Richtek NR10050 5a, 36v, 500khz current mode asynchronous step-down converter Datasheet

®
RT2805A
5A, 36V, 500kHz Current Mode Asynchronous Step-Down
Converter
General Description
Features
The RT2805A is a current mode asynchronous step-down
converter that achieves excellent load and line regulation.
Over a wide input voltage range from 5.5V to 36V and
supports output current up to 5A. The Current mode
operation provides fast transient response and eases loop
stabilization.
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An adjustable soft-start reduces the stress on the input
source at startup. In shutdown mode, the regulator draws
only 25μA of supply current. The RT2805A requires a
minimum number of readily available external
components, providing a compact solution. The RT2805A
provides protection functions inducing input under voltage
lockout, cycle-by-cycle current limit, short circuit
protection and thermal shutdown protection.
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Applications
The RT2805A is available in the SOP-8 (Exposed Pad)
package.
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Ordering Information
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RT2805A
z
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Distributive Power Systems
Battery Charger
DSL Modems
Pre-regulator for Linear Regulators
Marking Information
Lead Plating System
G : Green (Halogen Free and Pb Free)
RT2805AGSP : Product Number
RT2805A
GSPYMDNN
Note :
Richtek products are :
`
5A Output Current
Wide Operating Input Range 5.5V to 36V
Adjustable Output Voltage from 1.222V to 26V
High Efficiency up to 90%
Internal Compensation Minimizes External Parts
Count
Internal Soft-Start
110mΩ
Ω Internal Power MOSFET Switch
25μ
μA Shutdown Mode
Fixed 500kHz Frequency
Thermal Shutdown
Cycle-by-Cycle Current Limit
Available In an SOP8 (Exposed Pad) Package
RoHS Compliant and Halogen Free
YMDNN : Date Code
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
Simplified Application Circuit
VIN
VIN
CIN
BOOT
RT2805A
L1
SW
VOUT
D1
Chip Enable
EN
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
R1
COUT
FB
GND
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CBOOT
R2
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1
RT2805A
Pin Configurations
(TOP VIEW)
BOOT
NC
2
NC
3
FB
4
GND
9
8
SW
7
VIN
6
GND
5
EN
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
Pin Name
Pin Function
BOOT
Bootstrap Input for High Side Gate Driver. Connect a 10nF or greater capacitor
from SW to BOOT to power the high side switch.
2, 3
NC
No Internal Connection.
4
FB
Feedback Input. The feedback threshold is 1.222V.
5
EN
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN
higher than 1.4V to turn on the regulator, lower than 0.4V to turn it off. For
automatic startup, leave EN unconnected.
6,
9 (Exposed Pad)
GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
7
VIN
Power Input. A suitable large capacitor should be connected from the VIN to
GND to eliminate noise on the input to the IC.
8
SW
Switch Node. Note that a capacitor is required from SW to BOOT to power the
high side switch.
1
Function Block Diagram
VIN
Current Sense
Amplifier
+
Ramp
Generator
BOOT
EN
Regulator
Oscillator
500kHz
S
Q
Driver
+
Reference
FB
Error
+ Amplifier
-
12k
400k
30pF
R
Current
Comparator
SW
Bootstrap
Control
GND
13pF
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RT2805A
Operation
The RT2805A is a constant frequency, current mode
asynchronous step-down converter. In normal operation,
the high side N-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. While the N-MOSFET
is turned off, the inductor current conducts through the
external diode.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (V FB) with the internal 1.222V
reference. When the load current increases, it causes a
drop in the feedback voltage relative to the reference, the
error amplifier's output voltage then rises to allow higher
inductor current to match the load current.
Oscillator
The internal oscillator runs at fixed frequency 500kHz. In
short circuit condition, the frequency is reduced to 150kHz
for low power consumption.
Enable
The converter is turned on when the EN pin is higher than
1.4V and turned off when the EN pin is lower than 0.4V.
When the EN pin is open, it will be pulled up to logic-high
by 1μA current internally.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 5ms.
Thermal Shutdown
The over temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 30°C, the converter will
automatically resume switching.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high
side gate driver.
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RT2805A
Absolute Maximum Ratings
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(Note 1)
Supply Voltage, VIN ----------------------------------------------------------------------------------------Switching Voltage, SW ------------------------------------------------------------------------------------BOOT Voltage ------------------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------SOP-8 (Exposed Pad), 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 40V
−0.3V to (VIN + 0.3V)
(VSW − 0.3V) to (VSW + 6V)
−0.3V to 6V
2.04W
49°C/W
15°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Voltage, VIN ----------------------------------------------------------------------------------------- 5.5V to 36V
Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 12V, TA = −40°C to 85°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
TA = 25°C
1.202 1.222 1.239
R DS(ON)1
IOUT = 0A to 5A
Bias Gate Driver at VIN = 5.5V
1.196 1.222 1.245
-110
230
Low Side Switch-On Resistance
R DS(ON)2
Bias Gate Driver at VIN = 5.5V
Current Limit
Oscillator Frequency
Short Circuit Frequency
Maximum Duty Cycle
ILIM
fOSC
D MAX
Voltage Mode Test
VFB = 0.8V
VFB = 0V
VFB = 0.8V
Minimum On-Time
Under Voltage Lockout Threshold
Rising
Under Voltage Lockout Threshold
Hysteresis
Logic-High
EN Threshold
Voltage
Logic-Low
tON
Reference Voltage
VREF
High Side Switch-On Resistance
VIH
V
mΩ
--
10
15
Ω
6
400
-85
7.5
500
150
90
9
600
-95
A
kHz
kHz
%
Come from Maximum Duty Cycle
--
100
150
ns
VIN Rising, Check Switching
--
4.2
5
V
VIN Falling, Check Switching
--
315
--
mV
1.4
--
--
----3
-1
25
0.6
5
0.4
-45
1
10
μA
μA
mA
ms
--
160
--
°C
VIL
Let EN = 1.4V, Check IQ
Let EN = 0.4V, Check IQ
Enable Pull Up Current
Shutdown Current
Quiescent Current
Soft-Start Period
ISHDN
IQ
VEN = 0V
VEN = 2V, VFB = 1.5V
Thermal Shutdown
TSD
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Unit
V
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RT2805A
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. The EVB board copper area is 70mm2.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
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RT2805A
Typical Application Circuit
7
VIN
5.5V to 36V
CIN
4.7µF/
50V x 2
Chip Enable
BOOT
VIN
1
RT2805A
SW 8
5 EN
GND
L1
VOUT
D1
B550A
Open = Automatic
Startup
6, 9 (Exposed Pad)
CBOOT
10nF
CFF
R1
FB 4
COUT
22µF x 2
R2
Table 1. Recommended Component Selection
V OUT (V)
R1 (kΩ)
R2 (kΩ)
C FF (pF)
L (μH)
COUT (μF)
2.5
100
100
82
6.8
22 x 2
3.3
100
58.6
82
10
22 x 2
5
100
31.6
82
15
22 x 2
8
100
18
82
22
22 x 2
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RT2805A
Typical Operating Characteristics
Efficiency vs. Output Current
Reference Voltage vs. Input Voltage
100
1.230
Efficiency (%)
80
Reference Voltage (V)
90
VIN = 12V
VIN = 32V
VIN = 36V
70
60
50
40
30
20
1.226
1.222
1.218
1.214
10
VOUT = 5V
VOUT = 5V, IOUT = 0A
1.210
0
0
1
2
3
4
4
5
8
12
16
Output Current (A)
24
28
32
36
Output Voltage vs. Output Current
5.008
1.228
5.004
5.000
1.226
Output Voltage (V)
Reference Voltage (V)
Reference Voltage vs. Temperature
1.230
1.224
1.222
VIN = 12V
VIN = 24V
VIN = 36V
1.220
1.218
1.216
1.214
VIN = 36V
VIN = 24V
VIN = 12V
4.996
4.992
4.988
4.984
4.980
4.976
4.972
4.968
1.212
IOUT = 0A
1.210
-50
-25
0
25
50
75
100
4.964
VOUT = 5V
4.960
0
125
1
2
3
4
Frequency vs. Input Voltage
Frequency vs. Temperature
540
530
530
520
520
Frequency (kHz)
540
510
500
490
480
470
510
500
490
480
VIN = 12V
VIN = 24V
VIN = 36V
470
460
460
450
5
Output Current (A)
Temperature (°C)
Frequency (kHz)
20
Input Voltage (V)
450
VOUT = 5V, IOUT = 0A
VOUT = 5V
440
440
4
8
12
16
20
24
28
32
Input Voltage (V)
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36
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT2805A
Shutdown Current vs. Input Voltage
60
11
50
Shutdown Current (μA)
Current Limit (A)
Current Limit vs. Temperature
12
10
9
8
7
6
VIN = 12V
5
-50
-25
0
25
50
75
100
40
30
20
10
VEN = 0V
0
4
125
8
12
16
20
24
28
Temperature (°C)
Input Voltage (V)
Quiescent Current vs. Temperature
Load Transient Response
32
36
1
Quiescent Current (mA)
0.9
VOUT
(200mV/Div)
0.8
0.7
0.6
VIN = 36V
VIN = 24V
VIN = 12V
0.5
0.4
0.3
0.2
IOUT
(2A/Div)
0.1
VIN = 12V, VOUT = 5V, IOUT = 0.2A to 5A
0
-50
-25
0
25
50
75
100
Time (100μs/Div)
125
Temperature (°C)
Switching
Load Transient Response
VOUT
(200mV/Div)
VOUT
(10mV/Div)
VSW
(10V/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 5V, IOUT = 2.5A to 5A
Time (100μs/Div)
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IL
(5A/Div)
VIN = 12V, VOUT = 5V, IOUT = 5A
Time (1μs/Div)
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RT2805A
Power On from EN
Power Off from EN
VEN
(5V/Div)
VEN
(5V/Div)
VOUT
(5V/Div)
VOUT
(5V/Div)
IL
(5A/Div)
IL
(5A/Div)
VIN = 12V, VOUT = 5V, IOUT = 5A
Time (2.5ms/Div)
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VIN = 12V, VOUT = 5V, IOUT = 5A
Time (2.5ms/Div)
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RT2805A
Application Information
The RT2805A is an asynchronous high voltage buck
converter that can support the input voltage range from
5.5V to 32V and the output current can be up to 5A.
Output Voltage Setting
The resistive divider allows the FB pin to sense the output
voltage as shown in Figure 1.
VOUT
R1
FB
RT2805A
R2
GND
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive divider
according to the following equation :
VOUT = VREF ⎛⎜ 1+ R1 ⎞⎟
⎝ R2 ⎠
Where VREF is the reference voltage (1.222V typ.).
Soft-Start
The RT2805A contains an internal soft-start clamp that
gradually raises the output voltage. The typical soft-start
time is 5ms.
Chip Enable Operation
The EN pin is the chip enable input. Pull the EN pin low
(<0.4V) will shutdown the device. During shutdown mode,
the RT2805A quiescent current drops to lower than 25μA.
Drive the EN pin to high (>1.4V, <5.5V) will turn on the
device again. If the EN pin is open, it will be pulled to high
by internal circuit. For external timing control (e.g.RC),
the EN pin can also be externally pulled to High by adding
a 100kΩ or greater resistor from the VIN pin (see Figure
3).
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.
Where R1 = 100kΩ.
V
V
ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥
VIN ⎦
⎣ f ×L ⎦ ⎣
External Bootstrap Diode
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.
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 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 IN4148 or BAT54. The external 5V
can be a 5V fixed input from system or a 5V output of the
RT2805A.
⎡ VOUT ⎤ ⎡
VOUT ⎤
L =⎢
⎥ × ⎢1 − VIN(MAX) ⎥
f
I
×
Δ
L(MAX)
⎣
⎦ ⎣
⎦
5V
BOOT
RT2805A
10nF
SW
Figure 2. External Bootstrap Diode
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For the ripple current selection, the value of ΔIL = 0.2(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 :
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference.
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RT2805A
Table 2. Suggested Inductors for Typical
Application Circuit
Component
Dimensions
Series
Supplier
(mm)
TAIYO
NR10050
10 x 9.8 x 5
YUDEN
TDK
SLF12565
12.5 x 12.5 x 6.5
Diode Selection
When the power switch turns off, the path for the current
is through the diode connected between the switch output
and ground. This forward biased diode must have a
minimum voltage drop and recovery times. Schottky diode
is recommended and it should be able to handle those
current. The reverse voltage rating of the diode should be
greater than the maximum input voltage, and current rating
should be greater than the maximum load current. For
more detail please refer to Table 4.
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 current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
V
IRMS = IOUT(MAX) OUT
VIN
VIN
−1
VOUT
This formula has a maximum at VIN = 2VOUT, where
IRMS = I OUT / 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, two 4.7μF low ESR ceramic
capacitors are 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.
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The output ripple, ΔVOUT , is determined by :
1
⎤
ΔVOUT ≤ ΔIL ⎡⎢ESR +
8fCOUT ⎦⎥
⎣
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. A sudden inrush of current through the long
wires can potentially cause a voltage spike at VIN large
enough to damage the part.
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.
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RT2805A
is to add a resistor in series with the bootstrap
capacitor, CBOOT. But this method will decrease the driving
EMI Consideration
Since parasitic inductance and capacitance effects in PCB
circuitry would cause a spike voltage on SW pin when
high side MOSFET is turned-on/off, this spike voltage on
SW may impact on EMI performance in the system. In
order to enhance EMI performance, there are two methods
to suppress the spike voltage. One is to place an R-C
snubber between SW and GND and make them as close
as possible to the SW pin (see Figure 3). Another method
7
VIN
5.5V to 32V
REN*
CIN
4.7µF x 2
capability to the high side MOSFET. It is strongly
recommended to reserve the R-C snubber during PCB
layout for EMI improvement. Moreover, reducing the SW
trace area and keeping the main power in a small loop will
be helpful on EMI performance. For detailed PCB layout
guide, please refer to the section of Layout Consideration.
BOOT
VIN
RT2805A
5 EN
1
CBOOT
L
10nF 10µH
SW 8
RS*
CEN*
6, 9 (Exposed Pad)
RBOOT*
CS*
GND
D
B550C
VOUT
5V/5A
R1
10k
FB 4
COUT
47µFx2
(POSCAP)
R2
3.16k
* : Optional
Figure 3. Reference Circuit with Snubber and Enable Timing Control
Thermal Considerations
For continuous operation, do not exceed the maximum
operation junction temperature. The maximum power
dissipation depends on the thermal resistance of IC
package, PCB layout, the rate of surroundings airflow and
temperature difference between junction to ambient. The
maximum power dissipation can be calculated by following
formula :
PD(MAX) = (TJ(MAX) − TA ) / θJA
Where T J(MAX) is the maximum operation junction
temperature , TA is the ambient temperature and the 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
PSOP-8 package, the thermal resistance θJA is 75°C/W
on the standard JEDEC 51-7 four-layers thermal test board.
The maximum power dissipation at TA = 25°C can be
calculated by following formula :
P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W
(min.copper area PCB layout)
PD(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W (70mm2
copper area PCB layout)
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The thermal resistance θJA of SOP-8 (Exposed Pad) is
determined by the package architecture design and the
PCB layout design. However, the package architecture
design had been designed. If possible, it's useful to
increase thermal performance by the PCB layout copper
design. The thermal resistance θJA can be decreased by
adding copper area under the exposed pad of SOP-8
(Exposed Pad) package.
As shown in Figure 4, the amount of copper area to which
the SOP-8 (Exposed Pad) is mounted affects thermal
performance. When mounted to the standard
SOP-8 (Exposed Pad) pad (Figure 4a), θJA is 75°C/W.
Adding copper area of pad under the SOP-8 (Exposed
Pad) (Figure 4.b) reduces the θJA to 64°C/W. Even further,
increasing the copper area of pad to 70mm2 (Figure 4.e)
reduces the θJA to 49°C/W.
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 of derating
curves allows the designer to see the effect of rising
ambient temperature on the maximum power dissipation
allowed.
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RT2805A
2.2
Four Layer PCB
Power Dissipation (W)
2.0
1.8
Copper Area
70mm2
50mm2
30mm2
10mm2
Min.Layout
1.6
1.4
1.2
1.0
0.8
(d) Copper Area = 50mm2, θJA = 51°C/W
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 5. Derating Curve of Maximum Power Dissipation
(e) Copper Area = 70mm2, θJA = 49°C/W
Figure 4. Thermal Resistance vs. Copper Area Layout
Design
Layout Consideration
(a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W
Follow the PCB layout guidelines for optimal performance
of the RT2805A.
` Keep
the traces of the main current paths as short and
wide as possible.
` Put the input capacitor as close as possible to the device
pins (VIN and GND).
` SW node is with high frequency voltage swing and should
(b) Copper Area = 10mm2, θJA = 64°C/W
be kept at small area. Keep analog components away
from the SW node to prevent stray capacitive noise pickup.
` Connect feedback network behind the output capacitors.
Keep the loop area small. Place the feedback
components near the RT2805A.
` Connect all analog grounds to a common node and then
connect the common node to the power ground behind
the output capacitors.
(c) Copper Area = 30mm2, θJA = 54°C/W
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
DS2805A-00 November 2012
` An
example of PCB layout guide is shown in Figure 6
for reference.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT2805A
SW should be connected to inductor by
wide and short trace. Keep sensitive
components away from this trace.
SW
VOUT
CBOOT
R1
COUT
L1
BOOT
VOUT
COUT
SW
8
NC
2
NC
3
FB
4
GND
9
7
VIN
6
GND
5
EN
R2
The feedback components
should be connected as close
to the device as possible.
D1
CIN
CIN
Input capacitor should be
placed as close to the IC
as possible.
GND
Figure 6. PCB Layout Guide
Table 3. Suggested Capacitors for CIN and CO UT
Location
Component Supplier
Part No.
Capacitance (μF)
Case Size
CIN
MURATA
GRM32ER71H475K
4.7
1206
CIN
TAIYO YUDEN
UMK325BJ475MM-T
4.7
1206
COUT
MURATA
GRM31CR60J476M
47
1206
COUT
TDK
C3225X5R0J476M
47
1210
COUT
MURATA
GRM32ER71C226M
22
1210
COUT
TDK
C3225X5R1C22M
22
1210
Table 4. Suggested Diode
Component Supplier
Series
VRRM (V)
IOUT (A)
Package
DIODES
B550C
50
5
SMC
PANJIT
SK55
50
5
SMC
Copyright © 2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
is a registered trademark of Richtek Technology Corporation.
DS2805A-00 November 2012
RT2805A
Outline Dimension
H
A
M
EXPOSED THERMAL PAD
(Bottom of Package)
Y
J
X
B
F
C
I
D
Dimensions In Millimeters
Dimensions In Inches
Symbol
Min
Max
Min
Max
A
4.801
5.004
0.189
0.197
B
3.810
4.000
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.510
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.170
0.254
0.007
0.010
I
0.000
0.152
0.000
0.006
J
5.791
6.200
0.228
0.244
M
0.406
1.270
0.016
0.050
X
2.000
2.300
0.079
0.091
Y
2.000
2.300
0.079
0.091
X
2.100
2.500
0.083
0.098
Y
3.000
3.500
0.118
0.138
Option 1
Option 2
8-Lead SOP (Exposed Pad) Plastic 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.
DS2805A-00 November 2012
www.richtek.com
15