General Description
The MAX8677C 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 MAX8677C 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 bat-
tery. 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 MAX8677C is
available in a 4mm x 4mm, 24-pin TQFN-EP package.
Applications
PDAs, Palmtops, and Wireless Handhelds
Smart Cell Phones
Portable Media/MP3 Players
GPS Navigation
Digital Cameras
Features
oComplete Charger and Smart Power Selector
oNo External MOSFETs Required
oCommon or Separate USB and Adapter Inputs
oSystem Operates with Discharged or No Battery
oAutomatic Adapter/USB/Battery Switchover
oLoad Peaks Over Adapter Rating Are Supported
by Battery
oInput Overvoltage Protection to 16V
o40mΩSystem-to-Battery Switch
oThermal Regulation Prevents Overheating
oPREQ, CHG, DOK, UOK, and FLT Indicators
o4.35V (typ) SYS Regulation Voltage
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
________________________________________________________________
Maxim Integrated Products
1
MAX8677C
24
23
22
21
20
19
FLT
UOK
DOK
SYS
SYS
CHG
18 17 16 15 14 13
12
TQFN
(4mm x 4mm x 0.8mm)
3456
7
8
9
10
11
12
PSET
VL
GND
CT
ISET
THM
USUS
TSET
USB
USB
BAT
BAT
PEN2
PEN1
CEN
DC
DC
PREQ
Pin Configuration
Ordering Information
Q1
AC
ADAPTER
CHARGE AND
SYS LOAD
SWITCH
CHARGE
CURRENT
LOAD
CURRENT
USB USB BAT
SYS
GND
DC
Q2 Q3
BATTERY
SYSTEM
LOAD
MAX8677C
Typical Operating Circuit
19-0781; Rev 0; 4/07
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.
+
Denotes a lead-free package.
**
EP = Exposed paddle.
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX8677CETG+ -40°C to +85°C 24 TQFN-EP**
(4mm x 4mm)
T2444-4
Smart Power Selector is a trademark of Maxim Integrated
Products, Inc.
*
Protected by U.S. Patent #6,507,172.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
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.
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
PREQ, 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) .........................2.4ARMS
SYS Continuous Current (total in 2 pins) ........................2.4ARMS
USB Continuous Current (total in 2 pins) .......................2.0ARMS
BAT Continuous Current (total in 2 pins)........................2.4ARMS
Continuous Power Dissipation (TA= +70°C)
(derate 27.8mW/°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
PARAMETER CONDITIONS MIN TYP MAX UNITS
DC-TO-SYS PREREGULATOR
DC Operating Range 4.1 6.6 V
DC Standoff Voltage VBAT = VSYS = 0V 14 V
DC Undervoltage Threshold W hen V
DOK g oes l ow , V
D C
r i si ng , 500m V typ i cal hyster esi s 3.95 4.0 4.05 V
DC Overvoltage Threshold W hen V
DOK g oes hi g h, V
D C
r i si ng , 360m V typ i cal hyster esi s 6.8 6.9 7.0 V
ISYS = IBAT = 0mA, V
CEN = 0V 1 2
DC Supply Current ISYS = IBAT = 0mA, V
CEN = 5V 0.8 1.5 mA
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= 1.5kΩ1800 2000 2200
RPSET = 3kΩ900 1000 1100
RPSET = 6.3kΩ450 475 500
VPEN1 = 0V, VPEN2 = 5V
(500mA USB mode) 450 475 500
DC Current Limit
(See Table 2 for Input Source
Control)
VDC = 6V, VSYS = 5V,
TA = +25°C
VPEN1 = 0V, VPEN2 = 0V
(100mA USB mode) 80 95 100
mA
PSET Resistance Range 1.5 6.3 kΩ
SYS Regulation Voltage VDC = 6V, ISYS = 1mA to 1.75A, V
CEN = 5V 4.29 4.35 4.40 V
Connecting DC when no USB present 1.5 ms
Input Current Soft-Start Time 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) 5 %/°C
VL Voltage IVL = 0 to 10mA 3.0 3.3 3.6 V
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
_______________________________________________________________________________________ 3
PARAMETER CONDITIONS MIN TYP MAX UNITS
USB-TO-SYS PREREGULATOR
USB Operating Range 4.1 6.6 V
USB Standoff Voltage VBAT = VSYS = 0V 8 V
USB Undervoltage Threshold When V
UOK goes low, VUSB rising, 500mV hysteresis 3.95 4.0 4.05 V
USB Overvoltage Threshold When V
UOK goes high, VUSB rising, 100mV hysteresis 6.8 6.9 7.0 V
ISYS = IBAT = 0mA, V
CEN = 0V, VPEN2 = 0V 1 2
USB Supply Current ISYS = IBAT = 0mA, V
CEN = 5V, VPEN2 = 0V 0.9 1.5 mA
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
VPEN1 = 0V,
VPEN2 = 5V 450 475 500
USB Current Limit
(See Table 2 for Input Source
Control)
DC = unconnected,
VUSB = 5V,
TA = +25°C VPEN1 = 0V,
VPEN2 = 0V 80 95 100
mA
SYS Regulation Voltage DC = unconnected, VUSB = 6V;
ISYS = 1mA to 400mA, V
CEN = 5V 4.29 4.35 4.40 V
Input Limiter Soft-Start Time Input current ramp time 50 µs
Thermal-Limit Start Temperature +100 °C
Thermal-Limit Gain ISYS reduction/die temperature (above +100°C) 5 %/°C
VL Voltage DC = unconnected, VUSB = 5V; IVL = 0 to 10mA 3.0 3.3 3.6 V
CHARGER
BAT-to-SYS On-Resistance VDC = 0V, VBAT = 4.2V, ISYS = 1A 0.04 0.08 Ω
BAT-to-SYS Reverse Regulation
Voltage VPEN1 = VPEN2 = 0V, ISYS = 200mA 40 68 90 mV
TA = +25°C 4.179 4.2 4.221
BAT Regulation Voltage IBAT = 0mA TA = 0°C to +85°C 4.158 4.2 4.242 V
BAT Recharge Threshold Change in VBAT from DONE to fast-charge -135 -95 -45 mV
BAT Charge-Current Set Range RISET = 10kΩ to 2kΩ (Note 2) 0.3 1.5 A
RISET = 2.4kΩ1125 1250 1375
RISET = 4kΩ675 750 825
RISET = 10kΩ270 300 330
RISET = 4kΩ, VBAT = 2.5V
(prequal mode) 50 75.0 100
RISET = 6.2kΩ, VBAT = 2.5V
(prequal mode) 23 48 73
BAT Charge-Current Accuracy,
Charger Loop in Control
VSYS = 5.5V,
TA = 0°C to +85°C
RISET = 10kΩ, VBAT = 2.5V
(prequal mode) 30
mA
ELECTRICAL CHARACTERISTICS (continued)
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, CHG, DOK, UOK, FLT are unconnected,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 1)
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VDC = 5V, THM = CEN = USUS = GND, VBAT = 4V, VPEN1 = VPEN2 = 5V, USB, TSET, PREQ, 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 1.5 ms
BAT Prequal Threshold VBAT rising, 180mV hysteresis 2.9 3 3.1 V
No DC or USB power connected 3 6
BAT Leakage Current VBAT = 4.2V DC or USB connected, V
CEN = 5V 3 6 µA
VTSET = 0 5
VTSET = open 10
DONE Threshold as a
Percentage of Fast-Charge IBAT decreasing
VTSET = VL15
%
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 -20 +20 %
Timer Extend Threshold Percentage of fast-charge current below which timer
clock operates at half speed 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 3 % of VL
THM = GND or VL; TA = +25°C -0.1 0.001 +0.2
THM Input Leakage THM = GND or VL; TA = +85°C 0.01 µA
LOGIC I/O: CHG, FLT, PREQ, DOK, UOK, PEN1, PEN2, CEN, TSET, USUS
High level 1.3
Low level 0.4 V
Logic Input Thresholds
Hysteresis 50 mV
High level VL - 0.3
Midlevel 1.2 VL - 1.2
TSET Input Threshold
Low level 0.3
V
TSET = GND -20 -6
TSET Input-Bias Current TSET = VL620
µA
TA = +25°C 0.001 1
Logic Input-Leakage Current VINPUT = 0 to 5.5V TA = +85°C 0.01 µA
Logic Output Voltage, Low Sinking 1mA 25 100 mV
TA = +25°C 0.001 1
Logic Output-Leakage Current,
High VOUT = 5.5V TA = +85°C 0.01 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.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
USB QUIESCENT CURRENT
vs. USB VOLTAGE (CHARGER ENABLED)
MAX8677C toc01
USB VOLTAGE (V)
USB QUIESCENT CURRENT (mA)
764 52 31
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0
08
VBAT = 4.2, VUSUS = 0V
EXITING UVLO
ENTERING OVLO
CHARGER IN
DONE MODE
ISYS = 0V
PEN1 = X, PEN2 = 1
VUSB RISING
VUSB FALLING
USB QUIESCENT CURRENT
vs. USB VOLTAGE (CHARGER DISABLED)
MAX8677C toc02
USB VOLTAGE (V)
USB QUIESCENT CURRENT (mA)
7645231
0.2
0.4
0.6
0.8
1.0
1.2
0
08
VBAT = 4.2, VUSUS = 0V
EXITING UVLO
ENTERING OVLO
CEN = 1
ISYS = 0V
PEN1 = X, PEN2 = 1
VUSB RISING
VUSB FALLING
USB QUIESCENT CURRENT
vs. USB VOLTAGE (SUSPEND)
MAX8677C toc03
USB VOLTAGE (V)
USB QUIESCENT CURRENT (mA)
7645231
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0
08
VBAT = 4.2, USUS = 1
PEN1 = X, PEN2 = 1
BATTERY LEAKAGE CURRENT
vs. BATTERY VOLTAGE (USB DISCONNECTED)
MAX8677C toc04
BATTERY VOLTAGE (V)
BATTERY LEAKAGE CURRENT (μA)
45231
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
0
USB = OPEN
BATTERY LEAKAGE CURRENT
vs. TEMPERATURE
MAX8677C toc05
TEMPERATURE (°C)
BATTERY LEAKAGE CURRENT (μA)
60 8510 35-15
3.48
3.50
3.52
3.54
3.56
3.58
3.60
3.46
-40
VBAT = 4V
BATTERY LEAKAGE CURRENT
vs. BATTERY VOLTAGE (USB CONNECTED)
MAX8677C toc06
BATTERY VOLTAGE (V)
BATTERY LEAKAGE CURRENT (μA)
45231
1
2
3
4
5
6
7
0
0
VUSB = 5V
USUS = 1
CEN = 1
CHARGE CURRENT
vs. BATTERY VOLTAGE (100mA USB)
MAX8677C toc07
BATTERY VOLTAGE (V)
CHARGE CURRENT (mA)
45231
10
20
30
40
50
60
70
80
90
100
0
0
VUSB = 5V
PEN1 = X , PEN2 = 1
VBAT RISING
VBAT FALLING
CHARGE CURRENT
vs. BATTERY VOLTAGE (500mA USB)
MAX8677C toc08
BATTERY VOLTAGE (V)
CHARGE CURRENT (mA)
45231
50
100
150
200
250
300
350
400
450
500
0
0
VUSB = 5V
PEN1 = X, PEN2 = 1
VBAT RISING
VBAT FALLING
CHARGE CURRENT
vs. BATTERY VOLTAGE (1ADC)
MAX8677C toc09
BATTERY VOLTAGE (V)
CHARGE CURRENT (A)
45231
0.2
0.4
0.6
0.8
1.0
1.2
0
0
VDC = 5V
PEN1 = 1 , PEN2 = X
VBAT RISING
VBAT FALLING
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
SYS OUTPUT VOLTAGE
vs. USB VOLTAGE
MAX8677C toc12
VUSB (V)
VSYS (V)
48567231
4.05
4.10
4.15
4.20
4.30
4.25
4.35
4.40
4.00
0
VBAT = 4V
NO SYS LOAD
SYS OUTPUT VOLTAGE
vs. DC VOLTAGE
MAX8677C toc13
VDC (V)
VSYS (V)
1041486122
4.15
4.20
4.30
4.25
4.35
4.40
4.00
4.05
4.10
0
VBAT = 4V
NO SYS LOAD
SYS OUTPUT VOLTAGE vs. SYS OUTPUT
CURRENT (USB AND DC DISCONNECTED)
MAX8677C toc14
VSYS (V)
1.50.5 2.01.0
ISYS (A)
3.9
4.0
4.1
4.3
4.2
4.4
4.5
3.6
3.8
3.7
0
VBAT = 4V
THE SLOPE OF THIS LINE
SHOWS THAT THE BAT-TO-SYS
RESISTANCE IS 40mΩ
SYS OUTPUT VOLTAGE
vs. SYS OUTPUT CURRENT (DC)
MAX8677C toc15
VSYS (V)
2.0 2.51.00.5 3.01.5
ISYS (A)
4.3
4.7
5.1
5.5
3.5
3.9
0
VBAT = 4V
PEN1 = 1, PEN2 = X
CEN = 1
SYS OUTPUT VOLTAGE
vs. SYS OUTPUT CURRENT
MAX8677C toc16
VSYS (V)
2.0 2.51.00.5 3.01.5
ISYS (A)
4.1
4.5
4.3
4.9
4.7
5.1
3.5
3.9
3.7
0
VBAT = 4V
VUSB = 5V
PEN1 = X
CEN = 1
100mA
500mA USB
VL OUTPUT VOLTAGE
vs. DC VOLTAGE
MAX8677C toc17
VVL (V)
8121042146
VDC (V)
1.5
2.0
3.0
2.5
3.5
0
1.0
0.5
0
IVL = 0mA
IVL = 10mA
BATTERY REGULATION VOLTAGE
vs. TEMPERATURE
MAX8677C toc11
TEMPERATURE (°C)
BATTERY REGULATION VOLTAGE (V)
60 8510 35-15
4.185
4.195
4.190
4.200
4.205
4.180
-40
40ppm/°C
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
_______________________________________________________________________________________
7
CHARGE PROFILE —1400mAh BATTERY
ADAPTER INPUT—1A CHARGE
MAX8677C toc18
VBAT (V)
IBAT (A)
100 15050
TIME (min)
2.5
3.5
3.0
5.0
5.5
4.5
4.0
6.0
0
2.0
1.5
1.0
0.5
0.6
1.0
0.8
1.2
0.4
0.2
0
0
VBAT
IBAT
CHARGE PROFILE —1400mAh BATTERY
USB INPUT—500mA CHARGE
MAX8677C toc19
VBAT (V)
IBAT (A)
120 140 160 1804020 1008060
TIME (min)
2.0
3.0
2.5
4.0
4.5
3.5
5.0
0
1.5
1.0
0.5
0.25
0.40
0.45
0.30
0.35
0.50
0.15
0.20
0.05
0.10
0
0
VBAT
IBAT
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
DC CONNECT WITH USB CONNECTED
(RSYS = 25Ω)
MAX8677C toc20
200μs/div
VSYS
IDC
IUSB
IBAT
500mA/div
500mA/div
500mA/div
2V/div
CDC CHARGING
CSYS CHARGING
3.6V 3.68V
0A
0A
0A
4.35V
500mA
500mA
-335mA -330mA
NEGATIVE BATTERY CURRENT
FLOWS INTO THE BATTERY
(CHARGING)
BATTERY
CHARGER
SOFT-START
DC CONNECT WITH NO USB
(RSYS = 25Ω)
MAX8677C toc21
400μs/div
VBAT
VSYS
IDC
IBAT
500mA/div
500mA/div
CDC
CHARGING
CSYS CHARGING
3.6V3.6V
0A
-1A
1.2A
120mA
4.35V
NEGATIVE BATTERY
CURRENT FLOWS INTO
THE BATTERY (CHARGING)
BATTERY
CHARGER
SOFT-START
DC DISCONNECT WITH NO USB
(RSYS = 25Ω)
MAX8677C toc22
20μs/div
VSYS
IDC
IBAT
500mA/div
500mA/div
3.6V
0A
0.2A
-1A
1.2A
4.35V
NEGATIVE BATTERY
CURRENT FLOWS INTO
THE BATTERY (CHARGING)
USB CONNECT WITH NO DC
(RSYS = 20Ω)
MAX8677C toc23
200μs/div
VUSB
IUSB
VSYS
IBAT
500mA/div
500mA/div
5V/div
5V/div
10V/div
CUSB CHARGING
CSYS CHARGING
0V
4.3V
0A
-300mA
500mA
155mA
3V
3V
0V
0V
3.6V 4.35V
5V
BATTERY
CHARGER SOFT-START
VUOK
VCHG
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
8 _______________________________________________________________________________________
USB DISCONNECT WITH NO DC
(RSYS = 20Ω)
MAX8677C toc24
200μs/div
VUSB
IUSB
VSYS
I
BAT
500mA/div
1A/div
5V/div
5V/div
10V/div
0A
-300mA
475mA
120mA
3V
3V
0V
0V
3.6V
3.7V
5V
VUOK
VCHG
USB SUSPEND
MAX8677C toc25
200μs/div
VUSUS
IUSB
VSYS
I
BAT
500mA/div
500mA/div
5V/div
5V/div
-500mA 0A
0A
3V
0V
0V
3.6V
3.7V
500mA
3V
VCHG
USB RESUME
MAX8677C toc26
200μs/div
VUSUS
IUSB
VSYS
I
BAT
500mA/div
500mA/div
5V/div
5V/div
0A
0A
3V
3V
0V
0V
3.6V
4.35V 3.7V
-500mA
500mA
VCHG
CUSB CHARGING
BATTERY
CHARGER SOFT-START
Pin Description
PIN NAME FUNCTION
1PREQ Charge Prequal Output. Active-low, open-drain output pulls low when the charger enters the prequal state.
See Figure 5.
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.
4CEN 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.
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
_______________________________________________________________________________________ 9
Pin Description (continued)
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.
8VL
Logic LDO Output. VL is the output of an LDO that powers the MAX8667C internal circuitry. VL also provides
3.3V at up to 10mA to power external circuitry. Connect a 0.1µF capacitor from VL to GND.
9 GND Ground
10 CT 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.
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.
20, 21 SYS
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.
When a valid voltage is present at DC or USB, SYS is limited to 4.35V. When the system load (ISYS) exceeds the
D C or U S B cur r ent l i m i t, S Y S i s r eg ul ated to 68m V b el ow BAT, and b oth the U S B i np ut and the b atter y ser vi ce S Y S .
Bypass SYS to GND with a 10µF X5R or X7R ceramic capacitor. Both SYS pins must be connected together
externally.
22 DOK 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.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
10 ______________________________________________________________________________________
MAX8677C
DC POWER
MANAGEMENT
CURRENT-
LIMITED
VOLTAGE
REGULATOR
SET
INPUT
LIMIT
THERMISTOR
MONITOR
(SEE FIGURE 7)
CHARGE
TERMINATION
AND MONITOR
CHARGE
TIMER
PWR
OK
USB POWER
MANAGEMENT
CURRENT-
LIMITED
VOLTAGE
REGULATOR
CHARGER
CURRENT-
VOLTAGE
CONTROL BAT+
BAT-
T
NTC
INPUT AND
CHARGER
CURRENT LIMIT
SET LOGIC
IC
THERMAL
REGULATION
SET
INPUT
LIMIT
EP
PSET
USUS
PEN2
PEN1
USB
USB
UOK
DC MODE
500mA
100mA
USB
LIMIT USB
SUSPEND
DC
LIMIT
PWR
OK
Li+ BATTERY CHARGER
AND SYS LOAD SWITCH
SYS
ISET
BAT
THM
VL
CHG
PREQ
VL = 15%
TO
SYSTEM
LOAD
N.C. = 10%
5%
TSET
FLT
CT
CEN
GND
DOK
DC
AC
ADAPTER
Figure 1. Block Diagram
Circuit Description
The MAX8677C contains an Li+ battery charger, as
well as power MOSFETs and control circuitry to man-
age power flow in portable devices. See Figure 1. The
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
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
______________________________________________________________________________________ 11
MAX8677C
PREQ
1FLT
RPU
560kΩ
PREQUAL
CDC
4.7μF
ADAPTER
24
TO VL
RPU
3X 560kΩ
FAULT
OUTPUT
USB PWR
OK
DC PWR
OK
TO SYSTEM
LOAD
CHARGE
INDICATOR
1-CELL
Li+
VBUS
TO VL
560kΩ
USB
DC
2UOK 23
DC
3DOK 22
CEN
4
OFF
CHARGE ON
SYS 21
PEN1
5SYS 20
PEN2
6CHG 19
PSET
RPSET
RISET
10kΩ
7BAT 18
VL
8BAT 17
GND
9USB 16
CT
10 USB 15
ISET
11 TSET 14
THM
12 USUS 13
CSYS
10μF
CBAT
4.7μF
CUSB
4.7μF
GND
USB SUSPEND
TO VL: ITERM = 15%
OPEN: ITERM = 10%
GND: ITERM = 5%
500mA
CL
0.1μF
CT
0.068μF
NTC
10kΩ
+25°C
100mA
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 com-
mon connector.
In addition to charging the battery, the MAX8677C 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.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
12 ______________________________________________________________________________________
MAX8677C
PREQ
1FLT
560kΩ
PREQUAL
CDC
4.7μF
24
TO VL
3X 560kΩ
FAULT
OUTPUT
USB PWR
OK
DC PWR
OK
TO SYSTEM
LOAD
CHARGE
INDICATOR
1-CELL
Li+
TO VL
560kΩ
DC
2
VBUS
D-
D+
ID
GND
1
2
3
4
5
UOK 23
DC
3DOK 22
CEN
4
OFF
ON
CHARGE
DC-USB ID
SYS 21
PEN1
5SYS 20
PEN2
6CHG 19
PSET
RPSET
RISET
10kΩ
7BAT 18
VL
8BAT 17
GND
9USB 16
CT
10 USB 15
ISET
11 TSET 14
THM
12 USUS 13
CSYS
10μF
CBAT
4.7μF
USB SUSPEND
TO VL: ITERM = 15%
OPEN: ITERM = 10%
GND: ITERM = 5%
500mA
CL
0.1μF
CT
0.068μF
NTC
10kΩ
+25°C
100mA
HI = DC
LO = USB
MINI 5-STYLE
CONNECTOR
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 MAX8677C 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 sys-
tem load. If a system load peak exceeds the input
current limit, supplemental current is taken from the bat-
tery. 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 MAX8677C, this is no longer the case.
When the DC or USB source hits its limit, the battery
supplies supplemental current to maintain the load.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
______________________________________________________________________________________ 13
Table 1. External Components List for Figures 2 and 3
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
RPU (x 4) Logic output pullup resistors 560kΩ
THM Negative TC thermistor
Phillips NTC thermistor, P/N 2322-640-63103, 10kΩ ±5% at +25°C
RT 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 MAX8677C features OVP. Part of this protection is
a 4.35V voltage limiter at SYS. If the DC or USB input
exceeds 4.35V, SYS still limits at 4.35V.
The MAX8677C has numerous other charging and
power-management features, which are detailed in the
following sections.
Smart Power Selector
The MAX8677C Smart Power Selector seamlessly dis-
tributes 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:
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 supple-
mental 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
MAX8677C from overheating.
System Load Switch
An internal 40mΩMOSFET 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 sys-
tem load exceeds the input current limit. If that should
happen, the SYS-BAT switch turns on so that the bat-
tery 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.
Q1
AC
ADAPTER
CHARGE AND
SYS LOAD
SWITCH
CHARGE
CURRENT
LOAD
CURRENT
USB USB BAT
SYS
GND
DC
Q2 Q3
BATTE
R
SYSTEM
LOAD
MAX8677C
Figure 4. Smart Power Selector Block Diagram
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
14 ______________________________________________________________________________________
Input Limiter
The input voltage limiter is essentially an LDO regulator.
While in dropout, the regulator dissipates a small I2R loss
through the 0.2ΩMOSFET (Q1, Figure 4) between DC
and SYS. With an AC adapter or USB source connect-
ed, 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 MAX8677C
enters overvoltage lockout (OVLO). OVLO protects
the MAX8677C and downstream circuitry from high-
voltage 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.
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 40mΩswitch (Q3, Figure 4).
• Input Overcurrent Protection. The current at DC
and USB is limited to prevent input overload. This cur-
rent 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.
• Thermal Limiting. The MAX8677C reduces input lim-
iter 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 charge-
current 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 cur-
rent to prevent the SYS voltage from collapsing.
Maintaining a higher SYS voltage improves efficien-
cy 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
4.35V, so input voltages greater than 4.35V can
increase power dissipation in the limiter. The limiter
power loss is (VDC - 4.35) x I, but not less than I2x
0.2Ω. Also note that the MAX8677C turns off any
input that exceeds 6.9V (nominal).
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 cur-
rent limit as the input power source is changed. The
MAX8677C facilitates this by allowing different input
current limits for DC and USB as shown in Table 2.
POWER SOURCE DOK UOK PEN1
PEN2 USUS
DC INPUT
CURRENT
LIMIT
USB INPUT
CURRENT
LIMIT
MAXIMUM
CHARGE
CURRENT*
AC adapter at DC input L X H X X
3000/RPSET
3000/RISET
L X L L L 100mA 100mA
L X L H L 500mA 500mAUSB power at DC input
LX L X H
USB suspend
USB input off;
DC input has
priority
0
H L X L L 100mA
H L X H L 500mA
3000/RISET
USB power at USB input;
DC unconnected HL X X H
USB suspend
0
DC and USB unconnected H H X X X
No DC input
No USB input
0
Table 2. Input Limiter Control Logic
*
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.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
______________________________________________________________________________________ 15
When the input current limit is reached, the first action
taken by the MAX8677C is to reduce the battery charge
current. This allows the regulator to stay in dropout, or
at 4.35V, during heavy loads, thus reducing power dis-
sipation. 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 sup-
port the system load during the load peak.
The MAX8677C 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.
Separate Adapter and USB Connectors
When the AC adapter and USB have separate connec-
tors, 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 sus-
pend (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 cur-
rent 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 is 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 fast-
charge 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 bat-
tery 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 bat-
tery 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 con-
tinues, 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.
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
16 ______________________________________________________________________________________
ANY STATE
TIMER > tFSTCHG
(TIMER SLOWED BY 2X IF
ICHG < ICHGMAX/2, AND
PAUSED IF ICHG < ICHGMAX/5
WHILE BAT < 4.2V)
TIMER > 15s
UOK OR DOK = LOW
CEN = 0
RESET TIMER
TIMER > tPREQUAL
NOT READY
UOK AND DOK = HIGH IMPEDANCE
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
PREQ = HIGH IMPEDANCE
ICHG = 0mA
PREQUAL
UOK OR DOK = LOW
CHG = LOW
FLT = HIGH IMPEDANCE
PREQ = LOW
0V ≤ VBATT ≤ 3V
ICHG = ICHGMAX/10
FAST CHARGE
UOK OR DOK = LOW
CHG = LOW
FLT = HIGH IMPEDANCE
PREQ = HIGH IMPEDANCE
3V < VBATT < 4.2V
ICHG ≤ ICHGMAX
FAULT
UOK OR DOK = LOW
CHG = HIGH IMPEDANCE
FLT = LOW
PREQ = PREVIOUS STATE
ICHG = 0mA
TOP-OFF
UOK OR DOK = LOW
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
PREQ = HIGH IMPEDANCE
BATT = 4.2V
ICHG < ITERM
DONE
UOK OR DOK = 0V
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
PREQ = HIGH IMPEDANCE
4.1 < VBATT < 4.2V
ICHG = 0mA
CEN = HI
OR
REMOVE AND RECONNECT
THE INPUT SOURCE(S).
VBATT > 3V,
RESET TIMER
VBAT < 4.1V
RESET TIMER
VBATT < 2.82V,
RESET TIMER
ANY CHARGING
STATE
THM NOT OK
TIMER SUSPEND
THM OK
TIMER RESUME
TEMPERATURE
SUSPEND
ICHG = 0mA
UOK OR DOK = PREVIOUS STATE
CHG = HIGH IMPEDANCE
FLT = HIGH IMPEDANCE
PREQ = PREVIOUS STATE
ICHG < ITERM
AND VBAT = 4.2V
AND THERMAL
OR INPUT LIMIT
NOT EXCEEDED.
RESET TIMER.
ICHG > ITERM
RESET TIMER
VBATT < 2.8V
RESET TIMER
TOGGLE CEN
OR
REMOVE AND RECONNECT
THE INPUT SOURCE(S).
Figure 5. MAX8677C Charger State Flowchart
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
______________________________________________________________________________________ 17
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 out-
put. In many systems, there is no need for the system
controller (typically a microprocessor) to disable the
charger, because the MAX8677C Smart Power Selector
circuitry independently manages charging and
adapter/battery power hand-off. In these situations,
CEN can be connected to ground.
Setting the Charge Current
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 char-
acteristics 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 MAX8677C automat-
ically 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 bat-
tery. 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 indi-
cates the battery is being charged at the maximum set
fast-charge current; 0V indicates no charging. This volt-
age 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 filter-
ing of the charge-current monitor is necessary, add a
resistor of 100kΩor 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 over-
heating the system.
Charge Termination
When the charge current falls to the termination thresh-
old 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 charg-
ing 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%
Leave TSET open for ITERM = ICHGMAX x 10%
Connect TSET to VL for ITERM = ICHGMAX x 15%
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 cur-
rent 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. The charger exits the
DONE state, and fast charge resumes if the battery volt-
age subsequently drops 100mV or if CEN is cycled.
Charge Status Outputs
Charge Output (
CCHHGG
)
CHG is an open-drain, active-low output that is low dur-
ing 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 MAX8677C 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.
Prequal Output
PPRREEQQ
PREQ is an open-drain, active-low output that goes low
when the charger is in prequal state.
1.5
0
VISET = RISET
2000 x ICHG
MONITORING THE BATTERY
CHARGE CURRENT WITH VISET
02000 (1.5V / RISET)
BATTERY CHARGING CURRENT (A)
DISCHARGING
VISET (V)
Figure 6. Monitoring the Charge Current with the ISET Voltage
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
18 ______________________________________________________________________________________
When the MAX8677C is used in conjunction with a µP,
connect a pullup resistor between PREQ and the logic I/O
voltage to indicate charge status to the µP. Alternatively,
PREQ can sink up to 20mA for an LED indicator.
Fault Output (
FFLLTT
) 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:
While in fast-charge mode, a large system load or
device self-heating can cause the MAX8677C to
reduce charge current. Under these circumstances, the
fast-charge timer adjusts to ensure that adequate
charge time is still allowed. Consequently, the fast-
charge 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 volt-
age mode where charge current reduces due to cur-
rent tapering under normal charging.
To exit a fault state, toggle CEN or remove and recon-
nect the input source(s). Note also that thermistor out-
of-range or on-chip thermal-limit conditions are not
considered faults.
When the MAX8677C 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 tem-
perature 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 contin-
ues from where it left off. Connecting THM to GND dis-
ables the thermistor monitoring function. Table 3 lists
fault temperatures for different thermistors.
Since the thermistor monitoring circuit employs an exter-
nal bias resistor from THM to VL (RTB, Figure 7), the
thermistor is not limited only to 10kΩ(at +25°C).
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 10kΩat +25°C thermis-
tor, use 10kΩat RTB, and with a 100kΩat +25°C ther-
mistor, use 100kΩ.
tC
F
FSTCHG CT
=×300 0 068
min .
μ
tC
F
PREQUAL CT
=×30 0 068
min .
μ
RT
THM
GND
THM OK
DISABLE
CHARGER
VL
VL
0.74 VL
0.28 VL
0.03 VL
ALL COMPARATORS 60mV HYSTERESIS
COLD
HOT
RTB
THERMISTOR CIRCUITRY
BYPASS THM
RTP
RTS
ALTERNATE
THERMISTOR
CONNECTION
MAX8677C
CEN
RT
Figure 7. Thermistor Monitor Circuitry
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
______________________________________________________________________________________ 19
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 corre-
sponds to a 0°C to +50°C range when using a 10kΩ
NTC thermistor with a beta of 3500. The general rela-
tion of thermistor resistance to temperature is defined
by the following equation:
where:
RT = The resistance in Ωof the thermistor at tempe-
rature T in Celsius
R25 = The resistance in Ωof 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 MAX8677C THM temperature limits
for different thermistor material constants.
Some designs might prefer other thermistor tempera-
ture limits. Threshold adjustment can be accommodat-
ed by changing RTB, connecting a resistor in series
and/or in parallel with the thermistor, or using a thermis-
tor with different β. For example, a +45°C hot threshold
and 0°C cold threshold can be realized by using a ther-
mistor with a βof 4250 and connecting 120kΩin paral-
lel. 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
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
MAX8677C is dissipated into the PCB. The package’s
exposed paddle must be soldered to the PCB with mul-
tiple 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 MAX8677C package.
PCB Layout and Routing
Good design minimizes ground bounce and voltage
gradients in the ground plane, which can result in insta-
bility 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 power-
ground plane as close as possible to the IC. Keep high-
current traces, such as those to DC, SYS, and BAT, as
short and wide as possible. Refer to the MAX8677C
evaluation kit for a suitable PCB layout example.
RR e
TT
=× +−
⎛
⎝
⎜⎞
⎠
⎟
⎧
⎨
⎩
⎫
⎬
⎭
25
1
273
1
298
β
Thermistor β (K) 3000 3250 3500 3750 4250
RTB (kΩ) (Figure 7) 10 10 10 10 10
Resistance at +25°C (kΩ) 1010101010
Resistance at +50°C (kΩ) 4.59 4.30 4.03 3.78 3.32
Resistance at 0°C (kΩ) 25.14 27.15 29.32 31.66 36.91
Nominal Hot-Trip Temperature (°C) 55 53 51 49 46
Nominal Cold-Trip Temperature (°C) -3 -1 0 2 4.5
Table 3. Fault Temperatures for Different Thermistors
SINGLE-LAYER
PCB
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
Table 4. Package Thermal Characteristics
Chip Information
PROCESS: BiCMOS
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
20 ______________________________________________________________________________________
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
MAX8677C
1.5A Dual-Input USB/AC Adapter Charger
and Smart Power Selector
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.
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.)
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