UR5512 Datasheet, PDF (5/7 Pages) Unisonic Technologies – 2A DDR BUS TERMINATION REGULATOR

UR5512
FUNCTIONAL DESCRIPTION
LINEAR INTEGRATED CIRCUIT

General Information
The UR5512 is a linear regulator designed for DDR SDRAM bus terminator application. The output, V_OUT is
capable of sourcing or sinking current up to 2A peak while regulating the output voltage to within 20mV offset. The
UR5512 has excellent response to load regulation while preventing shoot through. Active-low shutdown mechanism
and fault protections. The UR5512 is available in several packages to meet different power dissipation and surface
mount applications.
Output Voltage Regulation
The output voltage tracks the reference voltage applied at V_REF pin. Two internal NPN pass transistors act as the
buffered output regulate the output voltage by sourcing current from V_IN pin or sinking current to GND pin. An internal
Kelvin sensing scheme is use at the V_OUT pin to improve load regulation at various load current. Since the UR5512
exhibits excellent response to load transient, lesser amount of capacitors can be used.
Current Limit
An internal current limiting sensor is used to monitor the maximum output current to prevent damages from
overload or short-circuit condition. Increasing the input voltage of V_IN or V_CNTL will get higher current-limit points.
Shutdown and Soft-Start
An additional function of the V_REF pin is acting as a shutdown control input that can be used for suspend to RAM
functionality. Applying and holding a voltage below 0.15V to V_REF pin shuts down the output of the regulator. An
external NPN transistor or N-channel MOSFET is used to pull down the V_REF pin voltage; while applying a “high”
signal to turn on the transistor. During shutdown condition, the two pass transistors are turned off and the output
V_OUT will tri-state; sourcing or sinking no current. When releasing the V_REF pin, the current through the resistor divider
charges the capacitor Css to initiate a soft-start cycle.
Thermal Shutdown
If the junction temperature exceeds the thermal shutdown (T_J= +150°C) then the part will enter a shutdown state.
A thermal sensor turns off both pass transistors, allowing the device to cool down. After the junction temperature
reduces by 40°C, the regulator starts to regulate again; resulting in a pulsed output during continuous thermal
overload conditions.
Power Inputs
Input power up sequence are not required for V_IN and V_CNTL. Be careful; do not apply voltage to V_OUT when there is
no V_CNTL voltage presented. This is due to the internal parasitic diodes between V_OUT to V_IN and V_OUT to V_CNTL which
will be forward bias.
Reference Voltage
The reference voltage is programmed by a resistor divider between V_IN and GND pins. The recommended resistor
is < 5kΩ to maintain the accuracy of the output voltage. For improved the performance, an external bypass capacitor
can be used, located close to V_REF pin to help with noise. A ceramic capacitor can be use and is selected to be
greater than 0.1µF. Do not place any additional loading on this reference input pin.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
5 of 7
QW-R101-017,A