Maxim MAX8568AETE Complete backup-management ics for lithium and nimh battery Datasheet

19-3450; Rev 0; 11/04
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
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
2.5
n-Channel Switch On-Resistance
ILX = 200mA
p-Channel Switch On-Resistance
ILX = 200mA
0.7
2
TA = +25°C
0.05
1
TA = +85°C
0.1
LX Leakage Current
µA
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
VBK(NILO) = 1.2V
VBK(NIHI) = 1.4V
VBK(NIMAX) = 1.8V
R5 = 953kΩ
1.36
3
2
1.34
VBK = 3.6V, VIN = 4V, R5 = 127kΩ
9.4
1.32
VBK = 1.4V, VIN = 4V, R5 = 169kΩ
9.2
3.0
1.30
4
2.8
CHARGE CURRENT
2.6
3
2
1
2.2
-15
10
35
60
2
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
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
6
3.2
PANASONIC VL2330
9.0
EFFICIENCY (%)
4
1.38
7
CHARGE CURRENT (mA)
BK VOLTAGE
BK VOLTAGE (V)
10.2
3.4
5
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. 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-
10
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.
______________________________________________________________________________________
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
1MΩ
τ =
⎛
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.
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
RCHGI
MAX1586
MAX8568
n-CHANNEL
MOSFET OR
OPEN-DRAIN
INVERTER
LBO
τ = RGS x CISS
−50µs
CHGI
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
A1
L
L
e
e
PACKAGE OUTLINE
12, 16L, THIN QFN, 3x3x0.8mm
E
21-0136
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
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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.)