Orister B340L 2a, 20v, 400khz dc/dc asynchronous step.down converter Datasheet

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RS6516
2A, 20V, 400KHz DC/DC Asynchronous Step‐Down Converter
General Description
The RS6516 is a high‐efficiency asynchronous step‐down DC/DC converter that can deliver up to 2A output current from
4.75V to 20V input supply. The RS6516's current mode architecture and external compensation allow the transient
response to be optimized over a wide range of loads and output capacitors. Cycle‐by‐cycle current limit provides protection
against shorted outputs and thermal shutdown protection.
The RS6516 also provides output under voltage protection and thermal shutdown protection. The low current (<30μA)
shutdown mode provides output disconnection, enabling easy power management in battery‐powered systems.
Features
Applications
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2A Output Current
Up to 93% Efficiency
Integrated 100mΩ Power MOSFET Switches
Fixed 400KHz Frequency
Cycle‐by‐Cycle Over Current Protection
Thermal Shutdown function
Wide 4.75V to 20V Operating Input Range
Output Adjustable from 1.23V to 18V
Programmable Under Voltage Lockout
Available in an SOP‐8 Package
RoHS Compliant and 100% Lead (Pb)‐Free and Green
(Halogen Free with Commercial Standard)
PC Motherboard, Graphic Card
LCD Monitor
Set‐Top Boxes
DVD‐Video Player
Telecom Equipment
ADSL Modem
Printer and other Peripheral Equipment
Microprocessor core supply
Networking power supply
Pre‐Regulator for Linear Regulators
Green Electronics/Appliances
Application Circuits
C1
10uF/35V
CERAMIC x2
OFF ON
8
1
5
IN
EN
BS
3
INPUT
4.75V to 21V
U1
2
C5
SW
NC
GND
L1
15uH
10nF
FB
COMP
RS6516‐ADS
D1
4
R1
B340A
16.9KΩ 1%
C2
6
7
OUTPUT
3.3V/2A
C6
R3
5.6KΩ
(Optional)
C3
R2
10KΩ 1%
22uF/6.3V
CERAMIC x2
8.2nF
This integrated circuit can be damaged by ESD. Orister Corporation recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
DS‐RS6516‐05
February, 2010
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Pin Assignments
SOP‐8
PACKAGE
SOP‐8
PIN
1
SYMBOL
NC
2
BS
3
IN
4
SW
5
GND
6
FB
7
COMP
8
EN
DESCRIPTION
No Connect.
Bootstrap. This capacitor (C5) is needed to drive the power switch’s gate above
the supply voltage. It is connected between the SW and BS pins to form a floating
supply across the power switch driver. The voltage across C5 is about 5V and is
supplied by the internal +5V supply when the SW pin voltage is low.
Supply Voltage. The RS6516 operates from a 4.75V to 20V unregulated input. C1
is needed to prevent large voltage spikes from appearing at the input.
Power Switching Output. SW is the switching node that supplies power to the
output. Connect the output LC filter from SW to the output load. Note that a
capacitor is required from SW to BS to power the high‐side switch.
Ground.
Feedback Input. FB senses the output voltage and regulates it. Drive FB with a
resistive voltage divider from the output voltage to ground. The feedback
threshold is 1.23V. See Setting the Output Voltage.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a series RC network from COMP to GND. In some cases, an additional
capacitor from COMP to GND is required. See Compensation.
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high
to turn on the regulator, drive it low to turn it off. For automatic startup, leave
EN unconnected.
Ordering Information
DEVICE
RS6516‐XX Y Z
DS‐RS6516‐05
DEVICE CODE
XX is nominal output voltage :
AD : ADJ
Y is package & Pin Assignments designator :
S : SOP‐8
Z is Lead Free designator :
P: Commercial Standard, Lead (Pb) Free and Phosphorous (P) Free Package
G: Green (Halogen Free with Commercial Standard)
February, 2010
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Block Diagram
Absolute Maximum Ratings
Symbol
VIN
VSW
VBS
VFB
VEN
VCOMP
TJ
TOPR
TSTG
TLEAD
DS‐RS6516‐05
Parameter
Supply Voltage
SW Pin Voltage
Boot Strap Voltage
Feedback Voltage
Enable/UVLO Voltage
Comp Voltage
Junction Temperature
Operating Temperature Range
Storage Temperature Range
Lead Temperature
February, 2010
Range
‐0.3 to +21
‐0.3 to VIN +0.3
VSW ‐0.3 to VSW +6
‐0.3 to +6
‐0.3 to +6
‐0.3 to +6
150
‐20 to +85
‐65 to +150
260
Units
V
V
V
V
V
V
o
C
o
C
o
C
o
C
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Electrical Characteristics (VIN=12V, TA=25°C, unless otherwise specified)
Symbol
VIN
VFB
RDS(ON)1
RDS(ON)2
ISw
ILIM
GCS
AVEA
GEA
FS
FOSC1
DMAX
tON
‐
‐
‐
‐
ISD
IQ
TSD
Parameter
Input Voltage
Feedback Voltage
Upper Switch On Resistance
Lower Switch On Resistance
Upper Switch Leakage
Current Limit (NOTE 1)
Current Sense Transconductance Output
Current to Comp Pin Voltage
Error Amplifier Voltage Gain
Error Amplifier Transconductance
Oscillator Frequency
Short Circuit Frequency
Maximum Duty Cycle
Minimum On Time
EN Shutdown Threshold
Enable Pull Up Current
EN UVLO Threshold Rising
EN UVLO Threshold Hysteresis
Supply Current (Shutdown)
Supply Current (Quiescent)
Thermal Shutdown
Conditions
‐
4.75V ≤ VIN ≤ 20V
‐
‐
VEN = 0V, VSW = 0V
‐
Min.
4.75
1.19
‐
‐
‐
‐
Typ.
‐
1.23
0.22
10
‐
3.8
Max.
20
1.26
‐
‐
10
‐
Unit
V
V
Ω
Ω
uA
A
‐
‐
1.95
‐
A/V
‐
‐
‐
VFB = 0V
VFB = 1.0V
‐
ICC>100uA
VEN = 0V
VIN Rising
‐
VIN ≤0.4V
VEN ≥3V
‐
‐
550
‐
‐
‐
‐
0.7
‐
2.35
‐
‐
‐
‐
400
830
400
240
90
100
1.0
1.0
2.50
200
23
1.1
160
‐
1150
‐
‐
‐
‐
1.3
‐
2.65
‐
36
1.3
‐
V/V
uA/V
KHz
KHz
%
ns
V
uA
V
mV
uA
mA
o
C
Notes:
1.
2.
3.
4.
5.
Slope compensation changes current limit above 40% duty cycle.
Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Devices are ESD sensitive. Handling precaution is recommended.
The device is not guaranteed to function outside its operating conditions.
θJA is measured in the natural convection at TA = 25°C on a high effective four layers thermal conductivity test board of
JEDEC 51‐7 thermal measurement standard.
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February, 2010
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Detail Description
The RS6516 is a synchronous high voltage buck converter that can support the input voltage range from 4.75V to 20V and the
output current can be up to 2A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1.
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive divider according to the following equation:
⎛
VOUT = VFB ⎜ 1 +
⎝
R1 ⎞
⎟
R2 ⎠
Where VFB is the feedback reference voltage (1.23V typ.).
External Bootstrap Diode
Connect a 10nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate driver voltage
for the high side MOSFET.
It is recommended to add an external bootstrap diode between an external 5V and the BOOT pin for efficiency improvement
when input voltage is lower than 5.5V or duty ratio is higher than 65%. The bootstrap diode can be a low cost one such as
1N4148 or BAT54.
Inductor Selection
The inductor value and operating frequency determine the ripple current according to a specific input and output voltage.
The ripple current ΔIL increases with higher VIN and decreases with higher inductance.
VOUT ⎤
⎡VOUT ⎤ ⎡
ΔIL = ⎢
× ⎢1 −
⎥
VIN ⎥⎦
⎣f × L ⎦ ⎣
Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High
frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve
this goal.
For the ripple current selection, the value of ΔIL = 0.2375(IMAX) will be a reasonable starting point. The largest ripple current
occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should
be chosen according to the following equation:
VOUT
VOUT ⎤
⎡
⎤ ⎡
L=⎢
× ⎢1 −
⎥
VIN (MAX ) ⎥⎦
⎣ f × ΔIL (MAX ) ⎦ ⎣
Inductor Core Selection
The inductor type must be selected once the value for L is known. Generally speaking, high efficiency converters can not
afford the core loss found in low cost powdered iron cores. So, the more expensive ferrite or mollypermalloy cores will be a
better choice.
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February, 2010
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The selected inductance rather than the core size for a fixed inductor value is the key for actual core loss. As the inductance
increases, core losses decrease. Unfortunately, increase of the inductance requires more turns of wire and therefore the
copper losses will increase.
Ferrite designs are preferred at high switching frequency due to the characteristics of very low core losses. So, design goals
can focus on the reduction of copper loss and the saturation prevention.
Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is
exceeded. The previous situation results in an abrupt increase in inductor ripple current and consequent output voltage
ripple.
Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current
relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy materials are small and do not radiate energy. However, they are usually
more expensive than the similar powdered iron inductors. The rule for inductor choice mainly depends on the price vs. size
requirement and any radiated field/EMI requirements.
CIN and COUT Selection
The input capacitance, CIN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large
ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by:
IRMS = IOUT (MAX ) ⋅
VOUT
VIN
⋅
−1
VIN
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 offer much relief.
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.
For the input capacitor, a 10μF x 2 low ESR ceramic capacitor is recommended. For the recommended capacitor, please refer
to table 3 for more detail. The selection of COUT is determined by the required ESR to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key for COUT selection to ensure that the control loop is stable. Loop
stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔVOUT , is
determined by:
1 ⎤
⎡
ΔVOUT ≤ ΔIL ⋅ ⎢ESR +
8 fCOUT ⎥⎦
⎣
The output ripple will be highest at the 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 requirement. Dry tantalum, special polymer,
aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer
very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors have the
highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost‐sensitive applications for
ripple current rating and long term reliability considerations. 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.
Higher values, 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 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 of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the part.
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February, 2010
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Output Rectifier Diode
The output rectifier diode supplies the current to the inductor when the high‐side switch is off. To reduce losses due to the
diode forward voltage and recovery times, use a Schottky diode.
Choose a diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating
is greater than the maximum load current.
Choose a rectifier who’s maximum reverse voltage rating is greater than the maximum input voltage, and who’s current
rating is greater than the maximum load current.
Checking Transient Response
The regulator loop response can be checked by looking at the load transient response. Switching regulators take several
cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD (ESR)
also begins to charge or discharge COUT generating a feedback error signal for the regulator to return VOUT to its steady‐state
value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem.
Table 1. Suggested Inductors for Typical Application Circuit
Component Supplier
MAGLAYERS
SUMIDA
TOKO
Series
MSCDRI‐124‐150M
CDRH104R
D104C
Dimensions (mm)
12 x 12 x 5.0
10.1 x 10 x 3.0
10 x 10 x 4.3
Table 2. Suggested Capacitors for CIN and COUT
Component Supplier
MURATA
TDK
MURATA
TDK
Part No.
GRM31CR61E106K
C3225X5R1E106K
GRM32ER71C226M
C3225X5R1C226M
Capacitance (uF)
10
10
22
22
Case Size
1206
1206
1200
1200
Table 3. Schottky Rectifier Selection Guide
VIN (Max.)
20V
26V
Part No.
B320
SK33
SS32
B330
B340L
SK33
MBRD330
SS33
DS‐RS6516‐05
February, 2010
2A Load Current
Vendor
Diodes, Inc. (www.diodes.com)
Pan Jit International (www.panjit.com.tw)
General Semiconductor (www.gensemi.com)
Diodes, Inc. (www.diodes.com)
Diodes, Inc. (www.diodes.com)
Diodes, Inc. (www.diodes.com)
On Semiconductor (www.onsemi.com)
Fairchild Semiconductor (www.fairchildsemi.com)
General Semiconductor (www.gensemi.com)
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SOP‐8 Dimension
NOTES:
A. All linear dimensions are in millimeters (inches).
B. This drawing is subject to change without notice.
C. Body length does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not
exceed 0.006 (0.15) per end.
D. Body width does not include interlead flash. Interlead flash shall not exceed 0.017 (0.43) per side.
E. Falls within JEDEC MS‐012 variation AA.
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Soldering Methods for Orister’s Products
1. Storage environment: Temperature=10oC~35oC Humidity=65%±15%
2. Reflow soldering of surface‐mount devices
Figure 1: Temperature profile
tP
Critical Zone
TL to TP
TP
Ramp-up
TL
tL
Temperature
Tsmax
Tsmin
tS
Preheat
25
Ramp-down
t 25oC to Peak
Time
Profile Feature
Sn‐Pb Eutectic Assembly
Pb‐Free Assembly
<3 C/sec
<3oC/sec
‐ Temperature Min (Tsmin)
100oC
150oC
‐ Temperature Max (Tsmax)
150oC
200oC
60~120 sec
60~180 sec
<3oC/sec
<3oC/sec
183oC
207oC
Average ramp‐up rate (TL to TP)
o
Preheat
‐ Time (min to max) (ts)
Tsmax to TL
‐ Ramp‐up Rate
Time maintained above:
‐ Temperature (TL)
‐ Time (tL)
60~150 sec
Peak Temperature (TP)
Time within 5oC of actual Peak
Temperature (tP)
Ramp‐down Rate
Time 25oC to Peak Temperature
o
o
60~150 sec
240 C +0/‐5 C
260oC +0/‐5oC
10~30 sec
20~40 sec
<6oC/sec
<6oC/sec
<6 minutes
<8 minutes
Peak temperature
Dipping time
245 C ±5 C
5sec ±1sec
3. Flow (wave) soldering (solder dipping)
Products
o
Pb devices.
Pb‐Free devices.
DS‐RS6516‐05
February, 2010
o
o
o
260 C +0/‐5 C
5sec ±1sec
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Important Notice:
© Orister Corporation
Orister cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an Orister product.
No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied.
Orister reserves the right to make changes to their products or specifications or to discontinue any product or service
without notice. Except as provided in Orister’s terms and conditions of sale, Orister assumes no liability whatsoever, and
Orister disclaims any express or implied warranty relating to the sale and/or use of Orister products including liability or
warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other
intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and
operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other
quality control techniques are utilized to the extent Orister deems necessary to support this warranty. Specific testing of
all parameters of each device is not necessarily performed.
Orister and the Orister logo are trademarks of Orister Corporation. All other brand and product names appearing in this
document are registered trademarks or trademarks of their respective holders.
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