®
RTQ2502A
2A, 6.5V, Ultra Low Noise, Ultra Low Dropout Linear Regulator
General Description
The RTQ2502A is a high-current (2A), low-noise (6μVrms),
high accuracy (1% over line, load, and temperature), low-
dropout linear regulator (LDO) capable of sourcing 2A with
extremely low dropout (max. 125mV). The device output
voltage is pin-selectable (up to 3.95V) using a PCB layout
without the need of external resistors, thus reducing overall
component count. Designers can achieve higher output
voltage with the use of external resistor divider. The device
supports single input supply voltage as low to 1.1V that
makes it easy to use.
The low noise, high PSRR and high output current capability
makes the RTQ2502A ideal to power noise-sensitive
devices such as analog-to-digital converters (ADCs),
digital-to-analog converters (DACs), and RF components.
With very high accuracy, remote sensing, and soft-start
capabilities to reduce inrush current, the RTQ2502A is
ideal for powering digital loads such as FPGAs, DSPs,
and ASICs.
The external enable control and power good indicator
function makes the sequence control easier. The output
noise immunity is enhanced by adding external bypass
capacitor on NR/SS pin. The device is fully specified over
the temperature range of T
J
=
−40°C
to 125°C and is offered
in the VQFN-20L 5x5 package.
Features
Input Voltage Range : 1.1V to 6.5V
Two Output Voltage Modes
½
0.8 V to 5.5V (Set by a Resistive Divider)
½
0.8 V to 3.95V (Set via PCB Layout, No External
Resistor Required)
Accurate Output Voltage Accuracy (1%) Over Line,
Load and Temperature
Ultra High PSRR : 40dB at 500kHz
Excellent Noise Immunity
½
6μV
RMS
at 0.8V Output
μ
Ultra Low Dropout Voltage : 125mV at 2A
Enable Control
Programmable Soft-Start Output
Stable with a 22μF or Larger Ceramic Output
μ
Capacitor
Support Power-Good Indicator Function
RoHS Compliant and Halogen Free
Applications
Portable Electronic Device
Wireless Infrastructure : SerDes, FPGA, DSP
RF, IF Components : VCO, ADC, DAC, LVDS
Ordering Information
RTQ2502A
Pin 1 Orientation
***
(2) : Quadrant 2, Follow EIA-481-D
Package Type
QV : VQFN-20L 5x5 (V-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
***Empty means Pin1 orientation is Quadrant 1
Richtek products are :
½
RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
Suitable for use in SnPb or Pb-free soldering processes.
½
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DSQ2502A-01
September 2019
www.richtek.com
1
RTQ2502A
Pin Configuration
(TOP VIEW)
VOUT
VOUT
GND
VIN
VIN
Marking Information
RTQ2502AGQV : Product Number
20
19
18
17
16
RTQ2502A
GQV
YMDNN
15
14
YMDNN : Date Code
VOUT
SNS
FB
PGOOD
50mV
1
2
3
4
5
21
6
7
8
9
10
VIN
EN
NR/SS
NC
1.6V
GND
13
12
11
200mV
GND
100mV
400mV
VQFN-20L 5x5
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
800mV
is a registered trademark of Richtek Technology Corporation.
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2
DSQ2502A-01
September 2019
RTQ2502A
Functional Pin Description
Pin No.
1, 19, 20
Pin Name
VOUT
Pin Function
LDO output pins. A 22F or greater of capacitance is required for stability.
Place the output capacitor as close to the device as possible and minimize
the impedance between VOUT pin to load.
Output voltage sense input pin. Connect this pin only if using PCB layout set
the VOUT voltage (No External Resistor Required). Keep SNS pin floating if
the VOUT voltage is set by external resistor.
2
SNS
3
4
5, 6, 7, 9, 10, 11
Feedback voltage input. This pin is used to set the desired output voltage
FB
via an external resistive divider. The feedback reference voltage is 0.8V
typically.
Power good indicator output. An open-drain output and active high when the
output voltage reaches 88% of the target. The pin is pulled to ground when
PGOOD
the output voltage is lower than its specified threshold, EN shutdown, OCP
and OTP.
Output voltage setting pins. Connect these pins to ground or leave floating.
50mV, 100mV, Connecting these pins to ground increases the output voltage by the value
200mV, 400mV, of the pin name; multiple pins can be simultaneously connected to GND to
800mV, 1.6V
select the desired output voltage. Leave these pins floating (open) if the
VOUT voltage is set by external resistor.
Ground. The exposed pad must be soldered to a large PCB and connected
to GND for maximum the power dissipation.
No internal connection. Leave these pins floating doesn’t affect the chip
functionality. By connecting these pins to GND, design engineers could
extend the GND copper coverage on the PCB top layer to enhance the
thermal convection.
Noise-reduction and soft-start pin. Decouple this pin to GND with an external
capacitor C
NR/SS
can not only reduce output noise to very low levels but also
slow down the VOUT rise like a soft-start behavior. For low noise
applications, a 10nF to 1F C
NR/SS
is suggested.
Enable control input. Connecting this pin to logic high enables the regulator
or driving this pin low puts it into shutdown mode. The device can have V
IN
and V
EN
sequenced in any order without causing damage to the device.
However, for the soft-start function to work as intended, certain sequencing
rules must be applied. Enabling the device after V
IN
are present is preferred.
Supply input. A minimum of 22F ceramic capacitor or greater of
capacitance is required and should be placed as close as possible to this
pin for better noise rejection.
8, 18,
GND
21 (Exposed Pad)
12
NC
13
NR/SS
14
EN
15, 16, 17
VIN
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DSQ2502A-01
September 2019
www.richtek.com
3
RTQ2502A
Functional Block Diagram
VIN
Charge
Pump
Gate
Driver
Current
Limit
0.72V
Active
Discharge
VOUT
Thermal
Protection
UVLO
UVLO
EN
Bandgap
Reference
Enable
Control
Logic
PGOOD
+
-
+
-
-
SNS
2R
FB
32R
16R
8R
4R
2R
1R
I
NR/SS
NR/SS GND
+
50mV 100mV 200mV 400mV 800mV 1.6V
Operation
The RTQ2502A operates with single supply input ranging
from 1.1V to 6.5V and capable to deliver 2A current to the
output. The device features high PSRR and low noise
provides a clean supply to the application.
A low-noise reference and error amplifier are included to
reduce device noise. The NR/SS capacitor filters the noise
from the reference and feed-forward capacitor filters the
noise from the error amplifier. The high power-supply
rejection ratio (PSRR) of the RTQ2502A minimize the
coupling of input supply noise to the output.
Enable and Shutdown
The RTQ2502A provides an EN pin, as an external chip
enable control, to enable or disable the device. V
EN
below
0.5 V turns the regulator off and enters the shutdown mode,
while V
EN
above 1.1V turns the regulator on. When the
regulator is shutdown, the ground current is reduced to a
maximum of 25μA. The enable circuitry has hysteresis
(typically 50mV) for use with relatively slowly ramping
analog signals.
If not used, connect EN to the largest capacitance on the
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
input as close as possible to prevent voltage droops on
the VIN line from triggering the enable circuit.
VOUT Programming Pins
The RTQ2502A built-in matched feedback resistor network
to set output voltage. The output voltage can be
programmed from 0.8V to 3.95V in 50mV steps when tying
these programming pins (Pins 5 to 11) to ground. Tying
any of the VOUT programming pins to SNS can lower the
value of the upper resistor divider. Hence the VOUT
programming resolution is increased.
Programmable Soft-Start
The noise-reduction capacitor (C
NR/SS
) accomplishes dual
purpose of both noise-reduction and programming the soft-
start ramp time during turn-on. When EN and UVLO exceeds
the respective threshold voltage, the RTQ2502A active a
quick-start circuit to charge the noise reduction capacitor
(C
NR/SS
) and then the output voltage ramps up.
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4
DSQ2502A-01
September 2019
RTQ2502A
Power Good
The power-good circuit monitors the feedback pin voltage
to indicate the status of the output voltage. The open-
drain PGOOD pin requires an external pull-up resistor to
an external supply, any downstream device can receive
power-good as a logic signal that can be used for
sequencing. Pull-up resistor from 10kΩ to 100kΩ is
recommended. Make sure that the external pull-up supply
voltage results in a valid logic signal for the receiving device
or devices.
After start-up, the PGOOD pin becomes high impedance
when the feedback voltage exceeds V
PGOOD_HYS
(Typically
90% of 0.8V reference voltage level). The PGOOD is pulled
to GND when the feedback pin voltage falls below the
V
IT_PGOOD
, EN low, current limit, and OTP.
Under Voltage Lockout (UVLO)
The UVLO circuit monitors the input voltage to prevent
the device from turning on before VIN rises above the V
UVLO
threshold. The UVLO circuit also disables the output of
the device when VIN fall below the lockout voltage
(V
UVLO
− ΔV
UVLO
). The UVLO circuit responds quickly to
glitches on VIN and attempts to disable the output of the
device if VIN collapse.
Internal Current Limit (I
LIM
)
The RTQ2502A 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.
Thermal shutdown can activate during a current limit event
because of the high power dissipation typically found in
these conditions. To ensure proper operation of the current
limit, minimize the inductances to the input and load.
Continuous operation in current limit is not recommended.
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 the device may work at
reverse voltage state.
Over-Temperature Protection (OTP)
The RTQ2502A implements thermal shutdown protection.
The device is disable when the junction temperature (T
J
)
exceeds 160°C (typical). The LDO automatically turn-on
again when the temperature falls to 140°C (typical).
For reliable operation, limit the junction temperature to a
maximum of 125°C. Continuously running the RTQ2502A
into thermal shutdown or above a junction temperature of
125°C reduces long-term reliability.
Output Active Discharge
When the device is disabled, the RTQ2502A discharges
the LDO output (via VOUT pins) through an internal several
hundred ohms to ground. Do not rely on the active
discharge circuit for discharging a large amount of output
capacitance after the input supply has collapsed because
reverse current can possibly flow from the output to the
input. External current protection should be added if the
device may work at reverse voltage state.
Copyright
©
2019 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DSQ2502A-01
September 2019
www.richtek.com
5
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