BD3531F_15 Datasheet, PDF (2/19 Pages) Rohm – Termination Regulator for DDR-SDRAMs

BD3531F
Pin Configuration
TOP VIEW
GND 1
EN 2
VTTS 3
VREF 4
8 VTT
7 _{VTT_IN}
6 _VCC
5 VDDQ
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
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 5V and maximum current consumption is 4mA. A
bypass capacitor of 10μF 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 50kΩ
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 (220Ω and 2.2μF, for instance,) may be used to reduce the noise input but
make sure that it will not significantly affect the voltage-divider’s output.
3. VTT_IN
VTT_IN is the power supply input pin for the VTT output. Input voltage may range from 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 a 100μF 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
BD3531F provides a constant voltage, VREF, which is independent from the VTT output and can serve as 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 the “Self Refresh” state of DRAMs.
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.
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.
www.rohm.com
© 2015 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
2/15
TSZ02201-0J2J0A900950-1-2
02.Nov.2015 Rev.001