MAXIM MAX8677AETG+

19-0722; Rev 1; 1/07
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
The MAX8677A is an integrated 1-cell Li+ charger and
Smart Power Selector™ with dual (DC and USB) power
inputs. It can operate with either separate inputs for
USB and AC adapter power*, or from a single input that
accepts both. All power switches for charging and
switching the load between battery and external power
are included on-chip. No external MOSFETs are
required.
The MAX8677A features a Smart Power Selector to
make the best use of limited USB or adapter power.
The battery charge current and input current limit are
independently set up to 1.5A and 2A, respectively.
Input power not used by the system charges the battery. USB input current can be set to 100mA or 500mA.
Automatic input selection switches the system load
from battery to external power.
Other features include overvoltage protection (OVP),
charge status and fault outputs, power-OK monitors,
charge timer, and battery thermistor monitor.
Additionally, on-chip thermal limiting reduces the battery
charge rate to prevent overheating. The MAX8677A is
available in a 4mm x 4mm, 24-pin TQFN-EP package.
Applications
.
PDAs, Palmtops, and Wireless Handhelds
Features
o Complete Charger and Smart Power Selector
o No External MOSFETs Required
o Common or Separate USB and Adapter Inputs
o System Operates with Discharged or No Battery
o Automatic Adapter/USB/Battery Switchover
o Load Peaks Over Adapter Rating Are Supported
by Battery
o Input Overvoltage Protection to 16V
o 40mΩ System-to-Battery Switch
o Thermal Regulation Prevents Overheating
o CHG, DOK, UOK, and FLT Indicators
o 5.3V (typ) SYS Regulation Voltage
Ordering Information
PART
TEMP RANGE
PINPACKAGE
MAX8677AETG+
-40°C to +85°C
24 TQFN-EP
(4mm x 4mm)
PKG
CODE
T2444-4
+Denotes a lead-free package.
Smart Cell Phones
Pin Configuration
GPS Navigation
BAT
BAT
USB
USB
TSET
USUS
Portable Media/MP3 Players
Digital Cameras
18
17
16
15
14
13
Typical Operating Circuit
SYS 20
11 ISET
SYS 21
SYS
DOK 22
8 VL
FLT 24
7 PSET
1
USB
Q3
Q2
BAT
CHARGE AND
SYS LOAD
SWITCH
MAX8677A
BATTERY
2
3
4
5
6
PEN2
UOK 23
PEN1
SYSTEM
LOAD
9 GND
CEN
LOAD
CURRENT
DC
CHARGE
CURRENT
10 CT
MAX8677A
DC
DC
Q1
USB
12 THM
DONE
AC
ADAPTER
CHG 19
TQFN
(4mm x 4mm x 0.8mm)
GND
*Protected by US Patent #6,507,172.
Smart Power Selector is a trademark of Maxim Integrated
Products, Inc.
________________________________________________________________ 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
MAX8677A
General Description
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
ABSOLUTE MAXIMUM RATINGS
DC, PEN1 to GND .................................................-0.3V to +16V
USB to GND .............................................................-0.3V to +9V
VL to GND ................................................................-0.3V to +4V
BAT, SYS, CEN, USUS, PEN2, TSET to GND...........-0.3V to +6V
THM, PSET, ISET, CT to GND .........................-0.3V to VL + 0.3V
DONE, CHG, DOK, UOK, FLT to GND.....................-0.3V to +6V
EP (exposed paddle) to GND ...............................-0.3V to +0.3V
DC Continuous Current (total in 2 pins) ........................2.4 ARMS
SYS Continuous Current (total in 2 pins) .......................2.4 ARMS
USB Continuous Current (total in 2 pins) ......................2.0 ARMS
BAT Continuous Current (total in 2 pins).......................2.4 ARMS
Continuous Power Dissipation (TA = +70°C)
(derate 27.8 mW/°C above +70°C) .......................... 2222mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature Range ............................-40°C to +125°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
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, DONE, CHG, DOK, UOK, FLT are unconnected,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DC-TO-SYS PREREGULATOR
DC Operating Range
4.1
DC Standoff Voltage
VBAT = VSYS = 0V
DC Undervoltage Threshold
When VDOK goes low, VDC rising, 500mV typical hysteresis
3.95
DC Overvoltage Threshold
When V DOK goes high, VDC rising, 100mV typical hysteresis
6.8
6.6
V
14
V
4.0
4.05
V
V
6.9
7.0
ISYS = IBAT = 0mA, V CEN = 0V
1
2
ISYS = IBAT = 0mA, V CEN = 5V
0.8
1.5
DC Shutdown Current
VDC = V CEN = USUS = 5V, VPEN1 = 0V
195
333
µA
DC-to-SYS On-Resistance
ISYS = 400mA, V CEN = 5V
0.2
0.35
Ω
DC-to-BAT Dropout Voltage
When SYS regulation and charging stops, VDC falling,
150mV hysteresis
10
50
90
mV
RPSET= 1.5kΩ
1800
2000
2200
RPSET = 3kΩ
900
1000
1100
RPSET = 6.3kΩ
450
475
500
VPEN1 = 0V, VPEN2 = 5V
(500mA USB mode)
450
475
500
VPEN1 = 0V, VPEN2 = 0V
(100mA USB mode)
80
95
100
DC Supply Current
DC Current Limit
(See Table 2 for Input Source
Control)
VDC = 6V, VSYS = 5V,
TA = +25°C
PSET Resistance Range
SYS Regulation Voltage
1.5
VDC = 6V, ISYS = 1mA to 1.75A, V CEN = 5V
5.1
6.3
5.3
5.5
mA
mA
kΩ
V
Connecting DC when no USB present
1.5
ms
Connecting DC with USB present
50
µs
Thermal-Limit Temperature
Die temperature at which charging and input current limits
are reduced
100
°C
Thermal-Limit Gain
ISYS reduction/die temperature (above +100°C)
VL Voltage
IVL = 0mA to 10mA
Input Current Soft-Start Time
2
5
3.0
3.3
_______________________________________________________________________________________
%/°C
3.6
V
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, DONE, CHG, DOK, UOK, FLT are unconnected,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
USB-TO-SYS PREREGULATOR
USB Operating Range
4.1
USB Standoff Voltage
VBAT = VSYS = 0V
USB Undervoltage Threshold
When V UOK goes low, VUSB rising, 500mV hysteresis
3.95
USB Overvoltage Threshold
When V UOK goes high, VUSB rising, 100mV hysteresis
6.8
6.6
V
8
V
4.0
4.05
V
V
6.9
7.0
ISYS = IBAT = 0mA, V CEN = 0V, VPEN2 = low
1
2
ISYS = IBAT = 0mA, V CEN = 5V, VPEN2 = low
0.9
1.5
USB Shutdown Current
DC = unconnected, VUSB = V CEN = VUSUS = 5V
190
333
µA
USB-to-SYS On-Resistance
DC = unconnected, VUSB = V CEN = 5V, ISYS = 400mA
0.2
0.31
Ω
USB-to-BAT Drop-Out Voltage
When SYS regulation and charging stops, VUSB falling,
250mV hysteresis
10
50
90
mV
USB Current Limit
(See Table 2 for Input Source
Control)
DC = unconnected,
VUSB = 5V,
TA = +25°C
VPEN1 = 0V,
VPEN2 = 5V
450
475
500
VPEN1 = 0V,
VPEN2 = 0V
80
95
100
SYS Regulation Voltage
DC = unconnected, VUSB = 6V;
ISYS = 1mA to 400mA, V CEN = 5V
5.1
5.3
5.5
Input Limiter Soft-Start Time
Input current ramp time
USB Supply Current
mA
Thermal-Limit Start Temperature
Thermal-Limit Gain
ISYS reduction/die temperature (above +100°C)
VL Voltage
DC = unconnected, VUSB = 5V; IVL = 0 to 10mA
mA
50
µs
100
°C
5
3.0
V
%/°C
3.3
3.6
V
0.04
0.08
Ω
68
90
mV
CHARGER
BAT-to-SYS On-Resistance
VDC = 0V, VBAT = 4.2V, ISYS = 1A
BAT-to-SYS Reverse Regulation
Voltage
VPEN1 = VPEN2 = 0V, ISYS = 200mA
BAT Regulation Voltage
IBAT = 0mA
BAT Recharge Threshold
Change in VBAT from DONE to fast-charge
BAT Charge-Current Set Range
RISET = 10kΩ to 2kΩ (Note 2)
TA = +25°C
4.179
4.2
4.221
TA = 0°C to +85°C
4.158
4.2
4.242
-135
-95
-45
mV
1.5
A
1250
1375
0.3
RISET = 2.4kΩ
BAT Charge-Current Accuracy,
Charger Loop in Control
VSYS = 5.5V,
TA = 0°C to +85°C
40
1125
RISET = 4kΩ
675
750
825
RISET = 10kΩ
270
300
330
RISET = 4kΩ, VBAT = 2.5V
(prequal mode)
50
75.0
100
RISET = 6.2kΩ, VBAT = 2.5V
(prequal mode)
23
48
73
RISET = 10kΩ, VBAT = 2.5V
(prequal mode)
V
mA
30
_______________________________________________________________________________________
3
MAX8677A
ELECTRICAL CHARACTERISTICS (continued)
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
ELECTRICAL CHARACTERISTICS (continued)
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, DONE, CHG, DOK, UOK, FLT are unconnected,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ISET Voltage
RISET = 4kΩ, IBAT = 500mA
(VISET = 1.5V at full charge current)
0.9
1.0
1.1
V
Charger Soft-Start Time
Charge-current ramp time
BAT Prequal Threshold
VBAT rising, 180mV hysteresis
BAT Leakage Current
VBAT = 4.2V
DONE Threshold as a
Percentage of Fast-Charge
IBAT decreasing
1.5
2.9
ms
3
3.1
V
No DC or USB power connected
3
6
µA
DC or USB connected, V CEN = 5V
3
6
µA
VTSET = 0
5
VTSET = open
10
VTSET = VL
15
%
Maximum Prequal Time
From V CEN falling to end of prequal charge,
VBAT = 2.5V, CT = 0.068µF
30
Min
Maximum Fast-Charge Time
From V CEN falling to VFLT falling, CT = 0.068µF
300
Min
Timer Accuracy
CT = 0.068µF
Timer Extend Threshold
Percentage of fast-charge current below which timer
clock operates at half speed
-20
+20
%
50
%
Timer Suspend Threshold
Percentage of fast-charge current below which timer
clock pauses
20
%
THM
THM Threshold, Cold
When charging is suspended, 2% hysteresis
72
74
76
% of VL
THM Threshold, Hot
When charging is suspended, 2% hysteresis
26
28
30
% of VL
THM Threshold, Disabled
When THM function is disabled
THM Input Leakage
3
THM = GND or VL; TA = +25°C
-0.1
THM = GND or VL; TA = +85°C
0.001
% of VL
+0.2
0.01
µA
LOGIC I/O: CHG, FLT, DONE, DOK, UOK, PEN1, PEN2, CEN, TSET, USUS
High level
Logic Input Thresholds
1.3
Low level
0.4
Hysteresis
50
High level
TSET Input Threshold
Midlevel
1.2
VL - 1.2
Logic Output Voltage, Low
Sinking 1mA
Logic Output-Leakage Current,
High
-20
TSET = VL
VINPUT = 0V to 5.5V
VOUT = 5.5V
V
0.3
TSET = GND
Logic Input-Leakage Current
mV
VL - 0.3
Low level
TSET Input-Bias Current
V
-6
6
20
TA = +25°C
0.001
1
TA = +85°C
0.01
25
100
TA = +25°C
0.001
1
TA = +85°C
0.01
µA
µA
mV
µA
Note 1: Limits are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design.
Note 2: Guaranteed by design.
4
_______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
0.7
0.6
VUSB RISING
VUSB FALLING
0.5
0.4
0.3
0.2
ENTERING OVLO
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
0
6
7
8
1
2
3
4
5
6
7
PEN1 = X, PEN2 = 1
0.30
0.25
0.20
0.15
0.10
0.05
0
0
8
1
2
3
4
5
6
7
8
USB VOLTAGE (V)
USB VOLTAGE (V)
BATTERY LEAKAGE CURRENT
vs. BATTERY VOLTAGE (USB DISCONNECTED)
BATTERY LEAKAGE CURRENT
vs. TEMPERATURE
BATTERY LEAKAGE CURRENT
vs. BATTERY VOLTAGE (USB CONNECTED)
2.5
2.0
1.5
1.0
3.58
3.56
3.54
3.52
3.50
7
1
2
3
4
-40
5
10
35
60
0
85
1
2
3
4
CHARGE CURRENT
vs. BATTERY VOLTAGE (500mA USB)
CHARGE CURRENT
vs. BATTERY VOLTAGE (1ADC)
400
CHARGE CURRENT (mA)
VUSB = 5V
PEN1 = X , PEN2 = 1
VBAT RISING
VBAT FALLING
30
VBAT RISING
VBAT FALLING
350
300
250
200
150
20
100
10
50
0
VUSB = 5V
PEN1 = X, PEN2 = 1
450
2
3
BATTERY VOLTAGE (V)
4
5
VDC = 5V
PEN1 = 1 , PEN2 = X
1.0
VBAT RISING
VBAT FALLING
0.8
0.6
0.4
0.2
0
0
1
1.2
CHARGE CURRENT (A)
MAX8677A toc07
500
5
MAX8677A toc09
CHARGE CURRENT
vs. BATTERY VOLTAGE (100mA USB)
70
0
2
BATTERY VOLTAGE (V)
80
40
3
TEMPERATURE (°C)
90
50
4
BATTERY VOLTAGE (V)
100
60
-15
MAX8677A toc08
0
5
0
3.46
0
VUSB = 5V
USUS = 1
CEN = 1
6
1
3.48
0.5
MAX8677A toc06
VBAT = 4V
BATTERY LEAKAGE CURRENT (µA)
3.0
MAX8677A toc05
3.5
3.60
BATTERY LEAKAGE CURRENT (µA)
MAX8677A toc04
USB = OPEN
BATTERY LEAKAGE CURRENT (µA)
0
0.35
USB VOLTAGE (V)
4.0
CHARGE CURRENT (mA)
VBAT = 4.2, USUS = 1
ENTERING OVLO
EXITING UVLO
0.1
EXITING UVLO
VUSB RISING
VUSB FALLING
CEN = 1
ISYS = 0V
PEN1 = X, PEN2 = 1
1.0
0.40
MAX8677A toc03
0.8
VBAT = 4.2, VUSUS = 0V
MAX8677A toc02
CHARGER IN
DONE MODE
ISYS = 0V
PEN1 = X, PEN2 = 1
1.2
USB QUIESCENT CURRENT (mA)
VBAT = 4.2, VUSUS = 0V
0.9
USB QUIESCENT CURRENT (mA)
MAX8677A toc01
1.0
USB QUIESCENT CURRENT
vs. USB VOLTAGE (SUSPEND)
USB QUIESCENT CURRENT
vs. USB VOLTAGE (CHARGER DISABLED)
USB QUIESCENT CURRENT (mA)
USB QUIESCENT CURRENT
vs. USB VOLTAGE (CHARGER ENABLED)
0
1
2
3
BATTERY VOLTAGE (V)
4
5
0
1
2
3
4
5
BATTERY VOLTAGE (V)
_______________________________________________________________________________________
5
MAX8677A
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
1.0050
1.0025
1.0000
0.9975
0.9950
4.200
MAX8677A toc12
5.2
VBAT = 4V
NO SYS LOAD
5.0
4.8
4.195
VSYS (V)
1.0075
4.205
MAX8677A toc11
VUSB = 5V, VBAT = 4V
BATTERY REGULATION VOLTAGE (V)
MAX8677A toc10
NORMALIZED CHARGE CURRENT
1.0100
SYS OUTPUT VOLTAGE
vs. USB VOLTAGE
BATTERY REGULATION VOLTAGE
vs. TEMPERATURE
NORMALIZED CHARGE CURRENT vs. AMBIENT
TEMPERATURE (LOW IC POWER DISSIPATION)
4.6
4.190
4.4
4.185
4.2
0.9925
40ppm/°C
4.0
4.180
-15
10
35
60
-40
85
-15
VBAT = 4V
NO SYS LOAD
5.2
3
4
5
7
VBAT = 4V
5.5
THE SLOPE OF THIS LINE
SHOWS THAT THE BAT-TO-SYS
RESISTANCE IS 40mΩ
VSYS (V)
4.1
4.0
VDC = 6V
5.1
8
VDC = 5V
4.7
4.3
3.9
4.4
3.8
4.2
3.9
VBAT = 4V
PEN1 = 1, PEN2 = X
CEN = 1
3.7
3.6
4.0
0
2
4
6
8
10
12
3.5
0
14
0.5
VDC (V)
1.0
1.5
2.0
1.0
3.5
3.0
2.5
VVL (V)
4.5
4.3
500mA
MAX8677A toc17
4.7
2.0
VL OUTPUT VOLTAGE
vs. DC VOLTAGE
VBAT = 4V
VUSB = 5V
PEN1 = X, PEN2 = 1
CEN = 1
4.9
1.5
ISYS (A)
MAX8677A toc16
5.1
VSYS (V)
0.5
0
ISYS (A)
SYS OUTPUT VOLTAGE
vs. SYS OUTPUT CURRENT (USB)
IVL = 10mA
2.0
IVL = 0mA
1.5
4.1
1.0
3.9
0.5
100mA
3.7
0
3.5
0
0.5
1.0
1.5
ISYS (A)
6
6
SYS OUTPUT VOLTAGE
vs. SYS OUTPUT CURRENT (DC)
4.3
VSYS (V)
2
SYS OUTPUT VOLTAGE vs. SYS OUTPUT
CURRENT (USB AND DC DISCONNECTED)
4.2
4.6
1
0
85
VUSB (V)
4.4
5.0
4.8
60
4.5
MAX8677A toc13
5.4
35
TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
SYS OUTPUT VOLTAGE
vs. DC VOLTAGE
10
MAX8677A toc14
-40
MAX8677A toc15
0.9900
VSYS (V)
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
2.0
2.5
3.0
0
2
4
6
8
10
12
VDC (V)
_______________________________________________________________________________________
14
2.5
3.0
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
MAX8677A toc18
1.0
0.6
2.5
2.0
1.5
0.4
0.2
1.0
0.5
0
0
50
100
0.40
IBAT
3.5
VBAT (V)
IBAT
3.0
0.30
2.5
0.25
2.0
0.20
1.5
0.15
1.0
0.10
0.5
0.05
0.00
0
150
0
20
40
60
80
100 120 140
TIME (min)
TIME (min)
DC CONNECT WITH USB CONNECTED
(RSYS = 25Ω)
DC CONNECT WITH NO USB
(RSYS = 25Ω)
VSYS
3.6V
500mA
0A
180
500mA/div
5V/div
5V
3.6V
CDC CSYS CHARGING
CHARGING
CDC CHARGING CSYS CHARGING
IDC
160
MAX8677A toc21
VBAT
4.6V
5V
4.2V
0.35
3.0
MAX8677A toc20
VSYS
5V/div
1.2A
IDC
500mA/div
0A
IUSB
0A
500mA
0A
IBAT
BATTERY
CHARGER
SOFT-START
BATTERY
-320mA CHARGER
-310mA
SOFT-START
NEGATIVE BATTERY
CURRENT FLOWS INTO
THE BATTERY
(CHARGING)
120mA
NEGATIVE BATTERY CURRENT
FLOWS INTO THE BATTERY
(CHARGING)
IBAT
200µs/div
400µs/div
DC DISCONNECT WITH NO USB
(RSYS = 25Ω)
USB CONNECT WITH NO DC
(RSYS = 25Ω)
5V
MAX8677A toc23
VUSB
3.6V
IUSB
500mA/div
0A
VSYS
VUOK
0.2A
500mA/div
IBAT
-1A
0V
2V/div
1.2A
IDC
NEGATIVE BATTERY
CURRENT FLOWS INTO
THE BATTERY
(CHARGING)
20µs/div
500mA/div
-1A
MAX8677A toc22
VSYS
0.50
0.45
4.0
0.8
0
VBAT
4.5
VBAT
5.0
4.5
4.0
3.5
MAX8677A toc19
5.0
1.2
IBAT (A)
VBAT (V)
6.0
5.5
CHARGE PROFILE —1400mAh BATTERY
USB INPUT—500mA CHARGE
IBAT (A)
CHARGE PROFILE —1400mAh BATTERY
ADAPTER INPUT—1A CHARGE
VCHG
IBAT
5V
CUSB CHARGING
10V/div
CSYS CHARGING
500mA/div
500mA
0A
5V
3.6V
4.3V
5V/div
3V
0V
5V/div
3V
0V
5V/div
140mA
-300mA
500mA/div
BATTERY
CHARGER SOFT-START
200µs/div
_______________________________________________________________________________________
7
MAX8677A
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
USB DISCONNECT WITH NO DC
(RSYS = 25Ω)
USB SUSPEND
MAX8677A toc24
VUSB
MAX8677A toc25
5V
0V
VUSUS
10V/div
475mA
IUSB
VSYS
500mA/div
0A
4.3V
IBAT
-300mA
3V
5V/div
3V
5V/div
120mA
5V/div
0A
500mA/div
4V
5V/div
0V
VUOK
4.6V
VSYS
3.6V
0V
VCHG
500mA
IUSB
5V
2V/div
VCHG
0V
3V
-500mA
0A
5V/div
IBAT
1A/div
500mA/div
200µs/div
200µs/div
USB RESUME
MAX8677A toc26
VUSUS
3V
CSYS CHARGING
IUSB
0A
VSYS
4V
VCHG
IBAT
5V/div
0V
500mA
4.6V
3V
500mA/div
2V/div
5V/div
0V
0A BATTERY
CHARGER
SOFT-START
-500mA
500mA/div
200µs/div
Pin Description
8
PIN
NAME
FUNCTION
1
DONE
2, 3
DC
DC Power Input. DC is capable of delivering up to 2A to SYS. DC supports both AC adapter and USB inputs. The
DC current limit is set with PEN1, PEN2, USUS, and RPSET. See Table 2. Both DC pins must be connected
together externally.
4
CEN
Charger Enable Input. Connect CEN to GND to enable battery charging when a valid source is connected at DC
or USB. Connect to VL or drive high with a logic signal to disable battery charging.
5
PEN1
DC Input Limit Control. If PEN1 is high, the DC input current limit is 3000/RPSET. If PEN1 is low, the DC limit is set
by PEN2 and USUS. See Table 2.
Charge Done Output. Active-low, open-drain output pulls low when the charger enters the DONE state. No
charging current flows when DONE is low. See Figure 5.
_______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
PIN
NAME
FUNCTION
6
PEN2
USB High/Low Control. PEN2 sets the DC or USB current limit to 100mA (PEN2 low) or 500mA (PEN2 high).
PEN2 controls both DC and USB current limits when PEN1 is low. See Table 2.
7
PSET
DC Input Current-Limit Set. Connect a resistor to ground to program the DC current limit to 3000/RPSET.
8
VL
9
GND
10
CT
11
ISET
Charge Current Set Input. A resistor (RISET) from ISET to GND programs the maximum charge current up to 1.5A.
The prequal charge current is 10% of the set maximum charge current.
12
THM
Thermistor Input. Connect a negative temperature coefficient (NTC) thermistor that has good thermal contact
with the battery from THM to GND. Connect a resistor equal to the thermistor +25°C resistance from THM to VL.
Charging is suspended when the thermistor is outside the hot and cold limits. Connect THM to GND to disable
the thermistor temperature sensor.
13
USUS
USB Suspend Input. With PEN1 low, driving USUS high turns off both the USB and DC inputs. With PEN1 high,
driving USUS high turns off only the USB input. See Table 2.
14
TSET
Termination Current Set Pin. Connect to GND, leave open, or connect to VL for a 5%, 10%, or 15% (of ICHGMAX)
termination current (ITERM) threshold.
15, 16
USB
USB Power Input. USB is capable of delivering up to 0.5A to SYS. The USB current limit is set with PEN2 and
USUS. See Table 2. Both USB pins must be connected together externally.
17, 18
BAT
Battery Connection. Connect to a single-cell Li+ battery. The battery charges from SYS when a valid source is
present at DC or USB. BAT powers SYS when neither DC nor USB power is present, or when the SYS load
exceeds the input current limit. Both BAT pins must be connected together externally.
19
CHG
Charger Status Output. Active-low, open-drain output pulls low when the battery is in fast-charge or prequal.
Otherwise, CHG is high impedance.
Logic LDO Output. VL is the output of an LDO that powers the MAX8667A internal circuitry. VL also provides
3.3V at up to 10mA to power external circuitry. Connect a 0.1µF capacitor from VL to GND.
Ground
Charge Timer Program Pin. A capacitor from CT to GND sets the fast-charge (tFSTCHG) and prequal (tPREQUAL)
fault timers. Connect to GND to disable the timer.
System Supply Output. SYS is connected to BAT through an internal 40mΩ system load switch when DC or USB
is invalid, or when the SYS load is greater than the input current limit.
20, 21
SYS
When a valid voltage is present at DC or USB, SYS is limited to 5.3V. When the system load (ISYS) exceeds the
DC or USB current limit, SYS is regulated to 68mV below BAT, and both the USB input and the battery service SYS.
22
DOK
Bypass SYS to GND with a 10µF X5R or X7R ceramic capacitor. Both SYS pins must be connected together
externally.
DC Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at DC.
23
UOK
USB Power-OK Output. Active-low, open-drain output pulls low when a valid input is detected at USB.
24
FLT
Fault Output. Active-low, open-drain output pulls low when the battery timer expires before prequal or
fast-charge complete.
—
EP
Exposed Paddle. Connect the exposed paddle to GND. Connecting the exposed paddle does not remove the
requirement for proper ground connections to the appropriate pins.
_______________________________________________________________________________________
9
MAX8677A
Pin Description (continued)
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
AC
ADAPTER
DC
DC POWER
MANAGEMENT
PWR
OK
DOK
MAX8677A
SYS
CURRENTLIMITED
VOLTAGE
REGULATOR
Li+ BATTERY CHARGER
AND SYS LOAD SWITCH
CHARGER
CURRENTVOLTAGE
CONTROL
SET
INPUT
LIMIT
TO
SYSTEM
LOAD
ISET
BAT
BAT+
BATT
USB
USB
USB POWER
MANAGEMENT
THERMISTOR
MONITOR
(SEE FIGURE 7)
THM
NTC
VL
PWR
OK
UOK
CURRENTLIMITED
VOLTAGE
REGULATOR
IC
THERMAL
REGULATION
CHARGE
TERMINATION
AND MONITOR
CHG
DONE
VL = 15%
TSET
SET
INPUT
LIMIT
DC MODE
500mA
USB 100mA
LIMIT
5%
FLT
CHARGE
TIMER
CT
PEN1
PEN2
USB
SUSPEND
N.C. = 10%
USUS
PSET
CEN
INPUT AND
CHARGER
CURRENT LIMIT
SET LOGIC
GND
EP
DC
LIMIT
Figure 1. Block Diagram
Circuit Description
The MAX8677A contains an Li+ battery charger, as well
as power MOSFETs and control circuitry to manage
power flow in portable devices. See Figure 1. The
10
charger has two power inputs, DC and USB. These can
be separately connected to an AC adapter output and
a USB port, or the DC input can be a single power
input that connects to either an adapter or USB. Logic
inputs, PEN1 and PEN2, select the correct current limits
______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
MAX8677A
RPU
3X 560kΩ
TO VL
RPU
560kΩ
CHARGE
DONE
ADAPTER
CDC
4.7µF
OFF
1
DONE
2
DC
3
DC
4
CHARGE ON
5
MAX8677A
CEN
PEN1
FLT
UOK
DOK
SYS
SYS
24
FAULT
OUTPUT
23
USB PWR
OK
22
DC PWR
OK
21
20
TO SYSTEM
LOAD
CSYS
10µF
560kΩ
TO VL
500mA
6
100mA
7
PEN2
PSET
CHG
BAT
19
18
RPSET
8
CL
0.1µF
CT
0.068µF
VL
BAT
17
USB
16
1-CELL
Li+
CBAT
4.7µF
USB
9
10
11
GND
CT
ISET
USB
15
12
THM
VBUS
CUSB
4.7µF
GND
TSET
14
RISET
10kΩ
CHARGE
INDICATOR
USUS
13
TO VL: ITERM = 15%
OPEN: ITERM = 10%
GND: ITERM = 5%
NTC
10kΩ
+25°C
USB SUSPEND
Figure 2. Typical Application Circuit Using Separate DC and USB Connectors
for two-input or single-input operation. Figure 2 is the
typical application circuit using separate DC and USB
connectors. Figure 3 is the typical application circuit
using a Mini 5-style connector or other DC/USB common connector.
In addition to charging the battery, the MAX8677A also
supplies power to the system through the SYS output.
The charging current is also provided from SYS so that
the set input current limit controls the total SYS current,
which is the sum of the system load current and the
battery-charging current. SYS is powered from either
the DC input pin or the USB input pin. If both the DC
and USB are connected, DC takes precedence.
______________________________________________________________________________________
11
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
3X 560kΩ
TO VL
560kΩ
CHARGE
DONE
MINI 5-STYLE
CONNECTOR
VBUS
DD+
ID
GND
1
2
3
CDC
4.7µF
1
DONE
2
DC
3
DC
4
5
OFF
CHARGE
ON
4
HI = DC
DC-USB ID
LO = USB
5
500mA
6
CEN
PEN1
MAX8677A
FLT
UOK
DOK
SYS
SYS
24
FAULT
OUTPUT
23
USB PWR
OK
22
DC PWR
OK
21
20
560kΩ
TO VL
100mA
7
PEN2
PSET
CHG
BAT
19
8
CL
0.1µF
CT
0.068µF
9
10
11
VL
GND
CT
BAT
17
USB
16
USB
15
ISET
TSET
THM
USUS
CHARGE
INDICATOR
18
RPSET
12
1-CELL
Li+
CBAT
4.7µF
14
RISET
10kΩ
TO SYSTEM
LOAD
CSYS
10µF
TO VL: ITERM = 15%
13
OPEN: ITERM = 10%
GND: ITERM = 5%
NTC
10kΩ
+25°C
USB SUSPEND
Figure 3. Typical Application Circuit Using Mini 5-Style Connector or Other DC/USB Common Connector
In some instances, there may not be enough adapter
current or USB current to supply peak system loads.
The MAX8677A Smart Power Selector circuitry offers
flexible power distribution from an AC adapter or USB
source to the battery and system load. The battery is
charged with any available power not used by the system load. If a system load peak exceeds the input
12
current limit, supplemental current is taken from the battery. Thermal limiting prevents overheating by reducing
power drawn from the input source. In the past, it might
have been necessary to reduce system functionality to
limit current drain when a USB source is connected.
However, in the MAX8677A, this is no longer the case.
When the DC or USB source hits its limit, the battery
supplies supplemental current to maintain the load.
______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
COMPONENT
(FIGURES 2, 3)
FUNCTION
PART
CIN
Input filter capacitor
4.7µF ceramic capacitor
CL
VL filter capacitor
0.1µF ceramic capacitor
CSYS
SYS output bypass capacitors
10µF ceramic capacitor
CBAT
Battery bypass capacitor
4.7µF ceramic capacitor
CT
Charger timing capacitor
0.068µF low TC ceramic capacitor
Logic output pullup resistors
560kΩ
RPU (x 4)
THM
RT
Negative TC thermistor
Phillips NTC thermistor, P/N 2322-640-63103, 10kΩ ±5% at +25°C
THM pullup resistor
10kΩ ±1%
RPSET
Input current-limit programming resistor
1.5kΩ ±1% for 2A limit
RISET
Fast-charge current programming resistor
3kΩ ±1% for 1A charging
The MAX8677A features OVP. Part of this protection is
a 5.3V voltage limiter at SYS. If the DC or USB input
exceeds 5.3V, SYS still limits at 5.3V. It is expected that
the SYS limiter will not need to operate, and will be in
dropout in most cases. A typical 5VAC adapter operates below the limit level, so both DC and SYS would
be at 5V in that case.
The MAX8677A has numerous other charging and
power-management features, which are detailed in the
following sections.
Smart Power Selector
The MAX8677A Smart Power Selector seamlessly distributes power between the external inputs, the battery,
and the system load (Figure 4). The basic functions
performed are:
•
With both an external power supply (USB or
adapter) and battery connected:
AC
ADAPTER
SYS
DC
Q1
USB
MAX8677A
Table 1. External Components List for Figures 2 and 3
CHARGE
CURRENT
LOAD
CURRENT
SYSTEM
LOAD
USB
Q3
Q2
BAT
CHARGE AND
SYS LOAD
SWITCH
MAX8677A
GND
BATTERY
When the system load requirements are less
than the input current limit, the battery is
charged with residual power from the input.
When the system load requirements exceed the
input current limit, the battery supplies supplemental current to the load.
•
When the battery is connected and there is no
external power input, the system is powered from
the battery.
•
When an external power input is connected and
there is no battery, the system is powered from the
external power input.
A thermal-limiting circuit reduces the battery charge
rate and external power-source current to prevent the
MAX8677A from overheating.
System Load Switch
An internal 40mΩ MOSFET connects SYS to BAT (Q3,
Figure 4) when no voltage source is available at DC or
USB. When an external source is detected at DC or
USB, this switch is opened and SYS is powered from
the valid input source through the input limiter.
The SYS-BAT switch also holds up SYS when the system load exceeds the input current limit. If that should
happen, the SYS-BAT switch turns on so that the battery supplies additional SYS load current. If the system
load continuously exceeds the input current limit, the
battery does not charge, even though external power is
connected. This is not expected to occur in most
cases, since high loads usually occur only in short
peaks. During these peaks, battery energy is used, but
at all other times the battery charges.
Figure 4. Smart Power Selector Block Diagram
______________________________________________________________________________________
13
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
Input Limiter
The input voltage limiter is essentially an LDO regulator
designed to run in dropout. While in dropout, the regulator dissipates a small I2R loss through the 0.2Ω MOSFET (Q1, Figure 4) between DC and SYS. With an AC
adapter or USB source connected, the input limiter distributes power from the external power source to the
system load and battery charger. In addition to the
input limiter’s primary function of passing power to the
system and charger loads at SYS, it performs several
additional functions to optimize use of available power:
• Input Voltage Limiting. If an input voltage is above
the overvoltage threshold (6.9V typ), the MAX8677A
enters overvoltage lockout (OVLO). OVLO protects
the MAX8677A and downstream circuitry from highvoltage stress up to 14V at DC and 8V at USB. In
OVLO, VL remains on, the input switch that sees
overvoltage (Q1, Q3, Figure 4) opens, and the
appropriate power-monitor output (DOK, UOK) is
high impedance, and CHG is high impedance.
•
Thermal Limiting. The MAX8677A reduces input limiter current by 5%/°C when its die temperature
exceeds +100°C. The system load (SYS) has priority
over the charger current, so input current is first
reduced by lowering charge current. If the junction
temperature still reaches +120°C in spite of chargecurrent reduction, no input (DC or USB) current is
drawn, the battery supplies the entire system load, and
SYS is regulated at 68mV below BAT. Note that this
on-chip thermal-limiting circuitry is not related to and
operates independently from the thermistor input.
•
Adaptive Battery Charging. While the system is
powered from DC, the charger draws power from
SYS to charge the battery. If the charger load plus
system load exceeds the input current limit, an
adaptive charger control loop reduces charge current to prevent the SYS voltage from collapsing.
Maintaining a higher SYS voltage improves efficiency and reduces power dissipation in the input limiter.
The total current through the switch (Q1 or Q2 in
Figure 4) is the sum of the load current at SYS and
the battery charging current. The limiter clamps at
5.3V, so input voltages greater than 5.3V can
increase power dissipation in the limiter. The limiter
power loss is (VDC - 5.3) x I, but not less than I2 x
0.2Ω. Also note that the MAX8677A turns off any
input that exceeds 6.9V (nominal).
If both DC and USB see overvoltage, both input
switches (Q1 and Q2, Figure 4) open and the
charger turns off. The BAT-SYS switch (Q3, Figure
4) closes, allowing the battery to power SYS.
An input is also invalid if it is less than BAT, or less
than the DC undervoltage threshold of 3.5V (falling).
With an invalid input voltage, SYS connects to BAT
through a 40mΩ switch (Q3, Figure 4).
Input Overcurrent Protection. The current at DC
and USB is limited to prevent input overload. This current limit can be selected to match the capabilities of
the source, whether it is a 100mA or 500mA USB
source, or an AC adapter. When the load exceeds
the input current limit, SYS drops to 68mV below BAT
and the battery supplies supplemental load current.
•
DC and USB Connections and
Current-Limit Options
Input Current Limit
The input and charger current limits are set as shown in
Table 2. It is often preferable to change the input current limit as the input power source is changed. The
MAX8677A facilitates this by allowing different input
current limits for DC and USB as shown in Table 2.
Table 2. Input Limiter Control Logic
POWER SOURCE
AC adapter at DC input
USB power at DC input
USB power at USB input;
DC unconnected
DC and USB unconnected
DOK
UOK
PEN1
PEN2
USUS
DC INPUT
CURRENT
LIMIT
L
X
H
X
X
3000/RPSET
USB INPUT
CURRENT
LIMIT
3000/RISET
USB input off;
DC input has
priority
L
X
L
L
L
100mA
L
X
L
H
L
500mA
L
X
L
X
H
USB suspend
H
L
X
L
L
100mA
H
L
X
H
L
500mA
H
L
X
X
H
H
H
X
X
X
No DC input
MAXIMUM
CHARGE
CURRENT*
100mA
500mA
0
3000/RISET
USB suspend
0
No USB input
0
*Charge current cannot exceed the input current limit. Charge may be less than the maximum charge current if the total SYS load
exceeds the input current limit.
14
______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
Separate Adapter and USB Connectors
When the AC adapter and USB have separate connectors, the adapter output connects to DC and the USB
source connects to USB. PEN1 is permanently tied high
(to DC or VL). The DC current limit is set by RPSET,
while the USB current limit is set by PEN2 and USUS.
Single Common Connector for USB or Adapter
When a single connector is used for both AC adapter
and USB sources, the DC input is used for both input
sources. When an AC adapter is connected at DC,
PEN1 should be pulled high to select the current limit
set by RPSET. When a USB source is connected, PEN1
should be low to select 500mA, 100mA, or USB suspend (further selected by PEN2 and USUS). PEN1 can
be pulled up by the AC adapter power to implement
hardware adapter/USB selection.
USB Suspend
Driving USUS high when PEN1 is low turns off charging,
as well as the SYS output and reduces input current to
190µA to accommodate USB suspend mode.
Power Monitor Outputs (UOK, DOK)
DOK is an open-drain output that pulls low when the
DC input has valid power. UOK is an open-drain output
that pulls low when the USB input sees valid power. A
valid input for DC or USB is between 4.1V and 6.6V. If a
single power-OK output is preferred, DOK and UOK
can be wire-ORed together. The combined output then
pulls low if either USB or DC sees a valid input.
Soft-Start
To prevent input transients that can cause instability in
the USB or AC adapter power source, the rate of
change of input current and charge current is limited.
When a valid DC or USB input is connected, the input
current limit is ramped from zero to the set current-limit
value (as shown in Table 2). If DC is connected with no
USB power present, input current ramps in 1.5ms. If
DC is connected with USB already present, input current ramps in 50µs. When USB is connected with no
DC present, input current ramps also ramps in 50µs. If
USB is connected with DC already present, the USB
input is ignored.
If an adapter is plugged into DC while USB is already
powered, the input current limit reramps from zero back
up to the DC current limit so that the AC adapter does
not see a load step. During this transition, if the input
current limit falls below the SYS load current, the battery supplies the additional current needed to support
the load. Additionally, capacitance can be added to
SYS to support the load during input power transitions.
When the charger is turned on, charge current ramps
from zero to the ISET current value in typically 1.5ms.
Charge current also ramps when transitioning to fastcharge from prequal and when changing the USB
charge current from 100mA to 500mA with PEN2. There
is no dI/dt limiting, however, if ISET is changed suddenly
using a switch at RISET.
Battery Charger
The battery charger state diagram is illustrated in
Figure 5. With a valid DC or USB input, the battery
charger initiates a charge cycle when the charger is
enabled. It first detects the battery voltage. If the battery voltage is less than the BAT prequal threshold
(3.0V), the charger enters prequal mode in which the
battery charges at 10% of the maximum fast-charge
current. This reduced charge rate ensures that the battery is not damaged by the fast-charge current while
deeply discharged. Once the battery voltage rises to
3.0V, the charger transitions to fast-charge mode and
applies the maximum charge current. As charging continues, the battery voltage rises until it approaches the
battery regulation voltage (4.2V) where charge current
starts tapering down. When charge current decreases
to 5%, 10%, or 15% (as set by TSET) of the fast-charge
current, the charger enters a brief 15s top-off, and then
charging stops. If the battery voltage subsequently
drops below the 4.1V recharge threshold, charging
restarts and the timers reset.
______________________________________________________________________________________
15
MAX8677A
When the input current limit is reached, the first action
taken by the MAX8677A is to reduce the battery charge
current. This allows the regulator to stay in dropout, or
at 5.3V, during heavy loads, thus reducing power dissipation. If, after the charge current is reduced to 0mA,
the load at SYS still exceeds the input current limit, SYS
begins to fall. When the SYS voltage drops to BAT, the
SYS-BAT switch turns on, using battery power to support the system load during the load peak.
The MAX8677A features flexible input connections (at
the DC and USB input pins) and current-limit settings
(set by PEN1, PEN2, PSET, and ISET) to accommodate
nearly any input power configuration. However, it is
expected that most systems use one of two external
power schemes: separate connections for USB and an
AC adapter, or a single connector that accepts either
USB or AC adapter output. Input and charger current
limit are controlled by PEN1, PEN2, RPSET, and RISET,
as shown in Table 2.
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
NOT READY
UOK AND DOK = HIGH IMPEDANCE
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
DONE = HIGH IMPEDANCE
ICHG = 0mA
UOK OR DOK = LOW
CEN = 0
RESET TIMER
CEN = HI
OR
REMOVE AND RECONNECT
THE INPUT SOURCE(S).
ANY STATE
TOGGLE CEN
OR
REMOVE AND RECONNECT
THE INPUT SOURCE(S).
PREQUAL
UOK OR DOK = LOW
CHG = LOW
FLT = HIGH IMPEDANCE
DONE = HIGH IMPEDANCE
0V ≤ VBATT ≤ 3V
ICHG = ICHGMAX/10
VBATT < 2.82V,
RESET TIMER
VBATT > 3V,
RESET TIMER
FAST CHARGE
VBATT < 2.8V
RESET TIMER
UOK OR DOK = LOW
CHG = LOW
FLT = HIGH IMPEDANCE
DONE = HIGH IMPEDANCE
3V < VBATT < 4.2V
ICHG ≤ ICHGMAX
ICHG < ITERM
AND VBAT = 4.2V
AND THERMAL
OR INPUT LIMIT
NOT EXCEEDED.
RESET TIMER.
ICHG > ITERM
RESET TIMER
ANY CHARGING
STATE
THM OK
TIMER RESUME
THM NOT OK
TIMER SUSPEND
TEMPERATURE
SUSPEND
ICHG = 0mA
UOK OR DOK = PREVIOUS STATE
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
DONE = HIGH IMPEDANCE
TIMER > tPREQUAL
FAULT
UOK OR DOK = LOW
CHG = HIGH IMPEDANCE
FLT = LOW
DONE = HIGH IMPEDANCE
ICHG = 0mA
TIMER > tFSTCHG
(TIMER SLOWED BY 2X IF
ICHG < ICHGMAX/2, AND
PAUSED IF ICHG < ICHGMAX/5
WHILE BAT < 4.2V)
TOP-OFF
UOK OR DOK = LOW
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
DONE = HIGH IMPEDANCE
BATT = 4.2V
ICHG < ITERM
VBAT < 4.1V
RESET TIMER
TIMER > 15s
DONE
UOK OR DOK = 0V
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
DONE = LOW
4.1 < VBATT < 4.2V
ICHG = 0mA
Figure 5. MAX8677A Charger State Flowchart
16
______________________________________________________________________________________
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
MONITORING THE BATTERY
CHARGE CURRENT WITH VISET
VISET =
RISET
2000
x ICHG
1.5
VISET (V)
Setting the Charge Current
MAX8677A
Charge Enable (CEN)
When CEN is low, the charger is on. When CEN is high,
the charger turns off. CEN does not affect the SYS output. In many systems, there is no need for the system
controller (typically a microprocessor) to disable the
charger, because the MAX8677A Smart Power Selector
circuitry independently manages charging and
adapter/battery power hand-off. In these situations,
CEN can be connected to ground.
ISET adjusts charge current to match the capacity of
the battery. A resistor from ISET to ground sets the
maximum fast-charge current:
ICHGMAX = 2000 x 1.5V/RISET = 3000/RISET
Determine the ICHGMAX value by considering the characteristics of the battery. It is not necessary to limit the
charge current based on the capabilities of the expected
AC adapter/USB charging input, the system load, or
thermal limitations of the PCB. The MAX8677A automatically adjusts the charging algorithm to accommodate
these factors.
Monitoring the Charge Current
In addition to setting the charge current, ISET can also
be used to monitor the actual current charging the battery. The ISET output voltage is:
VISET = ICHG x 1.5V/ICHGMAX = ICHG x RISET/2000
where ICHGMAX is the set fast-charge current and ICHG
is the actual battery charge current. A 1.5V output indicates the battery is being charged at the maximum set
fast-charge current; 0V indicates no charging. This voltage is also used by the charger control circuitry to set
and monitor the battery current. Avoid adding more
than 10pF capacitance directly to the ISET pin. If filtering of the charge-current monitor is necessary, add a
resistor of 100kΩ or more between ISET and the filter
capacitor to preserve charger stability. See Figure 6.
Note that the actual charge current can be less than
the set fast-charge current when the charger enters
voltage mode or when charge current is reduced by
the input current limiter or thermal limiter. This prevents
the charger from overloading the input source or overheating the system.
Charge Termination
When the charge current falls to the termination threshold AND the charger is in voltage mode, charging is
complete. Charging continues for a brief 15s top-off
period and then enters the DONE state in which charging stops. The termination current threshold (ITERM) is
set by TSET to a percentage of the fast-charge current:
Connect TSET to GND for ITERM = ICHGMAX x 5%
0
DISCHARGING
0
2000 (1.5V / RISET)
BATTERY CHARGING CURRENT (A)
Figure 6. Monitoring the Charge Current with the ISET Voltage
Leave TSET open for ITERM = ICHGMAX x 10%
Connect TSET to VL for ITERM = ICHGMAX x 15%
When the charger enters DONE 15s later, the DONE
output goes low. Note that if charge current falls to
ITERM as a result of the input or thermal limiter, the
charger does not enter DONE. For the charger to enter
DONE, the charge current must be less than ITERM, the
charger must be in voltage mode, and the input or thermal limiter must not be reducing the charge current.
Charge Status Outputs
Charge Output (CHG)
CHG is an open-drain, active-low output that is low during charging. CHG is low when the battery charger is in
its prequalification and fast-charge states. When charge
current falls to the charge termination threshold and the
charger is in voltage mode, CHG goes high impedance.
CHG goes high impedance if the thermistor causes the
charger to enter temperature suspend mode.
When the MAX8677A is used with a microprocessor (µP),
connect a pullup resistor between CHG and the logic I/O
voltage to indicate charge status to the µP. Alternatively,
CHG can sink up to 20mA for an LED indicator.
Charge Done Output (DONE)
DONE is an open-drain, active-low output that goes low
when charging is complete. The charger enters its
DONE state 15s after charge current falls to the
______________________________________________________________________________________
17
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
charge-termination threshold and the charger is in voltage mode. The charger exits the DONE state, and fastcharge resumes, if the battery voltage subsequently
drops 100mV, or if input power or CEN is cycled.
When the MAX8677A is used in conjunction with a µP,
connect a pullup resistor between DONE and the logic I/O
voltage to indicate charge status to the µP. Alternatively,
DONE can sink up to 20mA for an LED indicator.
Fault Output (FLT) and Charge Timer
FLT is an open-drain, active-low output that goes low
during a battery fault. The fault state occurs when either
the prequal or fast-charge timer expires. The prequal
and fast-charge fault timers are set by CCT:
CCT
tPREQUAL = 30 min ×
0.068µF
tFSTCHG = 300 min ×
CCT
0.068µF
While in fast-charge mode, a large system load or
device self-heating can cause the MAX8677A to
reduce charge current. Under these circumstances, the
fast-charge timer adjusts to ensure that adequate
charge time is still allowed. Consequently, the fastcharge timer is slowed by 2x if charge current is
reduced below 50% of the programmed fast-charge
level. If charge current is reduced to below 20% of the
programmed level, the fast-charge timer is paused. The
fast-charge timer is not adjusted if the charger is in voltage mode where charge current reduces due to current tapering under normal charging.
To exit a fault state, toggle CEN or remove and reconnect the input source(s). Note also that thermistor outof-range or on-chip thermal-limit conditions are not
considered faults.
When the MAX8677A is used in conjunction with a µP,
connect a pullup resistor between FLT and the logic I/O
voltage to indicate fault status to the µP. Alternatively,
FLT can sink up to 20mA for an LED indicator.
Thermistor Input (THM)
The THM input connects to an external negative temperature coefficient (NTC) thermistor to monitor battery
or system temperature. Charging is suspended when
the thermistor temperature is out of range. The charge
timers are suspended and hold their state but no fault
is indicated. When the thermistor comes back into
range, charging resumes and the charge timer continues from where it left off. Connecting THM to GND disables the thermistor monitoring function. Table 3 lists
fault temperatures for different thermistors.
Since the thermistor monitoring circuit employs an external bias resistor from THM to VL (RTB, Figure 7), the
thermistor is not limited only to 10kΩ (at +25°C).
CEN
VL
MAX8677A
VL
THERMISTOR CIRCUITRY
RTB
ALTERNATE
THERMISTOR
CONNECTION
0.74 VL
COLD
THM
RTS
0.28 VL
HOT
THM OK
RTP
RT
BYPASS THM
0.03 VL
RT
ALL COMPARATORS 60mV HYSTERESIS
GND
Figure 7. Thermistor Monitor Circuitry
18
______________________________________________________________________________________
DISABLE
CHARGER
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
For a typical 10kΩ (at +25°C) thermistor and a 10kΩ
RTB resistor, the charger enters a temperature suspend
state when the thermistor resistance falls below 3.97kΩ
(too hot) or rises above 28.7kΩ (too cold). This corresponds to a 0°C to +50°C range when using a 10kΩ
NTC thermistor with a beta of 3500. The general relation of thermistor resistance to temperature is defined
by the following equation:
hot threshold. Raising RTB lowers both the hot and cold
thresholds, while lowering RTB raises both thresholds.
Power Dissipation
It is important to ensure that the heat generated by the
MAX8677A is dissipated into the PCB. The package’s
exposed paddle must be soldered to the PCB with multiple vias tightly packed under the exposed paddle to
ensure optimum thermal contact to the ground plane.
This minimizes heat rise in the IC and ensures that
maximum charging current is maintained over the
widest range of external conditions. Table 4 shows the
thermal characteristics of the MAX8677A package.
Table 4. Package Thermal Characteristics
⎧ ⎛ 1
1 ⎞⎫
RT = R25 × e⎨⎩β⎜⎝ T +273 − 298 ⎟⎠ ⎬⎭
SINGLE-LAYER
PCB
where:
RT = The resistance in Ω of the thermistor at temperature T in Celsius
R25 = The resistance in Ω of the thermistor at +25°C
β = The material constant of the thermistor, which
typically ranges from 3000K to 5000K
T = The temperature of the thermistor in °C
Table 3 shows the MAX8677A THM temperature limits
for different thermistor material constants.
Some designs might prefer other thermistor temperature limits. Threshold adjustment can be accommodated by changing RTB, connecting a resistor in series
and/or in parallel with the thermistor, or using a thermistor with different β. For example, a +45°C hot threshold
and 0°C cold threshold can be realized by using a thermistor with a β of 4250 and connecting 120kΩ in parallel. Since the thermistor resistance near 0°C is much
higher than it is near +50°C, a large parallel resistance
lowers the cold threshold, while only slightly lowering
the hot threshold. Conversely, a small series resistance
raises the cold threshold, while only slightly raising the
MULTILAYER
PCB
Continuous
Power
Dissipation
1666.7mW
Derate 20.8mW/°C
above +70°C
2222.2mW
Derate 27.8mW/°C
above +70°C
θJA
48°C/W
36°C/W
θJC
2.7°C/W
2.7°C/W
PCB Layout and Routing
Good design minimizes ground bounce and voltage
gradients in the ground plane, which can result in instability or regulation errors. GND should connect to the
power-ground plane at only one point to minimize the
effects of power-ground currents. Battery ground should
connect directly to the power-ground plane. Connect
GND to the exposed paddle directly under the IC. Use
multiple tightly spaced vias to the ground plane under
the exposed paddle to help cool the IC. Position input
capacitors from DC, SYS, BAT, and USB to the powerground plane as close as possible to the IC. Keep highcurrent traces, such as those to DC, SYS, and BAT, as
short and wide as possible. Refer to the MAX8677A
evaluation kit for a suitable PCB layout example.
Table 3. Fault Temperatures for Different Thermistors
Thermistor β (K)
3000
3250
3500
3750
4250
RTB (kΩ) (Figure 7)
10
10
10
10
10
Resistance at +25°C (kΩ)
10
10
10
10
10
Resistance at +50°C (kΩ)
4.59
4.30
4.03
3.78
3.32
Resistance at 0°C (kΩ)
36.91
25.14
27.15
29.32
31.66
Nominal Hot-Trip Temperature (°C)
55
53
51
49
46
Nominal Cold-Trip Temperature (°C)
-3
-1
0
2
4.5
Chip Information
PROCESS: BiCMOS
______________________________________________________________________________________
19
MAX8677A
Any resistance thermistor can be used as long as the
value of RTB is equivalent to the thermistor’s +25°C
resistance. For example, with a 10kΩ at +25°C thermistor, use 10kΩ at RTB, and with a 100kΩ at +25°C thermistor, use 100kΩ.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
MAX8677A
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
20
______________________________________________________________________________________
E
1
2
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
E
2
2
Revision History
Pages changed at Rev 1: 1, 3, 21
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 ____________________ 21
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
MAX8677A
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)