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General Description

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.

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.

The MAX1538 is available in a space-saving 28-pin thin

QFN package with a maximum footprint of 5mm x 5mm.

Applications

Notebook and Subnotebook Computers

Internet Tablets

Dual-Battery Portable Equipment

Features

♦ 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

♦ Simplifies Power-Management µP Firmware

♦ 4.75V to 28V AC-Adapter Input Voltage Range

♦ Small 28-Pin Thin QFN Package (5mm x 5mm)

MAX1538

Power-Source Selector for

Dual-Battery Systems

________________________________________________________________ Maxim Integrated Products 1

19-3169; Rev 0; 1/04

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.

MAX1538

REVBLK

DISA

DISB

BATA

BATB

CHGB

CHGA

CHGIN

ADPIN

EXTLD

ADPBLK

AIRDET

ACDET

MINVA

MINVB

CHRG

BATSEL

RELRN

OUT2

OUT1

OUT0

GND

BATSUP

BATTERY

CHARGER

CHG_OUT

SYSTEM LOAD

ADAPTER

BATTERY B

BATTERY A

PART TEMP RANGE PIN-PACKAGE

MAX1538ETI -40°C to +85°C 28 Thin QFN

Ordering Information

Pin Configuration appears at end of data sheet.

Typical Operating Circuit

Summary of content (22 pages)

PAGE 1
9-3169; Rev 0; 1/04 Power-Source Selector for Dual-Battery Systems 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 presence 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.
PAGE 2
MAX1538 Power-Source Selector for Dual-Battery Systems ABSOLUTE MAXIMUM RATINGS VEXTLD, VBATSUP, VADPIN, VBATA, VBATB, VCHGIN to GND .................................................-0.3V to +30V VADPPWR to GND...................................-0.3V to (VADPIN + 0.3V) VREVBLK, VADPBLK to GND ...................-0.3V to (VEXTLD + 0.3V) VCHGA, VCHGB, VDISBAT to GND ..........-0.3V to (VCHGIN + 0.3V) VDISA to GND..........................................-0.3V to (VBATA + 0.3V) VDISB to GND...................
PAGE 3
Power-Source Selector for Dual-Battery Systems (VBATA = VBATB = VCHGIN = 16.8V, CVDD= 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 3.270 3.3 3.
PAGE 4
MAX1538 Power-Source Selector for Dual-Battery Systems ELECTRICAL CHARACTERISTICS (continued) (VBATA = VBATB = VCHGIN = 16.8V, CVDD= 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
Power-Source Selector for Dual-Battery Systems (VBATA = VBATB = VCHGIN = 16.8V, CVDD = 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) MIN MAX UNITS ADPIN, EXTLD Supply Voltage Range PARAMETER 4.75 28.00 V CHGIN, BATA, BATB, and BATSUP Supply Voltage Range 4.75 19.
PAGE 6
MAX1538 Power-Source Selector for Dual-Battery Systems ELECTRICAL CHARACTERISTICS (continued) (VBATA = VBATB = VCHGIN = 16.8V, CVDD = 1µF, VMINVA = VMINVB = 0.93V, VEXTLD = VADPIN = 28V, VCHRG = VBATSEL = VRELRN = 0, CADPPWR = CREVBLK = CADPBLK = CDISBAT = CDISA = CDISB = CCHGA = CCHGB = 4.7nF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL BAT_ Pack Removal Detection Threshold CONDITIONS VBAT_ falling MIN MAX UNITS 1.88 2.
PAGE 7
Power-Source Selector for Dual-Battery Systems VDD vs. TEMPERATURE 3.305 BATTERY INPUT CURRENT (µA) 3.297 35 MAX1538 toc02 MAX1538 toc01 3.298 IBAT_ vs. VBAT_ 3.310 VDD (V) 3.295 3.294 3.300 3.295 3.293 3.292 3.290 30 25 20 15 10 5 3.291 BAT_ HIGHEST SUPPLY 3.290 3.285 0.05 0.10 0.15 0.20 0 -40 -20 VDD LOAD CURRENT (mA) 0 20 40 60 80 4 TEMPERATURE (°C) 6 8 10 12 14 16 BATTERY VOLTAGE (V) ADAPTER INSERTION IBAT_ vs. VBAT_ MAX1538 toc05 4.
PAGE 8
MAX1538 Power-Source Selector for Dual-Battery Systems Typical Operating Characteristics (continued) (Circuit of Figure 1. TA = +25°C, unless otherwise noted.) BATTERY REMOVAL BATTERY INSERTION MAX1538 toc07 MAX1538 toc06 A CONTACT BOUNCE 10V 10V SYSTEM LOAD = 3A B 0V 0V VBATA 0V VOUT0 (10V/div) 0V VEXTLD 10V 5.00ms/div 5.00ms/div A: CONTACT BOUNCE B: BATTERY INSERTION BLANKING TIME = 22ms SOURCE SELECTION CHANGE BATTERY REMOVAL TIMING VBATA = 16.
PAGE 9
Power-Source Selector for Dual-Battery Systems BREAK-BEFORE-MAKE TIMING FIRST SOURCE INSERTION MAX1538 toc11 MAX1538 toc12 5V OUT1 0V OUT2, OUT0 tTRANS 16V MOSFET TURN-OFF TIME MOSFET TURN-ON TIME MOSFET FOR INITIAL DISCHARGE PATH 14V 20V VADPIN 12V MOSFET DRIVERS 10V VREVBLK 10V 8V 0V POWER-UP TIME MOSFET FOR FINAL DISCHARGE PATH 20V 10V VEXTLD 0V 1.00µs/div 200µs/div Pin Description PIN NAME FUNCTION 1 MINVA Minimum Battery A Voltage Set Point.
PAGE 10
MAX1538 Power-Source Selector for Dual-Battery Systems Pin Description (continued) 10 PIN NAME 14 ADPBLK 15, 21 N.C. 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. Not Internally Connected 16 EXTLD External Load. EXTLD is the supply rail for REVBLK and ADPBLK. 17 CHGIN Charger Node Input.
PAGE 11
Power-Source Selector for Dual-Battery Systems MAX1538 ADAPTER R1 R2 R3 CADAPTER ACDET CHRG AIRDET BATSEL ADPIN ADPPWR FOR RELEARN P1 MODE ONLY RELRN STEP-DOWN CHARGER MAX1538 REVBLK P2 SYSTEM LOAD CSYS RSNS CHARGER INPUT IN EXTLD LOGIC SUPPLY C2 CHARGER OUTPUT P3 ADPBLK CCHG OUT2 OUT P7 P6 CHGIN OUT1 CHGA OUT0 VDD CHGB DISB P8 P5 DISA MINVA BATB CBATB C1 0.1µF R10 R11 BATA D1 D2 CBATA BATSUP GND MINVB R12 C3 0.1µF R13 BATTERY B BATTERY A Figure 1.
PAGE 12
MAX1538 Power-Source Selector for Dual-Battery Systems ADAPTER R1 EXTERNAL AC/AIRDETECTION CIRCUIT R2 + R3 OUT CADAPTER ACDET CHRG AIRDET BATSEL ADPIN ADPPWR FOR RELEARN P1 MODE ONLY RELRN LOGIC SUPPLY STEP-UP CHARGER MAX1538 CHARGER INPUT IN OUT2 C2 CHARGER OUTPUT P2 OUT1 REVBLK CCHG SYSTEM LOAD OUT0 OUT EXTLD VDD CSYS P3 ADPBLK MINVA DISBAT P4 C1 1µF R10 R11 CHGIN R12 P7 P6 CHGA MINVB CHGB R13 DISB GND P8 P5 DISA BATB CBATB D1 CBATA BATTERY B BATA BATSUP D2 C3 0
PAGE 13
Power-Source Selector for Dual-Battery Systems MAX1538 4R BATB R BATTERY B UNDERVOLTAGE LATCH Q S 0.4V ADPIN ADPPWR R Q MINVB EXTLD 4R REVBLK BATA R BATTERY A UNDERVOLTAGE LATCH Q S 0.4V R ADPBLK CHGIN Q MINVA DISBAT ACDET CHGA STATE MACHINE 2V CHGB AIRDET BATA CHRG BATSEL RELRN DISA ADPIN BATSUP BATB LDO VDD DISB REF GND OUT0 OUT1 OUT2 MAX1538 N N N Figure 3.
PAGE 14
OUT1, and OUT0 indicate the state of the selector so the host can properly respond. The MAX1538 can be configured for use with a stepdown 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 support with the addition of P1. Relearn mode allows the system to relearn the battery’s capacity without user intervention.
PAGE 15
Power-Source Selector for Dual-Battery Systems ADAPTER ADAPTER SWITCH ADAPTER ADAPTER SWITCH SYSTEM SYSTEM BATTERY SWITCH CHARGER ADAPTER SWITCH BATTERY SWITCH CHARGER "A" SWITCH BATTERY SWITCH CHARGER "B" "A" SWITCH SWITCH "B" "A" SWITCH SWITCH BATTERY B DISCHARGE/ RELEARN "B" SWITCH BATTERY A BATTERY B BATTERY A BATTERY B BATTERY A CHARGE SYSTEM AC/AIR Figure 4.
PAGE 16
MAX1538 Power-Source Selector for Dual-Battery Systems 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.
PAGE 17
Power-Source Selector for Dual-Battery Systems Single Transition Break-Before-Make Selection The MAX1538 guarantees that no supplies are connected to each other during any transition by implementing a fixed delay time (tTRANS, the break-before-make transition timer). This is necessary as the batteries have very low impedances, and momentarily shorting batteries together can cause hundreds of amps to flow.
PAGE 18
MAX1538 Power-Source Selector for Dual-Battery Systems MOSFETs, they should be paired as shown in Figure 6 for optimal power dissipation. The MAX1538 provides asymmetric MOSFET gate drive, typically turning MOSFETs on faster than they are turned off. The tTRANS timer ensures that the MOSFETs that are turning on begin to turn on 10µs after those MOSFETs that are turning off begin to turn off.
PAGE 19
Power-Source Selector for Dual-Battery Systems MAX1538 OTHER POWER SOURCE 5 x VMINV OR AC/AIR THRESHOLD EXTLD MAX1538 VSYS_MIN tMINV OR tADP CSOURCE ISOURCE tOFF ADPBLK/REVBLK tTRANS tON PARASITIC INDUCTANCE (LSOURCE) REVBLK/ADPBLK TO BATTERY OR ADAPTER Figure 8. System Holdup Capacitor Timing crash, and CSYS is the total system holdup capacitance, which does not need to be near the MAX1538. The timing related to the system holdup capacitance is shown in Figure 8.
PAGE 20
BATB 21 N.C. 20 CHGB 19 CHGA BATSEL 3 MAX1538 * RELRN 4 18 DISBAT CHRG 5 17 CHGIN OUT0 6 16 EXTLD OUT1 7 15 N.C. IBAT *EXPOSED PADDLE 9 ADPBLK 10 11 12 13 14 8 REVBLK 19V × CBAT _ where IBAT_ is the 3.9µA BAT_ quiescent current (due to a 5MΩ internal resistor), and CBAT_ is the capacitance from BAT_ to GND. When CBAT_ = 1µF, tAbsence_delay corresponds to a 5s time constant. If this time is unacceptable, use a smaller capacitance or connect a resistor or current sink from BAT_ to GND.
PAGE 21
GND BATTERY A GND R11 GND C1 R3 OUT1 7 OUT0 6 CHRG 5 RELRN 4 BATSEL 3 MINVB 2 MINVA 1 4 P5 8 9 10 11 12 13 14 * EXPOSED PADDLE MAX1538 28 27 26 25 24 23 22 VDD OUT2 R2 CBATA GND ACDET 3 BATSUP AIRDET 2 BATA ADPIN R1 CBATSUP R10 P8 DISA ADPPWR 1 DISB REVBLK BATTERY B BATB ADPBLK CBATB 15 N.C. 16 EXTLD 17 CHGIN 18 DISBAT 19 CHGA 20 CHGB 21 N.C.
PAGE 22
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 CL D/2 PIN # 1 I.D. QFN THIN.EPS MAX1538 Power-Source Selector for Dual-Battery Systems 0.10 M C A B D2/2 k 0.15 C B PIN # 1 I.D. 0.35x45∞ E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e CL CL L L e e 0.10 C A C 0.