SI-8008TMX - Sanken Electric Co., Ltd.

SI-8000TM Series

Chopper Type Switching Regulator IC

SI-8008TM/TMX/TFE Series

4th Edition January 2010

SANKEN ELECTRIC CO., LTD.

Application Note

SI-8000TM/TMX/TFE Series

－－－ Contents －－－

1. General Description

1-1 Features －－－－－－－－－－ 3

1-2 Applications －－－－－－－－－－ 3

1-3 Type －－－－－－－－－－ 3

2. Specification

2-1 Package Information －－－－－－－－－－ 4

2-2 Ratings －－－－－－－－－－ 6

2-3 Circuit Diagram －－－－－－－－－－ 8

3. Operational Description

3-1 PWM Output Voltage Control －－－－－－－－－－ 10

3-2 Input /Output Current and Choke Coil Current －－－－－－－－－－ 11

3-3 Overcurrent Protection / Thermal Shutdown －－－－－－－－－－ 12

4. Cautions

4-1 External Components －－－－－－－－－－ 13

4-2 Pattern Design Notes －－－－－－－－－－ 17

4-3 Operation Waveform Check －－－－－－－－－－ 19

4-4 Thermal Design －－－－－－－－－－ 20

4-5 Static Electricity －－－－－－－－－－ 22

5. Applications

5-1 Output ON / OFF Control －－－－－－－－－－ 23

5-2 Controllable Output Voltage －－－－－－－－－－ 23

5-3 Reverse Bias Protection －－－－－－－－－－ 25

6. Terminology －－－－－－－－－－ 26

SI-8000TM/TMX/TFE Series

SI-8000T series (*) 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-8000T series includes the SI-8000TM series of surface mounting package type (T0252-5) and

SI-8000TFE series of insertion type package (TO220F-51ds).

● 1-1 Features

- Compact size and large output current of 1.5A

T0252-5 (corresponding with SC-63) compact size power package and the output current of 1.5A at

maximum

- High efficiency of 81% (SI-8008TM VIN = 15V / Vo = 5V, Io = 0.5A)

Heat dissipation is small due to high efficiency to allow for the downsizing of copper foil area.

- 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)

- Output ON/OFF function (enabling soft start)

The ON/OFF control of output is also possible (current consumption at OFF is reduced).

- By connecting an external capacitor, it is possible to delay the rise speed of the output voltage.

* The SI-8008TMX has no soft start function. (The output is turned off and the circuit current falls to zero when

the Vc Terminal is open or its voltage is 0.8V or less.)

● 1-2 Applications

For DVD recorders, FRD TV and others, 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)

1. General Description

SI-8000TM/TMX/TFE Series

● 2-1 Package Information

- SI-8008TMX

Unit mm

*2 *3

Products Weight：Approx.0.33g

*1 Type Number

*2 Logo mark

*3 Lot Number

1st letter: The last digit of year

2nd letter: Month

(1 to 9 for Jan. to Sept.,O for Oct. N for Nov. D

for Dec.)

3rd letter: day

1 to 9 day: for “1” to “9”

10 to 31 day: for “A” to “Z”

(But, “B”,”I”,”O”,”Q” is removed.

*4 Administer number (Seven digits)

８００８ＴＭ

ＳＫ

１２３４５

Pin assignment

1. IN

2. SW

3. GND

4. ADJ

5. SS

(SI-8008TMX is Vc terminal)

”8008TMX” for SI-8008TMX

2. Specification

SI-8000TM/TMX/TFE Series

- SI-8008TFE

Note:

(January to September) by Arabic number and

October to December by

O (October), N (November) and D (December)

● External Terminal Processing：

Sn-3Ag-0.5Cu dip

SI-8000TM/TMX/TFE Series

● 2-2 Ratings

*1: 900mm2 board equivalent to FR-4, copper foil area of 4. 3% (single side only)

*2: 900mm2 board equivalent to FR-4, copper foil area of 50% (single side only)

*3: The product incorporates the thermal shutdown circuit and it may be operated when the junction

temperature is 130°C or higher.

2-2-3 Recommended Conditions

Parameter

Symbol

SI-8008TM/TMX/TFE

SI-8050TFE

Unit

Conditions

DC Input Voltage

VIN

Vo+3V*1 - 40

8～40

Io=0 - 1.5A

Output Current

0 - 1.5

Vin≧Vo+3V

Junction Temperature in Operation

Tjop

-20 - +100

°C

Note: The variable output voltage range of the SI – 8008TM/TMX/TFE is 0.8 - 24V.

*1: The least value of input voltage range is 4.5V or Vo+3V, whichever higher.

2-2-1 Lineup

Product Name

Vo(V)

SI-8008TM/TMX

(variable type TO252)

0.8

(reference voltage)

SI-8008TFE

(variable type TO220F-5)

0.8

(reference voltage)

SI-8050TFE

(invariable type TO220F-5)

2-2-2 Absolute Maximum Ratings (SI-8008TM/TMX)

Parameter

Symbol

Rating

Unit

Input Voltage

VIN

On/Off Terminal (SI-8008TMX only)

VIN

Allowable Power Dissipation in Infinite Radiation

Pd1

1.06*1

Allowable Power Dissipation without Heat sink

Pd2

1.65*2

Junction Temperature

150*3

°C

Operational Ambient Temperature

Taop

-30 - +125

°C

Storage Temperature

Tstg

-40 - +150

°C

SI-8000TM/TMX/TFE Series

2-2-4 Electrical Characteristics (Ta=25°C)

*1: Output Voltage = 5V

MIN TYP MAX MIN TYP MAX MIN TYP MAX

Vo 0.784 0.800 0.816 4.90 5.00 5.10 0.784 0.800 0.816 V

Conditions

η81 81 81 %

Conditions

f300 300 300 kHz

Conditions

⊿VLi 25 80 40 100 25 80 mV

Conditions

⊿VLo 10 30 10 40 10 30 mV

Conditions

Low Level Voltage

VSSL 0.5 0.5 V

ISSL 10 40 10 40 μA

Conditions

Is 1.6 1.6 1.6 A

Conditions

ΔVo/ΔT

±0.１±0.5 ±0.１mV/ﾟC

Conditions

6 6 6 mA

Conditions

Iq(OFF) 200 400 200 400 0 1 μA

Conditions

VIN=20V，IO=0A

VIN=20V，Vc=0V

Unit

SI-8008TMX *1

VIN=20V/Io=0.5A

VIN=10 - 30V

VIN=20V

turns OFF at Vc＜0.8,

turns ON at Vc>2v,

turns OFF when it is

Circuit Current in

Nonoperation

VIN=20V，IO=0A

Circuit Current at OFF

VIN=20V，IO=0A

VIN=20V，Vss=0V

Line Regulation

(Iout=0.5A)

Load Regulation

Parameter

Set Output Voltage

Efficiency

Operation Frequency

(Iout=0.2 - 1.5A)

Overcurrent Protection Start

Current

Output Voltage

Temperature Variation

Tc=0 - 100℃

VIN=20V

VSSL=0V

Flow-out Current

at Low Level Voltage

Termi

nal

VIN=10 - 30V

Tc=0 - 100℃

VIN=20V

VSSL=0V

VIN=20V

Tc=0 - 100℃

Symbol

SI-8008TM/TFE *1

VIN=20V/Io=0.5A

SI-8050TFE

VIN=10 - 30V

VIN=20V/Io=0.5A

SI-8000TM/TMX/TFE Series

● 2-3 Circuit Diagram

2-3-1 Internal Equivalent Circuit

- SI-8050TFE

- SI-8008TM/TFE

Recommended Diode:

SJPB-H4 (SMD) RK-16(Insertion Type) (Sanken)

- SI-8008TMX

PReg

ﾗｯﾁ &

ﾄﾞﾗｲﾊﾞ

過電流保護

過熱保護

基準電圧

ON/

OFF

･Soft

Start

発振器

ﾘｾｯﾄ

ｺﾝﾊﾟﾚｰﾀ

ｴﾗｰｱﾝﾌﾟ

Vin 1

2VOL

Di C2

SI-8008TM

GND

ADJ

PReg

ﾗｯﾁ &

ﾄﾞﾗｲﾊﾞ

過電流保護

過熱保護

基準電圧

ON/

OFF

･Soft

Start

発振器

ﾘｾｯﾄ

ｺﾝﾊﾟﾚｰﾀ

ｴﾗｰｱﾝﾌﾟ

VIN 1

2VOL

Di C2

SI-8033TM, SI-8050TM, SI-8120TM

GND

VOS

Overcurrent

Protection

Latch and

Driver

Oscillator

Thermal

Protection

Reference

Voltage

Reset

Comparator

Error Amplifier

Overcurrent

Protection

Latch and

Driver

Oscillator

Thermal

Protection

Reference

Voltage

Reset

Comparator

Error Amplifier

Overcurrent

Protection

Latch and

Driver

Oscillator

Thermal

Protection

Reference

Voltage

Reset

Comparator

Error Amplifier

SI-8000TM/TMX/TFE Series

2-3-2 Typical Connection Diagram

- SI-8050TFE

- SI-8008TM/TMX/TFE

In the SI-8008TMX, terminal 5 corresponds with Vc terminal. The regulator is turned on and off by the

voltage applied to Vc terminal (Active Hi). The regulator is turned off when the Vc terminal is open.

Resistors R1, R2

R1 and R2 are a resistor for setting the output voltage. The output voltage should be set in a way that IADJ

may be 1mA or so (approx. ±20% is recommended, but there is no restriction toward a larger value.)

The equation to obtain R1 and R2 values is as follows:

       















 k

VVo

ADJ

ADJ 8.0

101

8.0

101

8.0

133 ≒，

Recommended Diode:

SJPB-H4 (SMD) RK-16 (insertion type) SFPB-66 (Sanken)

VIN

GND GND

GNDSS

VIN SW

ADJ

220uF 470uF

47μH

VOUT

1uF

VIN

GND GND

GNDSS

VIN SW

Vos

220uF 470uF

47μH

VOUT

SI-8000TM

1uF

SI-8050TFE

SI-8008TM/TMX/TFE

IADJ

In order not to be affected by the switching noise for stable operation,

the voltage detection line should be designed in a simple way.

SI-8000TM/TMX/TFE Series

● 3-1 PWM Output Voltage Control

In the SI-8000 series, the output voltage is controlled by the PWM system and the IC integrates the PWM

comparator, oscillator, error amplifier, reference voltage, output transistor drive circuit etc. The triangular

wave output (≈ 300KHz) from the oscillator and the output of the error amplifier are given to the input of

the PWM comparator. The PWM comparator compares the oscillator output with the error amplifier output

to turn on the switching transistor for a time period when the output of the error amplifier exceeds the

oscillator output.

The error amplifier output and the oscillator output are compared by the PWM comparator to

generate the drive signal of rectangular wave and to drive the switching transistor.

On the assumption that the output voltage attempts to rise, the output of the error amplifier is lowered,

because the error amplifier is of inverting type. As the output of the error amplifier is lowered, the time

period where 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 constant. As described above, the

output voltage is controlled by varying the ON time of the switching transistor with the fixed switching

frequency (the higher is VIN, the shorter is the ON time of the switching transistor.) The rectangular wave

output of the switching transistor is smoothed by the LC low pass filter composed of a choke coil and a

capacitor to supply stabilized DC voltage to the load.

PWM Control Chopper Type Regulator Basic Configuration

3. Operational Description

Drive

Circuit

Switching

Transistor

PWM

Comparator

Oscillator

Error Amplifier

Reference

Voltage

PWM Comparator Operation Diagram

発振器出力

誤差増幅器出力

ｽｲｯﾁﾝｸﾞﾄﾗﾝｼﾞｽﾀ出力

ON OFF

Oscillator Output

Error Amplifier Output

Switching Transistor Output

SI-8000TM/TMX/TFE Series

● 3-2 Input / Output Current and Choke Coil Current

The rectangular output which is generated by the switching transistor of the SI-8000T is converted into DC

output voltage by being smoothed by the LC filter composed of a choke coil and an output capacitor. The

operation of this LC filter significantly affects the stable operation of the chopper type regulator. The

relation between the choke coil and the current and the relation between the current and the ripple voltage

are shown below.

The current IL flowing across the choke coil is of triangular wave shape. This triangular wave is composed

of two kinds of current components, Itr and Idi. The current Itr is supplied from the input side through the

transistor when the transistor is ON and its average value is input current Iin. The current Idi is the current

that the energy stored in the choke coil is commutated via the flywheel diode Di when the transistor is OFF.

The total of Itr and Idi is the current IL of choke coil. In addition, the average value of IL is the DC output

current Io since the triangular wave component superimposed on the IL is smoothed by charging and

discharging of the capacitor C.

Emitter Voltage

(Switching Output)

switching

SI-8000TM/TMX/TFE Series

● 3-3 Overcurrent Protection / Thermal Shutdown

3-3-1 Output Voltage Characteristics in Overcurrent

SI-8000T integrates 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 up to the 50% of the rated value, the increase of current at low

output voltage is prevented by dropping linearly the switching frequency to about70kHz. When the

overcurrent condition is released, the output voltage will be automatically restored.

3-3-2 Output Voltage Characteristics in Thermal Shutdown

The thermal shutdown circuit detects the semiconductor junction temperature of the IC and when the

junction temperature exceeds the set value, 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.

* 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.

Output Voltage

Output Current

The oscillating

frequency is lowered

Junction Temperature

Protection

Setting

Temperature

Restoration Setting

Temperature

Output Voltage

SI-8000TM/TMX/TFE Series

● 4-1 External Components

4-1-1 Choke coil L

The choke coil L supplies current to the load side when the switching transistor is OFF, and plays a main

role in the chopper type switching regulator. 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.

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 following equation.

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 (1.5A) of the

SI-8000TM: output current × 0.2 - 0.3

- In the case that the output current to be used is approximately 0.5A or less: output current × 0.5 - 0.6

The larger is the inductance, the smaller will be

the ripple current/voltage. But the outer size of

the coil becomes larger.

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.

Large Inductance

Small Ripple Voltage/ Current

Small Inductance

Large Ripple Voltage/ Current

4. Cautions

SI-8000TM/TMX/TFE Series

fVIL VoVoV

LIN





)(

－－－(1)

For example, where VIN = 20V, VO = 5V, ΔIL = 0. 3A, frequency = 300 KHz,

HL μ≒ 42

10300203.0 5)520(3







As shown above, the coil of about 47μH may be selected.

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

The input capacitor is operated as a bypass capacitor of the input circuit to supply steep current 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.

In addition, in the case that the smoothing capacitor of the AC rectifier circuit is located in the input circuit,

the input capacitor may be also used as a smoothing capacitor, but similar attention should be paid.

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.

The ripple current of the input capacitor is increased in accordance with the increase of the load

current.

Current Flow of C1

Ripple Current

Current Waveform of C1

SI-8000TM/TMX/TFE Series

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:

Irms IN  2.1

－－(2)

For instance, where Io=1.5A, VIN=20V, Vo=5V,

AIrms 45.05.1

2.1 

Therefore, it is necessary to select the capacitor with the allowable ripple current of 0.45A or higher.

4-1-3 Output Capacitor C2

The output capacitor C2 composes a LC low pass filter together with a choke coil L 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. Additional points to be checked are DC equivalent series

resistance (ESR) and capacitance.

The following points should be taken into consideration.

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.

Allowable Ripple Current

The ripple current effective value of the output capacitor is obtained by the equation

Irms IL



2 3

－－－(3)

Current Flow of C2

Ripple Current

Current Waveform of C2

SI-8000TM/TMX/TFE Series

When ΔIL = 0.5A,

Irms A05

2 3 014

..≒

Therefore a capacitor having the allowable ripple current of 0.14A or higher is required.

DC equivalent series resistance (ESR)

It is necessary for the stable operation to select the ESR properly. When the ESR is too large or too small,

abnormal oscillation due to increase of ripple voltage or insufficient phase margin occurs respectively.

The output ripple voltage is determined by a product of the pulse current ΔIL (=C2 discharge and charge

current) of the choke coil current and the ESR, and the output ripple voltage which is 0.5 % - 1% of the

output voltage (for example, where 0.5% at Vo = 5V, 25mV) is good for the stable operation. Please refer

to the equations (4) and (5) to obtain the output ripple voltage. It should be noted that the ESR is

changeable subject to temperature and it is especially lowered at high temperature.

 

(4)--- 　　 ESR

fVL VoVoV

Vrip IN

IN 







)5(---　　　ESRILVrip 

When the ESR is too low (approx. 10 - 20Ω or lower), the phase delay becomes larger, resulting in

abnormal oscillation. Therefore, it is not appropriate that a tantalum capacitor or a laminated ceramic

capacitor is used for the output capacitor as an 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). In addition, in order to further

decrease the ripple voltage, as shown below, it is also effective to add one stage of the LC filter to form the

π type filter.

L2 ： 20uH

Co2 ： 200uF

It should be noted that the operating stability is more influenced by the ESR than the capacitance as

described above if the requirements of withstand voltage and allowable ripple current are met.

With respect to the layout of the output capacitor, if it is located far from the IC, it will give same effect as

the increase of ESR due to wiring resistance etc., therefore it is recommended to place it near the IC.

4-1-4 LC Filter Constants Selection Example

Based on the above description, the calculation methods of the inductance of choke coil and the ESR are

shown below. The following values are deemed as a target and in many cases, the larger are the

inductance and capacitance of output capacitor, the more stable operation will be achieved.

SI-8000T

SI-8000TM/TMX/TFE Series

Samples: SI-8050TFE, conditions: input voltage VIN: 20V, output voltage Vo: 5V, output current Io:

0.5A

- Inductance L of choke coil L

Choke coil ripple current ΔIL = Io x 0.5 – 0.6 ⇒0.3A

   

fVIL VoVoV

LIN



47:L42

300000203.0 5520 　　　













- Output capacitor ESR

The output ripple voltage Vrip shall be: 5V × 0.5% = 25 mV.

　　　　



 m

Vrip

ESRESRILVrip 3.83

4-1-5 Flywheel Diode Di

The flywheel diode Di 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 damaged by applying reverse voltage due to the recovery and ON

voltage.

● 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.

4-2-2 Input / Output Capacitor

The input capacitor C1 and the output capacitor C2 should be connected 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.

SI-8000T

SI-8000TM/TMX/TFE Series

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.

4-2-3 Sensing Terminal

The output voltage sensing terminal Vos shall be connected near the output capacitor C2 as much as

possible. (Vos terminal flow-in current is approx. 1mA.)

If it is connected far from C2, it should be noted that abnormal oscillation may happen due to the low

regulation and increased switching ripple.

4-2-4 Recommended Pattern

The recommended board pattern is shown on the right side.

Example: SI-8008TM (variable type)

The example of solder pattern design is shown below:

** In order to achieve the best operating conditions, the GND line shall be a 1-point GND wiring

with No. 3 terminal in the center

0.47 0.81.27

2.5

2.4

6.1

6.0

5.88

Improper Pattern Example

Proper Pattern Example

Board Pattern Example Top View

8000TM

C1 C2

Vout

GND

＋

SI-8000TM/TMX/TFE Series

● 4-3 Operation Waveform Check

It can be checked by the waveform between the pin 2 and 3 (SW waveform) of the SI-8000TM whether the

switching operation is normal or not.

The examples of waveforms at normal and abnormal operations are shown below:

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 and C2, jitter which disturbs the ON – OFF time of switching

will happen, as shown in the waveforms (3, 4). As described above, C1 and C2 should be connected close

to the IC.

1. Normal Operation (continuous area)

2. Normal Operation (discontinuous area)

3. When C1 is distant from IC

4. When C2 is distant from IC

SI-8000TM/TMX/TFE Series

● 4-4 Thermal Design

4-4-1 Calculation of Heat Dissipation

The heat dissipation of the surface mounting IC depends on size and quality of material of printed wiring

board and area of copper foil. Full attention should be paid to the heat dissipation and ample margin should

be taken in thermal design. In order to improve heat dissipation effect, it is recommended to enlarge the

copper foil area. Large copper foil area will contribute to the efficient heat dissipation.

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 (board heat

resistance).

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.

Pd Vo Io xVf Io Vo

Vin

  









  











100 1 1



－－－(6)

* ηx= efficiency (%), Vf= diode forward voltage

Note 1; Since the efficiency varies subject to input voltage and output current, it is obtained by the

following efficiency curve to substitute it. (it depends on the output voltage. Please refer to the product

specifications for more details.

Note 2. The thermal design of diodes should be made separately.

SI-8008TM／TFE　効率特性

Ta=25℃　Vo=5v設定時

0 0.5 1 1.5

Iout　A

効率　%

VIN=

8v,10v,15v,20v,30v,

40v

Vout=5V adjusted R1=4.2kΩ,R2=0.8kΩ

代表特性例

SI-8008TM/TFE Efficiency Characteristics

(Ta=25°C, Vo=5V)

Efficiency (%)

SI-8000TM/TMX/TFE Series

3) The copper foil area is determined by the intersection point of heat derating curve as shown below:

For the reference data, 1) copper foil area – junction part – ambient temperature thermal resistance θj – a

and 2) copper foil area – permissible loss are shown below:

SI-8000TM シリーズ熱減定格曲線

SI-8000TM Foil Area – Heat Resistance

Foil Area (mm2)

Allowable Power Dissipation PD (W)

Foil Area – Allowable Power Dissipation Tjmax=100℃

Glass Epoxy Board (equivalent to FR-4, one side) 30×30 mm

SI-8008TM series Heat Derating Curve

Allowable Power Dissipation PD (W)

copper foil area

Ambient Temperature Ta (°C)

copper foil area

SI-8000TM/TMX/TFE Series

The derating of 10 - 20% or more is generally used. In reality, the effect of heat dissipation varies

significantly due to different mounting methods.

Therefore, it is necessary to confirm the case temperature in the mounted state.

- How to obtain junction temperature

Temperature of lead portion of GND terminal:

The junction temperature is obtained by measuring Tc with the thermocouple etc. and substituting it in the

following equation.

CCjD TPTj  



(θj-c＝6°C/W)

● 4-5 Static Electricity

Some terminals may be damaged by static electricity, therefore attention should be paid to handling.

Tc measurement point

●

SI-8000TM/TMX/TFE Series

● 5-1 Output ON / OFF Control

The output ON-Off control is possible using the terminal 5 of SI-8000TM/TEF. The output is turned OFF

when the terminal 5 voltage falls to a low level by such as open collector. It is possible to use the soft start

together.

Since the soft start terminal has been already pulled up, no voltage shall be applied from the external side.

● 5-2 Controllable Output Voltage

The output voltage can be increased by connecting a resistor to the Vos terminal (pin 4).

Please refer to page 8 for the output voltage setting method of a variable type SI-8008TM/TFE.

5-2-1 Variable Output Voltage by One External Resistor

The output voltage adjustment resistance Rex is obtained by the following equation.

IVos

VosVout

x

'

－－－(1)

Vos: Set output voltage for product

Vout: Variable output voltage

Ivos: Vos terminal in-flow current ≈ 1mA

* Since no temperature compensation is made for Rex, the temperature characteristic of output voltage is

lowered. Ivos is variable at maximum ±20% depending on each IC product. Therefore, as the variation

range of the output voltage becomes wider, the semi-fixed type resistor is required for the adjustment of

accurate output voltage.

SI-8050TFE

Ivos

ON/OFF

SI-8000TM

SI-8000TFE

SI-8000TM

SI-8000TFE

5. Applications

SI-8000TM/TMX/TFE Series

The variation range of the output voltage including the variation of Rex, Ivos and Vos is shown as follows:

- Maximum output voltage (Vout MAX)

IvosMAXRexMAXVosMAXMAXVout' ＋＝

VosMAX: The maximum value of set output voltage. The MAX value of the set output voltage should be

put, shown in the electrical characteristics of the specifications.

RexMAX: The maximum value of Rex. It is obtained from the allowable tolerance.

IvosMAX: The maximum in-flow current of Vos terminal

- The minimum output voltage (Vout MIN)

Vout MIN = VosMIN + RexMIN x IvosMIN

VosMIN: The minimum value of set output voltage. The MIN value of the set output voltage should be put,

shown in the electrical characteristics of the specifications.

RexMAX: The minimum value of Rex. It is obtained from the allowable tolerance of resistance.

IvosMIN: The minimum in-flow current of Vos terminal

5-2-2 Variable Output Voltage by Two External Resistors

The output voltage adjustment resistors Rex1 and 2 are obtained by the following equation.

IVosS VosVout

x



'

1Re

－－－(3)

IVosS Vos

x

)1(

2Re

－－－(4)

S: Stability coefficient

The tolerance of temperature characteristics and output voltage is improved more by bypassing the current

to Rex2 than the method 5-2-1.

Stability coefficient S means the ratio of Rex 2 to the Vos terminal in-flow current Ivos. The larger is S, the

more is the variation of temperature characteristic and output voltage improved. (Normally, about 5 - 10)

The tolerance of the output voltage including variation of Rex 1, Rex 2, Ivos, Vos is shown below.

- Maximum output voltage (Vout MAX)

）＋＋＝ IvosMAX

Rex2MIN

VosMAX

Rex1MAX(VosMAXMAXVout'

SI-8050TFE

Ivos

SI-8000TM/TMX/TFE Series

VosMAX: The maximum value of set output voltage. The MAX value of set output voltage should be put,

shown in the electrical characteristics of the specifications.

Rex1MAX: The maximum value of Rex1. It is obtained from the tolerance of the resistor.

Rex2 MIN: The minimum value of Rex2. It is obtained from the tolerance of the resistor.

IvosMAX: The maximum in-flow current of Vos terminal

- The minimum output voltage (VoutMIN)

）＋＋＝ IvosMIN

Rex2MAX

VosMIN

Rex1MIN(VosMINMINVout'

VosMIN: The minimum value of the set output voltage. Please fill in the MIN value of the set output

voltage which is shown in the electrical characteristics of the specifications.

Rex1 MIN: The minimum value of Rex1. It will be obtained from the tolerance of the resistor.

Rex2MAX: The maximum value of Rex2. It will be obtained from the tolerance of the resistor.

IvosMIN: The minimum in-flow current of Vos terminal.

5-2-3 Cautions for variation of output voltages

The degradation of regulation and the increase in the output voltage temperature coefficient are assumed

when the output voltage is varied. If it is varied drastically, the increase of coil capacitance value may be

required since the overcurrent protection current is assumed to be lowered due to the increase in coil

current. Therefore, the use within the set output voltage +5V is recommended as for the upper limit of

output voltage variation. In addition, the MAX value of the set output voltage is recommended as for the

lower limit of output voltage variation.

● 5-3 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-8000T

SI-8000TM/TMX/TFE Series

- 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.

6. Terminology

SI-8000TM/TMX/TFE Series

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.