SA56600-42 Datasheet, PDF (2/12 Pages) NXP Semiconductors – System reset for lithium battery backup

Philips Semiconductors
System reset for lithium battery back-up
Product data
SA56600-42
GENERAL DESCRIPTION
The SA56600-42 is designed to protect SRAM data in computer
systems during periods of sagging power supply voltages and power
outages. When the power supply voltage drops to typically 4.2 V, the
CS output goes to a logic LOW state pulling CE to a LOW state,
disabling the SRAM device. In addition, a reset logic LOW is asserted
for system use. If the supply voltage drops further, to 3.3 V typically
or lower, the SA56600-42 switches the system’s operation from the
main power supply source to the Lithium back-up battery. As the
main supply is restored and the voltage rises to 3.3 V or higher, the
SRAM support voltage transfers from the Lithium back-up battery to
the main supply. When the main supply voltage rises to greater than
typically 4.2 V, the CS output goes to a logic HIGH state for SRAM
CE control. Reset assertion is released and normal operation is
resumed. This sequence ensures reliable preservation of SRAM
data during periods of supply deficiency and interruptions.
The SA56600-42 is offered in the SO8 surface mount package.
FEATURES
• Supply switching at 4.2 V_DC threshold (falling supply)
• RESET output
• Both CS and CS outputs available for SRAM control
• During battery back-up operation:
– Low supply current (0.3 µA typical)
– Low input/output voltage drop (0.3 V typical at 100 µA)
– Low reverse current leakage (0.1 µA max.)
• During normal operation:
– Low input/output voltage drop (0.2 V typical at 50 mA)
– 4.8 V typical output voltage at 50 mA with V_CC = 5.0 V
– Restoration of main supply operation at 3.3 V
SIMPLIFIED SYSTEM DIAGRAM
APPLICATIONS
• Memory cards (SRAM)
• PCs, word processors
• FAX machines, photocopiers, office equipment
• Sequence controllers
• Video games and other equipment with SRAM
V_CC
GND
SA56600-42
8
3.3 V
DETECTION
CITCUIT
6 ^VOUT
4 ^VBATT
V_CC
R_PU
2
RESET
R
LITHIUM
BATTERY
4.2 V
DETECTION
CITCUIT
1
7
Y
3 ^CS
5 CS
Figure 1. Simplified system diagram.
V_DD
SRAM
CE
GND
SL01277
ORDERING INFORMATION
PACKAGE
TYPE NUMBER
NAME
DESCRIPTION
SA56600-42D
SO8
plastic small outline package; 8 leads; body width 3.9 mm
TEMPERATURE
RANGE
–40 to +85 °C
2001 Jun 19
2
853–2249 26559