF = 1µA to 50µA REF Line Regulation VIN = 3V to 5.5V, IREF = 1µA INOK Threshold Voltage 2.5 10 mV 1 7 mV 2.43 2.48 VINOK rising 2.40 2.47 2.54 TA = +25°C 0.005 0.1 TA = +85°C 0.05 NI/LI Logic-Level High VBKSU = 3.3V NI/LI Logic-Level Low VBKSU = 3.3V µA 1.27 2.38 VINOK = 2V µA 1.25 VINOK falling INOK Input Current 2 1.23 0.05 µA 1.8 _______________________________________________________________________________________ V V µA V 0.4 V Complete Backup-Management ICs for Lithium and NiMH Batteries (Circuit of Figure 7, VIN = VINOK = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, VBKV = GND = PGND = 0V, VSTRTV = VTERMV = 1.2V, R5 = 250kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS NI/LI Input Current VBKSU = VNI/LI = 3.3V OD_ On-Resistance VBKSU = 3.6V OD_ Leakage Current VOD_ = 5.5V MIN TYP MAX TA = +25°C 0.05 1 TA = +85°C 0.1 11 30 TA = +25°C 0.01 1 TA = +85°C 0.1 UNITS µA Ω µA BACKUP STEP-UP (Note 2) BK Input Undervoltage Lockout VNI/LI = 0V, falling trip point 2.45 VNI/LI = VBKSU = 3.3V, falling trip point 1.05 1.12 BK Input Voltage 1.21 V 5.5 V Quiescent Current into BKSU ILDO = 0mA, not switching 17 25 µA Quiescent Current into BK IBKSU = ILDO = 0mA, not switching 2.4 4 µA Shutdown Current into BK VIN = VINOK = VBKSU = 0V TA = +25°C 0.001 0.5 TA = +85°C 0.1 BKV Feedback Voltage BKV Feedback Bias Current BKSU Output-Voltage Accuracy 1.162 VBKV = 1V 1.21 1.258 TA = +25°C 5 50 TA = +85°C 10 p-Channel Switch On-Resistance LX Leakage Current V nA VBKV = 0V 3.17 3.3 3.43 VBKV = VBKSU 2.4 2.5 2.6 5 V 0.4 1 Ω Ω BKSU Output Voltage Range n-Channel Switch On-Resistance µA 2.5 ILX = 200mA ILX = 200mA 0.7 2 TA = +25°C 0.05 1 TA = +85°C 0.1 V µA LX Current Limit (ILIM) 400 500 600 mA n-Channel Switch Maximum On-Time 3.5 5 6.5 µs 5 20 35 mA 5.0 V p-Channel Zero-Channel Crossing Current LOW-DROPOUT REGULATOR BKSU Input Voltage Range 2.7 MAX8568A 2.375 2.5 2.625 MAX8568B 1.71 1.8 1.89 LDO Output-Voltage Accuracy VBKSU = 3.3V LDO Line Regulation 2.7V < VBKSU < 5V, ILDO = 1mA LDO Load Regulation 1µA < ILDO < 10mA V 1 mV 2.5 mV _______________________________________________________________________________________ 3 MAX8568A/MAX8568B ELECTRICAL CHARACTERISTICS (continued) MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries ELECTRICAL CHARACTERISTICS (Circuit of Figure 7, VIN = VINOK = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, VBKV = GND = PGND = 0V, VSTRTV = VTERMV = 1.2V, R5 = 250kΩ, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3) PARAMETER CONDITIONS IN Voltage Range MIN MAX UNITS 2.8 5.5 V IN Operating Current Charger on, not including charge current 90 µA CHGI Current Limit RCHGI = 169kΩ, VBK = 1.3V 8 12 mA CHGI Resistor Range VBK = 1.3V 50 1800 kΩ VIN = 5.5V, VNI/LI = 0V 4.116 4.310 VIN = 3.8V, VNI/LI = 0V, VTERMV = 1V 3.420 3.605 VIN = VNI/LI = 3.6V 1.746 1.854 NiMH Mode BK High Threshold Voltage, VBK(NIHI) VTERMV = 1.2V 1.37 1.43 V NiMH Mode BK Low Threshold Voltage, VBK(NILO) VSTRTV = 1.2V 1.17 1.23 V REF Output Voltage IREF = 1µA 1.225 1.275 V REF Load Regulation IREF = 1µA to 50µA 10 mV REF Line Regulation VIN = 3V to 5.5V, IREF = 1µA 7 mV BK Charge Voltage Limit V VINOK falling 2.38 2.48 VINOK rising 2.40 2.54 NI/LI Logic-Level High VBKSU = 3.3V 1.8 NI/LI Logic-Level Low VBKSU = 3.3V 0.4 V OD_ On-Resistance VBKSU = 3.6V 30 Ω 1.21 V INOK Threshold Voltage V V BACKUP STEP-UP (Note 2) BK Input Undervoltage Lockout VNI/LI = VBKSU = 3.3V, falling trip point 1.05 BK Input Voltage 5.5 V Quiescent Current into BKSU ILDO = 0mA, not switching 25 µA Quiescent Current into BK IBKSU = ILDO = 0mA, not switching 4 µA V BKV Feedback Voltage BKSU Output-Voltage Accuracy 1.162 1.258 VBKV = 0V 3.17 3.43 VBKV = VBKSU 2.4 2.6 2.5 BKSU Output Voltage Range V 5.0 V n-Channel Switch On-Resistance ILX = 200mA 1 Ω p-Channel Switch On-Resistance ILX = 200mA 2 Ω 4 _______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries (Circuit of Figure 7, VIN = VINOK = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, VBKV = GND = PGND = 0V, VSTRTV = VTERMV = 1.2V, R5 = 250kΩ, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3) MIN MAX UNITS LX Current Limit (ILIM) PARAMETER CONDITIONS 400 600 mA n-Channel Switch Maximum On-Time 3.5 6.5 µs 5 35 mA 2.7 5.0 V MAX8568A 2.375 2.625 MAX8568B 1.71 1.89 p-Channel Zero-Channel Crossing Current LOW-DROPOUT REGULATOR BKSU Input Voltage Range LDO Output-Voltage Accuracy VBKSU = 3.3V V Note 1: All units are 100% production tested at TA = +25°C. Limits over the operating range are guaranteed by design. Note 2: All backup step-up converter specifications are with VIN = VINOK = 0V, unless otherwise noted. Note 3: Specifications to -40°C are guaranteed by design and not production tested. Typical Operating Characteristics (Circuit of Figure 7, VIN = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, TA = +25°C, unless otherwise noted.) NiMH CHARGE CURRENT vs. BACKUP BATTERY VOLTAGE 8 6 FALLING RISING 4 2 10 8 VIN = 3.9V VBK(LIMAX) = 3.4V 6 4 0.4 0.8 1.2 1.6 BACKUP BATTERY VOLTAGE (V) 2.0 4.178 4.177 4.176 4.175 4.174 4.173 4.171 0 0 4.179 4.172 2 VIN = 3.9V 0 MAX8568 toc03 MAX8568 toc02 VIN = 5V, VBK(LIMAX) = 4.2V 12 4.180 TERMINATION VOLTAGE (V) CHARGE CURRENT (mA) 10 Li-ION TERMINATION VOLTAGE vs. TEMPERATURE 14 LITHIUM CHARGE CURRENT (mA) MAX8568 toc01 12 LITHIUM CHARGE CURRENT vs. BACKUP BATTERY VOLTAGE 4.170 0 0.6 1.2 1.8 2.4 3.0 BACKUP BATTERY VOLTAGE (V) 3.6 4.2 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX8568A/MAX8568B ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (Circuit of Figure 7, VIN = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, TA = +25°C, unless otherwise noted.) 10.0 9.8 9.6 4 VBK(NILO) = 1.2V VBK(NIHI) = 1.4V VBK(NIMAX) = 1.8V R5 = 953kΩ 1.36 3 1.34 2 VBK = 3.6V, VIN = 4V, R5 = 127kΩ 9.4 1.32 VBK = 1.4V, VIN = 4V, R5 = 169kΩ 9.2 6 3.2 3.0 1.30 4 2.8 CHARGE CURRENT 2.6 3 2 1 2.2 -15 10 35 60 4 6 8 2 4 6 8 CHARGE TIME (HOURS) CHARGE TIME (HOURS) 3.3V STEP-UP EFFICIENCY vs. LOAD CURRENT 2.5V STEP-UP EFFICIENCY vs. LOAD CURRENT BKSU OUTPUT VOLTAGE vs. LOAD CURRENT VBK = 2.9V 60 VBK = 1.4V 50 80 EFFICIENCY (%) 70 40 70 60 30 20 10 0 VBK = 1.4V 40 20 L1 = MURATA LQH32CN100K VBK = 2.9V 50 30 1 10 100 TA = -40°C 3.32 TA = +25°C 3.30 TA = +85°C 3.28 3.26 3.24 3.22 L1 = MURATA LQH32CN100K 0 0.1 3.34 OUTPUT VOLTAGE (V) 80 90 3.20 0.01 0.1 1 10 100 LOAD CURRENT (mA) LOAD CURRENT (mA) BK SUPPLY CURRENT vs. INPUT VOLTAGE LIGHT-LOAD SWITCHING WAVEFORMS 0 10 20 30 MAX8568 toc10 BOOST AND LDO ACTIVE 60 40 50 60 LOAD CURRENT (mA) HEAVY-LOAD SWITCHING WAVEFORMS MAX8568 toc11 70 10 MAX8568 toc09 100 MAX8568 toc07 90 0.01 0 0 10 TEMPERATURE (°C) 100 10 2.0 0 2 0 85 MAX8568 toc08 -40 VBKSU MAX8568 toc12 VBKSU 20mV/div AC-COUPLED 20mV/div AC-COUPLED 2V/div 0 2V/div 50 VLX 40 VLX 0 30 20 200mA/div ILX 10 0 VBKSU = 3.3V C3 = 22µF LOAD = 1mA 200mA/div ILX 0 C3 = 22µF LOAD = 50mA 0 1 2 3 4 5 50µs/div INPUT VOLTAGE (V) 6 5 BK VOLTAGE 2.4 1 CHARGE CURRENT 7 PANASONIC VL2330 9.0 EFFICIENCY (%) 1.38 BK VOLTAGE (V) 10.2 3.4 5 BK VOLTAGE CHARGE CURRENT (mA) 1.40 8 VBK(LIMAX) = 3.4V R5 = 432kΩ VARTA V20HR BK VOLTAGE (V) CHARGE CURRENT (mA) 10.4 MAX8568 toc06 3.6 6 CHARGE CURRENT (mA) VBK = 3.6V, VIN = 4.2V, R5 = 127kΩ 10.6 MAX8568 toc05 1.42 MAX8568 toc04 10.8 CHARGE PROFILE FOR LiVeO5 CHARGE PROFILE FOR NiMH CHARGE CURRENT vs. TEMPERATURE 11.0 SUPPLY CURRENT (µA) MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries _______________________________________________________________________________________ 5µs/div Complete Backup-Management ICs for Lithium and NiMH Batteries BKSU LOAD TRANSIENT IBKSU 3.32 3.31 10mA/div 0 2V 2V/div 0 VLX MAX8568 PROVIDES 3.3V MAX1586 PROVIDES 3.3V 50mV/div AC-COUPLED VBKSU 20mV/div AC-COUPLED VBKSU BKSU OUTPUT VOLTAGE (V) 3V VINOK VBKSU vs. LDO LOAD CURRENT MAX8568 toc14 MAX8658 toc13 MAX8568 toc15 MAIN-TO-BK TRANSITION WAVEFORMS IBKSU = 20mA 3.30 3.29 IBKSU = 40mA 3.28 3.27 C3 = 22µF LOAD = 10mA SWITCHOVER POINT C3 = 22µF 3.26 200µs/div 200µs/div 1 0.1 10 100 LDO LOAD CURRENT (mA) LDO OUTPUT VOLTAGE vs. BK INPUT VOLTAGE MAX8568 toc18 MAX8568 toc17 MAX8568 toc16 2.0 1.8 LDO OUTPUT VOLTAGE (V) BKSU RESPONSE TO LDO LOAD TRANSIENT LDO LOAD TRANSIENT 1.6 MAX8568A/MAX8568B Typical Operating Characteristics (continued) (Circuit of Figure 7, VIN = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, TA = +25°C, unless otherwise noted.) ILDO ILDO 10mA/div 0 VLDO 20mV/div AC-COUPLED 10mA/div 0 1.4 1.2 1.0 0.8 0.6 20mV/div AC-COUPLED VBKSU 0.4 IBKSU = 0mA 0.2 C3 = 22µF 0 0 1 2 3 4 5 200µs/div 400µs/div BK INPUT VOLTAGE (V) VINOK RISING VINOK FALLING MAX8568 TOC20 MAX8568 toc19 1V/div 2V 5V/div 0 VINOK VLX 1V/div VOD2 VINOK 2V/div VLX 0V 5V/div 0 VOD2 1V/div 0 0 2V/div VOD1 2V/div VOD1 0 0 200µs/idv 4ms/div _______________________________________________________________________________________ 7 Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B Pin Description PIN NAME 1 IN Main Battery Input. Connect to a 2.8V to 5.5V battery or other power source. Bypass with a 4.7µF ceramic capacitor to GND. 2 BK Backup Battery Input. Connect to an NiMH or rechargeable lithium backup battery. Connect a ceramic bypass capacitor from BK to GND. See the Step-Up Capacitor Selection section for more details. 3 PGND Power Ground. Connect PGND to the ground side of the BK input capacitor and BKSU output capacitor. Use this connection as the star point for all grounds. See the PC Board Layout and Routing section for specific instructions regarding PGND. 4 LX 5 BKSU Step-Up Converter Output. Bypass with a 10µF to 22µF ceramic capacitor to PGND. The BKSU output voltage is set to either 3.3V or 2.5V without resistors, or to an adjustable voltage with an external resistor-divider. See the Setting the Step-Up Converter Voltage section. 6 LDO 2.5V (MAX8568A) or 1.8V (MAX8568B), 10mA LDO Output for Memory Supply. LDO is powered from BKSU. Bypass with a 4.7µF ceramic capacitor to GND. 7 OD1 11Ω Open-Drain Output. OD1 drives the gate of an external pMOS switch. 8 OD2 11Ω Open-Drain Output. OD2 drives the gate of an external pMOS switch. 9 NI/LI Selects NiMH or Rechargeable Lithium Backup Battery. Connect NI/LI to BKSU if an NiMH backup battery is used. Connect NI/LI to GND if a rechargeable lithium backup battery is used. 10 BKV Sets the BKSU Output Voltage. Connect to GND for 3.3V output at BKSU. Connect to BKSU for 2.5V output. Connect to the midpoint of a resistor-divider connected from BKSU to GND for adjustable output. See the Setting the Step-Up Converter Voltage section. 11 INOK Main Battery Monitor. When VINOK falls below 2.43V, charging stops and backup mode starts. The step-up converter and LDO turn on, and OD1 and OD2 go high impedance. 12 CHGI Sets Backup Battery Charge Current. Connect a resistor from CHGI to GND to set the charge current. See the Setting the Charge Current section for details. Inductor Connection for Low-IQ Step-Up DC-DC Converter 13 GND 14 STRTV Sets Fast-Charge Start Voltage for NiMH. See the Using an NiMH Backup Battery section. 15 TERMV Sets Fast-Charge Stop Voltage for NiMH, as Well as the Battery Regulation Voltage for Both Rechargeable Lithium and Maximum Voltage for NiMH. See the Using a Lithium Backup Battery section and the Using an NiMH Backup Battery section. 16 REF EP 8 FUNCTION — Ground. Connect to the exposed paddle. Star all grounds at the BKSU output capacitor ground. Reference Output. Bypass with a 0.22µF ceramic capacitor to GND. Exposed Paddle. Connect to the analog ground plane. EP also functions as a heatsink. Solder to the circuit-board analog ground plane. _______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries The MAX8568A/MAX8568B are compact ICs for managing backup battery charging and utilization in PDAs and other smart handheld devices. The MAX8568A/ MAX8568B are comprised of three major blocks: 1) A multichemistry charger for small lithium-ion, lithium-manganese, LiVeO5, and NiMH batteries; 2) a small verylow-current step-up DC-DC converter that generates a boosted backup supply when the backup battery output is less than required; and 3) an LDO that supplies a second backup voltage to an additional system block (typically low-voltage RAM). Multichemistry Charger The backup battery charger charges most types of rechargeable lithium and NiMH cells. Charging current can be set up to 25mA by a resistor connected from CHGI to GND. The charger operates a current-limited voltage source for rechargeable lithium batteries, and switches between fast and trickle charging for NiMH batteries. NiMH Charging Scheme The NiMH charger operates at two different charge currents based upon the voltages at TERMV and STRTV. VSTRTV sets the BK voltage below which fast charging (set by CHGI) occurs. VTERMV sets the upper BK trip point where fast charging stops and trickle charging begins, and also sets a maximum voltage limit for the NiMH battery. If VTERMV is 1.2V, then fast charge stops at 1.2 / 0.86 = 1.4V, and the maximum voltage limit is 1.2 / 0.67 = 1.791V. An NiMH battery fast charges until it hits 1.4V set by VTERMV. The charger then switches to trickle charge at a current that is 10% of fast charge (set by CHGI). If the voltage drops (due to loading or self-discharge) to 1.2V (with VSTRTV = 1.2V), fast charge resumes. If the voltage then increases back to 1.4V (with VTERMV = 1.2V), trickle charge resumes. If the cell voltage reaches 1.8V, the charge current falls to zero. Lithium Charging Scheme When charging rechargeable lithium-type batteries, VTERMV sets the charging voltage while VSTRTV is unused. Charge current is set by a resistor from CHGI to GND. There is no trickle charge for lithium mode. This charging scheme is essentially a current-limited voltage source. Step-Up DC-DC Converter If an NiMH battery or lower-voltage rechargeable lithium battery is used for backup, it may be necessary to boost the battery voltage to 2.5V, 3.3V, or some other voltage to power RAM, RTC, or other devices. The step-up DC-DC converter is powered by the backup battery but requires that the I/O supply be activated at least one time before the backup battery can be stepped up. This allows the end product to draw no backup battery current while “on the shelf” waiting for its first activation. The step-up DCDC converter is enabled, and reaches regulation, 50µs (typ) after INOK falls below 2.43V (typ). The step-up converter includes a built-in synchronous rectifier that reduces cost by eliminating the need for an external diode and improves overall efficiency. The converter also features a clamp circuit that reduces EMI due to inductor ringing. The output voltage is set to 3.3V or 2.5V by connecting BKV to either GND or BKSU, respectively. For adjustable output, connect BKV to a resistor-divider from BKSU to GND. LDO For designs that require two different backup voltages, the MAX8568 includes a small LDO that is powered from BKSU. This LDO can supply up to 10mA and uses only 5µA of operating current. The LDO output is preset to 2.5V in the MAX8568A and 1.8V in the MAX8568B. The LDO is activated after VINOK falls below 2.43V (typ). Switchover Behavior See Figure 1 for switchover timing. If the backup battery is connected to the system before main power, the MAX8568 remains off and draws very little current, typically less than 0.5µA. This allows the end product to draw no backup battery current while “on the shelf” waiting for its first activation. When main power is connected, the MAX8568 powers on, assuming the main battery is greater than 2.8V. The MAX8568 begins to charge the backup battery if needed (see the Multichemistry Charger section). The OD1 and OD2 outputs pull to GND and turn on the external p-channel MOSFETs. This allows the voltage on I/O IN and MEM IN (Figure 7) to pass through to the I/O OUT and MEM OUT outputs. These I/O and MEM voltages are typically provided by a MAX1586/MAX1587 power-supply IC. INOK monitors the main battery voltage and activates the backup boost converter and LDO when the voltage on V INOK falls below 2.43V. The backup converter starts 50µs after VINOK falls. OD1 and OD2 go high impedance and turn off the external p-channel MOSFETs. These MOSFETs disconnect the I/O IN and MEM IN inputs from the load. This ensures that the I/O and MEM main supplies do not draw current from the backup source (MAX8568). The charger also turns off when INOK is less than 2.43V. If the MAX8568 is being evaluated as a stand-alone device, note that the backup-battery boost converter will not operate unless I/O IN has been activated at least one time. The typical power removal sequence for testing is 1) main battery goes low, then 2) MEM IN and I/O IN go low. _______________________________________________________________________________________ 9 MAX8568A/MAX8568B Detailed Description MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries 1.12V BK CHARGER 50µs IN 2.43V INOK I/O IN I/O OUT STEP-UP DC-DC CONVERTER OD1 MEM IN MEM OUT LDO OD2 Figure 1. Timing Diagram Applications Information Setting the Charge Current Charge current is set by a resistor connected from CHGI to GND (R5 in Figure 7). The acceptable resistor range is from 50kΩ to 1800kΩ. RCHGI is calculated by the following. 1.1641 41.2 × ( VIN − VBK ) + 679.4 RCHGI (kΩ) = ICHG (mA) 10 where VBK is the nominal voltage of the charged backup battery. This is the fast-charge current for both NiMH and lithium batteries. For NiMH batteries, the trickle charge is 10% of the fast-charge current. Using a Rechargeable Lithium Backup Battery The MAX8568 can charge a lithium-type backup battery from the main battery connected at IN. Connect NI/LI to GND for lithium backup battery charging. STRTV is unused and should be connected to GND in lithium charge mode. ______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries 3.5 × VREF R11 = R12 VBK(LIMAX) − 1 where VREF =1.25V. Using an NiMH Backup Battery The MAX8568 can charge NiMH backup batteries from the main battery connected at IN. Connect NI/LI to BKSU for NiMH backup battery charging. VTERMV sets the maximum cell voltage and also the trip point for the fast-charge-to-trickle-charge transition. VSTRTV sets the trickle-to-fast-charge transition threshold. In NiMH charge mode (NI/LI connected to BKSU), the charger ramps the battery between two thresholds measured at the battery connection BK, VBK(NILO) and VBK(NIHI). When the battery falls to VBK(NILO), trickle charging stops and fast charging starts. When the battery rises to VBK(NIHI), fast charging stops and trickle charging begins. If, for any reason, the battery contin- REF ues to rise when trickle charged, all charging ceases at VBK(NIMAX). VBK(NILO), VBK(NIHI), and VBK(NIMAX) are set as follows: BK voltage where fast charge begins: VBK(NILO) = VSTRTV BK voltage where trickle charge begins: VBK(NIHI) = 1.163 x VTERMV BK voltage where all charging stops: VBK(NIMAX) = 1.493 x VTERMV Resistor-dividers (see Figure 3) set VSTRTV and VTERMV by dividing down REF. To minimize operating current, resistors between 100kΩ and 1MΩ should be used for R14 and R16 in Figure 3. The formulas for the upper divider-resistors in terms of VBK(NILO), VBK(NIHI), and VBK(NIMAX) are: V REF R13 = R14 VBK(NILO) 1.163 × VREF R15 = R16 VBK(NIHI) 1 − 1 Once VBK(NIHI) is selected, the maximum battery voltage is: VBK(NIMAX) = 1.283 x VBK(NIHI) REF 16 − 16 R13 R15 R11 TERMV TERMV 15 15 R16 R12 STRTV 14 STRTV 14 R14 Figure 2. Resistor-Divider for Setting the Maximum Battery Voltage, VBK(LIMAX), for Rechargeable Lithium-Type Backup Batteries Figure 3. 2-Resistor-Dividers for Setting VBK(NILO) and VBK(NIHI) ______________________________________________________________________________________ 11 MAX8568A/MAX8568B The lithium charger acts like a current-limited voltage source. The battery regulation voltage for lithium mode, VBK(LIMAX), is: VBK(LIMAX) = 3.5 x VTERMV If VTERMV = 1.2V, then the final charge voltage is 4.2V. Connect TERMV to a resistor-divider from REF to GND. Adjust VTERMV with resistors R11 and R12 (Figure 2). Select R12 to be in the 100kΩ to 1MΩ range. Calculate R11 as follows: MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries Note that both VBK(NILO) and VBK(NIHI) can be set with a 2-resistor voltage-divider as shown in the typical application circuit (see Figure 7) if the factory-set ratio between the two thresholds is acceptable. In that case: V REF R6 = R8 VBK(NILO) − REF R17 1 TERMV − 1 1.163 × VREF R17 = (R18 + R19) × VBK(NIHI) − 1 Setting the Switchover Voltage − 1 where VINOK = 2.43V, and VIN(BACKUP) must be set greater than 2.8V. Step-Up Converter The step up DC-DC converter is most likely used with NiMH backup batteries, but can also be used with rechargeable lithium backup batteries. If the backup battery voltage is greater than the set output voltage at BKSU, the output voltage follows the backup battery voltage. The voltage difference between the backup battery and BKSU never exceeds a diode forward-voltage drop. If I/O OUT (Figure 7) is less than BK during charge mode, no current flows from BK to I/O OUT. 12 STRTV 14 R19 Figure 4. 3-Resistor Divider Used to Set VBK(NILO) and VBK(NIHI) VINOK sets the IN voltage at which backup mode starts. INOK connects to a resistor-divider between IN and GND. The MAX8568 requires VIN greater than 2.8V for proper operation when not backing up, so the backup threshold, VIN(BACKUP), must be set for no less than 2.8V. Once VINOK drops below 2.43V (typ), VIN may be less than 2.8V. The resistor-divider for INOK is shown in Figure 7 (R9 and R10). Select resistor R10 to be in the 100kΩ to 1MΩ range. Calculate R9 as follows: VIN(BACKUP) R9 = R10 VINOK 15 R18 VBK(NIHI) = 1.163 x VBK(NILO) VBK(NIMAX) = 1.283 x VBK(NIHI) One 3-resistor-divider can be used to set both VBK(NILO) and VBK(NIHI) independently. Figure 4 shows the connections of R17, R18, and R19. Select R19 in the 100kΩ to 1MΩ range. The equations for the two upper divider-resistors are: V REF R18 = R19 VBK(NILO) 16 Step-Up Capacitor Selection Choose output capacitors to supply output peak currents with acceptable voltage ripple. Low equivalentseries-resistance (ESR) capacitors are recommended. Ceramic capacitors have the lowest ESR, but low-ESR tantalum or polymer capacitors offer a good balance between cost and performance. Output voltage ripple has two components: variations in the charge stored in the output capacitor with each LX pulse and the voltage drop across the capacitor’s ESR caused by the current into and out of the capacitor. The equations for calculating output ripple are: VRIPPLE = VRIPPLE(C) + VRIPPLE(ESR) VRIPPLE(ESR) = IPEAK x RESR(CBKSU) VRIPPLE(C) = 1 2 (VBKSU − L 2 IPEAK VBK )CBKSU where I PEAK is the peak inductor current (see the Inductor Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). Input capacitors connected to IN and BK should be X5R or X7R ceramic capacitors. CIN should be 4.7µF or greater. CBK should be 10µF or greater when using the step-up converter. If the step-up converter is not used, then CBK can be reduced to 1µF. Capacitance and ESR variation with temperature should be considered for best performance in applications with wide operating temperature ranges. ______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries L < VBK × t ON(MAX) ILIM where tON(MAX) is typically 5µs, and the current limit (ILIM) is typically 500mA (see the Electrical Characteristics table). For larger inductor values, determine the peak inductor current (IPEAK) by: IPEAK = VBK × t ON(MAX) L Setting the Output Voltage The output voltage is set to 2.5V or 3.3V, or is adjustable. Connect BKV to GND for 3.3V, and BKV to BKSU for 2.5V. The adjustable output voltage is set from 2.5V to 5V using external resistors R1 and R2 (Figure 7). Since FB leakage is 50nA (max), select feedback resistor R2 in the 100kΩ to 1MΩ range. Calculate R1 as follows: V R1 = R2 BKSU VBKV − 1 where VBKV = 1.21V. LDO The LDO output voltage is preset to 2.5V for the MAX8568A and 1.8V for the MAX8568B. The LDO can supply up to 10mA. The LDO output voltage is not adjustable. LDO Capacitor Selection Capacitors are required at the LDO output of the MAX8568 for stable operation over the full load and temperature range. A 4.7µF or greater X5R or X7R ceramic capacitor is recommended. To reduce noise and improve load-transient response, larger output capacitors up to 10µF can be used. Surface-mount ceramic capacitors have very low ESR and are commonly available in values up to 10µF. Note that some ceramic dielectrics, such as Z5U and Y5V, exhibit large capacitance and ESR variation with temperature and require larger than the recommended values to maintain stability and good load-transient response over temperature. External MOSFET Drivers—OD1, OD2 OD1 and OD2 are open-drain outputs and are designed to be connected to the gates of external pchannel MOSFETs (see Figure 7). These MOSFETs connect the main system power supplies (I/O IN and MEM IN) to the system loads (I/O OUT and MEM OUT) during normal operation. During backup, they disconnect the power supplies from the system loads to prevent the power supplies from drawing backup current away from the system. For this reason, the MOSFETs are connected “backwards” from what might be expected. The source of the MOSFETs are connected to the system load side (I/O OUT and MEM OUT). The MOSFETs’ purpose is to block current flow from the backup supply (BKSU) to the main supplies (I/O IN and MEM IN). They do not block current flow from I/O IN to I/O OUT and from MEM IN to MEM OUT. Even when off, the MOSFET body diodes allow current to pass in that direction. OD1 is intended to drive the MOSFET switch for I/O IN and I/O OUT, while OD2 is intended to drive the MOSFET switch for MEM IN and MEM OUT. See the Typical Operating Characteristics and Figure 1 for typical operation of OD1 and OD2. External MOSFET Selection The external MOSFET should be chosen based upon RDS(ON) and gate capacitance. When VINOK > 2.43V (main battery > 2.8V), the current required for normal operation of I/O and MEM goes through these external MOSFETs. Choose an R DS(ON) that minimizes the MOSFET voltage drop. When V INOK < 2.43V, the MOSFET turns off, and MEM and I/O are powered by the MAX8568. The gate capacitance of the external MOSFET must discharge through the external gate-tosource resistor. This discharge time determines how quickly the main supply is disconnected and isolated. ______________________________________________________________________________________ 13 MAX8568A/MAX8568B Inductor Selection The control scheme of the MAX8568 permits flexibility in choosing an inductor. A 10µH inductor performs well in most applications. Smaller inductance values typically offer smaller physical size for a given series resistance, allowing the smallest overall circuit dimensions. Circuits using larger inductance may provide higher efficiency and exhibit less ripple, but also may reduce the maximum output current. This occurs when the inductance is sufficiently large to prevent the LX current limit (ILIM) from being reached before the maximum on-time (tON(MAX)) expires. For maximum output current, choose the inductor value so that the controller reaches the current limit before the maximum on-time is reached: MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries Pullup resistors, R3 and R4 in Figure 7, should be selected to ensure that when OD1 and OD2 go high impedance, the gate of the external MOSFET discharges within 50µs to 100µs. This time allows the backup converters to start and provide power to I/O and MEM. Discharges longer than 50µs to 100µs could cause the main supply to back drain current from the MAX8568 and allow the I/O OUT and MEM OUT voltage to droop. The MOSFET gate-source resistor, RGS, is calculated from the following formulas: IN CHGI 1MΩ MAX1586 τ = ln 1 − VGS(TH) VBKSU where the MOSFET gate-source threshold, V GS(TH), and MOSFET input capacitance, CISS, are provided on the MOSFET data sheet. Connection with MAX1586 When the MAX8568 is used with the MAX1586 system power supply, it may be preferable to employ the MAX1586’s voltage monitors to determine when backup should start. The connection for this is shown in Figure 5 where the dead-battery output (DBO) of the MAX1586 drives the INOK input of the MAX8568. This, in effect, overrides the voltage-sensing circuit on the MAX8568 and uses the DBO monitor on the MAX1586. Refer to the MAX1586 data sheet for information on how to set the DBO threshold. The CHG connection in Figure 5 is described in the next section. Terminating Charging at a Voltage Other than the Switchover Voltage In normal operation, the MAX8568 charger is always active as long as the INOK voltage is valid (above 2.43V). In some systems, however, it may be desirable to terminate backup battery charging when the main battery is somewhat depleted but not so low as to trigger backup. An external voltage monitor, or a voltage monitor in a power-supply IC, such as the MAX1586, can disable charging by disconnecting the CHGI resistor. If CHGI is open, no charging current flows. This can be accomplished with the circuit in Figure 5. The low-battery output (LBO) of the MAX1586 pulls low when the battery falls below a user-set level (refer to the MAX1586 data sheet). This turns off the external n-channel MOSFET (or 14 MAX8568 n-CHANNEL MOSFET OR OPEN-DRAIN INVERTER LBO τ = RGS x CISS −50µs RCHGI 1MΩ DBO INOK Figure 5. Using a MAX1586 Power-Supply IC to Trigger Backup Switchover and to Disable Backup Battery Charging Prior to Switchover open-drain logic inverter) and disconnects the current path through RICHG. Backup charging can be stopped for any reason using this method. PC Board Layout and Routing Careful PC board layout is important for minimizing ground bounce and noise. Ensure that C1 (IN input capacitor), C2 (BK input capacitor), C3 (BKSU bypass capacitor), and C4 (LDO output capacitor) are as close as possible to the IC. Avoid using vias to connect C2 or C3 to their respective pins or GND. C2 and C3 grounds should be next to each other, and this connection can then be used as the star ground point. All other grounds should connect to the star ground. PGND should star at C2 and C3, and should not connect directly to the exposed pad (EP) of the MAX8568. Connect EP to the bottom layer ground plane, and then connect the ground plane to the star ground. Vias on the inductor path are acceptable if necessary. IN, BK, BKSU, and LDO traces should be as wide as possible to minimize inductance. Refer to the MAX8568 evaluation kit for a PC board layout example. Chip Information TRANSISTOR COUNT: 7902 PROCESS: BiCMOS ______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B MAX8568 REF NI/LI REF TERMV GND IN BK CHARGE CURRENT SOURCE STRTV 0.286 0.67 BK UVLO 1.13 1 LI 0.86 NI STEP-UP CONVERTER LX INOK 2.43V BKSU UVLO 2.25 PGND PFM BKV OD1 BKSU LDO LDO OD2 Figure 6. Functional Diagram ______________________________________________________________________________________ 15 MAX8568A/MAX8568B Complete Backup-Management ICs for Lithium and NiMH Batteries MAIN BATTERY 2.8V TO 5.5V 1 IN C1 4.7µF BACKUP BATTERY 2 L1 10µH 5 TERMV PGND R2 0Ω 10 7 MEM OUT 2.5V, 10mA 6 R7 0Ω GND 14 13 R8 1.2MΩ OD1 LDO INOK NI/LI CHGI R4 100kΩ MAIN BATTERY R9 357kΩ BKV C4 4.7µF MEM IN Q2 15 BKSU STRTV R3 100kΩ R6 50kΩ LX C3 10µF 3 Q1 C5 0.22µF MAX8568A I/O OUT 3.3V, 50mA I/O IN 16 C2 10µF 4 R1 OPEN REF BK 11 9 R10 1MΩ NI LI 12 R5 169kΩ 8 OD2 Figure 7. Typical Application Circuit 16 ______________________________________________________________________________________ Complete Backup-Management ICs for Lithium and NiMH Batteries 12x16L QFN THIN.EPS D2 0.10 M C A B b D D2/2 D/2 E/2 E2/2 CL (NE - 1) X e E E2 L k e CL (ND - 1) X e CL 0.10 C CL 0.08 C A A2 L A1 L e e PACKAGE OUTLINE 12, 16L, THIN QFN, 3x3x0.8mm E 21-0136 PKG 12L 3x3 MIN. NOM. MAX. MIN. NOM. MAX. A 0.70 0.75 0.80 0.70 0.75 0.80 EXPOSED PAD VARIATIONS PKG. CODES NOM. MAX. 1.25 0.95 1.10 1.25 0.35 x 45∞ WEED-1 NO T1233-3 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45∞ WEED-1 YES T1633-1 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45∞ WEED-2 NO T1633-2 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45∞ WEED-2 YES T1633F-3 0.65 0.80 0.95 0.65 0.80 0.95 0.225 x 45∞ WEED-2 N/A T1633-4 0.95 1.10 1.25 0.95 1.10 1.25 0.35 x 45∞ NO 0.30 0.20 0.25 0.30 3.10 2.90 3.00 3.10 T1233-1 E e 2.90 3.00 3.10 2.90 3.00 3.10 L 0.45 0.65 0.30 0.40 12 ND 3 4 NE 3 4 0 0.02 0.05 0 0.02 0.05 0.25 0.20 REF - - 0.25 0.20 REF - - A2 k 0.50 16 DOWN BONDS ALLOWED MIN. 1.10 0.25 3.00 N JEDEC MAX. 0.95 0.20 2.90 0.50 BSC. PIN ID NOM. D 0.50 BSC. E2 D2 MIN. b A1 2 16L 3x3 REF. 0.55 1 WEED-2 NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220 REVISION C. PACKAGE OUTLINE 12, 16L, THIN QFN, 3x3x0.8mm 21-0136 E 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 ____________________ 17 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc. MAX8568A/MAX8568B 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.)