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BD3538F-E2 Datasheet(PDF) 2 Page - Rohm

Part # BD3538F-E2
Description  Termination Regulators for DDR-SDRAMs
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Manufacturer  ROHM [Rohm]
Direct Link  http://www.rohm.com
Logo ROHM - Rohm

BD3538F-E2 Datasheet(HTML) 2 Page - Rohm

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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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