DS2657BQ 00

®
RT2657BQ
2.25MHz 600mA Synchronous Step-Down Converter
General Description
Features
The RT2657BQ is a high efficiency Pulse-WidthModulated (PWM) step-down DC/DC converter, capable
of delivering 600mA output current over a wide input voltage
range from 2.7V to 5.5V. The RT2657BQ is ideally suited
for portable electronic devices that are powered from 1cell Li-ion battery or from other power sources such as
cellular phones, PDAs, hand-held devices, game console
and related accessories.

VIN Range 2.7V to 5.5V

VOUT Range 0.6V to 5.5V (100% Duty Ratio Operation)
VREF = 0.6V
ISD ≤ 5μ
μA (VEN = 0V)
Current Mode Control, Internal Compensation
Fixed FSW 2.25MHz
R DS(ON) 230mΩ
Ω HS/250mΩ
Ω LS (P-MOSFET/
N-MOSFET)
Enable (VIH = 1V, VIL = 0.4V)
Internal Soft-Start (0.3ms)
Up to 600mA Output Current
Up to 90% Efficiency
Peak ILIMIT (1.5A Typical / 0.8A Min); UVLO; UVP;
VIN and VOUT OVP; and OTP (150°°C)
No Schottky Diode Required
Internal Compensation to Reduce External
Components
AEC-Q100 Grade 3 Certification
The internal synchronous rectifier with low R DS(ON)
dramatically reduces conduction loss at PWM mode.
No external Schottky diode is required in practical
applications. The RT2657BQ enters Low Dropout Mode
when normal Pulse -Width Mode cannot provide regulated
output voltage by continuously turning on the high-side
P-MOSFET. The RT2657BQ enters shut-down mode and
consumes less than 5μA when the EN pin is pulled low.
The switching ripple is easily smoothed-out by small
package filtering elements due to a fixed operating
frequency of 2.25MHz.
The RT2657BQ is available in the small WDFN-8L 3x3
package.
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Applications
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Automotive Audio, Information & Navigation
Industrial-Grade General Purpose Point-of -Load
Marking Information
5L= : Product Code
5L=YM
DNN
YMDNN : Date Code
Simplified Application Circuit
RT2657BQ
VIN
CIN
VOUT
C1
EN
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
R1
COUT
FB
GND
DS2657BQ-00 July 2014
L1
LX
VIN
R2
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1
RT2657BQ
Pin Configurations
Ordering Information
RT2657BQ
(TOP VIEW)
LX
NC
FB
NC
3
6
4
9
5
2
GND
VIN
EN
NC
8
1
GND
Package Type
QW : WDFN-8L 3x3 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
7
WDFN-8L 3x3
Note :
Richtek products are :

RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
Function Pin Description
Pin No.
Pin Name
Pin Function
1
LX
Switch Node. Connect to the external inductor.
2, 4, 5
NC
No Internal Connection. Connect to GND.
3
FB
Feedback Voltage Input. Connect to the external resistor divider.
6
EN
Enable Control Input (Activ e High).
7
VIN
Power Input. Connect to the input capacitor.
8,
GND
9 (Exposed Pad)
Power GND. The Exposed Pad must be soldered to a large PCB and connected
to GND f or maximum power dissipation.
Function Block Diagram
EN
OSC &
Shutdown
Control
Slope
Compensation
VIN
RS1
Current
Limit
Detector
Current
Sense
FB
Error
Amplifier
RC
Control
Logic
Driver
LX
PWM
Comparator
RS2
COMP
UVLO &
Power Good
Detector
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2
GND
VREF
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DS2657BQ-00 July 2014
RT2657BQ
Operation
The RT2657BQ is a synchronous low voltage step-down
converter that can support the input voltage range from
2.7V to 5.5V and the output current can be up to 0.6A.
The RT2657BQ uses a constant frequency, current mode
architecture. In normal operation, the high-side P-MOSFET
is turned on when the Switch Controller is set by the
oscillator (OSC) and is turned off when the current
comparator resets the Switch Controller.
The high-side MOSFET peak current is measured by
internal R SENSE. The current signal is where Slope
Compensator works together with sensing voltage of
RSENSE. The error amplifier EA adjusts COMP voltage by
comparing the feedback signal (VFB) from the output
voltage with the internal 0.6V reference. When the load
current increases, it causes a drop in the feedback voltage
relative to the reference. The COMP voltage then rises to
allow higher inductor current to match the load current.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
DS2657BQ-00 July 2014
UV Comparator
If the feedback voltage (VFB) is lower than threshold voltage
0.2V, the UV Comparator's output will go high and the
Switch Controller will turn off the high-side MOSFET.
Oscillator (OSC)
The internal oscillator runs at 2.25MHz.
Enable Comparator
The EN pin can be connected to VIN through a 100kΩ
resistor for automatic startup.
Soft-Start (SS)
An internal current source (25nA) charges an internal
capacitor (15pF) to build the soft-start ramp voltage (VSS).
The VFB voltage will track the internal ramp voltage during
soft-start interval. The typical soft-start time is 300μs.
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RT2657BQ
Absolute Maximum Ratings


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

(Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Voltage, LX ------------------------------------------------------------------------------------------------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) ---------------------------------------------------------------------------------------
Recommended Operating Conditions
−0.3V to 6.5V
−0.3V to (VIN + 0.3V)
−0.3V to 6V
1.667W
60°C/W
7°C/W
260°C
150°C
−65°C to 150°C
2kV
(Note 4)
Supply Input 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 = 3.6V, TA = −40°C to 85°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Output Current
IOUT
VIN = 2.7V to 5.5V
--
--
0.6
A
Quiescent Current
IQ
VEN = 1V, VFB = 0.5V
--
300
--
A
Feedback Voltage
VFB
VIN = 2.7V to 5.5V @ TA = 25C
588
600
612
VIN = 2.7V to 5.5V
585
600
615
VIN Rising
1.85
2.2
2.55
Hysteresis
--
0.2
--
VEN = 0V
--
--
5
A
--
2.25
--
MHz
Under-Voltage Lockout Threshold VUVLO
Shutdown Current
ISHDN
Switching Frequency
EN Input Voltage
VIH
1
--
VIN
Logic-Low
VIL
--
--
0.4
TSD
--
150
--
High-Side
RDS(ON)_H ISW = 0.2A
--
230
--
Low-Side
RDS(ON)_L ISW = 0.2A
--
250
--
0.8
1.5
--
A
--
1
--
%
Peak Current Limit
Output Voltage Load Regulation
ILIM
0mA < IOUT < 0.6A
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4
V
Logic-High
Thermal Shutdown Temperature
Switch
On-Resistance
mV
V
°C
m
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DS2657BQ-00 July 2014
RT2657BQ
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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2014 Richtek Technology Corporation. All rights reserved.
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RT2657BQ
Typical Application Circuit
RT2657BQ
7
VIN
CIN
4.7µF
VIN
6 EN
8, 9 (Exposed Pad)
GND
L1
2.2µH
VOUT
1.8V
C1
30pF
FB
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6
LX
1
3
R1
360k
COUT
10µF
R2
180k
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RT2657BQ
Typical Operating Characteristics
Efficiency vs. Output Current
100
Output Voltage vs. Input Voltage
2.00
VIN = 3.3V
90
1.95
VIN = 5V
1.90
Output Voltage (V)
Efficiency (%)
80
70
60
50
40
30
1.85
1.80
1.75
1.70
20
1.65
10
VOUT = 1.8V, IOUT = 0A
VOUT = 1.8V
0
1.60
0
0.1
0.2
0.3
0.4
0.5
0.6
2.5
3
3.5
Output Current (A)
Frequency vs. Input Voltage
5
5.5
Frequency vs. Temperature
2.40
2.35
2.4
VOUT = 1.2V
Frequency (MHz)1
VOUT = 1.2V
2.3
VOUT = 1.8V
2.2
2.1
2.0
1.9
2.30
VOUT = 1.8V
2.25
2.20
2.15
2.10
2.05
VIN = 5V, IOUT = 0.3A
IOUT = 0.3A
1.8
2.00
2.5
3
3.5
4
4.5
5
5.5
-50
-25
Input Voltage (V)
25
50
75
100
125
Output Current Limit vs. Temperature
1.8
2.5
1.7
Output Current Limit (A)
3.0
2.0
0
Temperature (°C)
Output Current Limit vs. Input Voltage
Output Current Limit (A)
4.5
Input Voltage (V)
2.5
Frequency (MHz)1
4
VOUT = 1.2V
1.5
VOUT = 1.8V
1.0
0.5
1.6
1.5
1.4
1.3
VIN = 5V, VOUT = 1.2V
0.0
1.2
2.5
3
3.5
4
4.5
5
Input Voltage (V)
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5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT2657BQ
VFB vs. Temperature
0.66
1.84
0.65
1.83
0.64
1.82
0.63
1.81
0.62
VFB (V)
Output Voltage (V)
Output Voltage vs. Temperature
1.85
1.80
1.79
0.61
0.60
1.78
0.59
1.77
0.58
1.76
VIN = 5V, VOUT = 1.8V, IOUT = 0.3A
1.75
0.57
VIN = 3.3V, VOUT = 0.6V
0.56
-50
-25
0
25
50
75
100
125
-50
25
50
75
Temperature (°C)
Output Ripple
Output Ripple
VOUT
(10mV/Div)
VLX
(2V/Div)
VLX
(5V/Div)
VIN = 5V, VOUT = 1.2V, IOUT = 0.6A
100
125
VIN = 5V, VOUT = 1.8V, IOUT = 0.6A
Time (250ns/Div)
Time (250ns/Div)
Load Transient Response
Load Transient Response
VOUT
(50mV/Div)
VOUT
(50mV/Div)
VIN = 5V, VOUT = 1.8V, IOUT = 0A to 0.6A
Time (100μs/Div)
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0
Temperature (°C)
VOUT
(10mV/Div)
IOUT
(500mA/Div)
-25
IOUT
(500mA/Div)
VIN = 5V, VOUT = 1.8V, IOUT = 0.2A to 0.6A
Time (100μs/Div)
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RT2657BQ
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IOUT
(500mA/Div)
IOUT
(500mA/Div)
VIN = 5V, VOUT = 1.8V, IOUT = 0.6A
VIN = 5V, VOUT = 1.8V, IOUT = 0.6A
Time (100μs/Div)
Time (100μs/Div)
UVLO vs. Temperature
EN Threshold vs. Temperature
2.8
1.00
0.95
2.6
EN Threshold (V)
0.90
UVLO (V)
2.4
Rising
2.2
2.0
Falling
0.85
0.80
Rising
0.75
0.70
0.65
0.60
1.8
VOUT = 1.2V
1.6
Falling
0.55
VIN = 5V, VOUT = 1.2V
0.50
-50
-25
0
25
50
75
100
Temperature (°C)
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DS2657BQ-00 July 2014
125
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT2657BQ
Application Information
The basic RT2657BQ application circuit is shown in Typical
Application Circuit. External component selection is
determined by the maximum load current and begins with
the selection of the inductor value and operating frequency
followed by CIN and COUT.
Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
R1
VOUT  VREF x (1
)
R2
where VREF equals to 0.6V typically. The resistive divider
allows the FB pin to sense a fraction of the output voltage
as shown in Figure 1.
VOUT
R1
The RT2657BQ is designed to operate down to an input
supply voltage of 2.7V. One important consideration at
low input supply voltages is that the RDS(ON) of the PChannel and N-Channel power switches increases. Users
should calculate the power dissipation when the
RT2657BQ is used at 100% duty cycle with low input
voltages to ensure that thermal limits are not exceeded.
Under-Voltage Protection (UVP)
The output voltage is continuously monitored for undervoltage protection. When the output voltage is less than
33% of its set voltage threshold after OCP occurs, the
under-voltage protection circuit will be triggered to auto
re-softstart.
Input Over-Voltage protection (VIN OVP)
FB
RT2657BQ
Low Supply Operation
When the input voltage (VIN) is higher than 6V, VIN OVP
will be triggered and the IC stops switching. Once the
input voltage drops below 6V, the IC will return to normal
operation.
R2
GND
Figure 1. Setting the Output Voltage
Output Over-Voltage Protection (VOUT OVP)
Soft-Start
The RT2657BQ contains an internal soft-start clamp that
gradually raises the clamp on the FB pin. Time from active
EN to reach 95% of VOUT nominal is within typical 300μs.
100% Duty Cycle Operation
When the input supply voltage decreases toward the output
voltage, the duty cycle increases toward the maximum
on-time. Further reduction of the supply voltage forces
the main switch to remain on for more than one cycle,
eventually reaching 100% duty cycle.
The output voltage will then be determined by the input
voltage minus the voltage drop across the internal
P-MOSFET and the inductor.
When the output voltage exceeds more than 5% of the
nominal reference voltage, the feedback loop forces the
internal switches off within 50μs. Therefore, the output
over-voltage protection is automatically triggered by the
loop.
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.
Table 1. Inductors
Component
Supplier
TAIYO YUDEN
Series
NR5018
T2R2M
Inductance (H)
2.2H
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DCR (m)
40
Current Rating (mA)
3000
Dimensions (mm)
4 X 4 X 1.8
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DS2657BQ-00 July 2014
RT2657BQ
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the Source of the high-side MOSFET.
To prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used. RMS
current is given by :
IRMS  IOUT(MAX)
VOUT
VIN
VIN
1
VOUT
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT/2. This simple worst case condition is commonly used
for design because even significant deviations do not result
in much difference. Choose a capacitor rated at a higher
temperature than required.
Several capacitors may also be paralleled to meet size or
height requirements in the design.
The selection of COUT is determined by the effective series
resistance (ESR) that is required to minimize voltage ripple
and load step transients, as well as the amount of bulk
capacitance that is necessary to ensure the control loop
is stable. Loop stability can be checked by viewing the
load transient response. The output ripple, ΔVOUT, is
determined by :

1 
VOUT  IL ESR 

8fCOUT 

The output ripple is highest at maximum input voltage
since ΔIL increases with input voltage. Multiple capacitors
placed in parallel may be needed to meet the ESR and
RMS current handling requirements. Dry tantalum, special
polymer, aluminum electrolytic and ceramic capacitors are
all available in surface mount packages. Special polymer
capacitors offer very low ESR, but have lower capacitance
density than other types. Tantalum capacitors have the
highest capacitance density, but it is important to only
use types that have been surge tested for use in switching
power supplies. Aluminum electrolytic capacitors have
significantly higher ESR, but can be used in cost-sensitive
applications provided that consideration is given to ripple
current ratings and long term reliability. Ceramic capacitors
have excellent low ESR characteristics, but can have a
high voltage coefficient and audible piezoelectric effects.
The high Q of ceramic capacitors with trace inductance
can also lead to significant ringing.
Using Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush current through the long wires can potentially cause
a voltage spike at VIN large enough to damage the part.
Table 2. Capacitors for CIN and COUT
Component Supplier
Part No.
Capacitance (F)
Case Size
MuRata
GRM31CR71A475KA01
4.7F
1206
MuRata
GRM31CR71A106KA01
10F
1206
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RT2657BQ
Thermal Considerations
Layout 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 :
Follow the PCB layout guidelines for optimal performance
of the RT2657BQ.

 LX node experiences high frequency voltage swing and
should be kept within a small area. Keep all sensitive
small-signal nodes away from the LX node to prevent
stray capacitive noise pick up.
PD(MAX) = (TJ(MAX) − TA) / θJA
For recommended operating condition specifications of
the RT2657BQ, the maximum junction temperature is
125°C and TA is the ambient temperature. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-8L 3x3 packages, the thermal resistance, θJA, is
60°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 :
PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W 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 2 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Maximum Power Dissipation (W)1
2.4
 Flood all unused areas on all layers with copper. Flooding
with copper will reduce the temperature rise of power
components. Connect the copper areas to any DC net
(VIN, VOUT, GND, or any other DC rail in the system).

Connect the FB pin directly to the feedback resistors.
The resistive voltage divider must be connected between
VOUT and GND.
LX should be connected to inductor by
wide and short trace. Keep sensitive
components away from this trace.
COUT
VOUT
L1
VOUT
C1
R1
LX
NC
FB
NC
8
1
3
GND
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
Connect the terminal of the input capacitor(s), CIN, as
close as possible to the VIN pin. This capacitor provides
the AC current into the internal power MOSFETs.
6
4
9
5
2
R2
7
GND
VIN
EN
NC
CIN
Input capacitor must
be placed as close to
the IC as possible.
Figure 3. PCB Layout Guide
Four-Layer PCB
2.0
1.6
1.2
0.8
0.4
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum Power Dissipation
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RT2657BQ
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.
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