RT9199
9
DS9199-11 April 2014 www.richtek.com
©
Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
General Regulator
The RT9199 could also serves as a general linear regulator.
The RT9199 accepts an external reference voltage at
REFEN pin and provides output voltage regulated to this
reference voltage as shown in Figure 6, where
V
OUT
= V
REFEN
x R2/(R1+R2)
As other linear regulator, dropout voltage and thermal issue
should be specially considered. Figure 7 shows the R
DS(ON)
over temperature of RT9199. The minimum dropout voltage
could be obtained by the product of R
DS(ON)
and output
current. For thermal consideration, please refer to the
relative sections.
Application Information
Consideration while designing the resistance of
voltage divider
Refer to the “Typical Application Circuit”. Make sure the
current sinking capability of pull-down NMOS is enough
for the chosen voltage divider to pull-down the voltage at
REFEN pin below 0.15V to shutdown the device.
In addition, the capacitor C
SS
and voltage divider form the
low-pass filter. There are two reasons doing this design;
one is for output voltage soft-start while another is for
noise immunity.
How to reduce power dissipation on Notebook PC
or the dual channel DDR SDRAM application?
In notebook application, using RichTek's Patent
“Distributed Bus Terminator Topology” with choosing
RichTek's product is encouraged.
Distributed Bus Terminating Topology
R0
R9
R8
R7
R6
R5
R4
R3
R2
R1
R(2N)
R(2N+1)
RT9199
RT9199
VOUT
VOUT
REFEN
BUS(0)
BUS(1)
BUS(2)
BUS(3)
BUS(4)
BUS(5)
BUS(6)
BUS(7)
BUS(8)
BUS(9)
BUS(2N)
BUS(2N+1)
Terminator Resistor
Input Capacitor and Layout Consideration
Place the input bypass capacitor as close as possible to
the RT9199. A low ESR capacitor larger than 470uF is
recommended for the input capacitor. Use short and wide
traces to minimize parasitic resistance and inductance.
Inappropriate layout may result in large parasitic inductance
and cause undesired oscillation between RT9199 and the
preceding power converter.
Figure 6
VCNTL
REFEN
GND
VIN
VOUT
RT9199
V
REFEN
R1
R2
Figure 7
R
DS(ON)
vs. Temperature
0.28
0.3
0.32
0.34
0.36
0.38
0.4
0.42
0.44
0.46
0.48
-50-250 255075100125
Temperature
R
DS(ON)
(Ω)
V
CNTL
= 5V, V
REFEN
= 1V
(°C)
