RT9173B Ver la hoja de datos (PDF) - Richtek Technology
Número de pieza
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Fabricante
RT9173B Datasheet PDF : 13 Pages
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RT9173B
Application Information
Internal parasitic diode
Avoid forward-bias internal parasitic diode, VOUT to VCNTL,
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.
Consideration while designs the resistance of voltage
divider
Make sure the sinking current capability of pull-down NMOS
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.
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.
REFEN
Distributed Bus Terminating Topology
Terminator Resistor
R0
R1
VOUT
R2
RT9173B
R3
R4
R5
R6
VOUT
R7
RT9173B
R8
R9
BUS(0)
BUS(1)
BUS(2)
BUS(3)
BUS(4)
BUS(5)
BUS(6)
BUS(7)
BUS(8)
BUS(9)
General Regulator
RN
R(N+1)
BUS(N)
BUS(N+1)
The RT9173B could also serves as a general linear
regulator. The RT9173B accepts an external reference
voltage at REFEN pin and provides output voltage regulated
to this reference voltage as shown in Figure 6, where
VOUT = VREF x R1/(R1+R2)
www.richtek.com
10
VREFEN
R1
VCNTL
VIN
RT9173B
REFEN
VOUT
R2
GND
Figure 6
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.
RDS(ON) vs. Temperature
0.45
SOP-8
0.43 VCNTL = 3.3V
0.41
0.39
0.37
0.35
0.33
0.31
0.29
0.27
0.25
0.23
-50 -25
0
25 50 75
Temperature (°C)
100 125
RDS(ON) vs. Temperature
0.48
TO-252
0.45 VCNTL = 3.3V
0.42
0.39
0.36
0.33
0.30
0.27
0.24
-50 -25
0
25 50
75
Temperature (°C)
100 125
DS9173B-09 March 2007
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