Complete Backup-Management ICs

for Lithium and NiMH Batteries

8

_______________________________________________________________________________________

Pin Description

PIN

NAME

FUNCTION

1IN

Main Battery Input. Connect to a 2.8V to 5.5V battery or other power source. Bypass with a 4.7µF

ceramic capacitor to GND.

2BK

Backup Battery Input. Connect to an NiMH or rechargeable lithium backup battery. Connect a ceramic

bypass capacitor from BK to GND. See the Step-Up Capacitor Selection section for more details.

3

PGND

Power Ground. Connect PGND to the ground side of the BK input capacitor and BKSU output

capacitor. Use this connection as the star point for all grounds. See the PC Board Layout and Routing

section for specific instructions regarding PGND.

4LX

5

BKSU

Step-Up Converter Output. Bypass with a 10µF to 22µF ceramic capacitor to PGND. The BKSU output

voltage is set to either 3.3V or 2.5V without resistors, or to an adjustable voltage with an external

resistor-divider. See the Setting the Step-Up Converter Voltage section.

6

LDO

2.5V (MAX8568A) or 1.8V (MAX8568B), 10mA LDO Output for Memory Supply. LDO is powered from

BKSU. Bypass with a 4.7µF ceramic capacitor to GND.

7

OD1

11

Ω Open-Drain Output. OD1 drives the gate of an external pMOS switch.

8

OD2

11

Ω Open-Drain Output. OD2 drives the gate of an external pMOS switch.

9

NI/LI

Selects NiMH or Rechargeable Lithium Backup Battery. Connect NI/LI to BKSU if an NiMH backup

battery is used. Connect NI/LI to GND if a rechargeable lithium backup battery is used.

10

BKV

Sets the BKSU Output Voltage. Connect to GND for 3.3V output at BKSU. Connect to BKSU for 2.5V

output. Connect to the midpoint of a resistor-divider connected from BKSU to GND for adjustable

output. See the Setting the Step-Up Converter Voltage section.

11

INOK

step-up converter and LDO turn on, and OD1 and OD2 go high impedance.

12

CHGI

Sets Backup Battery Charge Current. Connect a resistor from CHGI to GND to set the charge current.

See the Setting the Charge Current section for details.

13

GND

Ground. Connect to the exposed paddle. Star all grounds at the BKSU output capacitor ground.

14

STRTV

Sets Fast-Charge Start Voltage for NiMH. See the Using an NiMH Backup Battery section.

15

TERMV

Sets Fast-Charge Stop Voltage for NiMH, as Well as the Battery Regulation Voltage for Both

Rechargeable Lithium and Maximum Voltage for NiMH. See the Using a Lithium Backup Battery

section and the Using an NiMH Backup Battery section.

16

REF

Reference Output. Bypass with a 0.22µF ceramic capacitor to GND.

EP

—

Exposed Paddle. Connect to the analog ground plane. EP also functions as a heatsink. Solder to the

circuit-board analog ground plane.