RT2519W
Operation
very long if the CNR is not fully charged during 2ms and
opens the quick-start switch, the CNR will be charged
through higher resistance 224kΩ and takes much longer
time to finish the start up process.
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.
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 2μA (max.). If the shutdown mode
is not required, the EN pin can be directly tied to VIN pin
to keep the LDO on.
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.
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.
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
reduction capacitor (CNR). The switch of the quick-start
circuit is closed at start up.
To reduce the noise from bandgap, there is a low-pass
(RC) filter consist of the CNR and the resistance which is
connected with bandgap, as Functional Block Diagrams
present.
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.
At the start-up, the quick-start switch is closed, with only
35kΩ resistance between bandgap andNR pin. The quick-
start switch opens approximate 2ms after the device is
enabled, the resistance betweenNR and bandgap is about
224kΩ to form a very good low pass filter and with great
noise reduction performance.
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 30μs duration.
The 35kΩ 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 :
tSS (sec) = 160000 x CNR (F)
(1)
It is recommend the CNR value larger than 0.01μF to reduce
noise, and low leakage ceramic capacitors are suitable.
However, with too large CNR will extend the start-up time
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2519W-00 May 2019
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
