RT2519W

3

DS2519W-00 May 2019

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Copyright 2019 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Operation

The RT2519W is a low noise, high PSRR LDO which

supports very low dropout operation. The operating input

range from 2.2V to 6V and the output voltage is

programmable as low to 0.8V and the output current can

be up to 1A. The internal compensation network is well

designed to achieve fast transient response with good

stability.

In steady-state operation, the feedback voltage is

regulated to the reference voltage by the internal regulator.

When the feedback voltage signal is less than the

reference, the output current passes through the power

MOSFET will be increased. The extra amount of the

current is sent to the output until the voltage level of FB

pin returns to the reference.

On the other hand, if the feedback voltage is higher than

the reference, the power MOSFET current is decreased.

The excess charge at the output can be released by the

loading current.

Start-Up

The RT2519W has a quick-start circuit to charge the noise

circuit is closed at start up.

To reduce the noise from bandgap, there is a low-pass

connected with bandgap, as Functional Block Diagrams

present.

At the start-up, the quick-start switch is closed, with only

35k

Ω resistance between bandgap and NR pin. The quick-

start switch opens approximate 2ms after the device is

enabled, the resistance between NR and bandgap is about

224k

Ω to form a very good low pass filter and with great

noise reduction performance.

The 35k

Ω resistance is used to slow down the reference

voltage ramp to avoid inrush current at chip start-up, and

the start-up time can be calculated as :

(1)

μF to reduce

noise, and low leakage ceramic capacitors are suitable.

through higher resistance 224k

Ω and takes much longer

time to finish the start up process.

Enable and Shutdown Operation

The RT2519W goes into sleep mode when the EN pin is

in a logic low condition. In this condition, the pass transistor,

error amplifier, and bandgap are all turned off, reducing the

supply current to only 2

μA (max.). If the shutdown mode

is not required, the EN pin can be directly tied to VIN pin

to keep the LDO on.

Current Limit

The RT2519W continuously monitors the output current

to protect the pass transistor against abnormal operations.

When an overload or short circuit is encountered, the

current limit circuitry controls the pass transistor's gate

voltage to limit the output within the predefined range. By

reason of the build-in body diode, the pass transistor

conducts current when the output voltage exceeds input

voltage. Since the current is not limited, external current

protection should be added if device may work at reverse

voltage state.

Over-Temperature Protection (OTP)

The RT2519W has an over-temperature protection. When

the device triggers the OTP, the device shuts down until

the temperature back to normal state.

Under Voltage Lock-Out (UVLO)

The RT2519W utilizes an under voltage lock-out circuit to

keep the output shut off until the internal circuitry is

operating properly. The UVLO circuit has a de-glitch feature

so that it typically ignores undershoot transients on the

input if they are less than 30

μs duration.