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BD3538F-E2 Datasheet(PDF) 2 Page - Rohm |
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BD3538F-E2 Datasheet(HTML) 2 Page - Rohm |
2 / 20 page 2/16 TSZ02201-0J2J0A900980-1-2 © 2015 ROHM Co., Ltd. All rights reserved. 02.Nov.2015 Rev.001 www.rohm.com TSZ22111・15・001 BD3538F BD3538HFN Pin Configuration Pin Descriptions Pin No. Pin Name Pin Function 1 GND GND pin 2 EN Enable input pin 3 VTTS Detector pin for termination voltage 4 VREF Reference voltage output pin 5 VDDQ Reference voltage input pin 6 VCC VCC pin 7 VTT_IN Termination input pin 8 VTT Termination output pin Bottom FIN (Note 1) Substraight (Conntct to GND) (Note 1) Only BD3538HFN Description of Blocks 1. VCC The VCC pin is for the independent power supply input that operates the internal circuit of the IC. It is the voltage at this pin that drives the IC’s amplifier circuits. The VCC input ranges from 3.3V to 5.5V and maximum current consumption is 4mA. A bypass capacitor of 1 µF or so should be connected to this pin when using the IC in an application circuit. 2. VDDQ This is the power supply input pin for an internal voltage divider network. The voltage at VDDQ is halved by two 50 kΩ internal voltage-divider resistors and the resulting voltage serves as reference for the VTT output. Since VTT = 1/2VDDQ, the JEDEC requirement for DDR-SDRAM can be satisfied by supplying the correct voltage to VDDQ. Noise input should be avoided at the VDDQ pin as it is also included by the voltage-divider at the output. An RC filter consisting of a resistor and a capacitor (220 Ω and 2.2 µF, for instance) may be used to reduce the noise input but make sure that it will not significantly effect the voltage-divid er’s output. 3. VTT_IN VTT_IN is a power supply input pin for VTT output. Voltage in the range between 1.0V to 5.5V, but consideration must be given to the current limit dictated by the ON-Resistance of the IC and to the change in allowable loss due to input/output voltage difference. Generally, the following voltages are supplied: ・ DDR I VVTT_IN =2.5V ・ DDRII VVTT_IN =1.8V Take note that a high impedance voltage input at VTT_IN may result in oscillation or degradation in ripple rejection, so connecting 10µF capacitor with minimal change in capacitance to VTT_IN terminal is recommended. However, this impedance may depend on the characteristics of the power supply input and the impedance of the PC board wiring, which must be carefully checked before use. 4. VREF BD3538 provides a constant voltage, VREF, which is independent from the VTT output and can serve as a reference input for memory controllers and DRAMs. The voltage level of VREF is kept constant even if the EN pin is at “Low” level, making the use of this IC compatible with “Self Refresh” state of DRAM. In order to stabilize the output voltage, connecting the correct combination of capacitor and resistor to VREF is necessary. For this purpose, a combination of 1.0µF to 2.2µF ceramic capacitor, characterized by minimal variation in capacitance and a 0.5Ω to 2.2Ω phase compensating resistor is recommended. The maximum current capability of the VREF pin is 20mA but for an application which consumes a small amount of VREF current, using a capacitance of 1 µF or less will do. 5. VTTS VTTS is a sense pin for the load regulation of the VTT output voltage. In case the wire connecting VTT pin and the load is too long, connecting VTTS pin to the part of the wire nearer to the load may improve load regulation. 6. VTT This is the output for the DDR memory termination voltage and it has a sink/source current capability of ±1.0A. VTT voltage tracks the voltage at VDDQ pin divided in half. The output is turned to OFF when EN pin is “Low” or when either the VCC UVLO or the thermal shutdown protection function is activated. Always connect a capacitor to VTT pin for loop gain and phase compensation and for reduction in output voltage variation in the event of sudden load change. Be careful in choosing the capacitor as sufficient capacitance may cause oscillation and high ESR (Equivalent Series Resistance) may result in increase d output voltage variation during a sudden change in load. A 220µF or so ceramic capacitor is recommended, though ambient temperature and other conditions should also be considered. VTT_IN VDDQ GND EN VTTS VREF VTT VCC 1 2 3 4 5 6 7 8 TOP VIEW |
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