CM8500A
3A BUS TERMINATOR
FUNCTIONAL DESCRIPTION
The CM8500A is a switching regulator that is capable of
sinking and sourcing 3A of current without an external heat
sink. CM8500A uses a standard surface mount PTSSOP
and PSOP package with bottom metal exposed and the heat
can be piped through the bottom of the device and onto the
PCB.
The CM8500A integrates power MOSFETs that are capable
of source and sink 3A of current while maintaining excellent
voltage regulation. The output voltage can be regulated within
3% or less by using the external feedback. Separate voltage
supply inputs have been added to fit applications with various
power supplies for the databus and power buses.
VREF
The reference voltage could be ranged from 0V to VIN.
OUPUTS
The output voltage pins (VL1, VL2) are tied to the databus,
address, or clock lines via an external inductor. Output voltage
is determined by the VCCQ or VIN/2 inputs so it can be from
0V to VIN..
Internal Power Switches:
CM3708A has been integrated 2 Power MOSFETs whose
RDS(ON) is around 100m Ohm each.
Low Noise Current Limit:
CM3708A’s current limit is a low noise current limit. It increase
the system loop noise immunity while it is doing the current limit
protection for the system. The current limit is around 6A for the
normal 3A operation.
INPUTS
The input voltage pins (VCCQ or VIN/2) determine the output
voltages (VL1 or VL2). In the default mode, when the VIN/2 pin
is open, the output voltage is 50% of the VCCQ input.
If a specific voltage is forced at the VIN/2 pin, the output voltage
follows the voltage at the VIN/2 pin. VCCQ suggested
connecting to VCCQ of memory module for better tracking with
memory VCCQ.
OTHER SUPPLY VOLTAGES
Several inputs are provided for the supply voltages: PVDD1,
PVDD2, VCC1, and VCC2.
The PVDD1 and PVDD2 provide the power supply to the power
MOSFETs. VCC1 and VCC2 provide the voltage supply to the
logic section and internal error amplifiers.
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
Page 4
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
