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19-3450; Rev 0; 11/04
KIT ATION EVALU E AILABL AV
Complete Backup-Management ICs for Lithium and NiMH Batteries
General Description 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 17A Operating Current in Backup Mode Eliminate Many Discrete Components Tiny 3mm x 3mm Thin QFN Package
MAX8568A/MAX8568B
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 -40C to +85C operation.
Ordering Information
PART TEMP RANGE PINPACKAGE 16 Thin QFN 3mm x 3mm (T1633-4) 16 Thin QFN 3mm x 3mm (T1633-4) TOP MARK ACK
MAX8568AETE
-40C to +85C
Applications
PDAs and PDA Phones Smart Phones DSCs and DVCs Palmtops and Wireless Handhelds Internet Appliances and Web-Books
MAIN BATTERY 2.8V TO 5.5V IN BACKUP BATTERY BK
MAX8568BETE
-40C to +85C
ACL
Typical Operating Circuit
REF
Pin Configuration
INOK NI/LI BKV
TOP VIEW
CHGI
MAX8568A MAX8568B
TERMV
12
11
10
9
I/O OUT 3.3V, 50mA LX BKSU IN I/O IN STRTV
GND STRTV TERMV REF
13 14 15 16 1 IN 2 BK 3 PGND 4 LX
8 7
OD2 OD1 LDO BKSU
MEM OUT 1.8V OR 2.5V, 10mA MEM IN
PGND
GND
MAX8568A MAX8568B
6 5
BKV OD1 LDO
INOK CHGI
NI OD2 NI/LI LI
THIN QFN
________________________________________________________________ Maxim Integrated Products
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Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
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 = +70C) 16-Pin 3mm x 3mm Thin QFN (derate 15.6mW/C above +70C) .............................1250mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(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 = 250k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN Voltage Range IN Operating Current CHGI Current Limit CHGI Bias Voltage CHGI Resistor Range BK Charge Voltage Limit VBK = 1.3V VIN = 5.5V, VNI/LI = 0V VIN = 3.8V, VNI/LI = 0V, VTERMV = 1V VIN = VNI/LI = 3.6V BK Reverse Leakage Current to IN NiMH Mode BK High Threshold Voltage, VBK(NIHI) NiMH Mode BK Low Threshold Voltage, VBK(NILO) TERMV Input Current STRTV Input Current REF Output Voltage REF Load Regulation REF Line Regulation INOK Threshold Voltage INOK Input Current NI/LI Logic-Level High NI/LI Logic-Level Low VIN = 0V VTERMV = 1.2V VSTRTV = 1.2V VTERMV = 1.1V VSTRTV = 1.1V IREF = 1A IREF = 1A to 50A VIN = 3V to 5.5V, IREF = 1A VINOK falling VINOK rising VINOK = 2V VBKSU = 3.3V VBKSU = 3.3V TA = +25C TA = +85C 1.8 0.4 2.38 2.40 TA = +25C TA = +85C TA = +25C TA = +85C 1.23 TA = +25C TA = +85C 1.37 1.17 50 4.116 3.42 1.746 4.2 3.5 1.8 0.01 0.1 1.4 1.2 0.001 0.01 0.001 0.01 1.25 2.5 1 2.43 2.47 0.005 0.05 1.27 10 7 2.48 2.54 0.1 0.05 1.43 1.23 0.05 Charger off, VINOK = 1.5V TA = +25C TA = +85C 8 CONDITIONS MIN 2.8 3 3 50 10 600 1800 4.284 3.58 1.854 0.5 A V V A A V mV mV V A V V V 90 12 mA mV k TYP MAX 5.5 5 A UNITS V
Charger on, not including charge current RCHGI = 169k, VBK = 1.3V
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Complete Backup-Management ICs for Lithium and NiMH Batteries
ELECTRICAL CHARACTERISTICS (continued)
(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 = 250k, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER NI/LI Input Current OD_ On-Resistance OD_ Leakage Current BACKUP STEP-UP (Note 2) BK Input Undervoltage Lockout BK Input Voltage Quiescent Current into BKSU Quiescent Current into BK Shutdown Current into BK BKV Feedback Voltage BKV Feedback Bias Current BKSU Output-Voltage Accuracy BKSU Output Voltage Range n-Channel Switch On-Resistance p-Channel Switch On-Resistance LX Leakage Current LX Current Limit (ILIM) n-Channel Switch Maximum On-Time p-Channel Zero-Channel Crossing Current LOW-DROPOUT REGULATOR BKSU Input Voltage Range LDO Output-Voltage Accuracy LDO Line Regulation LDO Load Regulation VBKSU = 3.3V MAX8568A MAX8568B 2.7 2.375 1.71 2.5 1.8 1 2.5 5.0 2.625 1.89 V V mV mV ILX = 200mA ILX = 200mA TA = +25C TA = +85C 400 3.5 5 VBKV = 1V VBKV = 0V VBKV = VBKSU TA = +25C TA = +85C 3.17 2.4 2.5 0.4 0.7 0.05 0.1 500 5 20 600 6.5 35 ILDO = 0mA, not switching IBKSU = ILDO = 0mA, not switching VIN = VINOK = VBKSU = 0V TA = +25C TA = +85C 1.162 17 2.4 0.001 0.1 1.21 5 10 3.3 2.5 3.43 2.6 5 1 2 1 1.258 50 VNI/LI = 0V, falling trip point VNI/LI = VBKSU = 3.3V, falling trip point 1.05 2.45 1.12 1.21 5.5 25 4 0.5 V V A A A V nA V V A mA s mA CONDITIONS VBKSU = VNI/LI = 3.3V VBKSU = 3.6V VOD_ = 5.5V TA = +25C TA = +85C TA = +25C TA = +85C MIN TYP 0.05 0.1 11 0.01 0.1 30 1 MAX 1 UNITS A A
MAX8568A/MAX8568B
2.7V < VBKSU < 5V, ILDO = 1mA 1A < ILDO < 10mA
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Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
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 = 250k, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 3)
PARAMETER IN Voltage Range IN Operating Current CHGI Current Limit CHGI Resistor Range BK Charge Voltage Limit NiMH Mode BK High Threshold Voltage, VBK(NIHI) NiMH Mode BK Low Threshold Voltage, VBK(NILO) REF Output Voltage REF Load Regulation REF Line Regulation INOK Threshold Voltage NI/LI Logic-Level High NI/LI Logic-Level Low OD_ On-Resistance BACKUP STEP-UP (Note 2) BK Input Undervoltage Lockout BK Input Voltage Quiescent Current into BKSU Quiescent Current into BK BKV Feedback Voltage BKSU Output-Voltage Accuracy BKSU Output Voltage Range n-Channel Switch On-Resistance p-Channel Switch On-Resistance ILX = 200mA ILX = 200mA VBKV = 0V VBKV = VBKSU ILDO = 0mA, not switching IBKSU = ILDO = 0mA, not switching 1.162 3.17 2.4 2.5 VNI/LI = VBKSU = 3.3V, falling trip point 1.05 1.21 5.5 25 4 1.258 3.43 2.6 5.0 1 2 V V A A V V V Charger on, not including charge current RCHGI = 169k, VBK = 1.3V VBK = 1.3V VIN = 5.5V, VNI/LI = 0V VIN = 3.8V, VNI/LI = 0V, VTERMV = 1V VIN = VNI/LI = 3.6V VTERMV = 1.2V VSTRTV = 1.2V IREF = 1A IREF = 1A to 50A VIN = 3V to 5.5V, IREF = 1A VINOK falling VINOK rising VBKSU = 3.3V VBKSU = 3.3V VBKSU = 3.6V 2.38 2.40 1.8 0.4 30 8 50 4.116 3.420 1.746 1.37 1.17 1.225 CONDITIONS MIN 2.8 MAX 5.5 90 12 1800 4.310 3.605 1.854 1.43 1.23 1.275 10 7 2.48 2.54 V V V mV mV V V V V UNITS V A mA k
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Complete Backup-Management ICs for Lithium and NiMH Batteries
ELECTRICAL CHARACTERISTICS (continued)
(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 = 250k, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 3)
PARAMETER LX Current Limit (ILIM) n-Channel Switch Maximum On-Time p-Channel Zero-Channel Crossing Current LOW-DROPOUT REGULATOR BKSU Input Voltage Range LDO Output-Voltage Accuracy VBKSU = 3.3V MAX8568A MAX8568B 2.7 2.375 1.71 5.0 2.625 1.89 V V CONDITIONS MIN 400 3.5 5 MAX 600 6.5 35 UNITS mA s mA
MAX8568A/MAX8568B
Note 1: All units are 100% production tested at TA = +25C. 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 -40C 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 = +25C, unless otherwise noted.)
NiMH CHARGE CURRENT vs. BACKUP BATTERY VOLTAGE
MAX8568 toc01
LITHIUM CHARGE CURRENT vs. BACKUP BATTERY VOLTAGE
MAX8568 toc02
Li-ION TERMINATION VOLTAGE vs. TEMPERATURE
4.179 TERMINATION VOLTAGE (V) 4.178 4.177 4.176 4.175 4.174 4.173 4.172
MAX8568 toc03
12 10 CHARGE CURRENT (mA) 8 6 4 2 VIN = 3.9V 0 0 0.4 0.8 1.2 1.6
14 LITHIUM CHARGE CURRENT (mA) 12 10 8 6 4 2 0 VIN = 3.9V VBK(LIMAX) = 3.4V VIN = 5V, VBK(LIMAX) = 4.2V
4.180
FALLING
RISING
4.171 4.170 0 0.6 1.2 1.8 2.4 3.0 3.6 4.2 -40 -15 10 35 60 85 BACKUP BATTERY VOLTAGE (V) TEMPERATURE (C)
2.0
BACKUP BATTERY VOLTAGE (V)
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Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
Typical Operating Characteristics (continued)
(Circuit of Figure 7, VIN = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, TA = +25C, unless otherwise noted.)
CHARGE CURRENT vs. TEMPERATURE
MAX8568 toc04
CHARGE PROFILE FOR NiMH
1.42 VARTA V20HR 1.40 BK VOLTAGE BK VOLTAGE (V) 1.38 1.36 1.34 1.32 1.30 CHARGE CURRENT VBK(NILO) = 1.2V VBK(NIHI) = 1.4V VBK(NIMAX) = 1.8V R5 = 953k 4 3 2 1 0 0 2 4 6 8 10 CHARGE TIME (HOURS) 5 CHARGE CURRENT (mA) BK VOLTAGE (V) 3.4 3.2 3.0 2.8 2.6 2.4 2.2
MAX8568 toc05
CHARGE PROFILE FOR LiVeO5
6 3.6 VBK(LIMAX) = 3.4V R5 = 432k
MAX8568 toc06
11.0 10.8 10.6 CHARGE CURRENT (mA) 10.4 10.2 10.0 9.8 9.6 9.4 9.2 9.0 -40 -15 10 35 60 VBK = 3.6V, VIN = 4V, R5 = 127k VBK = 1.4V, VIN = 4V, R5 = 169k VBK = 3.6V, VIN = 4.2V, R5 = 127k
8 7 CHARGE CURRENT (mA) 6
BK VOLTAGE
5 4
CHARGE CURRENT
3 2 1
PANASONIC VL2330 2.0 0 2 4 6 8 10 CHARGE TIME (HOURS) 0 85
TEMPERATURE (C)
3.3V STEP-UP EFFICIENCY vs. LOAD CURRENT
MAX8568 toc07
2.5V STEP-UP EFFICIENCY vs. LOAD CURRENT
MAX8568 toc08
BKSU OUTPUT VOLTAGE vs. LOAD CURRENT
TA = -40C TA = +25C TA = +85C
MAX8568 toc09
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 LOAD CURRENT (mA) 10 L1 = MURATA LQH32CN100K VBK = 2.9V VBK = 1.4V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VBK = 2.9V VBK = 1.4V
3.34 3.32 OUTPUT VOLTAGE (V) 3.30 3.28 3.26 3.24 3.22
L1 = MURATA LQH32CN100K 3.20 0.01 0.1 1 LOAD CURRENT (mA) 10 100 0 10 20 30 40 50 60 LOAD CURRENT (mA)
100
BK SUPPLY CURRENT vs. INPUT VOLTAGE
MAX8568 toc10
LIGHT-LOAD SWITCHING WAVEFORMS
MAX8568 toc11
HEAVY-LOAD SWITCHING WAVEFORMS
MAX8568 toc12
70 60 SUPPLY CURRENT (A) 50 40 30 20 10 VBKSU = 3.3V 0 1 2 3 INPUT VOLTAGE (V) 4 5 BOOST AND LDO ACTIVE
VBKSU
VBKSU 20mV/div AC-COUPLED
20mV/div AC-COUPLED
VLX
2V/div 0
VLX
2V/div 0
ILX C3 = 22F 50s/div LOAD = 1mA
200mA/div 0 ILX C3 = 22F 5s/div LOAD = 50mA
200mA/div 0
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Complete Backup-Management ICs for Lithium and NiMH Batteries
Typical Operating Characteristics (continued)
(Circuit of Figure 7, VIN = 3.6V, VBK = 1.4V, VNI/LI = VBKSU = 3.3V, TA = +25C, unless otherwise noted.)
MAIN-TO-BK TRANSITION WAVEFORMS
MAX8658 toc13
MAX8568A/MAX8568B
BKSU LOAD TRANSIENT
MAX8568 toc14
VBKSU vs. LDO LOAD CURRENT
MAX8568 toc15
3.32 10mA/div 0 3.31 BKSU OUTPUT VOLTAGE (V) IBKSU = 20mA 3.30 3.29 IBKSU = 40mA 3.28 3.27
VINOK
3V 2V
IBKSU
VLX MAX8568 PROVIDES 3.3V MAX1586 PROVIDES 3.3V VBKSU C3 = 22F LOAD = 10mA
2V/div 0 20mV/div AC-COUPLED
50mV/div AC-COUPLED
VBKSU
SWITCHOVER POINT 200s/div
C3 = 22F 3.26 200s/div 0.1 1 10 100 LDO LOAD CURRENT (mA)
LDO OUTPUT VOLTAGE vs. BK INPUT VOLTAGE
1.8 LDO OUTPUT VOLTAGE (V) 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 1 2 3 4 5 VLDO
MAX8568 toc16
LDO LOAD TRANSIENT
MAX8568 toc17
BKSU RESPONSE TO LDO LOAD TRANSIENT
MAX8568 toc18
2.0
ILDO
10mA/div 0
ILDO
10mA/div 0
20mV/div AC-COUPLED
VBKSU
20mV/div AC-COUPLED
IBKSU = 0mA C3 = 22F 400s/div 200s/div
BK INPUT VOLTAGE (V)
VINOK FALLING
MAX8568 toc19
VINOK RISING
MAX8568 TOC20
VINOK VLX
1V/div 2V 5V/div 0
VINOK
2V/div 0V 5V/div 0 1V/div 0
VLX 1V/div VOD2 0 2V/div VOD1 0 4ms/div VOD1 VOD2
2V/div 0
200s/idv
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Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
Pin Description
PIN 1 2 NAME IN BK FUNCTION Main Battery Input. Connect to a 2.8V to 5.5V battery or other power source. Bypass with a 4.7F ceramic capacitor to GND. 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. 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. Inductor Connection for Low-IQ Step-Up DC-DC Converter Step-Up Converter Output. Bypass with a 10F to 22F 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. 2.5V (MAX8568A) or 1.8V (MAX8568B), 10mA LDO Output for Memory Supply. LDO is powered from BKSU. Bypass with a 4.7F ceramic capacitor to GND. 11 Open-Drain Output. OD1 drives the gate of an external pMOS switch. 11 Open-Drain Output. OD2 drives the gate of an external pMOS switch. 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. 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. 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. 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. Ground. Connect to the exposed paddle. Star all grounds at the BKSU output capacitor ground. Sets Fast-Charge Start Voltage for NiMH. See the Using an NiMH Backup Battery section. 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. Reference Output. Bypass with a 0.22F 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.
3 4 5
PGND LX BKSU
6 7 8 9
LDO OD1 OD2 NI/LI
10
BKV
11 12 13 14 15 16 EP
INOK CHGI GND STRTV TERMV REF --
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Complete Backup-Management ICs for Lithium and NiMH Batteries
Detailed Description
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). 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, 50s (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.
MAX8568A/MAX8568B
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.
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 5A 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 0.5A. 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 50s 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
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
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Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
1.12V BK
CHARGER
IN 2.43V INOK
50s
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 50k to 1800k. Charge current is calculated by the following. Charge Current = 1690 / RCHGI + (VIN - VBK - 2.3) x (1.05mA/V) where VBK is the nominal voltage of the charged backup battery. For lithium batteries charging at low cur-
rents, desired R CHGI may need to be determined emperically. 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.
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Complete Backup-Management ICs for Lithium and NiMH Batteries
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 100k to 1M range. Calculate R11 as follows: 3.5 x VREF R11 = R12 VBK(LIMAX) where VREF =1.25V.
-
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 100k and 1M 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)
-
MAX8568A/MAX8568B
1
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-
1
-
1.163 x VREF R15 = R16 VBK(NIHI)
1
Once VBK(NIHI) is selected, the maximum battery voltage is: VBK(NIMAX) = 1.283 x VBK(NIHI)
REF
16
REF
16
R13 R11 TERMV 15 TERMV 15
R15
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)
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11
Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
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 16
R17 TERMV 15
1
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 100k to 1M range. The equations for the two upper divider-resistors are: V REF R18 = R19 VBK(NILO)
-
R18 STRTV 14
R19
1
-
Figure 4. 3-Resistor Divider Used to Set VBK(NILO) and VBK(NIHI)
1.163 x VREF R17 = (R18 + R19) x VBK(NIHI)
1
Setting the Switchover Voltage
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 100k to 1M range. Calculate R9 as follows: VIN(BACKUP) R9 = R10 VINOK
-
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
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.
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 4.7F or greater. CBK should be 10F or greater when using the step-up converter. If the step-up converter is not used, then CBK can be reduced to 1F. Capacitance and ESR variation with temperature should be considered for best performance in applications with wide operating temperature ranges.
12
______________________________________________________________________________________
Complete Backup-Management ICs for Lithium and NiMH Batteries
Inductor Selection The control scheme of the MAX8568 permits flexibility in choosing an inductor. A 10H 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: L< VBK x t ON(MAX) ILIM LDO Capacitor Selection Capacitors are required at the LDO output of the MAX8568 for stable operation over the full load and temperature range. A 4.7F or greater X5R or X7R ceramic capacitor is recommended. To reduce noise and improve load-transient response, larger output capacitors up to 10F can be used. Surface-mount ceramic capacitors have very low ESR and are commonly available in values up to 10F. 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.
MAX8568A/MAX8568B
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.
where tON(MAX) is typically 5s, 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 x 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 100k to 1M range. Calculate R1 as follows: V R1 = R2 BKSU VBKV where VBKV = 1.21V.
-
1
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.
______________________________________________________________________________________
13
Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
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 50s to 100s. This time allows the backup converters to start and provide power to I/O and MEM. Discharges longer than 50s to 100s 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: = RGS x CISS =
-50s
IN 1M RCHGI n-CHANNEL MOSFET OR OPEN-DRAIN INVERTER 1M DBO INOK CHGI
MAX1586
LBO
MAX8568
ln 1
-
VGS(TH) VBKSU
where the MOSFET gate-source threshold, VGS(TH), and MOSFET input capacitance, CISS, are provided on the MOSFET data sheet.
Figure 5. Using a MAX1586 Power-Supply IC to Trigger Backup Switchover and to Disable Backup Battery Charging Prior to Switchover
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.
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.
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
Chip Information
TRANSISTOR COUNT: 7902 PROCESS: BiCMOS
14
______________________________________________________________________________________
Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
MAX8568
REF REF NI/LI
GND
TERMV
IN BK CHARGE CURRENT SOURCE
STRTV
BK UVLO 1.13 1 LI NI 0.86
0.67
0.286
STEP-UP CONVERTER LX
INOK 2.43V
BKSU UVLO 2.25
PGND
PFM
BKV OD1
BKSU
LDO
LDO OD2
Figure 6. Functional Diagram ______________________________________________________________________________________ 15
Complete Backup-Management ICs for Lithium and NiMH Batteries MAX8568A/MAX8568B
MAIN BATTERY 2.8V TO 5.5V C1 4.7F BACKUP BATTERY C2 10F
1
IN
2
BK
REF
16 C5 0.22F
L1 10H
MAX8568A
4 TERMV LX BKSU STRTV 14 15
R6 50k
I/O OUT 3.3V, 50mA
5 R1 OPEN
R7 0
C3 10F 3 PGND
I/O IN
Q1 R3 100k
R2 0 10 BKV
GND
13
R8 1.2M
MAIN BATTERY
R9 357k INOK 11 R10 1M LI
7 MEM OUT 2.5V, 10mA C4 4.7F
OD1
6
LDO
NI/LI
9
NI
MEM IN Q2 R4 100k
CHGI
12 R5 169k
8
OD2
Figure 7. Typical Application Circuit 16 ______________________________________________________________________________________
Complete Backup-Management ICs for Lithium and NiMH Batteries
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.)
D2 b
MAX8568A/MAX8568B
0.10 M C A B
D D/2
D2/2
E/2
E2/2
C L
E
(NE - 1) X e
E2
L
C L
e
k (ND - 1) X e
C L
0.10 C 0.08 C A A2 A1 L
C L
L
e
e
PACKAGE OUTLINE 12, 16L, THIN QFN, 3x3x0.8mm
21-0136
E
1
2
EXPOSED PAD VARIATIONS
DOWN BONDS ALLOWED
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 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
12x16L QFN THIN.EPS

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