RT9045
9
DS9045-05 April 2014
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Copyright 2014 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Application Information
Output Voltage Setting
The RT9045 is a high-speed linear regulator designed to
generate termination voltage in Double Data Rate (DDR)
memory system. Besides, the RT9045 could also serves
as a general linear regulator. The RT9045 accepts an
external reference voltage at the REFEN pin and provides
an output voltage regulated to this reference voltage level
as shown in Figure 6, where
V
OUT
= V
IN
x R2 / (R1 + R2)
Shutdown Control
Refer to the “Typical Application Circuit”. Make sure the
current sinking capability of pull-down N-MOSFET 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.
Soft-Start
The RT9045 builds in an internal soft-start circuit to prevent
inrush current during start-up. The internal soft-start time
depends on REFEN voltage. For DDRIII application
(REFEN = 0.75V), soft-start time is around 100μs.
Current Limit & Short Circuit Protection
The RT9045 implements the current limit and output short
protection circuit against the unexpected applications. The
current limit circuit monitors and controls the pass
transistor's gate voltage, providing the load current up to
at least 1.8A. If the load current exceeds the current limit
trip point, RT9045 will soon reduce the load current to
around 1.5A constantly, refer to Figure 8.
If the output voltage is abruptly pulled down to less than
0.2V, the short circuit protection is triggered and then
maintains the load current at 1.5A. It prevents RT9045
from being damaged in case an output short to ground
event occurs.
General Regulator
Like other linear regulator, dropout voltage and thermal
issue should be specially considered. Figure 7 shows
the R
DS(ON)
vs. Temperature curve of RT9045. 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 section.
Figure 7. R
DS(ON)
vs. Temperature
Figure 8. Output Voltage vs. Output Current
Output Voltage vs. Output Current
0.00
0.15
0.30
0.45
0.60
0.75
0.90
1.05
1.20
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
Output Current (A)
Output Voltage (V)
DDR II
DDR III
V
CNTL
= 5V
Low - V
DDR III
Figure 6. RT9045 Operating as a Linear Regulator
VIN
REFEN
GND
VCNTL
VOUT
RT9045
V
REFEN
R1
R2
5V
V
OUT
V
IN
R
DS(ON)
vs. Temperature
0.20
0.25
0.30
0.35
0.40
0.45
0.50
-50 -25 0 25 50 75 100 125
Temperature (°C)
R
DS(ON)
(Ω)
(Ω)
V
CNTL
= 5V
