TJ2995DP datasheet(6/9 Pages) HTC

6 / 9 page

DDR Termination Regulator

TJ2995

Oct. 2009 - Rev. 1.1

6/9

HTC

VSENSE

The purpose of the sense pin is to provide improved remote load regulation. In most motherboard

applications the termination resistors will connect to VTT in a long plane. If the output voltage was

regulated only at the output of the TJ2995, then the long trace will cause a significant IR drop, resulting in

a termination voltage lower at one end of the bus than the other. The VSENSE pin can be used to improve

this performance, by connecting it to the middle of the bus. This will provide a better distribution across

the entire termination bus. If remote load regulation is not used, then the VSENSE pin must still be

connected to VTT.

VREF

VREF provides the buffered output of the internal reference voltage VDDQ / 2. This output should be

used to provide the reference voltage for the Northbridge chipset and memory. Since these inputs

are typically an extremely high impedance, there should be little current drawn from VREF. For improved

performance, an output bypass capacitor can be used, located close to the pin, to help with noise. A

ceramic capacitor in the range of 0.1 µF to 0.01 µF is recommended. This output remains active

during the shutdown state and thermal shutdown events for the suspend to RAM functionality.

VTT

VTT is the regulated output that is used to terminate the bus resistors. It is capable of sinking and

sourcing current while regulating the output precisely to VDDQ / 2. The TJ2995 is designed to handle

peak transient currents of up to ± 3A with a fast transient response. If a transient is expected to last

above the maximum continuous current rating for a significant amount of time then the output capacitor

should be sized large enough to prevent an excessive voltage drop. Despite the fact that the TJ2995 is

designed to handle large transient output currents it is not capable of handling these for long durations,

under all conditions. The reason for this is the standard packages are not able to thermally dissipate the

heat as a result of the internal power loss. If large currents are required for longer durations, then care

should be taken to ensure that the maximum junction temperature is not exceeded. Proper thermal

derating should always be used (please refer to the Thermal Dissipation section).

THERMAL DISSIPATION

Since the TJ2995 is a linear regulator any current flow from VTT will result in internal power dissipation

generating heat.

To prevent damaging the part from exceeding the maximum allowable junction

temperature, care should be taken to derate the part dependent on the maximum expected ambient

temperature and power dissipation. The maximum allowable internal temperature rise, TRmax can be

calculated given the maximum ambient temperature, TAmax of the application and the maximum allowable

junction temperature, TJmax.

Rmax = TJmax − TAmax

From this equation, the maximum allowable power dissipation, P

Dmax of

the part can be

calculated:

Dmax

= T

Rmax

/ θ

TJ2995DP датащи(PDF) 6 Page - HTC Korea TAEJIN Technology Co.

TJ2995DP датащи(HTML) 6 Page - HTC Korea TAEJIN Technology Co.

Html Pages

1 2 3 4 5 6 7 8 9

датащи скачать

ссылки URL