RT2518 - Richtek

®
RT2518
1A, Ultra-Low Dropout Linear Regulator with Enable
General Description
Features
The RT2518 is a high performance positive voltage regulator
designed for applications requiring ultra-low input voltage
and ultra-low dropout voltage at up to 1 amperes. It operates
with an input voltage as low as 1.4V, and the output voltage
is adjustable as low as 0.5V. The RT2518 features ultra
low dropout, ideal for applications where output voltage is
very close to input voltage. Additionally, the RT2518 has
an enable pin to further reduce power dissipation while
shutdown. The RT2518 provides excellent regulation over
variations in line, load and temperature. The RT2518 is
available in the WDFN-8L 3x3 package. The output voltage
can be set by an external divider or fixed at 1.2V depending
on how the FB pin is configured.

Input Voltage as Low as 1.4V

Ultra-Low Dropout Voltage 200mV @ 1A
Adjustable Output Voltage from 0.5V to 5.5V
Over-Current Protection
Over-Temperature Protection
1μ
μA Input Current in Shutdown Mode
Enable Control
RoHS Compliant and Halogen Free






Applications




Ordering Information

RT2518


Package Type
QW : WDFN-8L 3x3 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)
Telecom/Networking Cards
Motherboards/Peripheral Cards
Industrial Applications
Wireless Infrastructures
Set-Top Boxes
Medical Equipments
Notebook Computers
Battery Powered Systems
Pin Configurations
Note :
(TOP VIEW)
Richtek products are :
NC
VOUT
ADJ
EN
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
8
1
3
GND

6
4
9
5
2
7
NC
VIN
IC
GND
WDFN-8L 3x3
Marking Information
3P= : Product Code
3P=YM
DNN
YMDNN : Date Code
Simplified Application Circuit
VIN
VIN
RT2518
VOUT
C1
Enable
R1
EN
DS2518-00
November 2013
C2
ADJ
GND
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
VOUT
R2
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT2518
Functional Pin Description
Pin No.
1, 8
Pin Name
Pin Function
NC
No Internal Connection.
VOUT
Output Voltage. A minimum of 10F capacitor should be placed directly at this pin.
3
ADJ
Feedback Voltage Input. When this pin is grounded, an internal resistor divider sets
the output voltage to 1.2V. If connected to the VOUT pin, the output voltage will be
set at 0.5V. If external feedback resistors are used, the output voltage will be
determined by the resistor ratio.
4
EN
Enable Control Input (Active-High). Pulling this pin below 0.4V turns the regulator
off, reducing the quiescent current to a fraction of its operating value. The device
will be enabled if this pin is left open. Connect to VIN if not used.
2
5,
GND
9 (Exposed pad)
6
7
Ground. The exposed pad must be soldered to a large PCB and connected to GND
for maximum power dissipation.
IC
Internal Connection. Leave floating and do not make connection to this pin.
VIN
Power Input. For regulation at full load, the input to this pin must be between (V OUT
+ 0.5V) and 5.5V. Minimum input voltage is 1.4V. A large bulk capacitance should
be placed closely to this pin to ensure that the input supply does not sag below
1.4V. Also, a minimum of 10F ceramic capacitor should be placed directly at this
pin.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
is a registered trademark of Richtek Technology Corporation.
DS2518-00
November 2013
RT2518
Function Block Diagram
RSENSE
VOUT
VIN
VPUMP
-
-
+
+
Mode
Select
+
VIN
ADJ
-
1µA
0.5V
EN
VIN
Thermal
Shutdown
VOUT
+
VIN
-
Reference
Generator
0.1V
GND
Reverse Voltage
Shutdown
Operation
The RT2518 is a low input voltage low dropout LDO that
can support the input voltage range from 1.4V to 6V and
the output current can be up to 1A. The RT2518 uses
internal charge pump to achieve low input voltage operation
and 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 on resistance of the power MOSFET is
decreased to increase the output current through the power
MOSFET, and the feedback voltage will be charge back to
reference. If the feedback voltage is less than the
reference, the power MOSFET current is decreased to
make the output voltage discharge back to reference by
the loading current.
Reverse Current Protection
The reverse current protection is guarantee by the NMOSFET with bulk capacitors connected to GND and the
internal circuit. The reverse voltage detection circuit shuts
the total loop down if the output voltage is higher than
input voltage.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2518-00
November 2013
Output Under-Voltage Protection (UVP) and OverCurrent Fold-Back
When the feedback voltage is lower than 0.15V after
internal soft-start end, the UVP is triggered. If the overcurrent condition is trigged during UVP state, the OC limit
current will be decreased to limit the output power and
change into re-soft start state at the same time.
Soft-Start
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The typical soft-start
time is 150μs. During the soft-start state, the output
current will be limited to prevent the inrush current.
Over-Temperature Protection (OTP)
The RT2518 has an over-temperature protection. When
the device triggers the OTP, the device shuts down until
the temperature back to normal and move to re-soft start
state.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT2518
Absolute Maximum Ratings








(Note 1)
Supply Voltage, VIN -----------------------------------------------------------------------------------------------------Other Pins ------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-8L 3x3 -------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-8L 3x3, θJA --------------------------------------------------------------------------------------------------------WDFN-8L 3x3, θJC -------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------CDM (Charged Device Model) ------------------------------------------------------------------------------------------
Recommended Operating Conditions


−0.3V to 7V
−0.3V to 7V
2.08W
49°C/W
8°C/W
260°C
150°C
−65°C to 150°C
2kV
1kV
(Note 4)
Supply Voltage, VIN ------------------------------------------------------------------------------------------------------ 1.4V to 6V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VIN = 1.4V to 6V, IOUT = 10μA to 1A, VADJ = VOUT, −40°C ≤ TA ≤ 85°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Quiescent Current
IQ
VIN = 3.3V, IOUT = 0A
--
0.7
1.5
mA
Shutdown Current
ISHDN
VIN = 5.5V, VEN = 0V
--
1.5
10
A
VIN = VOUT + 0.5V, IOUT = 10mA
TA = 25C
2
--
2
1.4V  VIN  5.5V, IOUT = 10mA
3
--
3
Output Voltage
(Fixed Output, VADJ = 0V)
VOUT
VIN = 1.8V, IOUT = 0.8A, TA = 25C
%
Line Regulation
VLINE
IOUT = 10mA
--
0.2
0.4
%/V
Load Regulation
VLOAD
IOUT = 10mA to 1A
--
0.5
1.5
%
Dropout Voltage
VDROP
IOUT = 1A, VIN  1.6V
--
120
200
IOUT = 1A, 1.4V < VIN < 1.6V
--
--
400
Current Limit
ILIM
VIN = 3.3V
1.05
1.6
--
VIN = 3.3V, VADJ = VOUT,
IOUT = 10mA, TA = 25C
0.495
--
0.505
VIN = 3.3V, VADJ = VOUT,
IOUT = 10mA
0.49
--
0.51
--
20
200
nA
0.05
0.1
0.15
V
mV
A
Feedback
ADJ Reference Voltage
VADJ
ADJ Input Current
IADJ
VADJ = 0.5V
ADJ Threshold
VTH_ADJ
VIN = 3.3V
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
V
is a registered trademark of Richtek Technology Corporation.
DS2518-00
November 2013
RT2518
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
1
10
A
Enable
EN Current
IEN
VEN = 0V, VIN = 5.5V
Logic-High
VIH
VIN = 3.3V
1.6
--
--
Logic-Low
VIL
VIN = 3.3V
--
--
0.4
OTP Threshold
--
160
--
°C
OTP Hysteresis
--
30
--
°C
EN Input
Voltage
V
Over-Temperature Protection
Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may
affect device reliability.
Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is
measured at the exposed pad of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2518-00
November 2013
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT2518
Typical Application Circuit
RT2518
7
VIN
VIN
VOUT
2
C1
10µF
4
Enable
VOUT =
0.5(R1+R2)
R2
VOUT
C2
10µF
R1
ADJ
3
R2
EN
GND
5,
9 (Exposed Pad)
(V)
Figure 1. Adjustable Voltage Regulator
RT2518
7
VIN
VIN
VOUT
2
C1
10µF
Enable
4
ADJ 3
C2
10µF
VOUT
1.2V
EN
GND
5,
9 (Exposed Pad)
Figure 2. Fixed Voltage Regulator
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
is a registered trademark of Richtek Technology Corporation.
DS2518-00
November 2013
RT2518
Typical Operating Characteristics
Output Voltage vs. Temperature
Quiescent Current vs. Temperature
2.55
Quiescent Current (mA)
1.15
Output Voltage (V)
2.52
VIN = 3.3V
VIN = 5V
2.49
2.46
2.43
0.95
0.75
0.55
VOUT = 2.5V
VIN = 3.3V, VOUT = 2.52V
2.40
0.35
-50
-25
0
25
50
75
100
125
-50
-25
0
Temperature (°C)
Shutdown Current vs. Temperature
50
75
100
125
UVLO vs. Temperature
1.8
1.5
1.4
1.4
1.3
UVLO (V)
Shutdown Current (µA)1
25
Temperature (°C)
1.0
Logic-High
1.2
Logic-Low
1.1
1.0
0.6
0.9
VIN = 3.3V
VEN = 5V
0.2
0.8
-50
-25
0
25
50
75
100
125
-50
-25
0
Temperature (°C)
50
75
125
1.2
EN Threshold Voltage (V)
125°C
150
25°C
100
−40°C
50
Logic-High
1.1
1.0
Logic-Low
0.9
VOUT = 2.5V
VIN = 5V
0.8
0
0
0.25
0.5
0.75
I OUT (A)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2518-00
100
EN Threshold Voltage vs. Temperature
Dropout Voltage vs. IOUT
200
Dropout Voltage (mV)
25
Temperature (°C)
November 2013
1
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT2518
Load Transient Response
Line Transient Response
VOUT
(10mV/Div)
VIN
(1V/Div)
IOUT
(1A/Div)
VOUT
(10mV/Div)
VIN = 3.3V, VOUT = 1.8V, IOUT = 0 to 1A
VIN = 3.3V to 4.3V, VOUT = 1.8V, IOUT = 1A
Time (100μs/Div)
Time (500μs/Div)
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
I IN
(1A/Div)
VIN = 2.5V, VOUT = 1.5V, IOUT = 1A
Time (100μs/Div)
I IN
(1A/Div)
VIN = 2.5V, VOUT = 1.5V, IOUT = 1A
Time (100μs/Div)
PSRR vs. Frequency
0
-10
IOUT = 300mA
PSRR (dB)
-20
IOUT = 1mA
-30
IOUT = 100mA
-40
-50
-60
-70
VIN = 3.25V to 3.35V, VOUT = 2.5V
-80
100
1000
10000
100000
1000000
Frequency (Hz)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
8
is a registered trademark of Richtek Technology Corporation.
DS2518-00
November 2013
RT2518
Application Information
The RT2518 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 RT2518 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 :
VOUT = VADJ   1+ R1 
 R2 
The RT2518 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 RT2518
output ensures stability. Nevertheless, the RT2518 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 no more than 0.5 inch from the output pin
of the RT2518.
Region of Stable COUT ESR vs. Load Current
100
where VADJ is the reference voltage with a typical value of
0.5V.
Unstable Range
The RT2518 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 RT2518 contains an independent current limit circuitry,
which controls the pass transistor's gate voltage, limiting
the output current to 1.6A (typ.).
COUT ESR (Ω)
10
Chip Enable Operation
1
Stable Range
0.1
0.01
VIN = 3.3V, VOUT = 2.5V, COUT = 10μF / X7R
0.001
0.0
0.3
0.5
0.8
1.0
Load Current (A)
Figure 3
CIN and COUT Selection
Thermal Considerations
Like any low dropout regulator, the external capacitors of
the RT2518 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 no 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.
Thermal protection limits power dissipation in the RT2518.
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.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2518-00
November 2013
The RT2518 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.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT2518
VOUT Short to GND
ILIM
ILIM＇
IOUT
IC Temperature
Maximum Power Dissipation (W)
VOUT
3.0
Four-Layer PCB
2.5
2.0
1.5
1.0
0.5
0.0
Figure 4. Short-Circuit Protection when Output ShortCircuit Occurs
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 5. Derating Curve of Maximum Power Dissipation
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 :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-8L 3x3 package, the thermal resistance, θJA, is
49°C/W on a standard JEDEC 51-7 four-layer thermal test
board. The maximum power dissipation at TA = 25°C can
be calculated by the following formula :
P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.08W for
WDFN-8L 3x3 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 5 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
is a registered trademark of Richtek Technology Corporation.
DS2518-00
November 2013
RT2518
Outline Dimension
D2
D
L
E
E2
1
e
SEE DETAIL A
b
2
1
2
1
A
A1
A3
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.200
0.300
0.008
0.012
D
2.950
3.050
0.116
0.120
D2
2.100
2.350
0.083
0.093
E
2.950
3.050
0.116
0.120
E2
1.350
1.600
0.053
0.063
e
L
0.650
0.425
0.026
0.525
0.017
0.021
W-Type 8L DFN 3x3 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
DS2518-00
November 2013
www.richtek.com
11