RT2515A
Application Information
The RT2515A is a low voltage, low dropout linear regulator
with an external bias supply input capable of supporting
an input voltage range from 1.4V to 6V with a fixed output
voltage from 1V to 2V in 0.1V increments.
Output Voltage Setting
The RT2515A output voltage is adjustable from 1.4V to
6V via the external resistive voltage divider. The voltage
divider resistors can have values of up to 800kΩ because
of the very high impedance and low bias current of the
sense comparator. The output voltage is set according to
the following equation :
V
OUT
= V
ADJ
× ⎛
1+ R1
⎞
⎜
⎟
⎝
R2
⎠
The RT2515A is designed specifically to work with low
ESR ceramic output capacitor for space saving and
performance consideration. Using a ceramic capacitor with
capacitance of at least 10μF and ESR larger than 1mΩ on
the RT2515A output ensures stability. Nevertheless, the
RT2515A can still work well with other types of output
capacitors due to its wide range of stable ESR. Figure 3
shows the allowable ESR range as a function of load
current for various output capacitance. Output capacitors
with larger capacitance can reduce noise and improve load
transient response, stability, and PSRR. The output
capacitor should be located at a distance of not more than
0.5 inch from the output pin of the RT2515A.
Region of Stable C
OUT
ESR vs. Load Current
100
where V
ADJ
is the reference voltage with a typical value of
0.5V.
Unstable Range
10
The RT2515A 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.
Current Limit
The RT2515A contains an independent current limit
circuitry, which monitors and controls the pass transistor's
gate voltage, limiting the output current to 3A (typ.).
C
IN
and C
OUT
Selection
Like any low dropout regulator, the external capacitors of
the RT2515A must be carefully selected for regulator
stability and performance. Using a capacitor of at least
10μF is suitable. The input capacitor must be located at a
distance of not more than 0.5 inch from the input pin of
the IC. Any good quality ceramic capacitor can be used.
However, a capacitor with larger value and lower ESR
(Equivalent Series Resistance) is recommended since it
will provide better PSRR and line transient response.
C
OUT
ESR (
Ω
)
Chip Enable Operation
1
Stable Range
0.1
0.01
V
IN
= 3.3V, V
OUT
= 2.5V, C
OUT
= 10μF / X7R
0.001
0.0
0.3
0.5
0.8
1.0
Load Current (A)
Figure 3
Thermal Considerations
Thermal protection limits power dissipation in RT2515A.
When the operation junction temperature exceeds 160°C,
the OTP circuit starts the thermal shutdown function and
turns the pass element off. The pass element turns on
again after the junction temperature cools by 30°C.
RT2515A output voltage will be closed to zero when output
short circuit occurs as shown in Figure 4. It can reduce
the IC temperature and provides maximum safety to end
users when output short circuit occurs.
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2515A-02 November 2012
www.richtek.com
7
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
