MAX1538ETI+ [MAXIM]
Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 5 X 5 MM, 0.80 MM HEIGHT, MO-220WHHD-1, TQFN-28;
| 型号： | MAX1538ETI+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 5 X 5 MM, 0.80 MM HEIGHT, MO-220WHHD-1, TQFN-28 电池 |
| 文件： | 总22页 (文件大小：492K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3169; Rev 0; 1/04
Power-Source Selector for
Dual-Battery Systems
General Description
Features
The MAX1538 selector provides power-source control
for dual-battery systems. The device selects between
an AC adapter and dual batteries based on the pres-
ence of the three power sources and the state of
charge of each battery. The MAX1538 includes analog
comparators to detect AC/airline-adapter presence and
determine battery undervoltage. Fast analog circuitry
allows the device to switch between power sources to
implement a break-before-make time, which allows hot
swapping of battery packs. The MAX1538 indepen-
dently performs power-source monitoring and selec-
tion, freeing the system power-management µP for
other tasks. This simplifies the development of µP
power-management firmware and allows the µP to enter
standby, reducing system power consumption.
♦ Automatically Detects and Responds to
Low-Battery Voltage Condition
Battery Insertion and Removal
AC-Adapter Presence
Airline-Adapter Presence
♦ Step-Down and Step-Up Charger Compatibility
♦ Fast Break-Before-Make Selection
Allows Hot Swapping of Power Sources
No External Schottky Diodes Needed
♦ 50µA Maximum Battery Quiescent Current
♦ Implements Battery Capacity Relearning
♦ Allows Usage of Aircraft Supply
♦ Direct Drive of P-Channel MOSFETs
The MAX1538 supports “relearn mode,” which allows
the system to measure and fully utilize battery capacity.
In this state, the part allows the selected battery to be
discharged even when an AC adapter is present. The
MAX1538 can also be used to power the system in an
aircraft. On detecting an airline adapter, the MAX1538
automatically disables charging or discharging of bat-
tery packs and only allows the system to be powered
from the adapter.
♦ Simplifies Power-Management µP Firmware
♦ 4.75V to 28V AC-Adapter Input Voltage Range
♦ Small 28-Pin Thin QFN Package (5mm x 5mm)
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX1538ETI
-40°C to +85°C
28 Thin QFN
The MAX1538 is available in a space-saving 28-pin thin
QFN package with a maximum footprint of 5mm x 5mm.
Typical Operating Circuit
Applications
Notebook and Subnotebook Computers
ACDET
CHRG
AIRDET
BATSEL
Internet Tablets
RELRN
ADPIN
OUT2
Dual-Battery Portable Equipment
OUT1
REVBLK
OUT0
EXTLD
BATTERY
CHARGER
MAX1538
ADPBLK
V
DD
CHG_OUT
CHGIN
CHGA
MINVA
MINVB
Pin Configuration appears at end of data sheet.
CHGB
DISB
GND
DISA
BATB
BATA
BATSUP
________________________________________________________________ Maxim Integrated Products
1
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.
Power-Source Selector for
Dual-Battery Systems
ABSOLUTE MAXIMUM RATINGS
V
, V
, V
, V
, V
,
Continuous Power Dissipation (T = +70°C)
EXTLD BATSUP ADPIN BATA BATB
A
V
to GND .................................................-0.3V to +30V
28-Pin Thin QFN 5mm x 5mm
(derate 20.8mW/°C above +70°C)..........................1666.7mW
Operating Temperature Range
MAX1538ETI....................................................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
CHGIN
V
V
V
V
V
V
to GND...................................-0.3V to (V
+ 0.3V)
+ 0.3V)
+ 0.3V)
+ 0.3V)
+ 0.3V)
ADPPWR
REVBLK ADPBLK
CHGA CHGB, DISBAT
DISA
DISB
ADPIN
EXTLD
CHGIN
BATA
BATB
, V
to GND ...................-0.3V to (V
, V
V
to GND ..........-0.3V to (V
to GND..........................................-0.3V to (V
to GND..........................................-0.3V to (V
, V
, V
, V
, V
, V
, V
,
DD CHRG BATSEL RELRN OUT0 OUT1 OUT2
V
, V
, V
, V
to GND..........-0.3V to +6V
MINVA MINVB AIRDET ACDET
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
(V
C
= V
= V
= 16.8V, C
= C
= 1µF, V
= C
= V
= 0.93V, V
= C
= V
= 28V, V
= V
= V
= 0,
BATA
BATB
CHGIN
= C
VDD
MINVA
MINVB
= C
EXTLD
ADPIN
CHRG
BATSEL
RELRN
= C
= C
= 4.7nF, T = 0°C to +85°C, unless otherwise noted.
CHGB
A
ADPPWR
REVBLK
ADPBLK
DISBAT
DISA
DISB
CHGA
Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
ADPIN, EXTLD Supply Voltage
Range
4.75
28.00
V
CHGIN, BATA, BATB and
BATSUP Supply Voltage Range
4.75
19.00
50
V
V
V
= highest,
ADPIN
21
23
= high
ADPPWR
V
V
= highest,
ADPIN
54
= low
ADPPWR
V
V
V
V
= 4.75V to 19V,
= 4.75V to 19V,
BATA
V
V
= highest,
= high
ADPIN, BATA, BATB, BATSUP
Quiescent Current (Current from
the Highest Voltage Supply)
BATA
DISA
BATB
21
24
21
42
50
42
= 4.75V to 19V,
µA
BATSUP
= 4.75V to 28V,
ADPIN
V
= highest, V
= low
= low
BATA
DISA
DISB
no external load at V
DD
V
V
= highest,
= high
BATB
DISB
V
V
= highest, V
24
18
50
40
BATB
= highest
= high
BATSUP
ADPIN Quiescent Current (ADPIN
Current When Not the Highest
Voltage)
V
V
V
V
V
V
0.01
2.6
3.9
7.0
3.9
7.0
0.5
6
ADPPWR
ADPPWR
V
= 4.75V to 18V,
ADPIN
µA
µA
no external load at V
DD
DD
DD
= low
BATA Quiescent Current (BATA
Current When Not the Highest
Voltage)
= high
6.0
12
6.0
12
DISA
DISA
DISB
DISB
V
= 4.75V to 19V,
BATA
no external load at V
= low
BATB Quiescent Current (BATB
Current When Not the Highest
Voltage)
= high
= low
V
= 4.75V to 19V,
BATB
µA
µA
no external load at V
Adapter selected (REVBLK or ADPBLK pins low)
3.0
0.02
0.03
3.1
6.1
1.0
1.5
6.2
EXTLD Quiescent Current
Adapter not selected (REVBLK and ADPBLK pins high)
AC or airline state (CHGA, CHGB, and DISBAT pins high)
Charge state (CHGA or CHGB pin low, DISBAT pin high)
CHGIN Quiescent Current
µA
Discharge or relearn state (CHGA or CHGB pin low,
DISBAT pin low)
6.1
12.1
2
_______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS (continued)
(V
BATA
C
= V
= V
= 16.8V, C
= C
= 1µF, V
= C
= V
= 0.93V, V
= C
= V
= 28V, V
= V
= V
= 0,
BATB
CHGIN
= C
VDD
MINVA
MINVB
= C
EXTLD
ADPIN
CHRG
BATSEL
RELRN
= C
= C
= 4.7nF, T = 0°C to +85°C, unless otherwise noted.
CHGB
A
ADPPWR
REVBLK
ADPBLK
DISBAT
DISA
DISB
CHGA
Typical values are at T = +25°C.)
A
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LINEAR REGULATOR
V
Output Voltage
I
= 0 to 100µA
VDD
3.270
3.3
3.330
1.0
V
DD
V
V
V
or V
= 5V to 19V, V
= 5V
ADPIN
BATA
BATA
BATB
BATB
= V
= 5V, V
= 5V to 28V
ADPIN
1.0
V
Ratio
Power-Supply Rejection
DD
mV/ V
mV
, V
, or V
= 5V to 19V, sawtooth at
ADPIN
BATA BATB
1
10V/µs, other supplies = 12V
V
Undervoltage Lockout
Rising edge, relative to regulation point
-55
0
-10
5.5
DD
COMPARATORS
ACDET, AIRDET Input Voltage
Range
V
ACDET, AIRDET Input Bias
Current
V
= V
= 3V
ACDET
0.1
1
µA
AIRDET
ACDET, AIRDET Trip Threshold
ACDET, AIRDET Hysteresis
MINV_ Operating Voltage Range
MINV_ Input Bias Current
Input falling
1.97
2.0
20
2.03
V
mV
V
0.93
-50
2.60
+50
V
V
= 0.93V to 2.6V
nA
MINV_
V
V
V
= 0.93V
= 1.5V
= 2.6V
4.605
7.455
12.93
4.65
7.5
13
4.695
7.545
13.07
MINV_
MINV_
MINV_
BAT_ Minimum Voltage Trip
Threshold
falling
V
BAT_
BAT_ Minimum Voltage
Hysteresis
125
mV
BAT_ Pack Removal Detection
Threshold
V
falling
1.90
2.0
85
2.10
V
BAT_
BAT_ Pack Removal Hysteresis
mV
GATE DRIVERS (Note 1)
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Source Current (PMOS
Turn-Off)
V
V
V
V
= 15V, V
= 15V, V
= 15V, V
= 15V, V
= 7.5V
= 13V
= 15V
= 9.5V
18
3
60
15
SOURCE
SOURCE
SOURCE
SOURCE
PIN
PIN
PIN
PIN
mA
mA
V
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Sink Current (PMOS
Turn-On)
20
70
10
55
V
V
= 8V to 19V (ADPPWR, REVBLK, and AOPBLK,
= 8V to 28V)
SOURCE
SOURCE
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-On Clamp Voltage
-11.0
-8.00
-9.0
-7.0
V
= 4.75V to 8V
-3.65
SOURCE
(V
PIN
to V
)
SOURCE
_______________________________________________________________________________________
3
Power-Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS (continued)
(V
BATA
C
= V
= V
= 16.8V, C
= C
= 1µF, V
= C
= V
= 0.93V, V
= C
= V
= 28V, V
= V
= V
= 0,
BATB
CHGIN
= C
VDD
MINVA
MINVB
= C
EXTLD
ADPIN
CHRG
BATSEL
RELRN
= C
= C
= 4.7nF, T = 0°C to +85°C, unless otherwise noted.
CHGB
A
ADPPWR
REVBLK
ADPBLK
DISBAT
DISA
DISB
CHGA
Typical values are at T = +25°C.)
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-On Time
V
V
= 15V, V
= 13V to V = 9V
PIN
0.3
0.88
µs
SOURCE
SOURCE
PIN
PIN
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-Off Time
= 15V, V
= 9V to V
= 13V
0.3
0.88
0.8
µs
PIN
STATE SELECTION INPUTS
CHRG, BATSEL, RELRN Input
Low Voltage
V
V
CHRG, BATSEL, RELRN Input
High Voltage
2.1
CHRG, BATSEL, RELRN Input
Leakage Current
V
= V
= V = 5.5V
RELRN
0.1
0.1
1
1
µA
CHRG
BATSEL
STATE OUTPUTS
V
V
= 0.4V
1
OUT_
OUT_
OUT0, OUT1, OUT2 Sink Current
mA
µA
= 5.5V
25
OUT0, OUT1, OUT2 Leakage
Current
V
OUT_
= 5.5V
TRANSITION TIMES
MINV_ Comparator Delay
t
V
_ = 5.5V to V _ = 4.45V
BAT
5.5
2.7
11
µs
µs
MINV
BAT
AIRDET and ACDET Comparator
Delay
t
Falling edge with -20mV overdrive
Falling edge with -20mV overdrive
6.0
ADP
BAT_ Removal Comparator Delay
Battery-Insertion Blanking Time
State-Machine Delay
10
21
50
7.5
µs
ms
ns
µs
t
13
5
31
10
BBLANK
MOSFET Turn-On Delay
t
TRANS
4
_______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS
(V
C
= V
= V
= 16.8V, C
= C
= 1µF, V
= C
= V
DISB
= 0.93V, V
= C
CHGB
= V
= 28V, V
= V
= V
= 0,
BATA
BATB
CHGIN
= C
VDD
MINVA
= C
MINVB
= C
EXTLD
ADPIN
CHRG
BATSEL
RELRN
= C
= 4.7nF, T = -40°C to +85°C, unless otherwise noted.)
ADPPWR
(Note 2)
REVBLK
ADPBLK
DISBAT
DISA
CHGA
A
PARAMETER
CONDITIONS
MIN
MAX
UNITS
ADPIN, EXTLD Supply Voltage
Range
4.75
28.00
V
CHGIN, BATA, BATB, and
BATSUP Supply Voltage Range
4.75
19.00
50
V
V
V
= highest,
ADPIN
= high
ADPPWR
V
V
= highest,
ADPIN
V
V
V
V
= 4.75V to 19V,
= 4.75V to 19V,
BATA
54
= low
ADPPWR
ADPIN, BATA, BATB, BATSUP
Quiescent Current (Current from
the Highest Voltage Supply)
BATB
= 4.75V to 19V,
V
V
V
V
V
= highest, V
= highest, V
= highest, V
= highest, V
= high
= low
= high
= low
42
50
42
50
40
µA
BATSUP
BATA
BATA
BATB
BATB
BATSUP
DISA
DISA
DISB
DISB
= 4.75V to 28V,
ADPIN
no external load at V
DD
= highest
= high
ADPIN Quiescent Current (ADPIN
Current When Not the Highest
Voltage)
V
V
V
V
V
V
1
ADPPWR
ADPPWR
V
= 4.75V to 18V,
ADPIN
µA
µA
no external load at V
DD
DD
DD
= low
9
BATA Quiescent Current (BATA
Current When Not the Highest
Voltage)
= high
7.5
16
7.5
16
DISA
DISA
DISB
DISB
V
= 4.75V to 19V,
BATA
no external load at V
= low
BATB Quiescent Current (BATB
Current When Not the Highest
Voltage)
= high
= low
V
= 4.75V to 19V,
BATB
µA
µA
no external load at V
Adapter selected (REVBLK or ADPBLK pins low)
9.5
1.0
1.5
10
EXTLD Quiescent Current
Adapter not selected (REVBLK and ADPBLK pins high)
AC or airline state (CHGA, CHGB, and DISBAT pins high)
Charge state (CHGA or CHGB pin low, DISBAT pin high)
CHGIN Quiescent Current
µA
Discharge or relearn state (CHGA or CHGB pin low,
DISBAT pin low)
18.5
LINEAR REGULATOR
V
V
Output Voltage
I
= 0 to 100µA
VDD
3.270
-60
3.330
-10
V
DD
DD
Undervoltage Lockout
Rising edge, relative to regulation point
mV
COMPARATORS
ACDET, AIRDET Input Voltage
Range
0
5.5
V
ACDET, AIRDET Trip Threshold
MINV_ Operating Voltage Range
Input falling
1.94
0.93
4.59
7.4
2.06
2.60
4.72
7.6
V
V
V
V
V
= 0.93V
= 1.5V
= 2.6V
MINV_
MINV_
MINV_
BAT_ Minimum Voltage Trip
Threshold
V
falling
V
BAT_
12.86
13.14
_______________________________________________________________________________________
5
Power-Source Selector for
Dual-Battery Systems
ELECTRICAL CHARACTERISTICS (continued)
(V
BATA
C
= V
= V
= 16.8V, C
= C
= 1µF, V
= C
= V
= 0.93V, V
= C
CHGB
= V
= 28V, V
= V
= V
= 0,
BATB
CHGIN
= C
VDD
MINVA
= C
MINVB
= C
EXTLD
ADPIN
CHRG
BATSEL
RELRN
= C
= 4.7nF, T = -40°C to +85°C, unless otherwise noted.)
ADPPWR
(Note 2)
REVBLK
ADPBLK
DISBAT
DISA
DISB
CHGA
A
PARAMETER
SYMBOL
CONDITIONS
MIN
MAX
UNITS
BAT_ Pack Removal Detection
Threshold
V
falling
1.88
2.12
V
BAT_
GATE DRIVERS (Note 1)
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Source Current (PMOS
Turn-Off)
V
V
V
= 15V, V
= 15V, V
= 15V, V
= 15V, V
= 7.5V
= 13V
= 15V
= 9.5V
18
3
SOURCE
SOURCE
SOURCE
PIN
PIN
PIN
PIN
mA
mA
V
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Sink Current (PMOS
Turn-On)
20
V
V
10
SOURCE
SOURCE
= 8V to 19V (ADPPWR, REVBLK,
= 8V to 28V)
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-On Clamp Voltage
-11.7
-8.00
-6.5
and ADPBLK, V
SOURCE
V
V
= 4.75V to 8V
-3.50
SOURCE
SOURCE
(V
PIN
to V
)
SOURCE
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-On Time
= 15V, V
= 15V, V
= 13V to V
= 9V
PIN
0.88
0.88
µs
µs
PIN
PIN
ADPPWR, REVBLK, ADPBLK,
DISBAT, DISA, DISB, CHGA,
CHGB Turn-Off Time
V
= 9V to V
= 13V
PIN
SOURCE
STATE SELECTION INPUTS
CHRG, BATSEL, RELRN Input
Low Voltage
0.8
V
V
CHRG, BATSEL, RELRN Input
High Voltage
2.1
STATE OUTPUTS
V
V
= 0.4V
1
OUT_
OUT_
OUT0, OUT1, OUT2 Sink Current
mA
= 5.5V
25
TRANSITION TIMES
MINV_ Comparator Delay
t
V
_ = 5.5V to V _ = 4.45V
BAT
11
6
µs
µs
MINV
BAT
AIRDET and ACDET Comparator
Delay
t
Falling edge with -20mV overdrive
ADP
Battery-Insertion Blanking Time
MOSFET Turn-On Delay
t
12
5
31
10
ms
µs
BBLANK
t
TRANS
Note 1: V
refers to the voltage of the driver output. V
BLK, DISBAT, DISA, DISB, CHGA, and CHGB gate drivers correspond to sources at ADPIN, EXTLD, EXTLD, CHGIN, BATA,
BATB, CHGIN, and CHGIN, respectively.
refers to the power source for the driver. ADPPWR, REVBLK, ADP-
PIN
SOURCE
Note 2: Guaranteed by design. Not production tested.
6
_______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
Typical Operating Characteristics
(Circuit of Figure 1. T = +25°C, unless otherwise noted.)
A
V
LOAD REGULATION
V
vs. TEMPERATURE
I
vs. V
BAT_ BAT_
DD
DD
3.299
3.298
3.297
3.296
3.295
3.294
3.293
3.292
3.291
3.290
3.310
3.305
3.300
3.295
3.290
3.285
35
30
25
20
15
10
5
BAT_ HIGHEST SUPPLY
10
0
0
0.05
0.10
0.15
0.20
-40
-20
0
20
40
60
80
4
6
8
12
14
16
V
DD
LOAD CURRENT (mA)
TEMPERATURE (°C)
BATTERY VOLTAGE (V)
I
vs. V
ADAPTER INSERTION
MAX1538 toc05
BAT_
BAT_
4.0
V
ADPIN
BAT_ NOT HIGHEST SUPPLY
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
20V
10V
0V
V
V
AND
ADPIN
EXTLD
V
EXTLD
V
REVBLK
20V
10V
0V
V
V
ADPBLK
t
ADP
REVBLK
V
5V
ADPBLK
V
OUT1
0V
0
5
10
15
20
10.0µs/div
BATTERY VOLTAGE (V)
_______________________________________________________________________________________
7
Power-Source Selector for
Dual-Battery Systems
Typical Operating Characteristics (continued)
(Circuit of Figure 1. T = +25°C, unless otherwise noted.)
A
BATTERY REMOVAL
BATTERY INSERTION
MAX1538 toc07
MAX1538 toc06
A
CONTACT BOUNCE
10V
0V
10V
SYSTEM LOAD = 3A
V
V
BATA
V
V
BATA
B
0V
OUT0
OUT0
0V
0V
(10V/div)
(10V/div)
10V
10V
0V
V
10V
10V
0V
DISB
V
DISB
(10V/div)
(10V/div)
V
DISA
V
DISA
V
BATB
= 16.8V
V
BATA
= 10V
20V
10V
20V
10V
V
EXTLD
V
BATA
= 10V
V
EXTLD
V
BATB
= 16.8V
5.00ms/div
5.00ms/div
A: CONTACT BOUNCE
B: BATTERY INSERTION BLANKING TIME = 22ms
SOURCE SELECTION CHANGE
BATTERY REMOVAL TIMING
MAX1538 toc09
MAX1538 toc08
10V
10.2V
10V
V
= 16.8V
BATTERY B
REMOVED
BATA
5 x MINV
V
BATSEL
0V
5V
0V
V
EXTLD
V
OUT0
9.8V
9.6V
10V
t
MINV
(t
FOR
V
ADP
DISB
10V
20V
10V
t
TRANS
ADAPTER
REMOVAL
TIMING)
(10V/div)
V
DISB
V
DISA
t
TRANS
0V
(10V/div)
INDUCTIVE KICK
10V
0V
C
BATB
= 1µF
V
V
DISA
SYSTEM LOAD = 3A
V
BATB
AC-COUPLED
(5V/div)
OUT0
SYSTEM LOAD = 3A
(10V/div)
0V
2.00µs/div
4.00µs/div
SOURCE SELECTION CHANGE
MAX1538 toc10
10V
V
BATSEL
0V
5V
0V
V
V
OUT0
DISB
(10V/div)
10V
20V
10V
V
DISA
t
TRANS
(10V/div)
INDUCTIVE KICK
NO CAPACITOR
AT BATB
V
BATB
AC-COUPLED
(5V/div)
2.00µs/div
8
_______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
Typical Operating Characteristics (continued)
(Circuit of Figure 1. T = +25°C, unless otherwise noted.)
A
BREAK-BEFORE-MAKE TIMING
FIRST SOURCE INSERTION
MAX1538 toc11
MAX1538 toc12
5V
0V
OUT1
OUT2, OUT0
t
TRANS
16V
MOSFET
TURN-OFF
TIME
V
14V
12V
20V
ADPIN
MOSFET
DRIVERS
MOSFET
TURN-ON
TIME
V
10V
0V
REVBLK
10V
8V
MOSFET FOR INITIAL
DISCHARGE PATH
POWER-UP TIME
20V
10V
0V
MOSFET FOR FINAL
DISCHARGE PATH
V
EXTLD
1.00µs/div
200µs/div
Pin Description
PIN
NAME
FUNCTION
Minimum Battery A Voltage Set Point. Battery A discharge is prevented if V
has fallen below 5 x
has fallen below 5 x
BATA
1
MINVA
V
.
MINVA
Minimum Battery B Voltage Set Point. Battery B discharge is prevented if V
BATB
2
MINVB
V
.
MINVB
Battery-Selection Input. Drive to logic low to charge battery A or give discharge preference to battery A.
Drive to logic high to charge battery B or give discharge preference to battery B.
3
4
5
BATSEL
RELRN
CHRG
Battery-Relearn Logic-Level Input. Drive RELRN high to enable battery-relearn mode.
Charge-Enable Logic-Level Input. Drive CHRG high to enable the charging path from the charger to the
battery selected by BATSEL.
6
7
8
OUT0
OUT1
OUT2
Selector-State Output. This open-drain output indicates the state of the MAX1538. See Table 1 for
information on decoding.
AC-Adapter Detection Input. When V
presence is detected.
is greater than the ACDET trip threshold (2V typ), adapter
ACDET
9
ACDET
AIRDET
ADPIN
Airline-Adapter Detection Input. When V
detected. Charging is disabled when an airline adapter is detected.
> 2V and V
< 2V, the airline-adapter presence is
ACDET
AIRDET
10
11
Adapter Input. When V > V , the MAX1538 is powered by ADPIN. ADPIN is the supply rail for
ADPIN
BATSUP
the ADPPWR MOSFET driver.
Adapter-Power P-Channel MOSFET Driver. Connect ADPPWR to the gate of P1 (Figure 1). P1 disconnects
the adapter from the system during relearn mode. Exclude P1 and leave ADPPWR disconnected if relearn
is not used. ADPPWR is driven relative to ADPIN. ADPPWR and REVBLK are driven with the same control
signal.
12
13
ADPPWR
Gate Drive for the Reverse-Blocking P-Channel MOSFET. Connect REVBLK to the gate of P2 (Figure 1). P2
REVBLK enables and disables the AC adapter’s power path. REVBLK is driven relative to EXTLD. REVBLK and
ADPPWR are driven with the same control signal.
_______________________________________________________________________________________
9
Power-Source Selector for
Dual-Battery Systems
Pin Description (continued)
PIN
NAME
FUNCTION
Gate Drive for the Adapter-Blocking P-Channel MOSFET. Connect ADPBLK to the gate of P3 (Figure 1). P3
enables and disables the battery discharge path. ADPBLK is driven relative to EXTLD. ADPBLK and
DISBAT are driven with the same control signal.
14
ADPBLK
15, 21
16
N.C.
Not Internally Connected
EXTLD
CHGIN
External Load. EXTLD is the supply rail for REVBLK and ADPBLK.
Charger Node Input. CHGIN is the supply rail for DISBAT, CHGA, and CHGB.
17
Gate Drive for the Battery-Discharge P-Channel MOSFET. Connect DISBAT to the gate of P4 (Figure 2). P4
disconnects the battery from the system load when charging from a step-up converter. Exclude P4 and
leave DISBAT disconnected if using a step-down charger. DISBAT is driven relative to CHGIN. DISBAT and
ADPBLK are driven by the same control signal.
18
19
DISBAT
CHGA
Gate Drive for the Charge Battery A P-Channel MOSFET. Connect CHGA to the gate of P6 (Figure 1). P6
enables and disables the charge path into battery A. CHGA is driven relative to CHGIN. CHGA and DISA
are driven by the same control signal.
Gate Drive for the Charge Battery B P-Channel MOSFET. Connect CHGB to the gate of P7 (Figure 1). P7
enables and disables the charge path into battery B. CHGB is driven relative to CHGIN. CHGB and DISB
are driven by the same control signal.
20
22
23
CHGB
BATB
DISB
Battery B Voltage Input. Battery undervoltage and absence is determined by measuring BATB. BATB is the
supply rail for DISB.
Gate Drive for the Discharge from Battery B P-Channel MOSFET. Connect DISB to the gate of P8 (Figure 1).
P8 enables and disables the discharge path from battery B. DISB is driven relative to BATB. DISB and
CHGB are driven by the same control signal.
Gate Drive for the Discharge from Battery A P-Channel MOSFET. Connect DISA to the gate of P5 (Figure 1).
P5 enables and disables the discharge path from battery A. DISA is driven relative to BATA. DISA and
CHGA are driven by the same control signal.
24
DISA
Battery A Voltage Input. Battery undervoltage and absence is determined by measuring BATA. BATA is the
supply rail for DISA.
25
26
BATA
BATSUP powers the MAX1538. Diode OR BATA and BATB to BATSUP externally. ADPIN is diode
connected to BATSUP internally. Bypass with a 0.1µF capacitor from BATSUP to GND.
BATSUP
GND
27
28
Ground
V
Linear-Regulator Output. Bypass with a 1µF capacitor from V
to GND.
DD
DD
10 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
ADAPTER
R1
R2
R3
C
ADAPTER
ACDET
AIRDET
CHRG
BATSEL
RELRN
ADPIN
FOR RELEARN
MODE ONLY
P1
ADPPWR
STEP-DOWN CHARGER
CHARGER INPUT
MAX1538
REVBLK
EXTLD
P2
P3
R
SNS
SYSTEM LOAD
IN
LOGIC SUPPLY
C
SYS
C2
CHARGER OUTPUT
ADPBLK
C
CHG
OUT2
OUT1
OUT0
OUT
CHGIN
CHGA
P7 P6
V
DD
CHGB
DISB
C1
0.1µF
R10
P5
P8
DISA
MINVA
BATB
BATA
R11
C
BATB
R12
D1
D2
BATSUP
GND MINVB
C3
0.1µF
C
BATA
R13
BATTERY B
BATTERY A
Figure 1. Step-Down Typical Application Circuit
______________________________________________________________________________________ 11
Power-Source Selector for
Dual-Battery Systems
ADAPTER
R1
EXTERNAL AC/AIR-
DETECTION CIRCUIT
R2 + R3
OUT
C
ADAPTER
ACDET
CHRG
AIRDET
ADPIN
BATSEL
RELRN
FOR RELEARN
MODE ONLY
P1
ADPPWR
LOGIC SUPPLY
STEP-UP CHARGER
MAX1538
CHARGER INPUT
C2
IN
OUT2
OUT1
OUT0
CHARGER OUTPUT
P2
REVBLK
C
CHG
OUT
SYSTEM LOAD
EXTLD
V
DD
C
SYS
C1
1µF
P3
P4
ADPBLK
R10
MINVA
DISBAT
R11
CHGIN
CHGA
R12
P7 P6
MINVB
GND
CHGB
DISB
R13
P5
P8
DISA
BATB
C
BATB
D1
BATA
BATSUP
C3
D2
C
BATA
0.1µF
BATTERY B
BATTERY A
Figure 2. Typical Application Circuit for Step-Up/Step-Down Charger
12 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
4R
BATB
R
BATTERY B
UNDERVOLTAGE
0.4V
LATCH
ADPIN
Q
Q
S
R
ADPPWR
MINVB
BATA
EXTLD
4R
REVBLK
R
BATTERY A
UNDERVOLTAGE
LATCH
0.4V
ADPBLK
Q
S
CHGIN
DISBAT
Q
R
MINVA
ACDET
CHGA
STATE
MACHINE
2V
CHGB
DISA
AIRDET
BATA
BATB
CHRG
BATSEL
RELRN
ADPIN
BATSUP
LDO
V
DD
DISB
REF
GND
OUT0
OUT1
OUT2
MAX1538
N
N
N
Figure 3. Functional Diagram
______________________________________________________________________________________ 13
Power-Source Selector for
Dual-Battery Systems
OUT1, and OUT0 indicate the state of the selector so
the host can properly respond.
Detailed Description
The MAX1538 performs power path selection between
an adapter input and two batteries, relieving the host
system from the burden of real-time response to power-
source changes. The integrated selector implements a
fixed break-before-make timer to ensure that power
sources are not connected together and yet the load is
not left unserviced. The MAX1538 monitors battery and
adapter state and presence to determine which source
to select and whether to charge the battery. Logic
inputs CHRG, BATSEL, and RELRN allow the host to
enable/disable charging, select which battery to use,
and impose battery discharge even with adapter pres-
ence. The MAX1538 automatically detects airline
adapters and prevents charging when an airline
adapter is detected. Open-drain logic outputs OUT2,
The MAX1538 can be configured for use with a step-
down battery charger, as shown in Figure 1, or with a
step-up/step-down battery charger, as shown in Figure
2. The minimum MAX1538 system requires only six
MOSFETs. The MAX1538 provides relearn-mode sup-
port with the addition of P1. Relearn mode allows the
system to relearn the battery’s capacity without user
intervention.
Table 1 summarizes the possible states and configura-
tions of the MAX1538.
Table 1. MAX1538 State Table
SOURCE STATE
LOGIC INPUTS
MOSFET STATE (See Figure 4)
Battery
System
(ADPPWR
and REVBLK) and DISBAT)
Battery
(ADPBLK
BATT A
(CHGA and (CHGB and
BATT B
STATE
Adapter
A
B
DISA)
DISB)
AC
AC
AC
AC
AC
X
X
N
X
X
X
X
N
1
0
0
1
1
0
1
0
1
On
On
Off
Off
On
Off
Off
On
On
Off
On
Off
On
Off
Off
Off
On
Off
On
Off
1
1
1
1
0
1
1
0
0
1
0
1
0
1
0
Charge A
Charge B
Relearn A
Relearn B
AC adapter
1
X
X
Otherwise
AIR
Absent
Absent
Absent
Absent
Absent
Legend
AC
X
N
N
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
X
1
X
X
On
Off
Off
On
Off
On
Off
Off
0
0
1
0
1
0
Airline
Discharge A
U
N
N
U
Off
Off
On
Off
Off
Off
On
Off
0
0
0
0
1
0
Discharge B
Idle
U
U
AC adapter is present. V
and V
are both above 2V.
ACDET
AIRDET
AIR
Airline adapter is present. V
is below 2V and V
is above 2V.
AIRDET
ACDET
Absent External adapter is absent. V
and V
are both below 2V.
AIRDET
ACDET
N indicates the battery is normal. The battery is normal when it has not tripped the undervoltage latch (5 x
). See the Battery Presence and Undervoltage Detection section.
N
V
MINV_
U indicates the battery has tripped the undervoltage comparator. An undervoltage battery is detected
U
when V
goes below 5 x V
. See the Battery Presence and Undervoltage Detection section.
MINV_
BAT_
Otherwise
Otherwise covers all cases not explicitly shown elsewhere in the table.
X indicates don’t care. The output does not depend on any inputs labeled X.
X
X
X
X
X
14 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
not allowed until the battery is removed or the charge
path to the battery is selected. Battery removal is
ADAPTER
ADAPTER
ADAPTER
detected when V
falls below 2V. For correct detec-
BAT_
tion of battery removal, ensure that the leakage current
into BAT_ is lower than the leakage current out of BAT_
so that BAT_ falls below 2V when the battery is
removed. The contributors to leakage current into BAT_
are D1, D2, P6, and P7.
ADAPTER
SWITCH
ADAPTER
SWITCH
ADAPTER
SWITCH
SYSTEM
SYSTEM
SYSTEM
BATTERY
SWITCH
BATTERY
SWITCH
BATTERY
SWITCH
Battery Relearn Mode
The MAX1538 implements a battery relearn mode,
which allows for host-device manufacturers to imple-
ment a mode for coulomb-counting fuel gauges (such
as the MAX1781) to measure battery capacity without
user intervention. In battery relearn mode, the AC
adapter is switched off and battery discharge is select-
ed. In this implementation, the host system could
prompt users when their battery capacity becomes
inaccurate, use the host system as a load to discharge
the battery, and then recharge the battery fully.
Coulomb-counting fuel-gauge accuracy is increased
after a relearning cycle.
CHARGER
CHARGER
CHARGER
"A"
SWITCH
"B"
"A"
"B"
"A"
"B"
SWITCH
SWITCH SWITCH
SWITCH SWITCH
CHARGE
DISCHARGE/
RELEARN
AC/AIR
Figure 4. MAX1538 Selection States
Battery Presence and
Undervoltage Detection
Battery relearn mode requires the addition of MOSFET
P1, which blocks current from the adapter to the sys-
tem. To enable relearn mode, drive RELRN high and
drive BATSEL low to relearn battery A or high to relearn
battery B. Relearn mode overrides the functionality of
the CHG pin. Battery relearn mode does not occur
when the selected battery’s undervoltage latch has
been set, or when the selector is in airline mode (see
the Airline Mode and AC Adapter section.) The RELRN
pin only applies when an AC adapter is present. If the
AC adapter is absent and RELRN is ignored, OUT[2:1]
= 10 when the MAX1538 is in battery relearn mode. If
CHG = 0, only OUT2 is needed to indicate that the
MAX1538 was properly placed in relearn mode.
The MAX1538 determines battery absence and under-
voltage and does not allow discharge from an under-
voltage battery. A battery is considered undervoltage
when V
< 5 x V
, and remains classified as
BAT_
MINV_
undervoltage until V
falls below 2V and again rises
BAT_
above 5 x V
MINV
. The undervoltage latch is also
cleared when the charge path is enabled. Set the bat-
tery undervoltage threshold using resistive voltage-
dividers R10, R11, R12, and R13, as shown in Figure 1.
The corresponding undervoltage threshold is:
R11
R10+R11
V
= 5 × V
×
BATA_Undervoltage
DD
If the selected battery trips the undervoltage latch when
in relearn mode, the AC adapter is switched in without
causing a crash to the system. OUT2 can indicate that
the relearn cycle is terminated due to battery undervolt-
age. Typically, after the host system performs a battery
relearn cycle, it either charges the discharged battery
or begins a relearn cycle on the other battery. To switch
to charge mode, drive RELRN low and CHG high.
Since RELRN overrides CHG, in many applications it is
best to permanently keep CHG high and reduce the IO
needed to control the selector.
R13
R12+R13
V
= 5 × V
DD
×
BATB_Undervoltage
To minimize error, use 1% or better accuracy divider
resistors, and ensure that the impedance of the divider
results in a current about 100 times the MINV_ input
bias current at the MINV_ threshold voltage. To opti-
mize error due to 50nA input bias current at MINV_ and
minimize current consumption, typically choose resis-
tors (R10 + R11) or (R12 + R13) smaller than 600kΩ.
When the AC adapter is available, it is used as the
power source for EXTLD unless the RELRN pin is high.
In this state, the charger can be enabled and a
battery charged.
Since batteries often exhibit large changes in their ter-
minal voltage when a load current is removed, further
discharge after the undervoltage latch has been set is
______________________________________________________________________________________ 15
Power-Source Selector for
Dual-Battery Systems
the adapter voltage is between V
AIR_Threshold
and
Airline Mode and AC Adapter
The MAX1538 provides compatibility with airline
adapters. For airplane safety, the use of an airline
adapter requires that the battery charger or charge
path is disabled. The MAX1538 disables the charge
path when an airline adapter is detected. In airline
mode, ADPPWR and REVBLK drive P1 and P2 on, and
all other MOSFETs are off, regardless of the state of
RELRN, CHG, BATSEL, or the batteries. If the AC
threshold is above the airline threshold, select a resis-
tive voltage-divider (as shown in Figure 1) according to
the following equations:
AC_Threshold
V
.
To minimize error, use 1% accuracy or better divider
resistors, and ensure that the impedance of the divider
results in a current about 100 times the ACDET and
AIRDET input bias current. To optimize error due to 1µA
input bias current at ACDET/AIRDET and minimize cur-
rent consumption, typically choose R3 less than 20kΩ.
See the Adapter Removal Debouncing section for more
information regarding R1, R2, and R3. Short R2 to dis-
able airline-adapter mode.
Optionally, an external circuit can be implemented to
determine the presence of an AC/airline adapter. The
circuit in Figure 5 provides fast detection of an airline
adapter, yet allows external circuitry to discriminate
R1+R2+R3
V
= V
×
AC_Threshold
ACDET_Threshold
R3
between airline and AC adapters. If V
<
AC_Threshold
R1+R2+R3
R2+R3
V
, this circuit must be used for airline-
AIR_Threshold
V
= V
×
Air_Threshold
AIRDET_Threshold
adapter detection. Other permutations that directly
drive AIRDET instead do not work properly on the
MAX1538 because adapter removal is not detected
fast enough, causing the system load to crash.
where V
and V
are typ-
ACDET_Threshold
ically 2.0V (see the Electrical Characteristics). An AC
AIRDET_Threshold
OUT[2:0] = 011 if the MAX1538 is in airline-adapter
mode. If RELRN = 0 and CHG = 0, only OUT[1:0] are
necessary to indicate airline-adapter mode.
adapter is detected when the adapter voltage is above
V
, and an airline adapter is detected when
AC_Threshold
ADAPTER INSERTION
EXTERNAL AC/AIRLINE
DETECTION CIRCUIT
ADAPTER
ACDET MUST WAIT
ADPIN
R1
R2 + R3
OUT
FOR AC ADAPTER
ACDET
FOR AIRLINE ADAPTER
AIRDET
ADPIN
ADPPWR
ACDET
P1
P2
MAX1538
ADAPTER REMOVAL
ACDET MAY OCCUR
REVBLK
EXTLD
BEFORE OR AFTER ADPIN
ADPIN
FOR AC ADAPTER
FOR AIRLINE ADAPTER
ACDET
Figure 5. Using an External Adapter Detection Circuit
16 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
case the system holdup capacitor is not large enough
to sustain the system load.
CHG Control
Toggle CHG to enable the charge path to the battery.
Charge control is overridden by RELRN (see the Battery
Relearn Mode section) or airline mode (see the Airline
Mode and AC Adapter section). When CHG is enabled,
the MAX1538 connects the selected battery (BATSEL = 0
for battery A and BATSEL = 1 for battery B) to the charg-
er. OUT[2:1] = 11 if the MAX1538 is in charge mode.
When the charge path is enabled, the corresponding
battery undervoltage latch is cleared. This allows charg-
ing of protected battery packs. In typical applications,
connect CHRG to VDD to reduce the system I/O.
Battery insertion is automatically debounced using the
battery-insertion blanking time (t
). A battery is
BBLANK
not discharged unless the battery has been above the
5 x V threshold for 21ms (typ). After t is
MINV
BBLANK
or the battery
expired, V
must exceed 5 x V
BAT_
MINV_
is detected as undervoltage.
Applications Information
MOSFET Selection
Select P-channel MOSFETs P1–P8 according to their
power dissipation, R
, and gate charge. Each
Single Transition Break-Before-Make
Selection
DSON
MOSFET must be rated for the full system load current.
Additionally, the battery discharge MOSFETs (P3, P5,
P6, P7, and P8) should be selected with low on-resis-
tance for high discharge efficiency. Since for any given
switch configuration at least half of the MOSFETs are
off, dual MOSFETs can be used without reducing the
effective MOSFET power dissipation. When using dual
The MAX1538 guarantees that no supplies are connect-
ed to each other during any transition by implementing
a fixed delay time (t , the break-before-make tran-
TRANS
sition timer). This is necessary as the batteries have very
low impedances, and momentarily shorting batteries
together can cause hundreds of amps to flow. For
example, when adapter removal is detected, ADPPWR
and REVBLK begin to turn off less than 10µs before
ADPBLK and DISBAT begin to turn on, connecting the
appropriate battery. For example, upon switching from
one battery to another, DISA and CHGA begin turning
off less than 10µs before DISB and CHGB begin to turn
on. To guarantee a break-before-make time, ensure that
ADAPTER
ADPIN
FOR RELEARN
MODE ONLY
P1
ADPPWR
the turn-off time of the MOSFETs is smaller than t
TRANS
(see the MOSFET Selection section).
MAX1538
The MAX1538 also guarantees that any change does
not cause unnecessary power-source transitions. When
switching from battery to battery; battery to adapter; or
adapter to battery because of adapter or battery inser-
tion or removal, or due to a change at BATSEL, a single
set of MOSFETs are turned off followed by another set
of MOSFETs turned on. No additional transitions are
necessary. The only exception occurs when RELRN is
high and the adapter is inserted because it is first
detected as an airline adapter and later detected as an
AC adapter. This results in a transition from discharge
mode to AC mode, followed by a transition from AC
mode to relearn mode. Although this extra transition is
generally harmless, it can be avoided by disabling
relearn mode when the adapter is absent.
STEP-DOWN
BATTERY CHARGER
P2
P3
REVBLK
EXTLD
SYSTEM LOAD
IN
ADPBLK
DUAL
FDS4935A
OUT
CHGIN
CHGA
DUAL
FDS4935A
P7 P6
CHGB
DISB
DUAL
FDS4935A
P5
P8
DISA
Blanking
The MAX1538 implements sophisticated blanking at the
adapter and the batteries to correctly determine bat-
tery/adapter insertion and removal. Logic inputs CHRG,
RELRN, and BATSEL should be debounced to ensure
that fast repetitive transitions do not occur, in which
BATB
BATA
BATTERY B
BATTERY A
Figure 6. Optimal Use of Power Dissipation Using Dual
MOSFETs
______________________________________________________________________________________ 17
Power-Source Selector for
Dual-Battery Systems
MOSFETs, they should be paired as shown in Figure 6
for optimal power dissipation.
slows down as the MOSFET approaches off. See the
Typical Operating Characteristics for a scope shot
showing MAX1538 turn-on and turn-off times when dri-
ving FDS6679 MOSFETs. The MAX1538 typically turns
the FDS6679 on in 0.7µs and off in 1µs.
The MAX1538 provides asymmetric MOSFET gate
drive, typically turning MOSFETs on faster than they are
turned off. The t
timer ensures that the MOSFETs
TRANS
that are turning on begin to turn on 10µs after those
MOSFETs that are turning off begin to turn off. Choose
MOSFETs with low enough gate charge that all off-tran-
sitioning MOSFETs turn off before any on-transitioning
MOSFET turns on. Use the following equations to esti-
mate the worst-case turn-on and turn-off times:
Combining the MAX1538 with a Charger
To configure the MAX1538 for use with a step-down
charger, use the circuit of Figure 7. Connect the charg-
er’s power input to EXTLD. Do not connect the charg-
er’s power input to ADPIN. This ensures that the
charger does not bias ADPIN through its high-side
MOSFET.
Q
V
∆V
∆V
I
OFF2
Q
V
G
1
2
G
t
=
+
=
× 0.93kΩ
ON
I
System Holdup Capacitor
G
OFF1
G
C
must be capable of sustaining the maximum sys-
SYS
tem load during the transition time between source
selection. Size the capacitor so that:
Q
5V
Q
G
G
t
=
×
=
× 0.25kΩ
ON
V
I
V
G
ON
G
5× V
− t
+ t
+ t
×
ON
(
)
MINV
MINV
TRANS
where t
G
is the turn-on time, t
is the turn-off time,
ON
OFF
I
SYS_MAX
> V
Q
is the MOSFET’s total gate charge specified at volt-
SYS_MIN
C
SYS
age V , I
is the 18mA (min) gate current when dri-
G
OFF1
ving the gate from 7.5V gate drive to 2V gate drive, ∆V
1
where t
is the battery undervoltage comparator
MINV
delay, t
is the voltage change during the 18mA gate drive
is the fixed time between switching
TRANS
(5.5V), I
is 3mA gate current when driving the gate
OFF2
MOSFETs off and switching MOSFETs on, t
is the
ON
from 2V to 0V, ∆V is the 2V change, and I
is the
ON
2
time to turn a MOSFET on (see the MOSFET Selection
turn-on current.
section), V
is the lower of V
and V
SYS_MIN
,
MINVB
MINV
MINVA
The MAX1538’s gate-drive current is nonlinear and is a
function of gate voltage. For example, the gate driver
I
is the maximum system load, V
is the
SYS_MAX
minimum allowable system voltage before system
ADAPTER
C
ADAPTER
MAX1538
1µF
ADPIN
DCIN
MAX1908
MAX1909 OR
MAX1535
P2
P3
REVBLK
EXTLD
SYSTEM LOAD
CSSP
CSSN
C2
C
SYS
ADPBLK
BATT
CHGIN
Figure 7. Combining the MAX1538 with a Charger
18 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
OTHER POWER SOURCE
5 x V
MINV
OR AC/AIR THRESHOLD
EXTLD
MAX1538
V
SYS_MIN
C
SOURCE
t
MINV
OR t
ADP
I
SOURCE
t
OFF
PARASITIC
INDUCTANCE
(L
ADPBLK/REVBLK
REVBLK/ADPBLK
t
ON
)
SOURCE
t
TRANS
TO BATTERY
OR ADAPTER
Figure 8. System Holdup Capacitor Timing
Figure 9. Inductive Kick Upon Source Disconnect
crash, and C
is the total system holdup capaci-
Inductive “Kick”
SYS
tance, which does not need to be near the MAX1538.
The timing related to the system holdup capacitance is
shown in Figure 8.
When the adapter or a battery is delivering a significant
current to the system and that path is disabled (typical-
ly to enable another path), a voltage spike is generated
at the source. This is due to a parasitic inductance
shown in Figure 9. When the adapter is disconnected, a
positive voltage spike occurs at ADPIN. When a dis-
charging battery is disconnected, a positive voltage
spike occurs at BAT_. Connect a capacitor from BAT_
or ADPIN to GND to limit this inductive kick. Choose the
source capacitance according to the following equation:
Charger output capacitance contributes to C
step-down charger topology (Figure 1), but not for the
step-up/step-down charger topology (Figure 2).
for the
SYS
Leakage Current into BAT_
Leakage current into BATA or BATB can interfere with
proper battery-removal detection. D1 and D2 must be
low leakage to ensure that battery removal is properly
detected. Choose MOSFETs P6 and P7 with low off-
leakage current. Board leakage current can also be a
problem. For example, neighbor pins BATA and
BATSUP should have greater than 50MΩ impedance
between each other. Proper battery-removal detection
requires that:
2
L
× I
SYS_MAX
SOURCE
2
C
>
SOURCE
2
30 − V
SOURCE
where V
is the maximum DC voltage of the
SOURCE
source in question, I
is the maximum system
(parasitic inductance) and
SYS_MAX
SOURCE
are shown in Figure 9.
load, and L
SOURCE
C
I
+ I
+ I
+ I
+
Board DS_OFF(P6) DS_OFF(P7) D1_leakage
During battery charge, the voltage spike during battery
disconnect is negative. To ensure that this negative
I
< I
D2_leakage BAT_Sink@2V
voltage spike does not go below 0V, choose C
according to the following equation:
BAT_
where I
is board leakage current, I
is the
D_Leakage
Board
DS_OFF
off-leakage current of MOSFETs P6 and P7, I
is the reverse leakage current of the diodes, and
is the BAT_ leakage current at 2V (0.4µA;
2
I
L
× I
BAT_Sink@2V
see the Typical Operating Characteristics).
BAT_
CHG_MAX
C
>
BAT_
2
V
BAT__MIN
______________________________________________________________________________________ 19
Power-Source Selector for
Dual-Battery Systems
where V
I
is the minimum battery voltage,
Layout
BAT__MIN
is the maximum charge current, and L
is
BAT_
The MAX1538 selector fits in a very small layout.
CHG_MAX
the battery’s inductance. C
values of 0.01µF are
Ensure that C1 is placed close to V
and GND.
BAT_
DD
adequate for typical applications. Adding capacitance
at BAT_ pins lengthens the time needed to detect bat-
tery removal. See the Battery-Absence-Detection Delay
section.
Connect the paddle to GND directly under the IC. A
complete layout example is shown in Figure 10.
Because BATA and BATB are high-impedance nodes,
prevent leakage current between BATA/BATB and
other high-voltage sources by carefully routing traces.
Note that flux remaining on the board can significantly
contribute to leakage current. See the Leakage Current
into BAT_ section.
Adapter Removal Debouncing
Upon adapter removal the adapter’s connector may
bounce. To avoid false detection of adapter reinsertion
select R1, R2, and R3 according to the following equation:
Minimize parasitic inductance in the BATA and BATB
path to reduce inductive kick during battery discon-
nect. This reduces the capacitance requirement at
BATA and BATB.
V
× t
Bounce
_Threshold
R1 + R2 + R3 <
C
× V
− V
ADPIN
Adapter _Threshold
where V
is the AC-adapter voltage when remov-
Pin Configuration
Adapter
ing an AC adapter and airline-adapter voltage when
removing an airline adapter, C is the capacitance
ADPIN
at ADPIN, and t
is the 5ms debounce time. See
Bounce
the Airline Mode and AC Adapter section for a defini-
tion of V
.
_Threshold
28 27 26 25 24 23 22
Battery-Absence-Detection Delay
When a selected battery is removed, the system load
quickly pulls BAT_ below 5 x V and another
N.C.
1
2
3
4
5
6
7
21
20
19
18
17
16
15
MINVA
MINVB
BATSEL
RELRN
CHRG
OUT0
CHGB
CHGA
DISBAT
CHGIN
EXTLD
N.C.
MINV_
source is selected. The battery is considered present
and undervoltage until V falls below 2V. Although
MAX1538 *
BAT_
another power source is quickly switched to the system
load, capacitance at BAT_ (see the Inductive "Kick"
section) delays the detection of the removed battery. If
another battery is inserted before this delay has
passed, it is considered undervoltage. Calculate the
delay using the following equation:
OUT1
8
9
10 11 12 13 14
19V × C
BAT_
t
=
Absence_delay
THIN QFN
I
BAT
(5mm x 5mm)
*EXPOSED PADDLE
where I
is the 3.9µA BAT_ quiescent current (due to
BAT_
a 5MΩ internal resistor), and C
is the capacitance
BAT_
from BAT_ to GND. When C
= 1µF, t
BAT_
Absence_delay
Chip Information
corresponds to a 5s time constant. If this time is unac-
ceptable, use a smaller capacitance or connect a resis-
tor or current sink from BAT_ to GND.
TRANSISTOR COUNT: 5431
PROCESS: BiCMOS
20 ______________________________________________________________________________________
Power-Source Selector for
Dual-Battery Systems
A D P B L K
R E V B L K
A D P P W R
A D P I N
T B B A
D I S B
D I S A
A T B A
T S B U
G N D
D D
R 1
R 2
A I R D E T
A C D E T
O U T 2
V
R 1 0
Figure 10. MAX1538 Layout Example
______________________________________________________________________________________ 21
Power-Source Selector for
Dual-Battery Systems
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
D2
0.15
C A
D
b
0.10 M
C A B
C
L
D2/2
D/2
k
PIN # 1
I.D.
0.15
C
B
PIN # 1 I.D.
0.35x45∞
E/2
E2/2
C
(NE-1) X
e
L
E2
E
k
L
DETAIL A
e
(ND-1) X
e
C
C
L
L
L
L
e
e
0.10
C
A
0.08
C
C
A3
A1
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE
16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
1
21-0140
C
2
COMMON DIMENSIONS
EXPOSED PAD VARIATIONS
NOTES:
1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
3. N IS THE TOTAL NUMBER OF TERMINALS.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1
SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE
ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm
FROM TERMINAL TIP.
6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
9. DRAWING CONFORMS TO JEDEC MO220.
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE
10. WARPAGE SHALL NOT EXCEED 0.10 mm.
16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm
APPROVAL
DOCUMENT CONTROL NO.
REV.
2
21-0140
C
2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
相关型号：
MAX1538ETI-T
Power Supply Support Circuit, Fixed, 1 Channel, BICMOS, 5 X 5 MM, 0.80 MM HEIGHT, MO-220WHHD-1, TQFN-28
MAXIM
MAX153CAP+T
ADC, Flash Method, 8-Bit, 1 Func, 1 Channel, Parallel, 8 Bits Access, CMOS, PDSO20, SSOP-20
MAXIM
MAX153CAP-T
ADC, Flash Method, 8-Bit, 1 Func, 2 Channel, Parallel, 8 Bits Access, CMOS, PDSO20, SSOP-20
MAXIM
MAX153CPP+
ADC, Flash Method, 8-Bit, 1 Func, 2 Channel, Parallel, 8 Bits Access, CMOS, PDIP20, 0.300 INCH, PLASTIC, DIP-20
MAXIM
MAX153EAP+
ADC, Flash Method, 8-Bit, 1 Func, 2 Channel, Parallel, 8 Bits Access, CMOS, PDSO20, SSOP-20
MAXIM
MAX153EAP+T
ADC, Flash Method, 8-Bit, 1 Func, 1 Channel, Parallel, 8 Bits Access, CMOS, PDSO20, SSOP-20
MAXIM
©2020 ICPDF网 联系我们和版权申明