MAX1538
Power-Source Selector for
Dual-Battery Systems
_______________________________________________________________________________________ 9
MINVA
Minimum Battery A Voltage Set Point. Battery A discharge is prevented if V
BATA
has fallen below 5 x
V
MINVA
.
2
MINVB
Minimum Battery B Voltage Set Point. Battery B discharge is prevented if V
BATB
has fallen below 5 x
V
MINVB
.
3
BATSEL
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.
4
RELRN
Battery-Relearn Logic-Level Input. Drive RELRN high to enable battery-relearn mode.
5 CHRG
Charge-Enable Logic-Level Input. Drive CHRG high to enable the charging path from the charger to the
battery selected by BATSEL.
6 OUT0
7 OUT1
8 OUT2
Selector-State Output. This open-drain output indicates the state of the MAX1538. See Table 1 for
information on decoding.
9
ACDET
AC-Adapter Detection Input. When V
ACDET
is greater than the ACDET trip threshold (2V typ), adapter
presence is detected.
10
AIRDET
Airline-Adapter Detection Input. When V
AIRDET
> 2V and V
ACDET
< 2V, the airline-adapter presence is
detected. Charging is disabled when an airline adapter is detected.
11
ADPIN
Adapter Input. When V
ADPIN
> V
BATSUP
, the MAX1538 is powered by ADPIN. ADPIN is the supply rail for
the ADPPWR MOSFET driver.
12
ADPPWR
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.
13
REVBLK
Gate Drive for the Reverse-Blocking P-Channel MOSFET. Connect REVBLK to the gate of P2 (Figure 1). P2
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.
BREAK-BEFORE-MAKE TIMING
MAX1538 toc11
1.00µs/div
14V
16V
MOSFET
DRIVERS
12V
10V
8V
t
TRANS
MOSFET
TURN-OFF
TIME
MOSFET
TURN-ON
TIME
MOSFET FOR INITIAL
DISCHARGE PATH
MOSFET FOR FINAL
DISCHARGE PATH
FIRST SOURCE INSERTION
MAX1538 toc12
200µs/div
0V
0V
0V
5V
V
ADPIN
V
REVBLK
V
EXTLD
OUT1
OUT2, OUT0
10V
20V
20V
10V
POWER-UP TIME
Typical Operating Characteristics (continued)
(Circuit of Figure 1. T
A
= +25°C, unless otherwise noted.)
Pin Description
