CM8500A Datasheet, PDF (4/13 Pages) List of Unclassifed Manufacturers – 3A BUS TERMINATOR

FUNCTIONAL DESCRIPTION
CM8500A
3A BUS TERMINATOR
The CM8500A is a switching regulator that is capable of
Low Noise Current Limit:
sinking and sourcing 3A of current without an external heat CM3708A’s current limit is a low noise current limit. It increase
sink. CM8500A uses a standard surface mount PTSSOP
the system loop noise immunity while it is doing the current limit
and PSOP package with bottom metal exposed and the heat protection for the system. The current limit is around 6A for the
can be piped through the bottom of the device and onto the normal 3A operation.
PCB.
INPUTS
The CM8500A integrates power MOSFETs that are capable The input voltage pins (VCCQ or VIN/2) determine the output
of source and sink 3A of current while maintaining excellent voltages (VL1 or VL2). In the default mode, when the VIN/2 pin
voltage regulation. The output voltage can be regulated within is open, the output voltage is 50% of the VCCQ input.
3% or less by using the external feedback. Separate voltage If a specific voltage is forced at the VIN/2 pin, the output voltage
supply inputs have been added to fit applications with various follows the voltage at the VIN/2 pin. VCCQ suggested
power supplies for the databus and power buses.
connecting to VCCQ of memory module for better tracking with
memory VCCQ.
VREF
The reference voltage could be ranged from 0V to VIN.
OTHER SUPPLY VOLTAGES
Several inputs are provided for the supply voltages: PVDD1,
OUPUTS
PVDD2, VCC1, and VCC2.
The output voltage pins (VL1, VL2) are tied to the databus,
address, or clock lines via an external inductor. Output voltage The PVDD1 and PVDD2 provide the power supply to the power
is determined by the VCCQ or VIN/2 inputs so it can be from MOSFETs. VCC1 and VCC2 provide the voltage supply to the
0V to VIN..
logic section and internal error amplifiers.
Internal Power Switches:
CM3708A has been integrated 2 Power MOSFETs whose
RDS_(ON) is around 100m Ohm each.
FEEDBACK
The VFB pin is an input that can be used for closed loop
compensation. This input is derived from the voltage output.
AGSEN pin is a contact node of internal resistor divider for
remote sense.
APPLICATIONS
USING THE CM8500A FOR SSTL BUS
TERMINATION
Figure 1 is the typical schematic of the CM8500ATEVAL that
shows the recommended approach for bus terminating
solutions for SSTL-2 bus. This circuit can be used in PC
memory and Graphics memory applications as shown in
Figure 2 and Figure 3.
Figure 4 shows the PCB layout of the CM8500ATEVAL.
Table 1details the key parameters of SSTL_2 specification.
Figure 5 shows two different approach of SSTL_2 Terminated
Output. (Refer to page 8 for detail description.)
2004/12/20
Champion Microelectronic Corporation
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