RT2652 - Farnell

®
RT2652
2A, 1.2MHz Synchronous Step-Down Converter
General Description
Features
The RT2652 is a high efficiency synchronous, step-down
DC/DC converter. The available input voltage range is from
2.7V to 5.5V the regulated output voltage is adjustable
from 0.6V to VIN while delivering up to 2A of output current.
The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. The switching frequency is
fixed internally at 1.2MHz. The 100% duty cycle provides
low dropout operation extending battery life in portable
systems. Current mode operation with internal
compensation allows the transient response to be
optimized. The RT2652 is available in the WDFN-10L 3x3
package.
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High Efficiency : Up to 95%
z
Fixed Frequency : 1.2MHz
No Schottky Diode Required
Internal Compensation
0.6V Reference Allows Low Output Voltage
100% Duty Cycle for Low Dropout Operation
OCP, UVP, OTP
RoHS Compliant and Halogen Free
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Applications
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Ordering Information
Enterprise Servers
Ethernet Switches & Routers
Global Storage
Telecom & Industrial
Cell Phones & DSC's
Pin Configurations
RT2652
EN
VIN
VIN
AGND
FB
Lead Plating System
G : Green (Halogen Free and Pb Free)
1
2
3
4
5
PGND
(TOP VIEW)
Package Type
QW : WDFN-10L 3x3 (W-Type)
10
9
11
8
7
6
PGND
PGND
LX
LX
AGND
Note :
WDFN-10L 3x3
Richtek products are :
`
RoHS compliant and compatible with the current require-
Marking Information
ments of IPC/JEDEC J-STD-020.
`
0K= : Product Code
Suitable for use in SnPb or Pb-free soldering processes.
0K=YM
DNN
YMDNN : Date Code
Simplified Application Circuit
RT2652
VIN
VIN
LX
EN
FB
VOUT
AGND PGND
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2652-01 February 2013
is a registered trademark of Richtek Technology Corporation.
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RT2652
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
EN
Enable Control Input. Pull high to turn on. Do not float.
2, 3
VIN
Power Input. Decouple this pin to GND with a 22μF ceramic capacitor at least.
4, 6
AGND
Analog Ground.
FB
Feedback Voltage Input. This pin receives the feedback voltage from an external
resistive divider connected across the output.
5
7, 8
LX
9, 10,
PGND
11 (Exposed Pad)
Power MOSFET Switch Node. Connect this pin to the inductor.
Power Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Function Block Diagram
EN
EN
POR
OSC
0.6V
FB
EA
VIN
ISEN
Slope
Comp.
Output
Clamp
OC Limit
SS
Driver
0.2V
UV
LX
Control Logic
NISEN
AGND
PGND
OTP
N-MOSFET Limit
Operation
The RT2652 is a monolithic, constant-frequency, current
mode step-down DC/DC converter. During normal
operation, the internal high side MOSFET is turned on at
the beginning of each cycle. Current in the inductor
increases until the peak inductor current reaches the value
defined by the internal error amplifier. The error amplifier
adjusts the voltage of its output by comparing the feedback
signal from a resistor divider on the FB pin with an internal
0.6V reference. When the load current increases, it causes
a reduction in the feedback voltage relative to the reference.
The error amplifier raises its output voltage until the average
inductor current matches the new load current. When the
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high side MOSFET turns off, the synchronous power
switch (N-MOSFET) turns on until either the bottom current
limit is reached or the beginning of the next cycle. The
operating frequency is set by the internal oscillator at
1.2MHz. In VIN larger than 6V condition, the high side
MOSFET is turned off and the low side MOSFET is
switched on until either the VIN over voltage condition is
cleared or the low side MOSFET's current limit is reached.
is a registered trademark of Richtek Technology Corporation.
DS2652-01 February 2013
RT2652
Absolute Maximum Ratings
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(Note 1)
Supply Voltage, VIN ----------------------------------------------------------------------------------------------Switch Node Voltage, LX -----------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-10L 3x3 -----------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-10L 3x3, θJA -----------------------------------------------------------------------------------------------WDFN-10L 3x3, θJC -----------------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------
Recommended Operating Conditions
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−0.3V to 6.5V
−0.3V to (VIN + 0.3V)
−0.3V to 6.5V
1.429W
70°C/W
8.2°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 2.7V to 5.5V
Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 3.3V, TA = 25°C unless otherwise specified)
Parameter
Symbol
Min
Typ
Max
Unit
0.594
0.6
0.606
V
--
0.1
0.4
μA
Active, VFB = 0.58V, not switching
--
--
--
μA
Shutdown
--
--
1
μA
Output Voltage Line Regulation
VIN = 2.7V to 5.5V
--
0.04
--
%/V
Output Voltage Load Regulation
IOUT = 10mA to 2000mA
--
0.2
--
%/A
Switch Leakage Current
EN = 0V
--
--
1
μA
0.96
1.2
1.44
MHz
Feedback Reference Voltage
VREF
Feedback Leakage Current
IFB
DC Bias Current
Test Conditions
Switching Frequency
Switch
On-Resistance
High-Side
RDS(ON)_H
--
110
130
Low-Side
RDS(ON)_L
--
70
90
2.5
3.5
--
A
VDD Rising
--
2.4
--
V
VDD Falling
--
2.2
--
V
P-MOSFET Current Limit
ILIM
Under Voltage Lockout Threshold
EN Input Voltage
Logic-High
VIH
1.5
--
--
Logic-Low
VIL
--
--
0.3
--
500
--
EN Pull Low Resistance
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2652-01 February 2013
mΩ
V
kΩ
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RT2652
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
--
150
--
°C
1.3
--
--
ms
VOUT Discharge Resistance
--
100
150
Ω
VOUT UVP (latch-off)
--
33
--
%
Over Temperature Protection (latch-off)
Soft-Start Time
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..
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is a registered trademark of Richtek Technology Corporation.
DS2652-01 February 2013
RT2652
Typical Application Circuit
RT2652
2, 3
VIN
CIN
22µF
VIN
LX
7, 8
L
VOUT
R1
1 EN
FB
CF
COUT
5
R2
4, 6
9, 10,
AGND PGND
11 (Exposed Pad)
Table 1. Recommended Component Selection
VOUT (V) R1 (kΩ)
R2 (kΩ)
CF (pF)
L (μH)
COUT (μF)
3.3
37
8.2
200
2
22
2.5
26
8.2
200
2
22
1.8
16.5
8.2
200
1.5
22
1.5
12.3
8.2
200
1.5
22
1.2
8.2
8.2
200
1.5
22
1
5.6
8.2
200
1.5
22
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RT2652
Typical Operating Characteristics
Efficiency vs. Output Current
100
90
90
80
80
VIN = 5V, VOUT = 3.3V
VIN = 5V, VOUT = 1.2V
VIN = 3.3V, VOUT = 1.2V
70
60
Efficiency (%)
Efficiency (%)
Efficiency vs. Output Current
100
50
40
30
VIN = 5V, VOUT = 3.3V
VIN = 3.3V, VOUT = 1.2V
VIN = 5V, VOUT = 1.2V
70
60
50
40
30
20
20
10
10
IOUT = 0 to 2A
IOUT = 0 to 2A
0
0
0.001
0.01
0.1
1
0
10
0.25
0.5
Output Current (A)
Output Voltage vs. Output Current
1.25
1.5
1.75
2
Output Voltage vs. Output Current
3.38
1.215
3.37
Output Voltage (V)
Output Voltage (V)
1
Output Current (A)
1.220
1.210
1.205
1.200
VIN = 5V
VIN = 3.3V
1.195
1.190
3.36
3.35
3.34
3.33
1.185
VOUT = 1.2V, IOUT = 0 to 2A
VIN = 5V, VOUT = 3.3V, IOUT = 0 to 2A
3.32
1.180
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
2
0.2
0.4
0.6
Output Current (A)
1.5
1.5
Switching Frequency (MHz)1
1.6
1.4
1.3
1.2
1.1
VIN = 3.3V
VIN = 5V
0.9
0.8
0.7
1
1.2
1.4
1.6
1.8
2
Switching Frequency vs. Temperature
1.6
1.0
0.8
Output Current (A)
Switching Frequency vs. Temperature
Switching Frequency (MHz)1
0.75
VOUT = 1.2V, IOUT = 0.6A
0.6
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
VIN = 5V, VOUT = 3.3V, IOUT = 0.6A
0.6
-50
-25
0
25
50
75
100
Temperature (°C)
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125
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
DS2652-01 February 2013
RT2652
Enable Voltage vs. Temperature
1.5
2.7
1.4
2.6
1.3
Enable Voltage (V)
VIN UVLO (V)
VIN UVLO vs. Temperature
2.8
2.5
Rising
2.4
2.3
2.2
Falling
2.1
1.2
Rising
1.1
1.0
Falling
0.9
2.0
0.8
1.9
0.7
0.6
1.8
-50
-25
0
25
50
75
100
-25
0
25
50
75
100
Temperature (°C)
Temperature (°C)
Load Transient Response
Load Transient Response
VOUT
(100mV/Div)
IOUT
(1A/Div)
-50
125
125
VOUT
(100mV/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 1A to 2A
IOUT
(1A/Div)
VIN = 5V, VOUT = 3.3V, IOUT = 1A to 2A
Time (100μs/Div)
Time (100μs/Div)
Output Ripple Voltage
Output Ripple Voltage
VLX
(5V/Div)
VLX
(5V/Div)
VOUT
(5mV/Div)
VOUT
(5mV/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 2A
Time (500ns/Div)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
DS2652-01 February 2013
VIN = 5V, VOUT = 3.3V, IOUT = 2A
Time (500ns/Div)
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RT2652
Power On from VIN
Power On from VIN
VIN
(5V/Div)
VIN
(5V/Div)
VLX
(5V/Div)
VLX
(5V/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 2A
Time (2.5ms/Div)
Time (2.5ms/Div)
Power Off from VIN
Power Off from VIN
VIN
(5V/Div)
VIN
(5V/Div)
VLX
(5V/Div)
VLX
(5V/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 2A
Time (5ms/Div)
Power On from EN
VEN
(5V/Div)
VEN
(5V/Div)
VLX
(5V/Div)
VLX
(5V/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 2A
Time (500μs/Div)
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VIN = 5V, VOUT = 3.3V, IOUT = 2A
Time (5ms/Div)
Power On from EN
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VIN = 5V, VOUT = 3.3V, IOUT = 2A
VIN = 5V, VOUT = 3.3V, IOUT = 2A
Time (500μs/Div)
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DS2652-01 February 2013
RT2652
Power Off from EN
Power Off from EN
VEN
(5V/Div)
VEN
(5V/Div)
VLX
(5V/Div)
VLX
(5V/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VOUT
(5V/Div)
IOUT
(5A/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 2A
Time (500μs/Div)
VIN = 5V, VOUT = 3.3V, IOUT = 2A
Time (500μs/Div)
Reference Voltage vs. Temperature
0.620
Reference Voltage (V)
0.615
0.610
0.605
0.600
0.595
0.590
0.585
IOUT = 0.6A
0.580
-50
-25
0
25
50
75
100
125
Temperature (°C)
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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is a registered trademark of Richtek Technology Corporation.
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RT2652
Application Information
The RT2652 is a single-phase buck PWM converter. It
provides single feedback loop, current mode control with
fast transient response. An internal 0.6V reference allows
the output voltage to be precisely regulated for low output
voltage applications. A fixed switching frequency (1.2MHz)
oscillator and internal compensation are integrated to
minimize external component count.
Output Voltage Setting
The output voltage is set by an external resistive voltage
divider according to the following equation :
VOUT = VREF ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
Where VREF is equals 0.6V (typ.).
The resistive voltage divider allows the FB pin to sense a
fraction of the output voltage as shown in Figure 1.
VOUT
R1
FB
RT2652
R2
GND
Figure 1. Setting the Output Voltage
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ΔIL increases with higher VIN and decreases
with higher inductance.
V
V
ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥
f
×
L
VIN ⎦
⎣
⎦ ⎣
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. Highest efficiency operation is achieved by reducing
ripple current at low frequency, but a large inductor is
required to attain this goal. For ripple current selection,
the value of ΔIL = 0.4(IMAX) is a reasonable starting point.
The largest ripple current occurs at the highest VIN. To
guarantee that the ripple current stays below a specified
maximum value, the inductor should be chosen according
to the following equation :
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⎡ VOUT ⎤ ⎡
VOUT ⎤
L =⎢
× ⎢1 −
⎥
⎥
⎣ f × ΔIL(MAX) ⎦ ⎣ VIN(MAX) ⎦
Slope Compensation and Inductor Peak Current
Slope compensation provides stability in constant
frequency architectures by preventing sub-harmonic
oscillations at duty cycles greater than 50%. It is
accomplished internally by adding a compensating ramp
to the inductor current signal. Normally, the maximum
inductor peak current is reduced when slope compensation
is added. In this IC, however, separated inductor current
signal is used to monitor over current condition and this
keeps the maximum output current relatively constant
regardless of duty cycle.
Low Dropout Operation
The RT2652 is designed to operate down to an input supply
voltage of 2.7V. One important consideration at low input
supply voltage is that the RDS(ON) of the P-Channel and NChannel power switches increases. The user should
calculate the power dissipation when the RT2652 is used
at 100% duty cycle with low input voltages to ensure that
thermal limits are not exceeded. Slope compensation and
inductor peak current slope compensation provides
stability in constant frequency architectures by preventing
sub-harmonic oscillations at duty cycles greater than
50%.It is accomplished internally by adding a
compensating ramp to the inductor current signal.
Normally, the maximum inductor peak current is reduced
when slope compensation is added. In the RT2652,
however, separated inductor current signals are used to
monitor over current condition. This keeps the maximum
output current relatively constant regardless of duty cycle.
Short Circuit Protection
When the output is shorted to ground, the inductor current
decays very slowly during a single switching cycle. A
current runaway detector is used to monitor inductor
current. As current increases beyond the control of current
loop, switching cycles will be skipped to prevent current
runaway from occurring.
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DS2652-01 February 2013
RT2652
The IC includes an input Under Voltage Lockout Protection
(UVLO). If the input voltage exceeds the UVLO rising
threshold voltage, the converter resets and prepares the
PWM for operation. If the input voltage falls below the
UVLO falling threshold voltage during normal operation,
the device stops switching. The UVLO rising and falling
threshold voltage includes a hysteresis to prevent noise
caused reset.
Thermal Shutdown
The device implements an internal thermal shutdown
function when the junction temperature exceeds 150°C.
The thermal shutdown disables the device until the junction
temperature drops below the hysteresis (20°C typ.). Then,
the device is re-enabled and automatically reinstates the
power up sequence.
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curves in Figure 2 allow the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Maximum Power Dissipation (W)1
Under Voltage Lockout Threshold
1.6
Four-Layer PCB
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Thermal Considerations
Figure 2. 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-10L 3x3 packages, the thermal resistance, θJA, is
70°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 formulas :
PD(MAX) = (125°C − 25°C) / (70°C/W) = 1.429W for
WDFN-10L 3x3 package
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
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RT2652
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
0.180
0.300
0.007
0.012
D
2.950
3.050
0.116
0.120
D2
2.300
2.650
0.091
0.104
E
2.950
3.050
0.116
0.120
E2
1.500
1.750
0.059
0.069
e
L
0.500
0.350
0.020
0.450
0.014
0.018
W-Type 10L DFN 3x3 Package
Richtek Technology Corporation
5F, No. 20, Taiyuen 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.
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DS2652-01 February 2013