First highly integrated power-management IC for DDR cache-memory battery backup eliminates multiple discrete components in existing solutions
(Product News, 07 Jul 2008 )
Maxim Integrated Products introduces the DS2731 integrated power-management IC (PMIC) for DDR cache-memory backup. This PMIC integrates a single-cell Li+ charger, power-steering system to control switchover between system power and battery power, and a 2MHz synchronous buck regulator that "regulates" the DDR memory supply. This unprecedented level of integration eliminates over 15 separate components in existing solutions, thus saving both cost and space. The DS2731 is compatible with the PCI Express(R) 12V power rail in DDRII and DDRIII, and is therefore well suited for RAID server/system memory cards, as well as RAID on motherboard (ROMB) and modular RAID on motherboard (MROMB) systems.
Integrated charge FETs enable the DS2731 to fast charge a single Li+ battery cell at a rate up to 1.5A from a 12V supply using the constant-current, constant-voltage (CCCV) charge method. The charge rate, charge voltage, and safety timer length are all user definable through external resistors, which increases implementation flexibility. Additionally, the DS2731 monitors charge status and reports results through three dedicated pins that can be used to drive LEDs.
An auxiliary supply voltage or battery provides the supply voltage for the cache-memory system. If the auxiliary supply falls below 2.93V, an internal comparator switches the supply from system power to battery power. This switchover occurs through internal power FETs, and is implemented as a break-before-make sequence to prevent current from flowing between the battery and the auxiliary supply. The DS2731 automatically switches back to auxiliary supply when the supply rises above a 3.03V threshold.
The DS2731's buck regulator provides up to 450mA to the DDR cache memory to maintain operation. At light loads, the regulator operates in burst mode for maximum efficiency. To prolong battery life, all nonessential functions of the DS2731 are disabled while it supplies holdup current to the cache memory. Additionally, when the battery voltage drops below a user-programmable threshold, the IC goes into very-low-power standby mode.
