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SI-8000HFE
Application Note
Chopper Type Switching Regulator IC
SI-8000HFE/HD Series
July 1,2015 Rev.4.0
SANKEN ELECTRIC CO., LTD.
SI-8000HFE/HD
---
Contents
---
1. General Description
1-1 Features
----------
3
1-2 Applications
----------
3
1-3 Type
----------
3
2-1 Package Information
----------
4
2-2 Ratings
----------
6
2-3 Circuit Diagram
----------
7
3-1 PWM Output Voltage Control
----------
8
3-2 Overcurrent Protection / Thermal Shutdown
----------
9
2. Specification
3. Operational Description
4. Cautions
4-1 External Components
---------- 11
4-2 Pattern Design Notes
----------
15
4-3 Operation Waveform Check
----------
18
4-4 Power Supply Stability
----------
19
4-5 Thermal Design (SI-8008HFE)
----------
23
4-6 Thermal Design (SI-8008HD)
----------
25
5-1 Soft Start
----------
28
5-2 Output ON / OFF Control
----------
29
5-3 Spike Noise Reduction
----------
29
5-4 Reverse Bias Protection
----------
30
6. Typical Characteristics
----------
31
7. Terminology
----------
33
5. Applications
2
SI-8000HFE/HD
1. General Description
The SI-8008HFE is a chopper type switching regulator IC which is provided with various functions
required for the buck switching regulator and protection functions. By using six external components, a
highly efficient switching regulator can be composed.
The SI-8008HD is a surface mounting (T0263-5) version of the SI-8008HFE.
● 1-1 Features
-
Compact size and large output current of 5.5 A
The maximum output current of 5.5 A for the outline of TO220F class
-
High efficiency of 83% (VIN = 15V/IO = 3A)
Heat dissipation is small due to high efficiency to allow for the downsizing of a heat sink.
-
Six external components
The regulator can be composed of input / output capacitor, diode, coil and resistors of Vout
setting.
-
Internal adjustment of output voltage and phase compensation having been done in production
Troublesome adjustment of output voltage and phase compensation by means of external
components is no longer required.
-
Reference oscillation by a built-in timing capacitor
No external capacitor for setting the oscillation frequency is required.
-
Built-in functions for overcurrent and thermal shutdown
A current limiting type protection circuit against overcurrent and overheat is built in. (automatic
restoration type)
-
Soft start function (capable of ON/OFF output)
By adding an external capacitor, it is possible to delay the rise speed of the output voltage.
ON/OFF control of the output is also possible.
-
No insulation plate required
No insulation plate is required, when it is fitted to the heat sink, because it is of full molding type.
● 1-2 Applications
For on-board local power supplies, power supplies for OA equipment, stabilization of secondary output
voltage of regulator and power supply for communication equipment
● 1-3 Type
-
Type: Semiconductor integrated circuits (monolithic IC)
-
Structure: Resin molding type (transfer molding)
3
SI-8000HFE/HD
2. Specification
● 2-1 Package Information
●Pin Assignment
1:IN
2:SW
3:GND
4:ADJ
5:SS
●製品質量:約 2.3g
Products Weight:Approx.2.3g
● External Terminal Processing:
Sn-3Ag-0.5Cu dip
(January to September) by Arabic number and
October to December by
O (October), N (November) and D (December)
4
INVI
4-[1.70±0.25]
4.
OS
5.
2.
3.
1.
N
SSS.S
ADJV
SWOUT
GND
PIN assignments
端子配列
5-0.80±0.10
φ 1.50 Dp : ±0.20
9.20±0.20
4.90±0.20
(15°)
15.30±0.30
(0.50)
(R0.30)
3-(R0.30)
4.50±0.20
PIN assignments
1. IN
2. SW
3. GND
4. ADJ
5. SS
(3°)
(3°)
2.00±0.10
(0.75)
9.90±0.20
15.30±0.30
0~6°
2.54
±0.30
(R0.30)
2.40±0.20
(3°)
+0.15
-0.10
+0.10
-0.05
0.10
1.30
(4.60)
(0.40)
5-0.80±0.10
2x(R0.45)
(4.40)
(8.00)
4-[1.70±0.25]
9.20±0.20
(6.80)
Notes:
1) Dimensions do not include molding burr.
) are shown
2) Figures in parentheses (
only for reference.
3) Figures in parentheses [ ] are dimensions
after lead forming.
4) Backside bumps: 0.8 mm at maximum
5) Unit: mm
(1.75)
10.00±0.20
SI-8000HFE/HD
SI-8008HD (surface mount: TO263-5) Package Information
Products Weight: Approx.1.48g
5
4.90±0.20
SI-8000HFE/HD
●2-2 Ratings
2-2-1 Absolute Maximum Ratings
Parameter
Symbol
Rating
Unit
Input Voltage
VIN
43 *1
V
Allowable Power Dissipation in Infinite Radiation
Pd1
25
W
Allowable Power Dissipation without Heat sink
Pd2
1.72
W
Junction Temperature
Tjmax
150 *1
°C
Storage Temperature
Tstg
-40 ~ +150
°C
In the SI-8008HD, only allowable power dissipations are different from the above values.
*1. Since the thermal shutdown is provided, it may be operated at Tj > 130°C
2-2-2 Recommended Conditions
Parameter
Symbol
SI-8008HFE/HD
Unit
DC Input Voltage
VIN
Vo+3v - 40
Output Current
IO
0 - 5.5
A
Junction Temperature in Operation
Tjop
-30 - +125
°C
*2
V
*2. VIN = 4.5V or Vout +3V, whichever higher value is recommended.
(Ta=25°C, Vo=5V, R1=4.2kΩ, R2=0.8kΩ)
2-2-3 Electrical Characteristics
Ratings
Parameter
Setting Reference Voltage
Reference Voltage Temperature Coefficient
Unit
Test Condition
Symbol
VADJ
MIN
TYP
MAX
0.784
0.800
0.816
ΔVADJ/ΔT
V
mV/°C
±0.1
VIN=15V, IO=1A
VIN=15, IO=1A,Tc=0 100℃
Efficiency *3
η
83
%
VIN=15V, IO=3A
Operation Frequency
fo
150
kHz
VIN=15V, IO=3A
Line Regulation
VLine
60
80
mV
VIN=10 - 30V, IO=3A
Load Regulation
VLoad
20
50
mV
VIN=15V, IO=0.2 - 5.5A
6.5
7.5
A
0.5
V
30
μA
VIN=15V,VSS=0V
mA
VIN=15V,IO=0A
μA
VIN=15V
Overcurrent Protection Start Current
IS
5.6
On/ Off
Low Level Voltage
VSSL
Terminal *4
Flow-out Current at Low Level Voltage
ISSL
10
Circuit Current in Non-operation 1
Iq
6
Circuit Current in Non-operation 2
Iq(off)
200
400
VIN=15V
VSS=0V
6
SI-8000HFE/HD
● 2-3 Circuit Diagram
2-3-1 Internal Equivalent Circuit
SI-8008HFE
VIN
1
SW
IN
C1
5
C2
protection
SS
ON
/
OFF
C3
VOUT
Di
過電流保護
Overcurrent
Overcurren
Protection
PReg
C4
L
2
Latch
ラッチ
&ドラand
イバ
Latch&driver
Driver
リセット
Reset
Reset
R1
発振器
Oscillator
Soft
Start
Oscillator
Comparator
過熱保護
Thermal
コンパレータ
Thermal
Protection
protection
ADJ
4
エラ ーアン プ
Error
amp.
R1
基準電圧
Reference
Reference
Voltage
voltage
GND
3
2-3-2 Typical Connection Diagram
1
VIN
IN
SW
C4
C1
SS
5
GND
3
ADJ 4
C1: 1500μF
L1
2
VO
C3: around 0.1μF
R1
Di
R2
C2
(only in use of soft start function)
C4: 4.7μF
C3(Css)
GND
C2: 1000μF
GND
[RPER11H475K5 (MURATA)]
L1: 100μH
Di: FMB-G16L (Sanken products)
7
SI-8000HFE/HD
3. Operational Description
● 3-1 PWM Output Voltage Control
The SI-8000HF series controls the output voltage by the PWM system and comprises PWM comparator,
oscillator, error amplifier, reference voltage, output transistor drive circuit etc. For the input of the PWM
comparator, the triangular wave output (≈ 150KHz) from the oscillator and the output of the error amplifier
are given.
The PWM comparator compares the oscillator output with the error amplifier output to control to turn on
the switching transistor at the time when the error amplifier exceeds the error amplifier output.
PWM Control Chopper Type Regulator Basic Configuration
VOUT
Switching
Transistor
スイッチングトランジスタ
VIN
PWM
Comparator
PWMコンパレータ
D1
C2
ドライブ回路
Drive Circuit
Error 誤差増幅器
Amplifier
Oscillator
発振器
Reference Voltage
基準電圧
The error amplifier output and oscillator output are compared by the PWM comparator to
generate the rectangular wave signal and this signal is inputted into the drive circuit to drive the
switching transistor.
On the assumption that the output voltage commences to rise, the output of the error amplifier will drop,
because the error amplifier is of inverting type.
As the output of the error amplifier falls down, the time period during which it falls below the triangular
wave level of the oscillator is increased to shorten the ON time of the switching transistor and as a result,
the output voltage is maintained at a certain level.
As described above, the output voltage is controlled by varying the ON time of the switching transistor,
while fixing the switching frequency.
(the higher is Vin, the larger is the ON time of the switching transistor.)
PWM Comparator Operation Diagram
Oscillator
発振器出力
Output
Error Amplifier
誤差増幅器出力
ON
OFF
Output
スイッチングトランジスタ出力
Switching Transistor
Output
8
SI-8000HFE/HD
The rectangular wave output of the switching transistor is smoothed by the LC low pass filter of a
choke coil and capacitor to supply stabilized DC voltage to the load.
● 3-2 Overcurrent Protection / Thermal Shutdown
Output過電流時出力電圧特性
Voltage Characteristics in Overcurrent
Output Voltage
As Vo drops, the oscillating frequency
is lowered.
Output Current
The SI-8000HF series incorporates a current limiting type overcurrent protection circuit. The overcurrent
protection circuit detects the peak current of a switching transistor and when the peak current exceeds the
set value, the ON time of the transistor is compulsorily shortened to limit the current by lowering the output
voltage.
In addition, when the output voltage is lowered, the increase of current at low output voltage is prevented
by dropping linearly the switching frequency to about 30 KHz. When the overcurrent condition is released,
the output voltage will be automatically restored.
Output
Voltage Characteristics in Thermal Shutdown
過熱保護時出力電圧特性
Output
Voltage
出力電圧
Restoration Setting
復帰設定温度
Temperature
Protection Setting Temperature
保護設定温度
Junction Temperature
接合温度
The thermal shutdown circuit detects the semiconductor junction temperature of the IC and when the
junction temperature exceeds the set value (around 150°C), the output transistor is stopped and the output is
turned OFF. When the junction temperature drops from the set value for overheat protection by around
15°C, the output transistor is automatically restored.
9
SI-8000HFE/HD
* Note for thermal shutdown characteristic
This circuit protects the IC against overheat resulting from the instantaneous short circuit, but it should be
noted that this function does not assure the operation including reliability in the state that overheat
continues due to long time short circuit.
10
SI-8000HFE/HD
4. Cautions
● 4-1 External Components
4-1-1 Choke coil L1
The choke coil L1 plays a main role in the chopper type switching regulator. In order to maintain the stable
operation of the regulator, such dangerous state of operation as saturation state and operation at high
temperature due to heat generation must be avoided.
The following points should be taken into consideration for the selection of the choke coil.
a) The choke coil should be fit for the switching regulator.
The coil for a noise filter should not be used because of large loss and generated heat.
b) The inductance value should be appropriate.
The larger is the inductance of the choke coil, the less is the ripple current flowing across the choke coil,
and the output ripple voltage drops and as a result, the overall size of the coil becomes larger.
On the other hand, if the inductance is small, the peak current flowing across the switching transistor and
diode is increased to make the ripple voltage higher and this operation state is not favorable for maintaining
the stable operation.
When the ripple voltage of the output voltage becomes too high, the operation is likely to be unstable and
waveform skipping or jitter may be generated.
It is recommended that the ripple voltage of the output voltage should be 1% or less of the set output
voltage.
The ripple voltage of the output voltage is determined as the product of ΔIL and ESR (equivalent series
resistance) of the output capacitor, therefore when the ESR is too large, a problem may happen. The ESR
should also be taken into account as well as the selection of the output capacitor.
Vout ripple = ΔIL x ESR of output capacitor
Large
Inductance
インダクタンス大
Small
Ripple Voltage/
リップル電圧・電流小
Current
C2
The larger is the inductance, the smaller will be
the ripple current/voltage. But the outer size of the
coil becomes larger.
Small
Inductance
インダクタンス小
Large
Ripple Voltage/
リップル電圧・電流大
Current
C2
The smaller is the inductance, the larger will be
the ripple current/voltage.
Although the outer size of the coil is smaller, the
operation is likely to be unstable.
The inductance value shown in the specifications should be considered as a reference value for the stable
operation and the appropriate inductance value can be obtained by the equation (1).
However, it should be noted that the ripple value should also be adjusted to be appropriate.
11
SI-8000HFE/HD
ΔIL shows the ripple current value of the choke coil and the lower limit of inductance is set as described in
the following.
-
In the case that the output current to be used is nearly equal to the maximum rating (5.5A) of the
SI-8000H: output current × 0.1 or so
-
In the case that the output current to be used is approximately 3A or less: output current × 0.3 - 0.4
L1 
(VIN  VOUT )  VOUT
IL  VIN  f
---(1)
For example, where VIN = 25V, VOUT = 5V, ΔIL = 0.5A, frequency = 150 KHz,
L1 
(25  5)  5
≒ 53.3uH
0.5  25  150  10 3
As shown above, the coil of about 54μH may be selected.
However, it is to be noted that the peak current of the switching transistor is increased depending on the
calculated inductance value.
Therefore, the peak current detection system is adopted for overcurrent detection and in this case, the
overcurrent detection point may become lower.
c) The rated current shall be met.
The rated current of the choke coil must be higher than the maximum load current to be used. When the
load current exceeds the rated current of the coil, the inductance is sharply decreased to the extent that it
causes saturation state at last. Please note that overcurrent may flow since the high frequency impedance
becomes low.
d) Noise shall be low.
In the open magnetic circuit core which is of drum shape, since magnetic flux passes outside the coil, the
peripheral circuit may be damaged by noise. It is recommended to use the toroidal type, EI type or EE type
coil which has a closed magnetic circuit type core as much as possible.
4-1-2 Input CapacitorC1, C4
The input capacitor is operated as a bypass capacitor of the input circuit to supply steep currents to the
regulator during switching and to compensate the voltage drop of the input side. Therefore, the input
capacitor should be placed as close as to the regulator IC.
Even in the case that the rectifying capacitor of the AC rectifier circuit is located in the input circuit, the
input capacitor cannot play a role of the rectifying capacitor unless it is placed near the SI-8000HF.
The selection of C1 shall be made in consideration of the following points:
a) The requirement of withstand voltage shall be met.
b) The requirement of the allowable ripple voltage shall be met.
12
SI-8000HFE/HD
Current Flow of C1
IIN
Current
Waveform of C1
C1電流波形
VIN
1.VIN
Ripple
Current
リップル電流
0
Iv
Ip
C1
Ton
D
T
Ton
T
The ripple current of the input capacitor is increased in accordance with the increase of the load
current.
If the withstanding voltages or allowable ripple voltages are exceeded or used without derating, it is in
danger of causing not only the decreasing the capacitor lifetime (burst, capacitance decrease, equivalent
impedance increase, etc) but also the abnormal oscillations of regulator.
Therefore, the selection with sufficient margin is needed.
The effective value of ripple current flowing across the input capacitor can be obtained by the following
equation (2):
Irms  1.2 
Vo
 Io
Vin
---(2)
For instance, where VIN = 20V, Io = 3A and Vo= 5V,
Irms  1.2 
5
 3  0.9 A
20
Therefore, it is necessary to select the capacitor with the allowable ripple current of 0.9A or higher.
In addition to the electrolytic capacitor C1, either a ceramic capacitor with the high frequency characteristic
or a film capacitor C4 is required.
For the film capacitor, 0.47μF is recommended, while 4.7μF is recommended for the ceramic capacitor in
which the capacitance is likely to be lowered due to applied voltage.
It is important to lay out C4 nearer to the IC than C1.
4-1-3 Output Capacitor C2
The output capacitor C2 composes a LC low pass filter together with a choke coil L1 and functions as a
rectifying capacitor of switching output.
The current equivalent to the pulse current ΔIL of the choke coil current is charged and discharged in the
output capacitor.
Therefore, it is necessary to meet the requirements of withstand voltage and allowable ripple current with
sufficient margin like the input capacitor.
13
SI-8000HFE/HD
Current Flow of C2
IL
Vout
L1
Ripple
Current
リップル電流
ESR
Current
Waveform of C2
C2電流波形
Io
0
RL
⊿IL
C2
The ripple current of the output capacitor is equal to the ripple current of the choke coil and does
not vary even if the load current increases or decreases.
The ripple current effective value of the output capacitor is obtained by the equation (3).
Irms 
IL
2 3
---(3)
When ΔIL = 0.5A,
Irms 
0.5
≒ 014
. A
2 3
Therefore a capacitor having the allowable ripple current of 0.14A or higher is required.
In addition, the output ripple voltage Vrip of the regulator is determined by a product of the pulse current
ΔIL of the choke coil current (= C2 charging/discharging current) and the equivalent series resistance ESR
of the output capacitor.
Vrip  IL  C2ESR
---(4)
It is therefore necessary to select a capacitor with low equivalent series resistance ESR in order to lower the
output ripple voltage. As for general electrolytic capacitors of same product series, the ESR shall be lower,
for the products of higher capacitance with same withstand voltage, or with higher withstand voltage
(almost proportional to larger externals) with same capacitance.
When ΔIL = 0.5A, Vrip = 40mV,
C2esr  40  05
.  80m
As shown above, a capacitor with the ESR of 80mΩ or lower should be selected. In addition, since the ESR
varies with temperature and increases at low temperature, it is required to examine the ESR at the actual
operating temperatures. It is recommended to contact capacitor manufacturers for the ESR value since it is
peculiar to capacitors.
However, if the ESR of the output capacitor is too low (10 - 30mΩ or lower), the phase margin within the
feedback loop of the regulator will be short to make the operation unstable. Therefore, it is not appropriate
that a tantalum capacitor or a laminated ceramic capacitor is used for the output capacitor as an
14
SI-8000HFE/HD
independent component. However, connecting a tantalum capacitor or a laminated ceramic capacitor in
parallel with an electrolytic capacitor is effective in reducing the output ripple voltage only when it is used
at low temperature (< 0°C).
4-1-4 Flywheel Diode D1
The flywheel diode D1 is to discharge the energy which is stored in the choke coil at switching OFF.
For the flywheel diode, the Schottky barrier diode must be used. If a general rectifying diode or fast
recovery diode is used, the IC may be destroyed by applying reverse voltage due to the recovery and ON
voltage.
In addition, since the output voltage from the SW terminal (pin 2) of the SI-8000HF series is almost
equivalent to the input voltage, the flywheel diode with the reverse withstand voltage of the input voltage or
higher should be used.
It is recommended not use the ferrite bead for the flywheel diode.
● 4-2 Pattern Design Notes
4-2-1 High Current Line
Since high current flows in the bold lines in the connection diagram, the pattern should be as wide and
short as possible.
SI-8008HFE
R1
R2
4-2-2 Input / Output Capacitor
The input capacitor C1 and the output capacitor C2 should be placed to the IC as close as possible. If the
rectifying capacitor for AC rectifier circuit is on the input side, it can be used as an input capacitor.
However, if it is not close to the IC, the input capacitor should be connected in addition to the rectifying
capacitor.
Since high current is discharged and charged through the leads of input/output capacitor at high speed, the
leads should be as short as possible.
A similar care should be taken for the patterning of the capacitor.
C1,C2
Improper Pattern Example
C1,C2
Proper Pattern Example
15
SI-8000HFE/HD
4-2-3 ADJ Terminal (Output Voltage Set-up)
The ADJ terminal is a feedback detection terminal for controlling the output voltage. It is recommended to
connect it as close as possible to the output capacitor C2. When they are not close, the abnormal oscillation
may be caused due to the poor regulation and increase of switching ripple. The output voltage set-up is
achieved by connecting R1 and R2. IADJ should be set to be around 1mA. (The IADJ lower limit is 0.8mA,
and the upper limit is not defined. However, it is necessary to consider that the consumption current shall
increase according to the IADJ value, resulting in lower efficiency.)
R1, R2 and output voltage are calculated from the following equations:
IADJ = VADJ / R2
R1 = (Vo-VADJ) / IADJ
*VADJ = 0.8V ±2%
R2 = VADJ / IADJ
VOUT = R1× (VADJ/R2) + VADJ
The layout of voltage detection line should be made in
compact form for stable operation in order to avoid the effect
of switching noise.
IADJ
が重要です。
-
R2 should be connected for the stable operation when set to Vo = 0.8V.
-
It is recommended to set the output voltage to 8% or higher of the input voltage.
Constants and variation range are shown in the following table in the case that the output voltage is set for
the output voltage setting resistors R1 and R2 by the resistance constants of existing accuracy of 1% and
0.5%,
16
SI-8000HFE/HD
Table of constants for R1/R2 Vo setting of SI-80008HFE
SI-8008HFE R1,R2Vo設定定数表
Target
目標Vout(V)
Resistance
Constants of Accuracy of 1%
1%精度抵抗定数での構成
Vout (V)
R1(Ω )
1.2
402
1.8
1000
2.5
1690
3.3
2490
5
4220
9
8250
12
11000
24
23200
Resistance
Constants of Accuracy of 0.5%
0.5%精度抵抗定数での構成
Accuracy (%)
Accuracy (%)
R2(Ω ) Calculated
計算精度(%)
R1(Ω ) R2(Ω ) Calculated
計算精度(%)
+2.61
+2.26
806
402
806
-2.73
-2.41
+2.72
+2.72
806
1010
806
-3.48
-2.41
+4.15
+2.64
787
1690
796
-2.64
-2.73
+2.67
+2.86
806
2490
796
-4.31
-2.67
+3.50
+2.68
806
4170
796
-3.85
-3.00
+3.75
+2.95
806
8160
796
-3.89
-2.88
+3.77
+2.58
787
11100
796
-3.96
-3.27
+3.25
+3.11
806
23400
806
-4.57
-2.84
The wiring of ADJ terminal, R1 and R2 that run parallel to the flywheel diode should be avoided, because
switching noise may interfere with the detection voltage to cause abnormal oscillation. It is recommended
to implement the wiring from the ADJ terminal to R2 as short as possible.
-
Mounting Board Pattern Example
Component Insertion Type (SI-8008HFE)
Surface Mount Type (SI-8008HD)
SI-8008HFE
C4
C1
Top View: Silk Print Side
17
SI-8000HFE/HD
● 4-3 Operation Waveform Check
It can be checked by the waveform between the pin 2 and 3 (SW - GND) of the SI-8000H whether the
switching operation is normal or not.
The examples of waveforms at normal and abnormal operations are shown below:
1. Normal Operation (continuous area)
2. Normal Operation (discontinuous area)
3. When C1 and C4 is distant from IC
4. When C2 is distant from IC
The continuous area is an area where the DC component of the triangular wave is superimposed on the
current flowing across the choke coil and the discontinuous area is an area where the current flowing across
the choke coil is intermittent (a period of zero current may happen.) because the current flowing across the
choke coil is low.
Therefore, when the load current is high, the area is a continuous area and when the same current is low,
the area is a discontinuous area.
In the continuous area, the switching waveform is formed in the normal rectangular waveform (waveform
1) and in the discontinuous area, damped oscillation is caused in the switching waveform (waveform 2), but
this is a normal operation without any problem.
In the meantime, when the IC is far from C1, C4 or C2 jitter which disturbs the ON - OFF time of
switching will happen as shown in the waveforms (3, 4). As described above, C1 and C4 should be
connected close to the IC.
18
SI-8000HFE/HD
● 4-4 Power Supply Stability
4-4-1 Phase Margin
This block diagram shows that the chopper type regulator is a negative feedback amplifier which controls
the output voltage by constantly comparing with the output voltage and the reference voltage which is set in
advance. Therefore, it has a negative feedback loop to control the output by detecting the variation of
output voltage with the error amplifier.
L1
Reference
Voltage
基
準
電
圧
Control
制御部
Block
基
準
電
圧
ESR
Reference
Voltage
-180deg
Negative
Feedback Loop
負帰還ループ
Load
負荷
C2
0deg
The phase within the negative feedback loop is displaced by 180° to negate the variation of the output
voltage, but in the event that the phase is further delayed by 180° in the state that the amplification degree
(gain) is 1 or more, the total phase delay amounts to 360° to deviate from the stable operation zone to cause
abnormal oscillation. This is called Barkhausen oscillation conditions. Therefore, the oscillation conditions
should not be accrued in the actual stabilized power supply.
It is possible to judge whether the Barkhausen oscillation conditions are accrued or not by means of
frequency and gain/phase characteristics of the negative feedback loop. The frequency-gain/phase
characteristics are called Bode diagram.
1-step Differential Amplifier
IN
OUT
Bode Diagram Example
20dB
0dB
9k
1k
-0deg
-45deg
-90deg
Gain
ゲイン
0.1fp
Frequency
周波数
Phase
位相
fp
10fp
In the Bode diagram, the frequency at which the gain is 1 (0 dB) is called gain intersection and the
frequency at which the phase of feedback loop is -180° is called phase intersection.
Unless the phase reaches -180° at the frequency of gain intersection, the oscillation conditions are not met.
In this respect, the phase at gain intersection - (-180°) is equal to the phase at gain intersection + 180° and
this value is used as a margin to -180° which is called phase margin. The more the phase margin is, the less
19
SI-8000HFE/HD
likely the abnormal oscillation is to occur against the variation of environmental conditions such as
input/output conditions and temperature. Therefore, sufficient phase margin should be taken into
consideration in order to maintain the stable operation.
Stability Judgment at Bode Diagram
Gain Characteristics
ゲイン特性
Gainゲイン特性
Characteristics
Gain
Intersection
ゲイン交点
0dB
Phase Characteristics
位相特性
0dB
Gain
Intersection
ゲイン交点
Frequency
周波数
Frequency
周波数
Phase 位相特性
Characteristics
位相余裕
Phase
Margin
(>0)
-180deg
Phase
位相交点
Intersection
位相交点
Phase Intersection
-180deg
Stable
安定な場合
Unstable
不安定な場合
位相余裕
Phase
Margin
(<0)
4-4-2 Phase Characteristics of Regulator IC
The phase characteristics of the chopper type regulator are synthesized by the phase characteristics inside
the regulator IC and that of the LC filter.
The phase characteristics inside the regulator IC are generally determined by the delay time of the control
block and the phase characteristic of the output error amplifier.
Among these two factors, the phase delay due to the delay time of the control block rarely causes problems
in actual use. Therefore, the phase characteristics of the error amplifier are important.
With respect to the compensation of phase characteristics of the output error amplifier, there are two types
of regulator ICs. One is that compensation is made in the IC in advance, while another type is that external
components such as resistors and capacitors are added to the IC for compensation.
In the former case, it is only a matter of selection of the LC filter, but in the latter case, appropriate phase
compensation should be made in accordance with the application of the product.
4-4-3 Phase Characteristics of LC Filter
The phase margin of the chopper type regulator depends largely on the phase characteristics of the LC filter
for output smoothing. The phase characteristic of the LC filter theoretically shows the characteristics of a
secondary delay factor. Resonance is caused at a specific frequency due to the combination of inductance
L1 of coil and of capacitance C2 of the capacitor and at frequency higher than the resonance point, the
20
SI-8000HFE/HD
phase is delayed by 180°at a maximum.
The resonance frequency is expressed as shown in the equation (5):
fLC 
1
---(5)
2 LC
The phase characteristics are 0° if they are lower than the resonance frequency fLC.
The phase characteristics are 180° if they are higher than the resonance frequency fLC.
Accordingly, when the LC filter for output smoothing shows the theoretical phase characteristics, the phase
delay reaches -180° in this filter portion and the phase margin will be zero for this regulator.
However, in the actual LC filter, the phase delay of the LC filter is less than 180° because of influence of
the equivalent series resistance (ESR) of capacitor. Consequently, the phase margin can be secured for the
regulator because of this phase compensation effect of the equivalent series resistance (ESR).
LC Filter
Phase Characteristics
LCフィルタ位相特性
L1
0deg
ESR
VIN
Phase
Delay
位相遅れ
VOUT
C2
ESR High
大
ESR:
ESR:
ESR Low
小
-180deg
ESR 00
ESR:
fLC
周波数
Frequency
Generally speaking, when such capacitors as tantalum capacitors or laminated capacitors are used for the
output LC filter, the phase delay of filters will be large.
Therefore, from the view point of securing the phase margin, use of the electrolytic capacitor is preferable.
4-4-4 Relation of Phase Characteristics of Internal IC and LC Filter
As described above, the phase characteristics of the chopper type regulator is almost determined by the
phase characteristics of the error amplifier and LC filter. In this respect, the relation between these two
characteristics is important.
When the gain lowering commencement frequency of the error amplifier, namely the first pole frequency fp
and the resonant frequency of the LC filter fLC are closer, the phase margin of the regulator is decreased
because of concentrated phase delay. In this respect, the proper distribution of fp and fLC is important.
Normally, the phase delay of error amplifier commences from 0.1 times of the first pole frequency fp.
In order to avoid the concentration of phase delay, the resonant frequency of the LC filter fLC should be
kept to be less than 0.1 times of the first pole frequency fp of the error amplifier.
21
SI-8000HFE/HD
Phase
位相
Phase Characteristics:
Phase Characteristics:
fpとfLCが近い場合の位相特性
when fp and fLC are close
Phase
位相
fpとf
LCが離れている場合の位相特性
when
fp and fLC are distant
fp
fp
増幅部
Amplification
Section
Amplification
増幅部
Section
LC
Filter
LCフィルタ
LC
Filter
LCフィルタ
fLC
-180deg
fLC
-180deg
Synthesized
Characteristics
合成特性
Long位相遅れ大
Phase Delay
Short
Phase Delay
位相遅れ小
合成特性
Synthesized
Characteristics
-180deg
Frequency
周波数
-180deg
Frequency
周波数
Generally, the frequency fp of the chopper type regulator IC is set from several KHz to higher than ten
KHz.
With respect to the constants of LC filters described in the applications of each regulator IC, if the
inductance of coil or capacitance of the capacitor is set to be less than the recommended values, the
resonant frequency fLC of the LC filter may rises to decrease the phase margin. Care should be taken to this
phenomenon.
The constants of peripheral components should be properly selected according to the applications of each
regulator I.C.
22
SI-8000HFE/HD
60
630
50
540
40
450
ゲイン
Gain
30
360
20
270
10
180
0
90
-10
-20
0
位相
Phase
位相(゜)
Phase (°)
Gain (dB)
ゲ イン(dB)
TypicalチョッパーReg
Characteristics
of Gain and Phase
ゲイン、位相特性例
-90
-30
-180
-40
100
1000
Frequency
(Hz)
周波数 (Hz)
-270
10000
● 4-5 Thermal Design (SI-8008HFE)
4-5-1 Calculation of Heat Dissipation
The relation among the power dissipation Pd of regulator, junction temperature Tj, case temperature Tc,
heat sink temperature Tfin and ambient temperature Ta is as follows:
Pd (Power dissipation)
Pd(損失)
Tj:ジャンクション
Junction temperature
(125°C MAX)
Tj
温度
(125℃ MAX)
Chip
チップ
θ jc(接合
-ケース
間熱抵抗)
θjc:
Thermal
resistance
between junction and case 5°C / W
5℃ /W
Case
ケース
Tc: ケース
Case温度(内部
temperatureフレーム
(internal
Tc
温 frame temperature)
度)
放熱器
Heat
sink
θi:
Thermal放熱器間熱抵抗)
resistance between case and heat sink) 0.4 – 0.6°C / W
θ i(ケース-
0.4~ 0.6℃ /W
T
fin:放熱器温度
Heat sink temperature
Tfin
θfin:
Heat sink thermal resistance
θ fin(放熱器熱抵抗)
Ta:
temperature
Ta Ambient
周囲温度
Tj  Tc
---(6)
jc
Tj  Tfin
Pd 
---(7)
jc  i
Pd 
23
SI-8000HFE/HD
Pd 
Tj  Ta
---(8)
jc  i  fin
The TjMAX is an inherent value for each product, therefore it must be strictly observed. For this purpose, it
is required to design the heat sink in compliance with PdMAX, TaMAX (determination of θfin). The heat
derating graphically describes this relation.
The designing of the heat sink is carried out by the following procedure:
1) The maximum ambient temperature Ta MAX in the set is obtained.
2) The maximum power dissipation PdMAX is obtained.
 100 
 VOUT 
Pd  VOUT  Io
 1  Vf  Io1 
 ---(9)
VIN 

 x

* ηx= efficiency (%), Vf= diode forward voltage
3) The size of heat sink is determined from the intersection of the heat derating.
The required thermal resistance of the heat sink can be also calculated. The thermal resistance required for
the heat sink is obtained by the following equation:
i  fin 
Tj  Ta
 jc
Pd
---(10)
An example of heat calculation for using SI-8008HFE under the conditions of VIN = 15V, Io = 4A and Ta =
85°C is shown below. Where efficiency η = 80% , Vf = 0.5V from the typical characteristics,
5
 100 

Pd  5  4  
 1  0.5  4  1   ≒ 3.67W
 80

 15 
125  85
i  fin 
 5 ≒ 5.9゚C / W
2.75
As a result, the heat sink with the thermal resistance of 5.9°C /W or less is required. As described above,
the heat sink is determined, but the derating of 10 - 20% or more is used. Actually, heat dissipation effect
significantly changes depending on the difference in component mounting. Therefore, heat sink
temperature or case temperature should be checked with the heat sink mounted.
The maximum rating Tjmax of the SI-8008HFE is 150°C, but it is recommended to design the heat sink at
TjMAX < 125°C since the thermal shutdown circuit may be operated at 130°C or higher.
4-5-2 Installation to Heat sink
Selection of silicon grease
When the SI-8000HFE is installed to the heat sink, silicon grease should be thinly and evenly coated
between the IC and heat sink. Without coating, thermal resistance θi is significantly increased because of
contact failure due to micro concavity/convexity between the backside of the IC and the surface of the heat
sink to accelerate the heating of the IC, resulting in shorter life of the IC.
In some kind of silicon grease to be used, oil component may be separated to penetrate into the IC,
resulting in the deformation of packages or the adverse effect on built-in elements.
Any other silicon grease than one based on the modified silicon oil shall not be used.
The recommended silicon greases are as follows:
24
SI-8000HFE/HD
Sanken’s recommended silicon greases:
Types
Suppliers
G746
Shin-Etsu Chemical Co., Ltd.
SC102
Toray Silicone Co., Ltd.
YG6260
Momentive Performance Materials Inc.
Tightening torque of fixing screws
In order to keep the thermal resistance between the IC and the heat sink at low level without damaging the
IC package, it is necessary to control the torque of fixing screws in a proper way.
Even if silicon grease is coated, the thermal resistance θi increases if the tightening torque is not enough.
Change rate of
thermal resistance (%)
熱抵抗変化率(%)
For the SI-8008HFE, 58.8 - 68.6Ncm (6.0 - 7.0 kg cm) are recommended.
110
105
100
95
90
0
20
40
60
締め付けトルク(N・cm)
Tightening
Torque (N cm)
80
100
* 1. The change rate of thermal resistance in the case that 58.8N cm (6kg cm) is expressed as
100% is shown above.
* 2. The silicon grease G746 shall be used.
● 4-6 Thermal Design (SI-8008HD)
4-6-1 Calculation of heat dissipation
In the case of the surface mounting type SI-8008HD, the thermal design shall be made below Tjmax in a
similar way to the insertion components as described above, but in the case of surface mounting, the heat is
dissipated toward the copper foil on the mounting board, therefore the thermal design should be made in
consideration of copper foil area, board material and number of copper foil layers.
The stem part of the backside of the SI-8008HD is connected with pin 3 (GND) by the inner frame and heat
dissipation performance is improved by taking the larger GND pattern which is directly connected with the
stem part.
In order to confirm the junction temperature, the temperature of the stem spot shown below should be
measured to calculate the temperature by the following equation.
25
SI-8000HFE/HD
Tj = Tc + Pd x 3°C /W * Tc = Actually measured stem temperature
Temperature measurement point
Junction thermal resistance: 3°C /W
D 特性Current-Power Dissipation
SI-8000H Series IO-PSI-8000Hシリーズ
Output
D Characteristics Io-P
Output Current-Power Dissipasion
10
VIN=8V
9
Power Dissipation (W)
電力損失 PD (W)
Power Dissipation
VIN=15V
8
VIN=30V
7
VIN=40V
6
5
4
3
2
1
0
0
1
2
3
4
5
6
Output
Current
出力電流
Io Io
(A)(A)
Output Current
Io - Pd reference data of the SI-8000H series is shown above.
Since the SI-8008HD is a surface mounting package, heat is radiated to the printed board Cu foil.
Therefore, it may be difficult to consume fully 5.5A from a view point of the heat radiation. Normally 2 3A is consumed and it is assumed that 5.5A may be consumed instantly.
The reference data of thermal resistance in the case that the copper foil area is changed on the single side
glass epoxy board FR4 is shown in the next page.
26
SI-8000HFE/HD
ガラスエポキシ基板上銅箔面積 vs 接合部―周囲温度間熱抵抗(代表値)
Copper area vs Junction to air (Typical)
55
50
45
40
35
30
0
200
400
600
800
1000
1200
1400
1600
1800
27
SI-8000HFE/HD
5. Applications
● 5-1 Soft Start
When a capacitor is connected to terminal 5, the soft start is activated when the input voltage is applied.
Vout rises in relation with the charging voltage of Css. Therefore, the rough estimation is done by the time
constant calculation of Css charging.
The capacitor Css controls the rise time by controlling the OFF period of PWM control. The rise time tss is
obtained approximately by the following equation:
The terminal 5 should be open, when the soft start is not used.
VIN
SI-8008H
SI-8000FF
tss = (Css × VssA) / IssL (sec)
VssA ≈ 2.3V
5.SS
VOUT
Css
Tss
Since the SS terminal is pulled up (3.6V TYP) with the internal power supply of IC, the external voltage
can not be applied.
If Css is high, it takes time to discharge Css after Vin is turned OFF. It is recommended to use the Css with
the value of 10μF or less. When Vin drops, the charges of Css are discharged from the Vin terminal.
SI-8008 HFE
Css vs起動時間
– Start-up Time
SI-8008HFE Css
Vo=5V Co=680uF
Vo=5v設定 Co=680uF
10000
1000
Start-up Time (ms)
起動時間 ms
起動時間実測値
Measured value of start-up time
計算値
Calculated value
100
10
1
0.1
0.001
0.01
0.1
Css
(uF)
Css uF
1
10
28
SI-8000HFE/HD
The reference data of calculated value and actual value of start-up time of CSS are shown above.
If there is no Css or it is extremely low, Vout rises at the time constants charging the output capacitor with
the output current restricted by the overcurrent protection Is.
At CSS = 0. 001μF in the start-up time graph above, time constants charging output capacitors with output
current restricted by overcurrent protection are predominant rather than time constants by Css.
Time constants at output capacitor start-up
t = (Co × Vo) / Is・・・・(at no load)
* The amount of load current is deducted from the Is value at load.
● 5-2 Output ON/ OFF Control
The output ON-Off control is possible using the SS (No.5) terminal. The output is turned OFF when the
terminal 5 voltage falls below VssL (0.5V) by such as open collector. It is possible to use the soft start
together.
Since the soft start terminal has been already pulled up (3.7V TYP), no voltage shall be applied from the
external side.
SI-8000H
SI-8000S,SS
SI-8000H
SI-8000S,SS
5.SS
5.SS
C3
Css
SS+ON/OFF
ON/OFF
● 5-3 Spike Noise Reduction
In order to reduce the spike noise, it is possible to compensate the output waveform of the SI-8000H and
the recovery time of the diode by a capacitor, but it should be noted that the efficiency is also slightly
reduced.
around
10Ω
10Ω 程度
IN
11.VIN
around
1000pF
1000pF程度
2.SW
2.SW
SI-8000H
SI-8000FF
around
10Ω
10Ω 程度
3.GND
around
1000pF
1000pF程度
29
SI-8000HFE/HD
Without noise reduction circuit
With noise reduction circuit
A resistor of 10Ω and a capacitor of 2200pF
are connected to external resistor
*When the spike noise is observed with an oscilloscope, the lead wire may function as an antenna and the
spike noise may be observed extremely higher than usual if the probe GND lead wire is too long. In the
observation of spike noise, the probe lead wire should be as short as possible and be connected with the
root of the output capacitor.
● 5-4 Reverse Bias Protection
A diode for reverse bias protection will be required between input and output when the output voltage is
higher than the input terminal voltage, such as in battery chargers.
SI-8000H
SI-8001FFE
SI-8000S,SS
30
SI-8000HFE/HD
6. Typical Characteristics
(1) Efficiency
SI-8008H Io vs
効率
SI-8000H
IO - Efficiency
VOVo=1.2v
=1.2V
70
Vin=4.5v
5v
5.5v
8v
10v
65
効率 %
Efficiency (%)
60
55
50
45
40
35
30
0
1
2
3
4
Io A
5
IO - Efficiency
Io vs 効率
Vo=3.3V
Vo=3.3V
85
Vin=6V
10V
15V
20V
25V
30V
40V
80
Efficiency n (%)
効率 η [%]
6
75
70
65
60
0.0
1.0
2.0
3.0
Output Current Io[A]
4.0
5.0
6.0
SI-8008HFE 効率
SI-8008HFE
Efficiency
Vo=5v
Vo=5V
90
85
効率 %
Efficiency (%)
80
Vin=8v
Vin=10v
Vin=15v
Vin=20v
Vin=30v
Vin=40v
75
70
65
60
0
1
2
3
Iout A
4
5
6
31
SI-8000HFE/HD
IO - Io
Efficiency
vs 効率
VOVo=12V
= 12V
95
90
効率 η [%]
Efficiency n (%)
85
15V
20V
25V
30V
40V
80
75
70
0.0
(2)Rising
2.0
3.0
Output Current Io[A]
Characteristics
(4)Over
4.0
5.0
6.0
Current Protection
6
6
Io=0A
Output Voltage VO (V)
Output Voltage VO (V)
1.0
5
4
Io=5.5A
3
Io=1A~4A
2
5
4
VIN=10V
3
VIN=15V
VIN=20V
VIN=30V
2
VIN=40V
1
1
0
2
4
6
8
10
0
(5)Thermal
Input Voltage
Load Regulation
(3)ロードレギュレーション
5.06
Output Voltage VO (V)
5.04
VIN=40v
出力電圧 Vout (V)
Output Voltage
6
8
Output Current
Protection
6
Load regulation
30v
20v
5
4
Output Current Io (A)
Input Voltage VIN (V)
5.02
2
15v
4.98
VIN=15V, Io=10mA
5
4
3
2
4.96
8v
1
4.94
4.92
0
0
1
2
3
4
出力電流 Iout (A)
Output
Current Iout (A)
Output Current
5
40
80
120
160
6
Junction Temperature Tj (°C)
32
SI-8000HFE/HD
7. Terminology
-
Jitter
It is a kind of abnormal switching operations and is a phenomenon that the switching pulse width varies in
spite of the constant condition of input and output. The output ripple voltage peak width is increased when
a jitter occurs.
-
Recommended Conditions
It shows the operation conditions required for maintaining normal circuit functions. It is required to meet
the conditions in actual operations.
-
Absolute Maximum Ratings
It shows the destruction limits. It is required to take care so that even one item does not exceed the
specified value for a moment during instantaneous or normal operation.
-
Electrical Characteristics
It is the specified characteristic value in the operation under the conditions shown in each item. If the
operating conditions are different, it may be out of the specifications.
-
PWM (Pulse Width Modulation)
It is a kind of pulse modulation systems. The modulation is achieved by changing the pulse width in
accordance with the variation of modulation signal waveform (the output voltage for chopper type
switching regulator).
-
ESR (Equivalent Series Resistance)
It is the equivalent series resistance of a capacitor. It acts in a similar manner to the resistor
series-connected to the capacitor.
33
SI-8000HFE/HD
Notice
・The contents of this description are subject to change without prior notice for improvement etc. Please
make sure that any information to be used is the latest one.
・Any example of operation or circuitry described in this application note is only for reference, and we are
not liable to any infringement of industrial property rights, intellectual property rights or any other rights
owned by third parties resulting from such examples.
・In the event that you use any product described here in combination with other products, please review the
feasibility of combination at your responsibility.
・Although we endeavor to improve the quality and reliability of our product, in the case of semi-conductor
components, defects or failures which occur at a certain rate of probability are inevitable.
The user should take into adequate consideration the safety design in the equipment or the system in order to
prevent accidents causing death or injury, fires, social harms etc..
・Products described here are designed to be used in the general-purpose electronic equipment (home
appliances, office equipment, communication terminals, measuring equipment etc.).
If used in the equipment or system requiring super-high reliability (transport machinery and its control
equipment, traffic signal control equipment, disaster/crime prevention system, various safety apparatus etc.),
please consult with our sales office. Please do not use our product for the equipment requiring ultrahigh
reliability (aerospace equipment, atomic control, medical equipment for life support etc.) without our written
consent.
・The products described here are not of radiation proof type.
・The contents of this brochure shall not be transcribed nor copied without our written consent.
34