3 A, Buck Converter IC
SI-8000SD Series
Data Sheet
Description
Package
SI-8000SD series are buck converter ICs whose
maximum output current is 3 A.
These products have various functions including the
Soft Start Function, the Output On/Off Function, the
Overcurrent Protection and the Thermal Shutdown, and
achieve a buck converter circuit with few external
components.
TO263-5L
Not to scale
Features
● High Efficiency 84%
(SI-8050SD: VIN = 20 V, IOUT = 1 A)
● Few Components
● Downsized Choke Coil
(Switching Frequency 60 kHz (typ.))
● Fixed Output Voltage
● Soft Start Function
● On/Off Function
● Low Supply Current during Output Off
● Protection Functions
Overcurrent Protections (OCP): Drooping Type,
Auto-restart
Thermal Shutdown (TSD): Auto-restart
Selection Guide
Part Number
SI-8033SD
SI-8050SD
Output Voltage
3.3 V
5V
Applications
For the systems requiring power supplies such as:
● Audio Visual Equipment
● Office Automation Equipment (e.g., Printer)
● Onboard power supply
Typical Application
VIN
SW
GND
VOS
SS
SI-8000SD
1
VIN
CIN
2
3
4
5
L1
C3
VOUT
D1
COUT
GND
GND
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SI-8000SD
Contents
Description ------------------------------------------------------------------------------------------------------ 1
Contents --------------------------------------------------------------------------------------------------------- 2
1. Absolute Maximum Ratings----------------------------------------------------------------------------- 3
2. Thermal Resistance Characteristics ------------------------------------------------------------------- 3
3. Recommended Operating Conditions ----------------------------------------------------------------- 4
4. Electrical Characteristics -------------------------------------------------------------------------------- 5
4.1. SI-8033SD --------------------------------------------------------------------------------------------- 5
4.2. SI-8050SD --------------------------------------------------------------------------------------------- 5
5. Block Diagram --------------------------------------------------------------------------------------------- 6
6. Pin Configuration Definitions --------------------------------------------------------------------------- 6
7. Typical Application --------------------------------------------------------------------------------------- 7
8. Physical Dimensions -------------------------------------------------------------------------------------- 8
8.1. Land Pattern Example ----------------------------------------------------------------------------- 8
9. Marking Diagram ----------------------------------------------------------------------------------------- 9
10. Operational Description ------------------------------------------------------------------------------- 10
10.1. PWM Output Voltage Control------------------------------------------------------------------ 10
10.2. Input/output Current and Inductor Current ------------------------------------------------ 10
10.3. Overcurrent Protection Function (OCP) ----------------------------------------------------- 11
10.4. Thermal Shutdown (TSD) ----------------------------------------------------------------------- 11
10.5. Soft Start Function -------------------------------------------------------------------------------- 11
10.6. Output On/Off Function ------------------------------------------------------------------------- 12
11. Design Notes ---------------------------------------------------------------------------------------------- 13
11.1. Selecting External Components ---------------------------------------------------------------- 13
11.1.1. Inductor, L1 ---------------------------------------------------------------------------------- 13
11.1.2. Input Capacitor, CIN ------------------------------------------------------------------------ 13
11.1.3. Output Capacitor, COUT -------------------------------------------------------------------- 14
11.1.4. Freewheeling Diode, D1 -------------------------------------------------------------------- 15
11.1.5. Spike Noise Reduction ---------------------------------------------------------------------- 15
11.1.6. Reverse Biasing Protection ---------------------------------------------------------------- 16
11.2. PCB Layout----------------------------------------------------------------------------------------- 16
11.2.1. High Current Line -------------------------------------------------------------------------- 16
11.2.2. Input/ Output Capacitor ------------------------------------------------------------------- 16
11.3. Operational Waveforms Confirmation ------------------------------------------------------- 17
11.4. Thermal Design ------------------------------------------------------------------------------------ 18
12. Pattern Layout Example ------------------------------------------------------------------------------- 19
13. Typical Characteristics --------------------------------------------------------------------------------- 20
13.1. SI-8033SD ------------------------------------------------------------------------------------------- 20
13.2. SI-8050SD ------------------------------------------------------------------------------------------- 21
13.3. Thermal Derating Curve------------------------------------------------------------------------- 23
Important Notes ---------------------------------------------------------------------------------------------- 24
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SI-8000SD
1.
Absolute Maximum Ratings
Current polarities are defined as follows: current going into the IC (sinking) is positive current (+); current coming
out of the IC (sourcing) is negative current (−). Unless specifically noted, TA = 25 °C.
Parameter
Symbol
Conditions
Rating
Unit
Remarks
Input Voltage
VIN
Allowable Power Dissipation
PD(1)
(2)
35
V
SI-8033SD
43
V
SI-8050SD
3
W
Junction Temperature
TJ
125
°C
Storage Temperature
TSTG
−40 to 125
°C
(1)
Limited by the thermal shutdown.
Glass-epoxy board (40 mm × 40 mm), copper area 100%
(2)
2.
Thermal Resistance Characteristics
Parameter
Symbol
Thermal Resistance between Junction
and Ambient
Thermal Resistance between Junction
and Lead
θJ-A
θJ-L
Conditions
Mounted on the board.*
See Figure 2-1.
Min.
Typ.
Max.
Unit
—
—
33.3
°C/W
—
—
3
°C/W
TC
Figure 2-1.
*
Case Temperature Measurement Point
Glass-epoxy board (40 mm × 40 mm), copper area 100%
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SI-8000SD
3.
Recommended Operating Conditions
Parameter
Input Voltage
Symbol
Conditions
VIN
Min.
Max.
Unit
Remarks
5.5
28
V
SI-8033SD
7
40
V
SI-8050SD
*
IOUT
0
3
A
Operating Junction Temperature
TJOP
−30
125
°C
Operating Ambient Temperature
TOP
−30
125
°C
Output Current
*
Must be used in the range of thermal derating (see Figure 13-13).
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SI-8000SD
4.
Electrical Characteristics
4.1.
SI-8033SD
Current polarities are defined as follows: a current flow going into the IC (sinking) is positive current (+); and a
current flow coming out of the IC (sourcing) is negative current (−).
Unless otherwise specified, TA = 25 °C.
Parameter
Output Voltage
Output Voltage Temperature
Coefficient
Efficiency
*
Operating Frequency
Symbol
VOUT
Typ.
Max.
Unit
3.17
3.30
3.43
V
—
±0.5
—
mV/°C
η
VIN = 15 V, IOUT = 1 A
—
79
—
%
fO
VIN = 15 V, IOUT = 1 A
—
60
—
kHz
VIN = 8 V to 20 V,
IOUT = 1 A
VIN = 15 V,
IOUT = 0.5 A to 1.5 A
—
25
80
mV
—
10
30
mV
VIN = 15 V
3.1
—
—
A
—
0.2
—
V
15
25
35
μA
VLINE
Load Regulation
VLOAD
IS
SS Pin Low Level Voltage
VSSL
SS Pin Source Current at
Low Level
ISSL
4.2.
VIN = 15 V, IOUT = 1 A
Min.
ΔVOUT/ΔT
Line Regulation
Overcurrent Protection Start
Current
Conditions
VSSL = 0.2 V
SI-8050SD
Current polarities are defined as follows: a current flow going into the IC (sinking) is positive current (+); and a
current flow coming out of the IC (sourcing) is negative current (−).
Unless otherwise specified, TA = 25 °C.
Parameter
Output Voltage
Output Voltage Temperature
Coefficient
Symbol
VOUT
Conditions
Min.
Typ.
Max.
Unit
4.8
5.0
5.2
V
—
±0.5
—
mV/°C
VIN = 20 V, IOUT = 1 A
ΔVOUT/ΔT
Efficiency *
η
VIN = 20 V, IOUT = 1 A
—
84
—
%
Operating Frequency
fO
VIN = 20 V, IOUT = 1 A
48
60
72
kHz
VIN = 10 V to 30 V,
IOUT = 1 A
VIN = 20 V,
IOUT = 0.5 A to 1.5 A
—
40
100
mV
—
10
40
mV
VIN = 20 V
3.1
—
—
A
—
0.2
—
V
20
30
40
μA
Line Regulation
VLINE
Load Regulation
VLOAD
Overcurrent Protection Start
Current
IS
SS Pin Low Level Voltage
VSSL
SS Pin Source Current at
Low Level
ISSL
*
VSSL = 0.2 V
Efficiency is calculated by the following equation.
η(%) =
VOUT × IOUT
× 100
VIN × IIN
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SI-8000SD
5.
Block Diagram
VIN
1
2 SW
Internal
Regulator
Overcurrent
Protection
Reset
Latch and
Driver
OSC
Comp.
Thermal
Shutdown
Error amp.
4 VOS
Reference
Voltage
5
SS
Pin Configuration Definitions
VIN
SW
GND
VOS
SS
6.
3
GND
1
2
3
4
5
Pin
Number
1
Pin
Name
VIN
2
SW
3
GND
Ground
4
VOS
5
SS
Feedback Pin
Soft start period adjustment capacitor connection,
on/off signal input
Description
Input pin
Output pin
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SI-8000SD
7.
Typical Application
VIN
SW
GND
VOS
SS
SI-8000SD
1
2
3
4
5
L1
VIN
VOUT
CIN
C3
D1
COUT
GND
GND
Figure 7-1.
Typical Application
Table 7-1. Reference Value of External Components
Symbol
Part Type
Reference Value
Remarks
CIN
Electrolytic capacitor
50 V/1000 μF
See Section 11.1.2.
COUT
Electrolytic capacitor
50 V/1000 μF
See Section 11.1.3.
C3
Ceramic capacitor
D1
Schottky diode
L1
Choke coil
0.01 μF
Soft start period adjustment capacitor. See Section 10.5.
60 V, 5 A
See Section 11.1.4.
150 μH
See Section 11.1.1.
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SI-8000SD
8.
Physical Dimensions
● TO263-5L
E
L1
A
(E)
H
D
D1
L4
(L1)
C2
E1
A2
A1
c
e
L
c
Symbol
A
A1
A2
b
b1
c
c1
C2
D
D1
E
E1
e
b
L3
b
PLATING
b1
c
c1
BASE METAL
SECTION C-C
H
L
L1
L3
L4
θ
θ1
θ2
Min.
4.40
0
2.59
0.77
0.76
0.34
0.33
1.22
9.05
6.86
10.06
7.50
Nom.
4.57
0.10
2.69
—
0.81
—
0.38
—
9.15
—
10.16
—
1.70
BSC
14.70
15.10
2.00
2.30
1.17
1.27
0.25 BSC
2.00 REF
0°
—
5°
7°
1°
3°
Max.
4.70
0.25
2.79
0.90
0.86
0.47
0.43
1.32
9.25
7.50
10.26
8.30
15.50
2.60
1.40
8°
9°
5°
NOTES:
● Dimensions in millimeters
● Bare lead frame: Pb-free (RoHS compliant)
● Dimensions do not include mold burrs.
8.1.
Land Pattern Example
11 ±0.2
9 ±0.2
6.8 ±0.1
9 ±0.1
3.7 ±0.05
4 ±0.1
1.7 ±0.1
1 ±0.05
Dimensions in millimeters
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SI-8000SD
9.
Marking Diagram
Specific Device Code (See Table 9-1)
YMDXXX
1
Lot Number
Y is the last digit of the year of manufacture (0 to 9)
M is the month of the year (1 to 9, O, N, or D)
D is the period of days represented by:
1: the first 10 days of the month (1st to 10th)
2: the second 10 days of the month (11th to 20th)
3: the last 10–11 days of the month (21st to 31st)
XXX is the control number
5
Table 9-1. Specific Device Code
Specific Device Code
Part Number
8033SD
SI-8033SD
8050SD
SI-8050SD
SI-8000SD-DSE Rev.2.1
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SI-8000SD
10. Operational Description
All the characteristic values given in this section are
typical values, unless they are specified as minimum or
maximum.
10.1. PWM Output Voltage Control
The SI-8000SD series control the output voltage by the
PWM method and have a built-in PWM comparator,
oscillator, error amplifier, reference voltage, output
transistor drive circuit, etc. The PWM comparator
outputs the switching transistor control signal as a square
wave by comparing the triangular wave output (≈60 kHz)
from the oscillator with the error amplifier output. The
PWM comparator controls the switching transistor to
turn on during the period when the error amplifier output
exceeds the oscillator output. When the output voltage
rises, the output of the error amplifier decreases because
the error amplifier is an inverting type. When the error
amplifier output decreases, the period below the
oscillator triangle wave level decreases. Thus, the turn-on
period of the switching transistor is shortened. In this
way, the output voltage is regulated by changing the
turn-on time of the switching transistor with the
switching frequency fixed. The higher the V IN, the
shorter the turn-on period of the switching transistor. The
square wave output of the switching transistor is
smoothed by an LC low-pass filter consisting of an
inductor and a capacitor. As a result, a regulated DC
voltage is supplied to the load.
Switching
Transistor
VIN
L1
PWM
Comparator
D1
Drive
Circuit
VOUT
10.2. Input/output Current and Inductor
Current
The square wave output generated by the switching
transistor built in the IC is smoothed by the LC filter
composed of the inductor and the output capacitor, and
converted to the DC output voltage. The operation of the
LC filter significantly affects the stable operation of the
switching regulator. Figure 10-3 shows the schematic
diagram of the current flowing through the circuit, and
Figure 10-4 shows the waveforms of the current flowing
through each element.
ITR
IL = ITR + IDI
L1
TR
VIN
D1
Figure 10-3.
IDI
COUT
IOUT
Schematic Diagram of Circuit Current
TON TOFF
TR
Emitter Voltage
(Switching Output)
VIN
ITR
ILP
0
COUT
IIN
IDI
ILP
Oscillator
Error Amplifier
0
Reference
Voltage
IL
ΔIL
Figure 10-1.
IOUT
Basic Structure of Switching Regulator
with PWM Control
0
Figure 10-4.
Oscillator Output
Error Amplifier Output
ON OFF
Figure 10-2.
Switching Transistor Output
PWM Comparator Operation Diagram
ILP
Waveforms of Current through Each
Element
As shown in Figure 10-3, the current, IL, flowing
through the inductor has a triangular waveform. This
triangular waveform is composed of two types of current
components, ITR and IDI. The current, ITR, is the current
supplied from the input side through the transistor at
transistor turn-on, and the average value is the input
current, IIN. The current, IDI, is the current that the energy
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SI-8000SD
stored in the inductor is commutated through the
freewheeling diode at transistor turn-off.
The inductor current, IL, is the sum of ITR and IDI.
Moreover, the average IL is the DC output current, IOUT,
because the triangular wave component on which IL is
superimposed is smoothed by the capacitor, COUT.
10.5. Soft Start Function
When a capacitor, C3, is connected to the SS pin, soft
start is activated at input voltage turned-on. The soft start
time, tSS, until VOUT rises is calculated by the Equation
(1).
t SS = t d + t S
10.3. Overcurrent Protection Function
(OCP)
The IC has the drooping type overcurrent protection
(OCP) circuit. The overcurrent protection circuit detects
the peak current of the switching transistor. When the
peak current exceeds the set value, the current is limited
by forcibly shortening the on-time of the transistor and
reducing the output voltage. When the output voltage
decreases further to 50% of the rated value, the switching
frequency is decreased to about 30 kHz. As a result, the
current increase at the low output voltage is suppressed.
When the overcurrent state is released, the output voltage
restarts automatically.
Output
Voltage
(1)
td =
0.7 × C3
20 × 10−6
(2)
tS =
VOUT × 0.9 × C3
VIN × 20 × 10−6
(3)
Where:
td is delay time (s),
tS is rising time (s),
VOUT is output voltage (V), and
VIN is input voltage (V).
Oscillation frequency
decreases at this point
VIN
VOUT
td
Output Current
Figure 10-5.
Overcurrent Protection Characteristics
tSS
Figure 10-7.
10.4. Thermal Shutdown (TSD)
The thermal shutdown (TSD) circuit of the IC detects
the junction temperature of the IC. When the junction
temperature exceeds the set value, the TSD turns off the
output by stopping the output transistor. When the
junction temperature drops for about 15 °C from the
thermal shutdown set value, the TSD automatically
restarts the normal operation.
Output Voltage
Restart Set
Temperature
Protection Set
Temperature
Junction Temperature
Figure 10-6.
tS
Soft Start Waveform
U1
SS 5
GND
3
Figure 10-8.
C3
Soft Start Function
The voltage cannot be externally applied because the
SS pin is pulled up to the internal power supply. Leave
the SS pin open if the soft start function is not used.
Increasing the capacitance of C3 increases the
discharging time at input voltage off. A capacitor of ≤
10 μF should be used.
When the IC operates in discontinuous conduction
mode, the rising time, tS, in actual operation may be
shorter than the calculated value.
Thermal Shutdown Characteristics
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SI-8000SD
10.6. Output On/Off Function
Output can be turned on/off using the SS pin. To use
on/off function, connect a transistor as shown in Figure
10-9. When the SS pin voltage decreases to be VSSL or
lower, the output is stopped.
U1
SS 5
GND
3
Figure 10-9.
On/Off Function
The soft start function can be used in combination with
on/off function by connecting a transistor and a capacitor
as shown in Figure 10-10. In this case, the discharge
current of C3 flows through the transistor for on/off
function. Therefore, protection such as current limiting is
required when the capacitance of C3 is large.
U1
GND
SS 5
C3
3
Figure 10-10.
Soft Start Function, On/Off Function
The voltage cannot be externally applied because the
SS pin is pulled up to the internal power supply. Leave
the SS pin open if the soft start function is not used.
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11. Design Notes
Low Inductance
11.1. Selecting External Components
11.1.1. Inductor, L1
a)
An inductor should be for switching regulator
Do not use an inductor for noise filter because it has
a large loss.
b) Rated current
The inductor rated current must be larger than the
maximum load current according to your application.
When the load current exceeds the rated current of
the inductor, the inductance decreases significantly,
resulting in saturation. Note that in this state, the
high frequency impedance decreases and an
excessive current flows.
c)
Low noise
In the open magnetic circuit core such as drum type,
the peripheral circuit may be significantly affected
by noise because the magnetic flux passes outside
the coil. It is recommended to use a closed magnetic
circuit core coil such as a toroidal type, EI type, or
EE type.
d) Inductance value should be appropriate
The larger the inductance of the choke coil, the
larger the external size of the coil. On the other hand,
the ripple current flowing through the coil decreases
and the output ripple voltage also decreases (see
Figure 11-1).
The smaller the inductance, the larger the peak
current that flows through the switching transistor or
diode. Thus, the loss increases and the ripple voltage
also increases (see Figure 11-2).
High Inductance
COUT
Figure 11-2.
The inductor, L, supplies the current to the load side at
switching transistor turn-off. For the regulator stable
operation, it is required to avoid saturating the inductor
and excessive self-heating. The following are the key
considerations and the guidelines for selecting an
inductor.
Small Ripple Voltage, Current
COUT
Large Ripple Voltage, Current
Ripple Voltage and Current (Low
Inductance)
Inductance is calculated by the Equation (4).
L=
(VIN − VOUT ) × VOUT
∆IL × VIN × f
(4)
In the Equation, (4), ΔIL shows the ripple current value
of the choke coil, and the reference value is set as
follows:
● When the output current in your application is close to
the maximum rating (3 A): 0.2 to 0.3 times the output
current
● When the output current in your application is
approximately 1 A or less: 0.3 to 0.4 times the output
current
For example, when VIN = 25 V, VOUT = 5 V,
ΔIL = 0.5 A, and f = 60 kHz, L is calculated as follows:
L=
(25 − 5) × 5
≒ 133 μH
0.5 × 25 × 60 × 103
Thus, the inductor of about 130 μH should be selected.
11.1.2. Input Capacitor, CIN
The input capacitor, CIN, operates as a bypass
capacitor for the input circuit. CIN compensates for the
voltage drop in the input side by supplying a steep
current at switching to the regulator. Therefore, CIN
should be placed as close as possible to the IC. When the
smoothing capacitor of AC rectifier circuit is in the input
circuit, the smoothing capacitor can also be used as the
input capacitor.
The following are the key considerations and the
guidelines for selecting CIN.
a) Within the rated voltage
b) Within the allowable ripple current
Figure 11-1. Ripple Voltage and Current
(High Inductance)
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for selecting COUT.
U1
IIN
VIN
IL
1 VIN
L1
Ripple current
GND
CIN
Ripple current
3
ESR
IP
D = TON / T
The ripple current of the output capacitor is
equal to the ripple current of the choke coil and
does not change even if the load current
increases or decreases.
As the load current increases, the ripple
current of the input capacitor increases.
Figure 11-3.
Figure 11-4.
CIN Current Flow
Exceeding the rated voltage or the allowable ripple
current or using without considering the derating may
cause abnormal oscillation of the switching regulator as
well as shorten the life of the capacitor. Therefore, select
CIN with sufficient margin for the rated voltage and
allowable ripple current. The ripple effective current,
IRMS, flowing through the input capacitor is calculated by
Equation (5).
IRMS ≈ 1.2 ×
VOUT
× IOUT
VIN
5
× 3 = 0.9 A
20
Thus, select a capacitor that has an allowable ripple
current of > 0.9 A.
11.1.3. Output Capacitor, COUT
The output capacitor, COUT, operates as an LC lowpass filter along with the inductor, L1, and operates as a
smoothing capacitor for switching output. The output
capacitor is charged and discharged with a current equal
to the ripple current of the choke coil, ΔI L. Therefore, as
in the input capacitor, CIN, COUT is selected with
sufficient margin and equivalent series resistance (ESR)
for the rated voltage and allowable ripple current. The
following are the key considerations and the guidelines
COUT Current Flow
● Allowable ripple current
The ripple effective current of the output capacitor is
calculated by Equation (6).
IRMS =
∆IL
(6)
2√3
For example, when ΔIL is 0.5 A, IRMS is calculated as
follows:
(5)
For example, when IOUT = 3 A, VIN = 20 V, and
VOUT = 5 V, IRMS is calculated as follows:
IRMS ≈ 1.2 ×
ΔIL
0
T
IOUT
COUT current waveform
IV
TON
RL
COUT
CIN current waveform
0
VOUT
IRMS =
0.5
2√3
≈ 0.14 A
Thus, select a capacitor that has an allowable ripple
current of > 0.14 A.
● Equivalent series resistance (ESR)
Select an appropriate value for ESR for stable
operation. If the ESR is too large, the output ripple
voltage increases, and abnormal oscillation may be
caused. On the other hand, if the ESR is too small, the
phase margin becomes insufficient. The output ripple
voltage is determined by the product of the inductor
ripple current, ΔIL (= COUT charge/discharge current) and
ESR. For stable operation, the output ripple voltage
should be 0.5% to 2% of the output voltage. The output
ripple voltage is calculated using equations (7) and (8).
ESR changes with temperature. Note that the ESR
decreases at high temperatures.
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SI-8000SD
VRIP
11.1.5. Spike Noise Reduction
(VIN − VOUT ) × VOUT
≈
× ESR
L1 × VIN × f
(7)
VRIP ≈ ∆IL × ESR
(8)
If the ESR is too small (about 10 mΩ to 30 mΩ or
less), the phase delay becomes large and abnormal
oscillation may occur. Do not use tantalum capacitors
and monolithic ceramic capacitors alone for COUT as they
have low ESR. When used at low temperature (0 °C or
less), connecting a tantalum capacitor or a laminated
ceramic capacitor in parallel with the electrolytic
capacitor is effective in reducing the output ripple
voltage. In order to further reduce the output ripple
voltage, it is effective to add an LC filter to configure a
pi filter (see Figure 11-5). When an LC filter is added,
connect the point A to the VOS pin so that point A in
Figure 11-5 is the output voltage detection point. If point
A is not set as the output voltage detection point,
abnormal oscillation may occur.
To reduce spike noise, add a noise reduction circuit
between the input and output of the IC and both ends of
the freewheeling diode, D1. Note that the efficiency is
decreased.
When measuring spike noise with an oscilloscope,
connect the probe to the root of the output capacitor with
the shortest probe lead wire. If the probe ground lead
wire is long, the spike noises may be measured
abnormally large because the lead wire acts as an antenna.
0 Ω to 20 Ω 100 pF to 3000 pF
U1
1 VIN
SW 2
0 Ω to 20 Ω
GND
3
D1
Figure 11-6.
100 pF to 4000 pF
Spike Noise Reduction
A
U1
1 VIN
L2
L1
SW 2
GND VOS 4
3
D1
COUT
COUT2
Figure 11-5. Pi Filter
(L2: 20 μH, COUT2: 200 μF)
The output capacitor should be placed as close as
possible to the IC.
Figure 11-7.
Without Noise Reduction Circuit
11.1.4. Freewheeling Diode, D1
The freewheel diode is used to release the energy
stored in the inductor at switching off. Be sure to use a
Schottky diode for the freewheeling diode. If a diode
with a long recovery time and a large forward voltage,
such as a general-purpose rectifier diode, is used, a
reverse voltage is applied to the IC, which may damage
the IC.
The voltage output from the SW pin is close to the
input voltage. Therefore, use a freewheeling diode whose
reverse breakdown voltage is higher than the input
voltage. Do not add ferrite beads to the freewheeling
diode.
Figure 11-8.
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With Noise Reduction Circuit
15
SI-8000SD
11.1.6. Reverse Biasing Protection
CIN, COUT
For the applications where the output pin voltage is
higher than the input pin voltage (e.g., battery charger),
add a diode for reverse bias protection between the input
and output.
CIN, COUT
Improper Pattern Example
Protection Diode
Figure 11-11.
Proper Pattern Example
Pattern Example
U1
1 VIN
Figure 11-9.
SW 2
Addition of Reverse Bias Protection
Diode
11.2. PCB Layout
11.2.1. High Current Line
Traces where the switching current flows (bold line in
Figure 11-10) should be as wide and short as possible.
L1
VIN
1 VIN
CIN
U1
VOUT
SW 2
VOS 4
COUT
GND
3
D1
GND
GND
Figure 11-10.
High Current Line
11.2.2. Input/ Output Capacitor
The input capacitor, CIN, and the output capacitor,
COUT, must be placed as close as possible to the IC.
When CIN and COUT are far from the IC, it may cause
poor regulation or abnormal oscillation due to increased
switching ripple.
When a smoothing capacitor for the AC rectifier
circuit is in the input side, the smoothing capacitor can
also be used as the input capacitor. When the input
smoothing capacitor and the IC are distant, connect an
input capacitor separated from the smoothing capacitor.
Since the large current is charged and discharged to the
input/output capacitor at high speed, the lead wire should
be as short as possible. The pattern of the capacitor
should also be the shortest.
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SI-8000SD
11.3. Operational Waveforms Confirmation
Whether the switching operation is normal can be
confirmed by the waveform between the SW and GND
pins of the IC. Figure 11-12 shows examples of
waveforms in normal operation and abnormal oscillation.
When the load current is large, the IC operates in
continuous conduction mode. In continuous conduction
mode, the period when the current through inductor
becomes zero does not occur. The switching waveform
has the shape of a normal square wave (waveform 1).
When the load current is small, the IC operates in
discontinuous conduction mode. In discontinuous
conduction mode, the period when the current through
inductor becomes zero occurs. The damped oscillation
occurs in the switching waveform, which is normal
operation (waveform 2).
If the IC and CIN, COUT are distant from each other,
abnormal on/off time of switching is disturbed, and
abnormal oscillation occurs as shown in waveform 3 and
waveform 4.
1. Normal operation (continuous conduction mode) 2. Normal operation (discontinuous conduction mode)
異常発振動作（C
が離れている場合）
3. Abnormal
oscillation IN
(when
CIN is distant)
Figure 11-12.
異常発振動作（C
が離れている場合）
4. Abnormal
oscillationOUT
(when
COUT is distant)
Waveform Examples
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SI-8000SD
11.4. Thermal Design
Generally, the heat dissipation of an IC depends on the
size and material of the board and the copper area. To
improve the thermal performance, the copper area of the
part where the backside of the IC is soldered should be as
large as possible.
Figure 13-13 shows the thermal derating of the IC.
When using the IC, ensure a sufficient margin.
Follow the procedure below to design heat dissipation.
(1) Measure the maximum ambient temperature,
TA(MAX) of the IC.
(2) PD(MAX) is calculated by changing the input/output
conditions and checking the power dissipation, PD.
PD is calculated by Equation (9).
Junction-to-Ambient Thermal Resistance, θJ-A (°C/W)
100
VO
PD = VO × IO (
− 1) − VF × IO (1 −
)
η
VIN
Where:
VOUT is the output voltage
VIN is the input voltage
IOUT is the output current
η is the efficiency (%) (calculated by Figure 13-1 and
Figure 13-7)
VF is D1 forward voltage
(3) Determine the copper area by confirming the
intersection of ambient temperature and power
dissipation by the thermal derating characteristics
shown in Figure 13-13.
For reference, Figure 11-13 shows the relationship
between the copper area and thermal resistance of a
single-sided copper foil board, FR-4.
(9)
Glass-epoxy Board (40 mm × 40 mm)
Copper Area (mm2)
Figure 11-13.
Thermal Resistance - Copper Area Reference Characteristics
(Single-sided Copper Foil Board, FR-4)*
*
Limited by the condition of the input voltage and output current because the power dissipation of the IC package is
3 W.
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SI-8000SD
12. Pattern Layout Example
Connect the ground traces to the GND pin at a single point. Place control components near the IC with a minimal
length of PCB traces.
Figure 12-1.
Pattern Layout Example
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SI-8000SD
13. Typical Characteristics
13.1. SI-8033SD
Efficiency, η (%)
Output Voltage, VOUT (V)
Unless specifically noted, TA = 25 °C.
Output Current, IOUT (A)
Output Current, IOUT (A)
Figure 13-1.
Efficiency
Figure 13-2.
Overcurrent Protection Characteristics
Output Voltage, VOUT (V)
Output Voltage, VOUT (V)
VIN = 15 V, IOUT = 0 A
Input Voltage, VIN (V)
Figure 13-3.
Rising Characteristics
Ambient Temperature, TA (°C)
Figure 13-4.
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Thermal Shutdown Characteristics
20
Output Voltage, VOUT (V)
VIN = 15 V, IOUT = 1 A
Frequency (kHz)
Output Voltage, VOUT (V)
Efficiency, η (%)
SI-8000SD
Ambient Temperature, TA (°C)
Output Current, IOUT (A)
Figure 13-5.
Load Regulation
Figure 13-6.
Temperature Characteristic
13.2. SI-8050SD
Efficiency, η (%)
Output Voltage, VOUT (V)
Unless specifically noted, TA = 25 °C.
Output Current, IOUT (A)
Output Current, IOUT (A)
Figure 13-7.
Efficiency
Figure 13-8.
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Overcurrent Protection Characteristics
21
SI-8000SD
Output Voltage, VOUT (V)
Output Voltage, VOUT (V)
VIN = 20 V, IOUT = 0 A
Ambient Temperature, TA (°C)
Input Voltage, VIN (V)
Rising Characteristics
Figure 13-10.
Thermal Shutdown Characteristics
VIN = 20 V, IOUT = 1 A
Output Current, IOUT (A)
Figure 13-11.
Load Regulation
Output Voltage, VOUT (V)
Frequency (kHz)
Output Voltage, VOUT (V)
Efficiency, η (%)
Figure 13-9.
Ambient Temperature, TA (°C)
Figure 13-12.
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Temperature Characteristic
22
SI-8000SD
13.3. Thermal Derating Curve
Allowable Power Dissipation, PD (W)
Copper area
40 mm × 40 mm (θJ-A = 33.3 °C/W)
20 mm × 40 mm (θJ-A = 37 °C/W)
20 mm× 20 mm (θJ-A = 44 °C/W)
10 mm × 10 mm (θJ-A = 53 °C/W)
Ambient Temperature, TA (°C)
Figure 13-13.
Thermal Derating
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SI-8000SD
Important Notes
● All data, illustrations, graphs, tables and any other information included in this document (the “Information”) as to Sanken’s
products listed herein (the “Sanken Products”) are current as of the date this document is issued. The Information is subject to any
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please put your signature, or affix your name and seal, on the specification documents of the Sanken Products and return them to
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equipment and its control systems, traffic signal control systems or equipment, disaster/crime alarm systems, various safety
devices, etc.), you must contact a Sanken sales representative to discuss the suitability of such use and put your signature, or affix
your name and seal, on the specification documents of the Sanken Products and return them to Sanken, prior to the use of the
Sanken Products. The Sanken Products are not intended for use in any applications that require extremely high reliability such as:
aerospace equipment; nuclear power control systems; and medical equipment or systems, whose failure or malfunction may result
in death or serious injury to people, i.e., medical devices in Class III or a higher class as defined by relevant laws of Japan
(collectively, the “Specific Applications”). Sanken assumes no liability or responsibility whatsoever for any and all damages and
losses that may be suffered by you, users or any third party, resulting from the use of the Sanken Products in the Specific
Applications or in manner not in compliance with the instructions set forth herein.
● In the event of using the Sanken Products by either (i) combining other products or materials or both therewith or (ii) physically,
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such uses in advance and proceed therewith at your own responsibility.
● Although Sanken is making efforts to enhance the quality and reliability of its products, it is impossible to completely avoid the
occurrence of any failure or defect or both in semiconductor products at a certain rate. You must take, at your own responsibility,
preventative measures including using a sufficient safety design and confirming safety of any equipment or systems in/for which
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