RT2517B
Application Information
The RT2517B is a low voltage, low dropout linear regulator
with an external bias supply input capable of supporting
an input voltage range from 2.2V to 6V and adjustable
output voltage from 1.2V to (V
IN
−
V
DROP
).
Output Voltage Setting
The RT2517B output voltage is adjustable via the external
resistive voltage divider. The output voltage is set according
to the following equation :
V
OUT
�½
V
ADJ
1
R1
R2
For ADJ pin noise immunity, the resistive divider total value
of R1 and R2 are suggested not over 100kΩ, where V
ADJ
is the reference voltage with a typical value of 1.2V.
Feed-Forward Capacitor (C
FF
)
The RT2517B is designed to be stable without the external
feed-forward capacitor (C
FF
). However, an external
feedforward capacitor between VOUT and ADJ pin is often
adopted to optimizes the transient, noise, and PSRR
performance. Regarding to the resistance value of the
voltage divider, the recommended C
FF
values are as below :
C
FF
= 1nF, for both R1 and R2 are larger than 1kΩ
C
FF
= 10nF, for both R1 and R2 are smaller than 1kΩ
RT2517B
V
IN
C
IN
R1
EN
GND
ADJ
R2
VIN
VOUT
*C
FF
V
OUT
C
OUT
Chip Enable Operation
The RT2517B goes into sleep mode when the EN pin is in
a logic low condition. In this condition, the pass transistor,
error amplifier, and band gap are all turned off, reducing
the supply current to only 10μA (max.). The EN pin can
be directly tied to VIN to keep the part on.
UVLO Protection
The RT2517B provides an input Under Voltage Lockout
protection (UVLO). When the input voltage exceeds the
UVLO rising threshold voltage (1.61V typ.), the device
resets the internal circuit and prepares for operation. If
the input voltage falls below the UVLO falling threshold
voltage during normal operation, the device will be shut
down. A hysteresis (220mV typ.) between the UVLO rising
and falling threshold voltage is designed to avoid noise.
Current Limit
The RT2517B contains an independent current limit
circuitry, which controls the pass transistor's gate voltage,
limiting the output current to 2A (typ.).
C
IN
and C
OUT
Selection
The RT2517B is designed specifically to work with low
ESR ceramic output capacitor for space saving and
performance consideration. Using a ceramic capacitor with
capacitance range from 10μF to 47μF on the RT2517B
output ensures stability.
Input capacitance is selected to minimize transient input
droop during load current steps. For general application,
the requirement of input capacitor with a 10μF is
recommended to minimize input impedance and provide
the desired effect and do not affect stability.
Figure 2. Application Circuit with C
FF
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
8
DS2517B-05
September 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
