MAXIM MAX1773

19-1796; Rev 1; 1/03
KIT
ATION
EVALU
E
L
B
A
AVAIL
Power Source Selector for
Dual-Battery Systems
Features
♦
♦ Automatically Detects and Responds to:
Low Battery Voltage Condition
Battery Insertion and Removal
AC Adapter Presence
♦ Direct Drive of P-Channel MOSFETs
♦ Simplifies Power Management µP Firmware
♦ Extends Battery Life by Allowing Power
Management µP to Enter Standby
♦ 4.75V to 28V AC Adapter Input Voltage Range
♦ Integrated LDO with 1mA Drive Capability
♦ Small Footprint 20-Pin TSSOP Package
Ordering Information
PART
Notebook and Subnotebook Computers
PDAs and Handy-Terminals
Internet Tablets
Dual-Battery Portable Equipment
†
20 TSSOP
MAX1773AEUP
-40°C to +85°C
20 TSSOP
Covered by U.S. Patent number 5,764,032.
FROM HOST µP
VDD
ACPRES
BATSTAT
MINV
ACDET
PDS
BATTERY
A
PIN-PACKAGE
-40°C to +85°C
Typical Operating Circuit
BATSEL
3.3V
TEMP. RANGE
MAX1773EUP
Pin Configuration appears at end of data sheet.
SYSTEM LOGIC SUPPLY
AC ADAPTER
INPUT
Topology Offers Low-Cost
Solution
________________________Applications
TO HOST µP
Patented† 7-MOSFET
3.3V
MAX1773
MAX1773A
EXTLD
THMA
BATA
TCOMP
COMA
DISA
COMB
DISB
CHGA
CHGB
THMB
BATB
STEP-DOWN
CHARGER
OUTPUT
INPUT
BATTERY
B
OUTPUT
3.3V DC-DC
CONVERTER
INPUT
SYSTEM LOAD
________________________________________________________________ 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
MAX1773/MAX1773A
General Description
The MAX1773/MAX1773A highly integrated ICs serve
as the control logic for a system with multiple power
sources. They directly drive external P-channel
MOSFETs to select from an AC adapter and dual battery sources for charge and discharge. The selection is
made based on the presence of the power sources and
the state of the batteries. The MAX1773/MAX1773A
detect low battery conditions using integrated analog
comparators and check for the presence of a battery
by using battery thermistor outputs.
The MAX1773/MAX1773A are designed for use with a
buck topology charger. They provide a simple and easily
controlled solution to a difficult analog power control problem. The MAX1773/MAX1773A provide most of the power
source monitoring and selection, freeing the system power
management microprocessor (µP) for other tasks. This not
only simplifies development of the power management
firmware for the µP but also allows the µP to enter standby,
thereby reducing system power consumption.
The MAX1773A is recommended for new designs.
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
ABSOLUTE MAXIMUM RATINGS
VBATA, VBATB to GND ............................................-0.3V to +20V
VCOMA to GND........................................-0.3V to (VBATA + 0.3V)
VCOMB to GND........................................-0.3V to (VBATB + 0.3V)
VCHGA, VCHGB, VEXTLD, VACDET to GND ..............-0.3V to +30V
VPDS, VDISA, VDISB to GND ...................-0.3V to (VEXTLD + 0.3V)
VDD, VBATSEL, V ACPRES, VBATSTAT, VTCOMP,
VMINV to GND.......................................................-0.3V to +6V
VTHMA, VTHMB (Note 1)............................................ -0.3V to +6V
Continuous Current out of THMA, THMB............................20mA
I ACPRES, IBATSTAT Sink Current..........................................30mA
Continuous Power Dissipation (TA = +70°C)
20-Pin TSSOP (derate 7.0mW/°C above +70°C) ........560mW
Operating Temperature ......................................-40°C to +85°C
Storage Temperature ........................................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1: Signals on THMA and THMB below -0.3V are clamped by internal diodes limit forward diode current to maximum continuous current. When voltage
on these pins is below -0.3V.
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
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = 0°C to +85°C, unless otherwise noted.)
PARAMETER
EXTLD Supply Voltage Range
CONDITIONS
VEXTLD > VBATA and VBATB
BATA, BATB Supply Voltage Range
MIN
TYP
MAX
28.00
V
4.75
19.00
V
VBATA = 4.75V to 19V,
VBATB = 4.75V to 19V,
IVDD = 0
VACDET = 28V
5
8
BATA, BATB Quiescent Current
(Current from the higher voltage supply)
VACDET = 2.2V to
VBATA and VBATB
40
70
VBATA = 4.75V to 19V,
VBATB = 4.75V to 19V,
IVDD = 0
VACDET = 28V
5
8
BATA, BATB Quiescent Current
(Current from the lower voltage supply)
VACDET = 2.2V to
VBATA and VBATB
8
13
VACDET = 28V, VEXTLD = 28V
35
55
VACDET= 2.2V to VBATA and VBATB,
VEXTLD = 16V
5
8
EXTLD Quiescent Current
UNITS
4.75
µA
µA
µA
LINEAR REGULATOR
VDD Output Voltage
VDD Power-Supply Rejection Ratio
VDD Undervoltage Lockout
IVDD = 0 to 100µA
3.234
3.3
3.367
IVDD = 100µA to 1mA
3.168
3.3
3.432
VBATA or VBATB = 5V to 19V, VEXTLD = 5V
1.0
VBATA = VBATB = 5V, VEXTLD = 5V to 28V
1.0
VBATA, VBATB, or VEXTLD = 5V to 19V,
sawtooth at 10V/µs, other supplies = 12V
Hysteresis is typically 50mV
V
mV/V
1
2.0
2.5
3.0
V
COMPARATORS
TCOMP Undervoltage Lockout
(Note 2)
THM_ Input Voltage Range
THM_ Input Leakage Current
TCOMP Input Voltage Range
2
0
1.1
V
0
5.5
V
100
nA
VTHM_ = 5.5V
0.1
VTHMA = VTHMB = 0 to 5.5V
0
5.5
VTHMA = VTHMB = 0 to 5.5V, VBATA = VBATB
= VEXTLD = 4.75V
0
4.3
_______________________________________________________________________________________
V
Power Source Selector for
Dual-Battery Systems
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = 0°C to +85°C, unless otherwise noted.)
PARAMETER
CONDITIONS
TCOMP Input Leakage Current
VTCOMP = 5.5V
THM_ to TCOMP Trip Threshold
THM_ falling with respect to TCOMP
-30
15
(Note 3)
mV
28.0
VACDET = 3V, VACDET < VBATB, VBATA = 0
5
9
VACDET falling with respect to VBATB
6
11
50
100
mV
100
150
200
mV
0
50
100
mV
100
150
200
mV
2.60
V
+100
nA
VBATA = VBATB = 5 × VMINV
0.93
MINV Input Bias Current
VMINV = 0.93V to 2.6V
-100
VMINV = 0.93V
4.55
4.65
4.75
VMINV = 2.6V
12.7
13
13.3
VBAT_ falling
BATSEL Input Low Voltage
Typical hysteresis is 100mV
BATSEL Input High Voltage
V
0.8
V
1
µA
100
µs
2.0
V
VBATSEL = 5.5V
BATSEL Action Delay
µA
0
MINV Operating Voltage Range
BAT_ Minimum Voltage Trip Threshold
V
V
8
ACDET to BATB Hysteresis
BATSEL Input Leakage Current
nA
mV
4
ACDET to BATA Hysteresis
ACDET to BATB Trip Threshold
100
VACDET = 3V, VACDET < VBATA and VBATB
VACDET falling with respect to VBATA
UNITS
+30
2.2
VACDET = 28V, VACDET > VBATA and VBATB
ACDET to BATA Trip Threshold
MAX
50
2.2
ACDET Logic Threshold High
ACDET Input Bias Current
TYP
0.1
THM_ to TCOMP Hysteresis
ACDET Operating Voltage Range
MIN
20
GATE DRIVERS
COM_ Initial Source Current
COM_ Final Source Current
VBAT_ = 16.8V, VCOM_ = 14.8V
5
VBAT_ = 16.8V, VCOM_ = 16.4V
10
VBAT_ = 16.8V, VCOM_ = 14.8V
50
COM_ Sink Current (PMOS Turn-On)
VCOM_ = 11.8V, VBAT_ = 16.8V (Note 4)
COM_ Turn-On Clamp Voltage
(VCOM_ to VBAT_)
VBAT_ = 8V to 19V
-11.5
VBAT_ = 4.75V to 8V
-8.00
VPDS = 10V, VEXTLD = 12V
PDS Sink Current (PMOS Turn-On)
VPDS = 2V to 28V
PDS Leakage Current (PMOS Off)
VPDS = 28V
CHG_ Sink Current (PMOS Turn-On)
VCHG_ = 2V to 22V
CHG_ Leakage Current (PMOS Off)
VCHG_ = 28V
DIS_ Initial Source Current
VEXTLD = 15V, VDIS_ = 13V
5
VEXTLD = 15V, VDIS_ = 14.6V
10
VEXTLD = 15V, VDIS_ = 13V
50
VEXTLD = 16.8V, VDIS_ = 11.8V (Note 5)
4
DIS_ Sink Current (PMOS Turn-On)
100
150
-9.5
-7.5
4
PDS Source Current (PMOS Turn-Off)
DIS_ Final Source Current
mA
mA
-4.25
5
0.8
0.7
µA
V
mA
1.0
1.2
mA
0.1
2
µA
1.0
1.3
mA
0.1
2
µA
mA
100
150
µA
mA
_______________________________________________________________________________________
3
MAX1773/MAX1773A
ELECTRICAL CHARACTERISTICS (continued)
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS (continued)
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = 0°C to +85°C, unless otherwise noted.)
PARAMETER
DIS_ Turn-On Clamp Voltage
(VDIS_ to VEXTLD)
MIN
TYP
MAX
VEXTLD = 8V to 28V
CONDITIONS
-11.5
-9.5
-7.5
VEXTLD = 4.75V to 8V
-8.00
-4.25
UNITS
V
STATUS OUTPUTS
ACPRES Sink Current
V ACPRES = 0.4V
1
V ACPRES = 5.5V
30
1
mA
BATSTAT Sink Current
VBATSTAT = 0.4V
VBATSTAT = 5.5V
ACPRES Leakage Current
V ACPRES = 5.5V
0.1
1
µA
BATSTAT Leakage Current
VBATSTAT = 5.5V
0.1
1
µA
VACDET = 2.2V, VMINV = 0.93V (Note 6)
5
µs
Battery Action Delay
VACDET = 2.2V, VMINV = 0.93V (Note 7)
260
µs
Thermistor Action Delay
VACDET = 2.2V, VMINV = 0.93V (Note 8)
12
µs
AC to Battery Switchover Delay
VACDET = 2.2V, VMINV = 0.93V (Note 9)
10
µs
Battery to AC Switchover Delay
VACDET = 2.2V, VMINV = 0.93V (Note 10)
260
µs
CHG_ Turn-On Delay
(Note 11)
530
µs
mA
TRANSITION TIMES
Battery Switchover Delay
130
300
ELECTRICAL CHARACTERISTICS
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = -40°C to +85°C, unless otherwise noted.)
PARAMETER
EXTLD Supply Voltage Range
CONDITIONS
VEXTLD > VBATA and VBATB
BATA, BATB Supply Voltage Range
BATA, BATB Quiescent Current
(Current from the higher voltage supply)
VBATA = 4.75V to 19V, VACDET = 28V
VBATB = 4.75V to 19V, VACDET = 2.2V to
IVDD = 0
VBATA and VBATB
BATA, BATB Quiescent Current
(Current from the lower voltage supply)
VBATA = 4.75V to 19V, VACDET = 28V
VBATB = 4.75V to 19V, VACDET = 2.2V to
IVDD = 0
VBATA and VBATB
EXTLD Quiescent Current
MAX
UNITS
4.75
MIN
TYP
28.00
V
4.75
19.00
V
8
70
µA
8
13
VACDET = 28V, VEXTLD = 28V
55
VACDET = 2.2V to VBATA and VBATB, VEXTLD = 16V
8
µA
µA
LINEAR REGULATOR
VDD Output Voltage
VDD Power-Supply Rejection Ratio
VDD Undervoltage Lockout
IVDD = 0 to 100µA
3.234
3.367
IVDD = 100µA to 1mA
3.168
3.432
VBATA or VBATB = 5V to 19V, VEXTLD = 5V
1.0
VBATA = VBATB = 5V, VEXTLD = 5V to 28V
1.0
Hysteresis is typically 50mV
V
mV/V
2.0
3.0
V
0
1.1
V
COMPARATORS
TCOMP Undervoltage Lockout
4
(Note 2)
_______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = -40°C to +85°C, unless otherwise noted.)
PARAMETER
CONDITIONS
THM_ Input Voltage Range
THM_ Input Leakage Current
TCOMP Input Voltage Range
ACDET Operating Voltage Range
MIN
0
VTHM_= 5.5V
5.5
V
NA
5.5
VBATA = VBATB = VEXTLD = 4.75V
0
4.3
2.2
28.0
(Note 3)
2.2
V
V
V
8
VACDET = 3V, VACDET < VBATB, VBATA = 0
9
VACDET = 28V, VACDET > VBATA and VBATB
11
VACDET falling with respect to VBATA
UNITS
100
0
VACDET = 3V, VACDET < VBATA and VBATB
ACDET to BATA Trip Threshold
MAX
VTHMA = VTHMB = 0 to 5.5V
ACDET Logic Threshold High
ACDET Input Bias Current
TYP
µA
-35
+125
mV
100
200
mV
VACDET falling with respect to VBATB
-35
+125
mV
100
200
mV
MINV Operating Voltage Range
VBATA = VBATB = 5 × VMINV
0.93
2.60
V
MINV Input Bias Current
VMINV = 0.93V to 2.6V
-100
+100
nA
BAT_ Minimum Voltage Trip Threshold
VBAT_ falling
VMINV = 0.93V
4.55
4.75
VMINV = 2.6V
12.7
13.3
BATSEL Input Low Voltage
Typical hysteresis is 100mV
ACDET to BATA Hysteresis
ACDET to BATB Trip Threshold
ACDET to BATB Hysteresis
BATSEL Input High Voltage
BATSEL Input Leakage Current
0.8
2.0
VBATSEL = 5.5V
BATSEL Action Delay
20
V
V
V
1
µA
100
µs
GATE DRIVERS
COM_ Initial Source Current
COM_ Final Source Current
VBAT_ = 16.8V, VCOM_ = 14.8V
4
VBAT_ = 16.8V, VCOM_ = 16.4V
10
VBAT_ = 16.8V, VCOM_ = 14.8V
50
mA
150
COM_ Sink Current (PMOS Turn-On)
VCOM_ = 11.8V, VBAT_ = 16.8V (Note 4)
COM_ Turn-On Clamp Voltage
(VCOM_ to VBAT_)
VBAT_ = 8V to 19V
-11.5
-7.25
VBAT_ = 4.75V to 8V
-8.00
-4.25
PDS Source Current (PMOS Turn-Off)
VPDS = 10V, VEXTLD = 12V
PDS Sink Current (PMOS Turn-On)
VPDS = 2V to 28V
PDS Leakage Current (PMOS Off)
VPDS = 28V
CHG_ Sink Current (PMOS Turn-On)
VCHG_ = 2V to 22V
2
mA
4
0.7
0.6
µA
V
mA
1.3
mA
2
µA
1.4
mA
_______________________________________________________________________________________
5
MAX1773/MAX1773A
ELECTRICAL CHARACTERISTICS (continued)
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS (continued)
(VBATA = VBATB = 16.8V, CVDD = 3.3µF, VMINV = 0.93V, VEXTLD = VACDET = 28V, VTCOMP = 3V, VTHMA = VTHMB = 1.65V,
VBATSEL = 0, CCOMA = CCOMB = CDISA = CDISB = CCHGA = CCHGB = CPDS = 5nF, TA = -40°C to +85°C, unless otherwise noted.)
DIS_ Sink Current (PMOS Turn-On)
VEXTLD = 16.8V, VDIS_ = 11.8V (Note 5)
DIS_ Turn-On Clamp Voltage
(VDIS_ to VEXTLD)
VEXTLD = 8V to 28V
-11.50
2
-7.25
mA
VEXTLD = 4.75V to 8V
-8.00
-4.25
V
STATUS OUTPUTS
ACPRES Sink Current
BATSTAT Sink Current
V ACPRES = 0.4V
1
V ACPRES = 5.5V
VBATSTAT = 0.4V
30
1
mA
mA
VBATSTAT = 5.5V
30
ACPRES Leakage Current
V ACPRES = 5.5V
1
µA
BATSTAT Leakage Current
VBATSTAT = 5.5V
1
µA
Battery Switchover Delay
VACDET = 2.2V, VMINV = 0.93V (Note 6)
5
µs
Battery Action Delay
VACDET = 2.2V, VMINV = 0.93V (Note 7)
260
µs
Thermistor Action Delay
VACDET = 2.2V, VMINV = 0.93V (Note 8)
12
µs
AC to Battery Switchover Delay
VACDET = 2.2V, VMINV = 0.93V (Note 9)
10
µs
Battery to AC Switchover Delay
VACDET = 2.2V, VMINV = 0.93V (Note 10)
260
µs
CHG_ Turn-On Delay
(Note 11)
530
µs
TRANSITION TIMES
130
TCOMP undervoltage lockout sets the MAX1773/MAX1773A’s internal status bits for the batteries to be designated as
“absent” (VTHM_ > VTCOMP).
Note 3: VACDET must remain above 2.2V, except in power-up.
Note 4: COMA cannot sink current until VCOMB > VBATB - 2V. Likewise, COMB cannot sink current until VCOMA > VBATA - 2V.
Note 5: DISA cannot sink current until VDISB > VEXTLD - 2V. Likewise, DISB cannot sink current until VDISA > VEXTLD - 2V.
Note 6: Battery Switchover Delay starts when either VCOM_ or VDIS_ of the connected battery begins to rise and ends when both
VCOM_ and VDIS_ of the other battery have fallen 3V below their sources (Figures 1 and 2).
Note 7: Battery Action Delay starts when the connected battery’s voltage falls below 5 ✕ VMINV and ends when both VCOM_ and
VDIS_ of the other battery have fallen 3V below their sources (Figures 1 and 2).
Note 8: Thermistor Action Delay begins when VTHM_ of the connected battery rises above VTCOMP and ends when both VCOM_
and VDIS_ of the other battery have fallen 3V below their sources (Figures 3 and 4).
Note 9: AC to Battery Switchover Delay begins when VACDET falls below its threshold and ends when both VCOM_ and VDIS_ of the
battery being switched to have fallen 3V below their sources (Figure 5).
Note 10: Battery to AC Switchover Delay begins when VACDET rises above its threshold and ends when VDIS_ of the battery being
switched from has begun to rise (Figure 6).
Note 11: CHG_ Turn-on Delay begins when VCHG_ of the battery being switched from begins to rise and ends when VCHG_ of the
battery being switched to begins to fall (Figures 7 and 8).
Note 2:
6
_______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
VDD ERROR vs. IDD
0.5
MAX1773-02
MAX1773-01
VIN = VACDET, BAT_ = OPEN
VDD ERROR vs. TEMPERATURE
0
MAX1773-03
VDD ERROR vs. INPUT VOLTAGE
0.04
0
0
VDD ERROR (%)
ERROR (%)
ERROR (%)
-1
-0.04
-2
-0.5
IDD = 5µA
-1.0
IDD = 1mA
-1.5
-0.08
-2.0
VIN = VBAT_, VACDET = 3.3V
-0.12
5
10
15
20
25
-3
0.01
-2.5
0.1
1
10
-40
-15
10
35
60
VIN (V)
IDD (mA)
TEMPERATURE (°C)
BATTERY CURRENT vs. BATTERY VOLTAGE
(VACDET = 20V)
TRANSITION FROM
BATTERY A TO BATTERY B (MINV)
(IEXTLD = 1A, CEXTLD = 66µF)
TRANSITION FROM
BATTERY A TO BATTERY B (MINV)
(IEXTLD = 1A, CEXTLD = 66µF)
MAX1773-04
10
IBATTERY_ (µA)
TOTAL CURRENT FROM THE BATTERY
30
MAX1773-05
MAX1773-06
15V
VBATB
5V
8
5V
VCOMA
0
10V
15V
6
85
VEXTLD
VDISA
4
5V
VBATA
0
VCOMB
10V
0
12V
2
5 ✕ VMINV
VDISB
5V
0
2V
0
0
4
8
12
VBATTERY_ (V)
16
20
100µs/div
VBATA = 12V, BATTERY A REMOVED AT 100µs
VBATB = 10.75V
VMINV = 1.4V
5µs/div
VBATA = 12V
VBATB = 10.75V
_______________________________________________________________________________________
7
MAX1773/MAX1773A
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
TRANSITION FROM
BATTERY A TO BATTERY B (TCOMP)
(IEXTLD = 4A, CEXTLD = 66µF)
TRANSITION FROM
BATTERY A TO BATTERY B (TCOMP)
(IEXTLD = 4A, CEXTLD = 66µF)
TRANSITION FROM
BATTERY A TO BATTERY B (BATSEL)
(IEXTLD = 4A, CEXTLD = 66µF)
MAX1773-08
MAX1773-07
12V
MAX1773-09
10V
VCOMA
11V
0
11V
10V
VDISA
VEXTLD
4V
VEXTLD
10V
VBATSEL
4V
0
10V
VCOMB
0
VTHMA
0
VDISB
10V
0
0
5µs/div
10µs/div
50µs/div
VBATA = 10.5V AT 4A
VBATB = 12V AT 4A
VBATA = 10.5V AT 4A
VBATB = 12V AT 4A
TRANSITION FROM
TRANSITION FROM BATTERY A TO AC ADAPTER
(IEXTLD = 4A, CEXTLD = 66µF)
TRANSITION FROM
AC ADAPTER TO BATTERY A
(IEXTLD = 4A, CEXTLD = 66µF)
MAX1773-10
MAX1773-11
20V
VACDET
VBATA
VBATA = 9.4V AT 4A
VBATB = 10.8V AT 4A
10V
-10A
VBATA
12V
0
10V
20V
VEXTLD
10V
VDISA
10V
VDISA
0
VCHGA
10V
0
20µs/div
VBATA = 10.8V AT 4A
VACADAPTER = 17.5V AT 4A
8
10A
IBATA
(CURRENT FROM
THE BATTERY)
0
100µs/div
VACADAPTER = 17.5A AT 4A
VBATA = 10.5V AT 4A
VACADAPTER APPLIED AT 240µs
CHARGER INPUT OPEN
_______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
PIN
NAME
FUNCTION
1
BATA
Battery A Connection
2
THMA
Thermistor A Input
3
CHGA
Open-Drain Gate Driver for Charge Path MOSFET to Battery A
4
DISA
5
COMA
6
GND
Ground
7
MINV
Minimum Operating Voltage Set Point. The battery voltage switchover set point is 5 × VMINV.
8
EXTLD
9
PDS
10
ACDET
11
BATSTAT
Open-Drain Battery Status Output. Use a pullup resistor to the system logic supply.
12
ACPRES
Open-Drain AC Presence Output. Use a pullup resistor to the system logic supply.
13
BATSEL
Battery Select Digital Input. Selects which battery to charge or discharge.
14
TCOMP
Externally Set Thermistor Trip Point. Sets the thermistor voltage level for detecting the battery’s
presence.
15
VDD
16
COMB
17
DISB
18
CHGB
Open-Drain Gate Driver for Charge Path MOSFET to Battery B
19
THMB
Thermistor B Input
20
BATB
Battery B Connection
Gate Driver for Discharge Path MOSFET to Battery A. Switches from VEXTLD to (VEXTLD - 9.5V).
Gate Driver for Common Path MOSFET to Battery A. Switches from VBATA to (VBATA - 9.5V).
External Load Connection. Source connection for the PDS, DISA, and DISB MOSFETs.
Gate Driver for the AC Adapter MOSFET
AC Adapter Detection Input
Linear Regulator Output
Gate Driver for Common Path MOSFET to Battery B. Switches from VBATB to (VBATB - 9.5V).
Gate Driver for Discharge Path MOSFET to Battery B. Switches from VEXTLD to (VEXTLD - 9.5V).
_______________________________________________________________________________________
9
MAX1773/MAX1773A
Pin Description
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
Transition Time Diagrams
(VCOM_GS = COM_ turn-on clamp voltage, VDIS_GS = DIS_ turn-on clamp voltage, VCHARGER = system step-down charger output.)
MAX1773-Fig-02
MAX1773-Fig-01
5 ✕ VMINV
VBATA
VBATA
VCOMA
VBATA + VCOM_GS
VEXTLD
VEXTLD + VDIS_GS
VDISA
3V VBATB
VCOMB
VBATB + VCOM_GS
3V VEXTLD
VDISB
5 ✕ VMINV
VBATB
VBATB
VCOMB
VBATB + VCOM_GS
VEXTLD
VDISB
VEXTLD + VDIS_GS
VCOMA
3V VBATA
VDISA
3V VEXTLD
VBATA + VCOM_GS
VEXTLD + VDIS_GS
VEXTLD + VDIS_GS
BATTERY ACTION
DELAY
BATTERY ACTION
DELAY
VTHMA < VTCOMP
VTHMB < VTCOMP
VTHMA < VTCOMP
VTHMB < VTCOMP
BATTERY SWITCHOVER
DELAY
Figure 1. Battery Delay (Battery A to Battery B)
Figure 2. Battery Delay (Battery B to Battery A)
MAX1773-Fig-04
MAX1773-Fig-03
VTHMA
VTCOMP
VBATA
VCOMA
VBATA + VCOM_GS
VEXTLD
VDISA
BATTERY SWITCHOVER
DELAY
VTHMB
VTCOMP
VBATB
VCOMB
VBATB + VCOM_GS
VEXTLD
VDISB
VEXTLD + VDIS_GS
VEXTLD + VDIS_GS
3V VBATB
VCOMB
3V VBATA
VCOMA
VBATA + VCOM_GS
VBATB + VCOM_GS
3V VEXTLD
VDISB
3V VEXTLD
VEXTLD + VDIS_GS
VDISA
VEXTLD + VDIS_GS
VTHMB < VTCOMP
THERMISTOR ACTION DELAY
BATTERY SWITCHOVER DELAY
Figure 3. Thermistor Switchover Delay (Battery A to Battery B)
10
VTHMA < VTCOMP
THERMISTOR ACTION DELAY
BATTERY SWITCHOVER DELAY
Figure 4. Thermistor Switchover Delay (Battery B to Battery A)
______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
MAX1773-Fig-05
MAX1773-Fig-06
ACDET TO BAT_ TRIP
THRESHOLD
VACDET
ACDET TO BAT_ TRIP
THRESHOLD
VACDET
VEXTLD
VEXTLD
3V
VDIS_
VDIS_
VEXTLD + VDIS_GS
AC TO BATTERY SWITCHOVER DELAY
VBAT_ > 5 ✕ VMINV
VTHM_ < VTCOMP
VEXTLD + VDIS_GS
BATTERY TO AC SWITCHOVER DELAY
VBAT_ > 5 ✕ VMINV
VTHM_ < VTCOMP
Figure 5. AC to Battery Switchover Delay
Figure 6. Battery to AC Switchover Delay
MAX1773-Fig-07
MAX1773-Fig-08
VBATSEL
VBATSEL
VCHARGER
VCHGA
VCHARGER
VCHGB
VCHARGER
VCHGB
VCHARGER
VCHGA
CHG_ TURN-ON DELAY
VTHMA < VTCOMP
VTHMB < VTCOMP
Figure 7. Charge Turn-On Delay (Battery A to Battery B)
CHG_ TURN-ON DELAY
VTHMA < VTCOMP
VTHMB < VTCOMP
Figure 8. Charge Turn-On Delay (Battery B to Battery A)
______________________________________________________________________________________
11
MAX1773/MAX1773A
Transition Time Diagrams (continued)
(VCOM_GS = COM_ turn-on clamp voltage, VDIS_GS = DIS_ turn-on clamp voltage, VCHARGER = system step-down charger output.)
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
Table 1. AC Adapter States
BATSEL
BATTERY A
BATTERY B
BATSTAT
CONNECTION STATE
0
Present
X
0
AC adapter is connected to load. Battery A’s charge path connected.
0
Absent
X
1
AC adapter is connected to load.
1
X
Present
1
AC adapter is connected to load. Battery B’s charge path connected.
1
X
Absent
0
AC adapter is connected to load.
X = Don’t care, Present: VTHM_ < VTCOMP, Absent: VTHM_ > VTCOMP, ACPRES = 0
Table 2. Simplified Standard Battery States (without latches)
BATSEL
BATTERY A
VBATA
BATTERY B
VBATB
BATSTAT
CONNECTION STATE
0
Present
>5 × VMINV
X
X
0
X
Present
>5 × VMINV
Absent
X
0
Battery A is connected to the load.
X
Present
>5 × VMINV
X
< 5 × VMINV
0
Battery A is connected to the load.
X
X
<5 × VMINV
Present
> 5 × VMINV
1
Battery B is connected to the load.
X
Absent
X
Present
> 5 × VMINV
1
Battery B is connected to the load.
1
X
X
Present
> 5 × VMINV
1
Battery B is connected to the load.
Battery A is connected to the load.
X = Don’t care, Present: VTHM_ < VTCOMP, Absent: VTHM_ > VTCOMP
Detailed Description
The MAX1773/MAX1773A provide the functions necessary to allow an external controller to manage the
power connections needed for two battery packs, an
AC adapter input, a battery charger, and the system
load. The MAX1773/MAX1773A use seven PMOS FETs
to provide all the switching necessary in systems using
a step-down charger powered by the AC adapter
(Figures 9 and 10). The MAX1773/MAX1773A automatically adapt to many transient conditions—such as AC
plug-in, battery hot swapping, and battery switchover—
to provide constant power to the system without requiring real-time support from an external controller. The
MAX1773/MAX1773A draw their power from the highest
voltage supply present (Figure 11).
Battery Detection
The MAX1773/MAX1773A monitor the battery’s thermistor voltage to determine the presence of the battery.
The devices compare the battery’s thermistor voltage
(VTHM_) to the thermistor trip point (VTCOMP). If VTHM_
< VTCOMP, then the MAX1773/MAX1773A assume that
the battery is present. However, if VTHM_ > VTCOMP,
the MAX1773/MAX1773A assume that the battery is
absent and do not charge or discharge the battery.
Modes of Operation
The MAX1773/MAX1773A provide three modes of operation. Start-up States mode provides functionality when
the MAX1773/MAX1773A are initially powered by a bat12
tery when no AC adapter is present. AC adapter States
mode provides functionality when an AC Adapter is present. Standard Battery States mode provides functionality
when one or both batteries are present, the AC adapter is
not present, and EXTLD is above 2.2V. The Standard
Battery States mode requires an external supply with an
output voltage between 2.2V and 4.5V for ACDET, as
shown in Figure 10. The external power supply must be
powered from EXTLD.
AC Adapter States
The MAX1773/MAX1773A check for the presence of an
AC adapter by sensing the voltage at ACDET. When
VACDET exceeds the batteries’ voltage and 4.75V, then
the MAX1773/MAX1773A use the AC adapter to power
the load. In addition, if the selected battery is present,
the MAX1773/MAX1773A connect the selected battery’s
charge path. See Table 1 for a detailed listing of the
MAX1773/MAX1773A states for operation with an AC
adapter detected.
Standard Battery States
When the AC adapter power supply is not present, the
MAX1773/MAX1773A use the batteries to supply the
load. BATSEL allows an external controller to select a
battery. Table 2 shows the simplified standard battery
states that normally control operation. However, the
Battery Switchover Latch, the Low-Battery Latch, and
the Discharged Battery Latch are able to suspend the
state table and provide additional functionality.
______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
MAX1773/MAX1773A
STEP-DOWN
CHARGER
AC-ADAPTER
SUPPLY
R12
R14
VBATB+
VBATA+
COMA
CHGA
CHGB
DISA
DISB
EXTLD
PDS
COMB
POWER CONNECTIONS
SYSTEM
Figure 9. 7-MOSFET Topology
Table 3. Startup States
VBATA
VBATB
BATTERY A
BATTERY B
CONNECTION STATE
>5 × VMINV
X
Present
X
Battery A is connected to the load.
<5 × VMINV
>5 × VMINV
Present
Present
Battery B is connected to the load.
X
>5 × VMINV
Absent
Present
Battery B is connected to the load.
X
X
Absent
Absent
No connections.
<5 × VMINV
<5 × VMINV
X
X
No connections.
<5 × VMINV
X
X
Absent
No connections.
X
<5 × VMINV
Absent
X
No connections.
X = Don’t care, Present: VTHM_ < VTCOMP, Absent: VTHM_ > VTCOMP
The Battery Switchover Latch stops the MAX1773/
MAX1773A from oscillating when the device switches
from the selected battery and then the selected battery’s voltage recovers. According to the state table,
the MAX1773/MAX1773A would switch back to the
selected battery as soon as the battery’s voltage
recovered. The Battery Switchover Latch suspends the
state table as soon as the MAX1773/MAX1773A switch
over to the nonselected battery. This causes the
MAX1773/MAX1773A to continue to power from the
nonselected battery unless the latch is cleared. The
Battery Switchover Latch is cleared when BATSEL is
toggled (to select the other battery), when in the
Startup States mode, in the AC Adapter States mode,
and when the selected battery is removed (VTHM_ >
VTCOMP).
To prevent the MAX1773/MAX1773A from switching to a
discharged battery, the Low-Battery Latch suspends the
state table when the unconnected battery’s voltage is
below 5 ✕ VMINV and the discharging battery’s voltage
drops below 5 ✕ VMINV. Instead of switching to the
unconnected battery, the MAX1773/MAX1773A continue
to power from the discharging battery. This latch is
cleared when the unconnected battery is removed
(VTHM_ > VTCOMP), when in the Startup States mode,
when in the AC Adapter States mode, and if the unconnected battery’s voltage rises above 5 ✕ VMINV.
The Discharged Battery Latch sets whenever the
MAX1773/MAX1773A are in the Standard Battery States
mode, both batteries are present (VTHM_ < VTCOMP),
one of the batteries is low (VBAT_ < 5 ✕ VMINV), and the
other battery’s voltage is below V ACDET . While the
______________________________________________________________________________________
13
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
SYSTEM LOGIC SUPPLY
500kΩ
FROM HOST µP
500kΩ
VDD
BATSEL
ACPRES
TO HOST µP
28.7kΩ
0.33µF
BATSTAT
3.3kΩ
AC ADAPTER
INPUT
100kΩ
PDS
100kΩ
0.1µF
10kΩ
R13
8kΩ
P7
3.3V
MINV
ACDET
EXTLD
3.3V
MAX1773
MAX1773A
10kΩ
TCOMP
100kΩ
10kΩ
BATTERY
A
THMA
BATTERY
B
THMB
BATA
BATB
COMA
COMB
DISA
DISB
1.5µF
1.5µF
CHGA
P1
CHGB
R12
8kΩ
R14
8kΩ
P4
STEP-DOWN
CHARGER
OUTPUT
3.3V DC-DC
CONVERTER
OUTPUT
INPUT
INPUT
SYSTEM LOAD
66µF
Figure 10. Standard Application Circuit
Discharged Battery Latch is set, the state table is suspended, the MAX1773/MAX1773A are not allowed to
switch batteries, and the Low Battery Latch is cleared.
The Discharged Battery Latch is cleared when both
batteries are above VACDET, in the AC Adapter States
mode, and in the Startup States mode.
14
Startup States
When V ACDET rises at startup, the MAX1773/
MAX1773A use Startup States. See Table 3 for a
detailed listing of the MAX1773/MAX1773A states in
this mode. Note that once ACDET rises above 2.2V, the
MAX1773/MAX1773A are no longer in the Startup
______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
MAX1773/MAX1773A
BATA
BATB
LINEAR
REGULATOR
VDD
UVLO
EXTLD
MAX1773
MAX1773A
9.5V
COMB
LOGIC
+
_
ACDET
9.5V
COMA
+
_
+
_
GND
9.5V
DISA
MINV
_
9.5V
+
DISB
PDS
CHGA
THMA
+
TCOMP
_
CHGB
VDD
_
+
THMB
ACPRES
DELAY
60µs
BATSEL
BATSTAT
Figure 11. Functional Diagram
States mode and enters either the Standard Battery
States mode or the AC Adapter States mode.
Status and Configuration
BATSTAT and ACPRES provide information to an external controller. Table 4 shows the different states of
BATSTAT and ACPRES.
In the AC Adapter States mode, the BATSEL Action
Delay (see Electrical Characteristics) allows the external controller to tell if both batteries are absent. When
both batteries are absent in the AC Adapter States
mode and BATSEL changes states, BATSTAT is immediately updated. However, changes to the connection
states are delayed (see Table 1 for connection states).
______________________________________________________________________________________
15
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
Table 4. Status Bits
MODE
All
STATUS
BATSTAT
VDD Undervoltage Lockout
Startup States
ACPRES
1
1
1
1
Standard Battery States
Selected Battery Discharge Path Connected
BATSEL
1
Standard Battery States
Other Battery Discharge Path Connected
BATSEL
1
AC Adapter States
Selected Battery Charge Path Connected
BATSEL
0
AC Adapter States
Selected Battery Absent
BATSEL
0
If BATSEL is returned to its original state within the
BATSEL Action Delay, then changes to the connection
states are never made. Note that in the Standard
Battery States mode and in the AC Adapter States
mode when one or both batteries are present, both
BATSTAT and the connection states are delayed during
the BATSEL Update Delay.
MOSFET Drivers
To minimize the time when no supply is connected to
the external load during switchover transients, the
MAX1773/MAX1773A use active pullup drivers for the
discharge paths (DIS_) and the common paths
(COM_). When the MAX1773/MAX1773A initially begin
to pull up one of these pins, they use a large current
(Initial COM_ Source Current and Initial DIS_ Source
Current; see Electrical Characteristics). Once the
COM_ voltage rises to within 2V of VBAT_ or the DIS_
voltage rises to within 2V of VEXTLD, then a weaker driver is used to hold up the voltage (Final COM_ Source
Current and Final DIS_ Source Current; see Electrical
Characteristics).
The MAX1773/MAX1773A are designed to prevent
shoot-through from one battery to the other when transitioning from discharging one battery to discharging the
other battery. To accomplish this, the MAX1773/
MAX1773A do not connect the second battery to
EXTLD until it senses that the first battery is disconnected from EXTLD. See Notes 4 and 5 of Electrical
Characteristics.
To allow flexibility when choosing the higher voltage
PDS PMOS FET (P7, Figure 10), the MAX1773/
MAX1773A do not limit the gate-to-source voltage
applied to the PDS PMOSFET. The minimum VGS is set
by the MAX1773/MAX1773A PDS sink current (see
Electrical Characteristics) and the external resistor from
PDS to EXTLD (R13):
VGS(MIN) = -IPDS(SINK) ✕ RPDS
16
where V GS(MIN) is the minimum P7 gate-to-source
voltage, IPDS(SINK) is the PDS sink current, and RPDS is
R13.
The MAX1773/MAX1773A use open-collector drivers to
open the charge paths. Minimize the value of the pullup
resistors on the charge paths (R12 and R14) to allow
the MAX1773/MAX1773A to quickly turn on the PMOS
FETs; however, keep the value large enough to prevent
a lower VGS than specified by the PMOS FET. The minimum VGS is:
VGS(MIN) = -ICHG_(SINK) ✕ RCHG_
where VGS(MIN) is the minimum P1 or P4 gate-to-source
voltage, I CHG_(SINK) is the CHG_ sink current (see
Electrical Characteristics), and RCHG_ is R12 or R14.
VDD Regulator
The MAX1773/MAX1773A feature an internal linear regulator to provide power for itself and external circuitry.
The linear regulator’s output is available at VDD and is
nominally 3.3V. When the linear regulator is not used to
power external circuitry, bypass it with a 0.33µF ceramic capacitor. To supply external loads up to 1mA,
bypass the linear regulator with a 3.3µF tantalum
capacitor.
Applications Information
Load Switchover Transients
When power switches from one power source to another, a transient is created on the load. This transient
(∆VEXTLD) is minimized by the capacitance on the load
(CEXTLD). The voltage transient can be approximated
as:
i
× t SWITCHOVER
∆VEXTLD = EXLTLD
CEXTLD
where tSWITCHOVER is the time where no supply is connected to the EXTLD.
______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
ES
EN
T,
N
IN
BA SE O BA
TB RT
TT
E
ER
IN
IES
SE D
RT
,A
E
SE
D
AC
LE
AD
CT
AP
ED
TE
RR
E
MO
VB
VE
AT
AF
D
A
EX
L
L
TE
S
R
B
VB NAL ELO
W
AT
B F CON
5
AC ALL TR ✕ V
O
AD S B LL MIN
E
AP
E
V
TE LOW R RE
RA
AC
5
✕
T
PP
LIE VM S
D
IN
V,
SY
ST
EM
EX
SH
TE
UT
RN
SD
AL
OW
CO
N
NT
RO
LL
ER
RE
AC
TS
TA
PR
BA
AC
MAX1773/MAX1773A
20V
VACDET
3.3V
20V
VEXTLD
8V
VBATA
12.6V
8V
VBATB
12.6V
8V
BATSEL
BATSTAT
0
1
0
0
0
ACPRES
t0
0
0
0
t1
0
0
0
t2
0
1
1
t3
1
1
1
t4
1
0
1
t5
1
1
1
t6
0
0
0
0
0
0
t7
t8
0
t9
Figure 12. Charge/Discharge Example
In applications where the battery voltage always falls
away slowly, tSWITCHOVER is primarily composed of the
Battery Switchover Delay. However, in applications
where the battery voltage can suddenly fall away,
tSWITCHOVER is substantially increased because it is
primarily composed of the Battery Action Delay (Figures
1 and 2).
Ideally, when a battery is removed from the system, the
thermistor connection is broken before the battery’s
power path is broken. In this case, tSWITCHOVER is typically bound by the Thermistor Action Delay (Figures 3
and 4). However, if the battery’s power path is broken
first, then tSWITCHOVER primarily consists of the shorter
of the following times: time until the thermistor connection is broken plus the Thermistor Action Delay, or the
Battery Action Delay.
Source Switchover Transients
When the MAX1773/MAX1773A suddenly switch a
power supply to the load, they create a current transient
from the source to charge up the capacitance on the
load. The peak current drawn is approximated by:
IPK =
∆VEXTLOAD
RSOURCE + RSWITCH + RESR
where ∆VEXTLOAD is the voltage difference between the
supply switched off and the supply switched on,
RSOURCE is the source resistance of the power supply
switched on, RSWITCH is the RDS(ON) of the PMOS FETs
in the path, and RESR is the equivalent series resistance
of the output capacitance.
The duration of the current transient is determined by
RSOURCE, RSWITCH, RESR, and the output capacitance.
Smaller resistances and less output capacitance reduce
the transient duration.
Typical Operation
Figure 12 shows a typical discharge and charge cycle
for a system utilizing the MAX1773/MAX1773A, two
3-cell lithium-ion (Li+) batteries, and a 20V AC adapter
power supply. The diagram starts with the AC adapter
applied, no batteries present, and battery A selected
(see AC Adapter States). BATSTAT = BATSEL = 1 indicates that battery A is not present and battery A’s
______________________________________________________________________________________
17
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
Table 5. Recommended Manufacturers
SUPPLIER
PHONE
FAX
Fairchild
408-822-2000
408-822-2102
IR
310-322-3331
310-322-3332
Siliconix
408-988-8000
408-970-3950
charge path is not connected. If the external controller
polled the MAX1773/MAX1773A as described in Status
and Configuration, then BATSTAT would return BATSEL
(0) to indicate that battery B is not present.
At t 1 , battery A is inserted and the MAX1773/
MAX1773A connect battery A’s charge path. Note that
BATSTAT changes to BATSEL (0) to indicate that battery A is present.
At t2, battery B is inserted. BATSTAT does not change
and still indicates that battery A is present.
At t 3 , the AC adapter is removed and the
MAX1773/MAX1773A automatically disconnect battery
A’s charge path and connect battery A’s discharge
path (see Standard Battery States). ACPRES changes
to 1 to indicate that the AC adapter source is no longer
present. BATSTAT = BATSEL (0) to indicate that battery
A is present and supplying the load. Between t3 and t4,
battery A discharges as it supplies the load.
At t4, battery A’s voltage falls below 5 ✕ VMIN, and the
MAX1773/MAX1773A automatically disconnect battery
A’s discharge path and connect battery B’s discharge
path. BATSTAT goes to BATSEL (1) to indicate that battery A is no longer supplying the load.
Shortly after BATSTAT goes high, the external controller
should catch up to the MAX1773/MAX1773A and
change BATSEL. This is shown at t5. BATSTAT remains
at 1, indicating that battery B is present and supplying
the load.
At t 6 , battery B falls below 5 ✕ V MIN, and the
MAX1773/MAX1773A automatically disconnect battery
B’s discharge path and connect battery A’s discharge
path. BATSTAT changes to BATSEL (0) to indicate that
battery B is no longer supplying the load. At this point,
the external controller orders a controlled shutdown of
the system and drastically reduces the supply current.
At t7, the AC adapter supply is reconnected to the system. The MAX1773/MAX1773A automatically disconnect battery A’s discharge path, connects the AC
adapter’s load path (PDS switch), and connects battery
B’s charge path. BATSTAT goes to BATSEL (1) to indicate that battery B is present. ACPRES goes to 0 to
indicate that the AC adapter source is present.
18
At t8, the external controller recognizes that battery B is
charged and changes BATSEL to battery A. BATSTAT
goes to BATSEL (0) to indicate that battery A is present.
After t9, the batteries are fully charged and the system
is ready for another cycle.
Power MOSFET Selection
The MAX1773/MAX1773A do not place stringent
requirements on the external PMOS FETs. Use PMOS
FETs with low VGS thresholds (logic level FETs). Low
RDS(ON) PMOS FETs are desirable since the PMOS
FET’s resistance directly contributes to power losses.
Also, ensure that the PMOS FET’s VDS and VGS ratings
exceed the specific circuit requirements. See Table 5
for a list of recommended manufacturers.
Layout Guidelines
The MAX1773/MAX1773A do not use fast switching
times or high frequencies. Therefore, the layout requirements are minimal. Keep the gate connections to the
external PMOS FETs short to minimize capacitive coupling, reduce parasitic inductance, and ensure stability.
In addition, minimize the power path length when possible to reduce the path’s resistance. See the MAX1773
evaluation kit for a layout example.
Pin Configuration
TOP VIEW
BATA 1
20 BATB
THMA 2
19 THMB
CHGA 3
18 CHGB
DISA 4
17 DISB
COMA 5
GND 6
MAX1773
MAX1773A
16 COMB
15 VDD
MINV 7
14 TCOMP
EXTLD 8
13 BATSEL
PDS 9
12 ACPRES
ACDET 10
11 BATSTAT
TSSOP
Chip Information
TRANSISTOR COUNT: 5245
PROCESS: BiCMOS
______________________________________________________________________________________
Power Source Selector for
Dual-Battery Systems
This section discusses the differences between the
MAX1773 and MAX1773A for the situations detailed.
Note that the MAX1773 and MAX1773A are pin-to-pin
compatible.
PDS FET Switching
MAX1773: If battery B is selected but absent, and battery A is inserted with a voltage less than five times
MINV, when an adapter is inserted, the PDS FET does
not turn on. The problem also occurs if battery A is
selected but absent, and battery B is inserted with a
voltage less than five times MINV, when an adapter is
inserted, the PDS FET does not turn on.
In the MAX1773A, when the sequences discussed are
encountered, the part has been changed to enable the
PDS FET. This results in the PDS FET having to dissipate less energy in the MAX1773A.
Selected Battery Present
But Under-Voltage
MAX1773: When the selected battery is present and
less than five times the MINV voltage, and a battery
above five times the MINV voltage is inserted at the
nonselected slot. In this case, the MAX1773 will not
enable discharge from the nonselected slot if the THM_
pin of the nonselected battery is valid after the TCOMP
pin goes high.
In the MAX1773A the order in which the THM_ and
TCOMP pins become enabled is unimportant for these
states. This results in this behavior not being encountered in the MAX1773A.
Switchover to Nonselected Battery
Upon Adapter Removal
MAX1773: When the selected battery is present and
less than five times MINV, and the nonselected battery
is present and greater than five times MINV. The
MAX1773 enables the discharge path from the nonselected battery, which has a voltage greater than five
times MINV, which is an expected operation for the
part. If the AC adapter is then inserted, the charge path
to the selected battery is enabled, this is also expected
operation. When the adapter is removed, the MAX1773
does not switch to the nonselected battery, which is
the issue.
In the MAX1773A, when the AC adapter is removed in
the scenario detailed, three separate conditions are
possible:
1) A charger is present but does not charge the
selected battery. This can happen if the input current-limit feature in the charger has been activated,
reducing the charger current to zero. The AC
adapter is then removed. In this case the
MAX1773A allows discharge from the unselected
battery, whose voltage was above 5 x MINV.
2) A charger is present and charges the selected battery. The battery is charged sufficiently so that it
can support the system load for more then 10ms.
(Assuming the typical application circuit with
100kΩ and 0.1µF on the AC adapter input.) When
the AC adapter is removed, the MAX1773A correctly allows discharge from the selected battery.
3) In the third scenario, the charger charges the
selected battery, but before the battery is sufficiently charged to support the system load, the AC
adapter is removed. In this case, the MAX1773A
does not allow discharge from the unselected battery, whose voltage is above 5 x MINV. The limiting
condition is that the battery has to be sufficiently
charged to support the system load for 10ms.
______________________________________________________________________________________
19
MAX1773/MAX1773A
Differences Between MAX1773
and MAX1773A
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.)
TSSOP4.40mm.EPS
MAX1773/MAX1773A
Power Source Selector for
Dual-Battery Systems
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.
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