RT9045GSP 데이터 시트보기 (PDF) - Richtek Technology

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RT9045GSP

Cost-Effective, 1.8A Sink/Source Bus Termination Regulator

Richtek Technology 

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

VOUT = VIN x R2 / (R1 + R2)

VIN

5V

VREFEN

R1

VIN

VCNTL

RT9045

REFEN

VOUT

R2

GND

VOUT

Figure 6. RT9045 Operating as a Linear Regulator

General Regulator

Like other linear regulator, dropout voltage and thermal

issue should be specially considered. Figure 7 shows

the RDS(ON) vs. Temperature curve of RT9045. The minimum

dropout voltage could be obtained by the product of RDS(ON)

and output current. For thermal consideration, please refer

to the relative section.

RDS(ON) vs. Temperature

0.50

0.45

0.40

0.35

0.30

0.25

0.20

-50 -25

VCNTL = 5V

0

25 50

75

Temperature (°C)

100 125

Figure 7. RDS(ON) vs. Temperature

RT9045

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 CSS 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.

Output Voltage vs. Output Current

1.20

1.05

DDR II

0.90

DDR III

0.75

0.60

0.45

Low - VDDR III

0.30

0.15

0.00

VCNTL = 5V

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)

Figure 8. Output Voltage vs. Output Current

DS9045-04 August 2011

www.richtek.com

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