RT9173B
V
REFEN
Application Information
VCNTL
VIN
Internal parasitic diode
R1
R2
RT9173B
REFEN
Avoid forward-bias internal parasitic diode, VOUT to VCNTL
,
VOUT
and VOUT to VIN, the VOUT should not be forced some
voltage respect to ground on this pin while the VCNTL or
VIN is disappeared.
GND
Figure 6
Consideration while designs the resistance of voltage
divider
Make sure that VCNTL >= VIN in all conditions including
power on and off.As other linear regulator, dropout voltage
and thermal issue should be specially considered. Figure
6 and 7 show the RDS(ON) over temperature of RT9173B in
SOP-8 and TO-252 packages respectively. The minimum
dropout voltage could be obtained by the product of RDS(ON)
and output current. For thermal consideration, please refer
to the relative sections.
Make sure the sinking current capability of pull-downNMOS
if the lower resistance was chosen so that the voltage on
VREFEN is below 0.2V.
In addition, the capacitor 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.
RDS(ON) vs. Temperature
How to reduce power dissipation on Notebook PC or
the dual channel DDR SDRAM application?
0.45
SOP-8
0.43
VCNTL = 3.3V
In notebook application, using RichTek’ s Patent
“Distributed Bus Terminator Topology” with choosing
RichTek’ s product is encouraged.
0.41
0.39
0.37
0.35
0.33
0.31
0.29
0.27
0.25
0.23
Distributed Bus Terminating Topology
Terminator Resistor
R0
BUS(0)
R1
BUS(1)
R2
R3
R4
R5
R6
R7
R8
R9
VOUT
RT9173B
BUS(2)
BUS(3)
BUS(4)
-50
-25
0
25
50
75
100
125
REFEN
(°C)
Temperature
BUS(5)
BUS(6)
BUS(7)
RDS(ON) vs. Temperature
VOUT
RT9173B
0.48
0.45
0.42
0.39
0.36
0.33
0.30
0.27
0.24
TO-252
BUS(8)
BUS(9)
VCNTL = 3.3V
RN
BUS(N)
R(N+1)
BUS(N+1)
General Regulator
The RT9173B could also serves as a general linear
regulator. The RT9173B accepts an external reference
voltage at REFENpin and provides output voltage regulated
to this reference voltage as shown in Figure 6, where
-50
-25
0
25
50
75
100
125
(°C)
Temperature
VOUT = VREF x R1/(R1+R2)
www.richtek.com
10
DS9173B-09 March 2007
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
