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PDF MAX1259 Data sheet ( Hoja de datos )

Número de pieza MAX1259
Descripción Battery Manager
Fabricantes Maxim Integrated 
Logotipo Maxim Integrated Logotipo



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MAX1259
Battery Manager
General Description
The MAX1259 battery manager provides backup-battery
switching for CMOS RAM, microprocessors, or other low-
power logic ICs. It automatically switches to the backup
battery when the primary power supply is interrupted.
Low-loss switches guarantee an input-to-output differ-
ential of only 200mV while supplying 250mA from the
primary power supply or 15mA from the battery.
Battery discharge during shipping does not occur in the
MAX1259, since the backup battery can be disconnected
by strobing the RST input.
A battery-fail output signal indicates when the backup bat-
tery is below +2V, and a power-fail output signal indicates
when the primary power supply is low. The MAX1259
monitors the backup battery, warns of impending power
failures, and switches the memory to the battery when
failures occur. The MAX1259 is pincompatible with the
DS1259, but consumes three times less supply current.
Commercial, extended, and military temperature range
devices are available.
Applications
● Battery Backup for CMOS RAM
● Uninterruptible Power Supplies
● Computers
● Controllers
Functional Diagram
VCCI
VCCO
VBATT
RESET
LOGIC
RST
PF
REF MAX1259
GND
BF
BAT
Features
● Switches to Backup Battery if Power Fails
● Consumes Less than 100nA of Battery Current
● Power-Fail Output Signals Primary Power-Supply
Loss
● Battery Monitor Indicates Low Battery
● Battery Can Be Disconnected to Prevent Discharge
During Shipping
● Battery Automatically Reconnected when VCC is
Applied
● Pin-Compatible with the DS1259
● Supply Current Three Times Lower than DS1259
● Available in Extended-Industrial and Military
Temperature Ranges
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX1259C/D
0°C to +70°C
Dice*
MAX1259CPE
0°C to +70°C
16 PDIP
MAX1259CWE
0°C to +70°C
16 Wide SO
MAX1259EPE
-40°C to +85°C 16 PDIP
MAX1259EWE
-40°C to +85°C 16 Wide SO
MAX1259MJE
-55°C to +125°C 16 CERDIP
*Contact factory for dice specifications.
Note: Devices in PDIP and SO packages are available in both
leadedPb) and lead(Pb)-free packaging. Specify lead-free by
adding the “+” symbol at the end of the part number when
ordering. Lead-free not available for CERDIP package.
Pin Configuration
TOP VIEW
N.C. 1
16 VCCI
VBATT 2
BF 3
MAX1259
15 VCCI
14 N.C.
N.C. 4
13 VCCO
BAT 5
12 VCCO
RST 6
11 PF
GND 7
10 N.C.
GND 8
9 N.C.
DIP/SO
19-4638; Rev 3; 9/14

1 page




MAX1259 pdf
MAX1259
Battery Manager
VCCI
+4.25V
+3V
tF
tPF
PF
tR tREC
BATTERY
CURRENT
Figure 1. Power-Down/Power-Up Conditions
Detailed Description
Battery Switchover and VCCO
Figure 2 shows a typical application for the MAX1259.
CMOS RAM is powered from VCCO. The battery switcho-
ver circuit compares VCC to the VBATT input, and con-
nects VCCO to whichever is higher.
Switchover occurs when VCC equals VBATT as VCC falls,
and when VCC is 60mV greater than VBATT as VCC rises.
This hysteresis prevents repeated, rapid switching if VCC
falls very slowly or remains nearly equal to the battery
voltage. Low-loss switches guarantee an input-to-output
differential of only 200mV, while supplying 250mA from
the primary power supply or 15mA from the battery.
Note: With adequate filtering, the MAX1259 need only
supply the average current drawn by the CMOS RAM.
Many RAM data sheets specify a 75mA maximum sup-
ply current, but this peak current spike lasts only 100ns.
If the sum of the peak currents is greater than 250mA, a
capacitor placed on the VCCO output can supply the high
instantaneous current, while VCCO need only supply the
average current, which is much less.
The MAX1259 operates with battery voltages from 2.5V to
3.7V. High-value capacitors—either standard electrolytic
or farad-sized, double-layer capacitors—can also be used
for short-term memory backup (Figure 3).
RAM16
RAM2
RAM1
CE15
15, 16
VCC
VCCI
12, 13
VCCO
CE1
CE0
MAX1259
2
VBATT
11
PF
GND
7, 8
NMI
µP
ADDRESS
DECODE
Figure 2. Typical Application Circuit
VCC
3k
6.2k
15, 16
VCCI
12, 13
VCC0 TO RAM
MAX1259
2N3904
0.22F
MAXCAP
2
VBATT
GND
7, 8
NOTE: LARGE VALUE CAPACITORS, SUCH AS A 0.22F MAXCAP,
MAY BE USED FOR SHORT-TERM MEMORY BACKUP.
Figure 3. Using a MAXCAP as a Backup Battery
www.maximintegrated.com
Maxim Integrated 5

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