SI-8000TM Series Application Note Chopper Type Switching Regulator IC SI-8008TM/TMX/TFE Series 4th Edition January 2010 SANKEN ELECTRIC CO., LTD. SI-8000TM/TMX/TFE Series －－－ 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 －－－－－－－－－－ 8 －－－－－－－－－－ 10 3-2 Input /Output Current and Choke Coil Current －－－－－－－－－－ 11 －－－－－－－－－－ 12 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 5-1 Output ON / OFF Control －－－－－－－－－－ 23 5-2 Controllable Output Voltage －－－－－－－－－－ 23 5-3 Reverse Bias Protection －－－－－－－－－－ 25 －－－－－－－－－－ 26 2. Specification 3. Operational Description 3-1 PWM Output Voltage Control 3-3 Overcurrent Protection / Thermal Shutdown 4. Cautions 5. Applications 6. Terminology 2 SI-8000TM/TMX/TFE Series 1. General Description 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) 3 SI-8000TM/TMX/TFE Series 2. Specification Unit mm ● 2-1 Package Information - SI-8008TMX ”8008TMX” for SI-8008TMX *1８００８ＴＭ ＳＫ *2 *3 *4 １ ２ ３ ４ ５ *1 Type Number *2 Logo *3 Lot mark 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) Pin assignment Products Weight：Approx.0.33g 1. IN 2. SW 3. GND 4. ADJ 5. SS (SI-8008TMX is Vc terminal) 4 SI-8000TM/TMX/TFE Series - SI-8008TFE (January to September) by Arabic number and October to December by O (October), N (November) and D (December) Note: Note: ● External Terminal Processing： Sn-3Ag-0.5Cu dip 5 SI-8000TM/TMX/TFE Series ● 2-2 Ratings 2-2-1 Lineup Product Name Vo(V) SI-8008TM/TMX 0.8 (variable type TO252) (reference voltage) SI-8008TFE 0.8 (variable type TO220F-5) (reference voltage) SI-8050TFE 5 (invariable type TO220F-5) 2-2-2 Absolute Maximum Ratings (SI-8008TM/TMX) Parameter Symbol Rating Unit Input Voltage VIN 43 V On/Off Terminal (SI-8008TMX only) Vc VIN V Allowable Power Dissipation in Infinite Radiation Pd1 1.06*1 W Allowable Power Dissipation without Heat sink Pd2 1.65*2 W Tj 150*3 °C Operational Ambient Temperature Taop -30 - +125 °C Storage Temperature Tstg -40 - +150 °C Junction Temperature *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 DC Input Voltage Output Current Junction Temperature in Operation Symbol SI-8008TM/TMX/TFE VIN *1 Vo+3V - 40 SI-8050TFE 8～40 Unit Conditions V Io=0 - 1.5A Vin≧Vo+3V Io 0 - 1.5 A 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. 6 SI-8000TM/TMX/TFE Series 2-2-4 Electrical Characteristics Parameter Set Output Voltage Efficiency Operation Frequency Line Regulation (Iout=0.5A) Load Regulation (Iout=0.2 - 1.5A) Symbol Vo Conditions η Conditions f Conditions ⊿VLi Conditions ⊿VLo Conditions SS Low Level Voltage Termi nal Flow-out Current at Low Level Voltage Overcurrent Protection Start Current Output Voltage Temperature Variation ISSL Conditions Is Conditions ΔVo/ΔT Conditions Circuit Current in Nonoperation Conditions Circuit Current at OFF VSSL Iq Iq(OFF) Conditions (Ta=25°C) SI-8008TM/TFE *1 SI-8050TFE SI-8008TMX *1 Unit MIN TYP MAX MIN TYP MAX MIN TYP MAX 0.784 0.800 0.816 4.90 5.00 5.10 0.784 0.800 0.816 V VIN=20V/Io=0.5A VIN=20V/Io=0.5A VIN=20V/Io=0.5A 81 81 81 % VIN=20V/Io=0.5A VIN=20V/Io=0.5A VIN=20V/Io=0.5A 300 300 300 kHz VIN=20V/Io=0.5A VIN=20V/Io=0.5A VIN=20V/Io=0.5A 25 80 40 100 25 80 mV VIN=10 - 30V VIN=10 - 30V VIN=10 - 30V 10 30 10 40 10 30 mV VIN=20V VIN=20V VIN=20V turns OFF at Vc＜0.8, 0.5 0.5 turns ON at Vc>2v, V turns OFF when it is 10 40 10 40 μA VSSL=0V VSSL=0V 1.6 1.6 1.6 A VIN=20V VIN=20V VIN=20V ±0.5 ±0.１ ±0.１ mV/ﾟC Tc=0 - 100℃ Tc=0 - 100℃ Tc=0 - 100℃ 6 VIN=20V，IO=0A 200 400 VIN=20V，Vss=0V 6 VIN=20V，IO=0A 200 400 VIN=20V，Vss=0V 6 VIN=20V，IO=0A 0 1 VIN=20V，Vc=0V mA μA *1: Output Voltage = 5V 7 SI-8000TM/TMX/TFE Series ● 2-3 Circuit Diagram 2-3-1 Internal Equivalent Circuit - SI-8050TFE SI-8033TM, SI-8050TM, SI-8120TM VIN 1 IN SW C1 SS ON/ C3 OFF Soft･ Start VO C2 Di Overcurrent 過電流保護 Protection PReg 5 L 2 Latch ﾗｯﾁ &and Driver ﾄﾞﾗｲﾊﾞ ﾘｾｯﾄ Reset R1 Oscillator 発振器 ｺﾝﾊﾟﾚｰﾀ Comparator VOS Thermal 過熱保護 Protection 4 Error Amplifier ｴﾗｰｱﾝﾌﾟ Reference 基準電圧 Voltage GND 3 - SI-8008TM/TFE SI-8008TM Vin 1 C1 C3 SS L 2 Di Overcurrent 過電流保護 PReg 5 SW IN VO C2 Protection ON/ OFF Soft･ Start Reset ﾘｾｯﾄ Latch and ﾗｯﾁ & Driver R1 ﾄﾞﾗｲﾊﾞ Oscillator 発振器 Comparator ｺﾝﾊﾟﾚｰﾀ Thermal 過熱保護 Protection Error Amplifier ｴﾗｰｱﾝﾌﾟ ADJ 4 R2 Reference 基準電圧 Voltage GND 3 Recommended Diode: SJPB-H4 (SMD) RK-16(Insertion Type) (Sanken) - SI-8008TMX Overcurrent Protection Reset Latch and Driver Oscillator Comparator Thermal Protection Error Amplifier Reference Voltage 8 SI-8000TM/TMX/TFE Series 2-3-2 Typical Connection Diagram - SI-8050TFE 1 VIN VIN SW Vos SI-8050TFE SI-8000TM SS 5 220uF 47μ H 2 VOUT 4 GND 470uF Di 3 1uF GND GND - SI-8008TM/TMX/TFE 1 VIN VIN 2 SW SS GND R1 ADJ Di 3 5 VOUT 4 SI-8008TM/TMX/TFE 220uF 47μ H R2 470uF 1uF GND GND 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: R1 Vo V ADJ Vo 0.8 V ，R2 ADJ I ADJ 110 3 I ADJ 0.8 ≒ 0.8k 110 3 Recommended Diode: SJPB-H4 (SMD) RK-16 (insertion type) SFPB-66 (Sanken) In order not to be affected by the switching noise for stable operation, the voltage detection line should be designed in a simple way. IADJ 9 SI-8000TM/TMX/TFE Series 3. Operational Description ● 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. PWM Control Chopper Type Regulator Basic Configuration Switching Transistor PWM Comparator Drive Circuit Oscillator Error Amplifier Reference Voltage 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. PWM Comparator Operation Diagram Oscillator 発振器出力 Output Error Amplifier 誤差増幅器出力 ON OFF Output ｽｲｯﾁﾝｸﾞﾄﾗﾝｼﾞｽﾀ出力 Switching Transistor Output 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. 10 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. Emitter Voltage (Switching Output) switching 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. 11 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. Output Voltage The oscillating frequency is lowered Output Current 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 Restoration Setting Temperature Protection Setting Temperature Junction Temperature 12 SI-8000TM/TMX/TFE Series 4. Cautions ● 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. Large Inductance Small Inductance Large Ripple Voltage/ Current Small Ripple Voltage/ Current 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. 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 13 SI-8000TM/TMX/TFE Series L (VIN Vo) Vo IL VIN f －－－(1) For example, where VIN = 20V, VO = 5V, ΔIL = 0. 3A, frequency = 300 KHz, L (20 5) 5 ≒ 42μH 0.3 20 300 103 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. Current Flow of C1 Current Waveform of C1 Ripple Current The ripple current of the input capacitor is increased in accordance with the increase of the load current. 14 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 1.2 Vo Io VIN －－(2) For instance, where Io=1.5A, VIN=20V, Vo=5V, Irms 1.2 5 1.5 0.45 A 20 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. Current Flow of C2 Current Waveform of C2 Ripple Current 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) 15 SI-8000TM/TMX/TFE Series 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. 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. Vrip VIN Vo Vo ESR - - - (4) L VIN f Vrip IL ESR - - - (5) 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 SI-8000T 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. 16 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 L - VIN Vo Vo IL VIN f 20 5 5 0.3 20 300000 42H L : 47H Output capacitor ESR The output ripple voltage Vrip shall be: 5V × 0.5% = 25 mV. Vrip IL ESR ESR Vrip 83.3m IL 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. SI-8000T 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. 17 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. Improper Pattern Example Proper Pattern Example 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: 6.0 GND 8000TM C1 C2 6.1 C3 ＋ ＋ IN 2.4 R1 SW 5.88 R2 Di Vout 2.5 L 1.27 0.47 0.8 Board Pattern Example Top View ** 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 18 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: 1. Normal Operation (continuous area) 2. Normal Operation (discontinuous area) 3. When C1 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 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. 19 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. 100 Vo Pd Vo Io 1 Vf Io1 Vin x －－－(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. 代表特性例 SI-8008TM/TFE Efficiency Characteristics SI-8008TM／TFE 効率特性 (Ta=25°C, Vo=5V) Ta=25℃ Vo=5v設定時 Vout=5V adjusted 85 R1=4.2kΩ,R2=0.8kΩ Efficiency 効率 %(%) 80 75 70 VIN= 8v,10v,15v,20v,30v, 40v 65 60 55 0 0.5 1 1.5 Iout A Note 2. The thermal design of diodes should be made separately. 20 SI-8000TM/TMX/TFE Series 3) The copper foil area is determined by the intersection point of heat derating curve as shown below: SI-8008TM series Heat Derating Curve SI-8000TM シリーズ熱減定格曲線 Allowable Power Dissipation PD (W) copper foil area copper foil area copper foil area copper foil area copper foil area copper foil area Glass Epoxy Board (equivalent to FR-4, one side) 30×30 mm Ambient Temperature Ta (°C) 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 Foil Area – Heat Resistance Allowable Power Dissipation PD (W) Foil Area (mm2) Foil Area – Allowable Power Dissipation Tjmax=100℃ Foil Area (mm2) 21 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. Tj PD j C TC Tc measurement point (θj-c＝6°C/W) ● ● 4-5 Static Electricity Some terminals may be damaged by static electricity, therefore attention should be paid to handling. 22 SI-8000TM/TMX/TFE Series 5. Applications ● 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. SI-8000TM SI-8000TFE SI-8000TM SI-8000TFE ON/OFF ON/OFF ● 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. Re x Vout'Vos IVos －－－(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. 23 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) Vout' MAX＝VosMAX＋RexMAX IvosMAX 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 Ivos The output voltage adjustment resistors Rex1 and 2 are obtained by the following equation. Vout'Vos S IVos Vos Re x2 (S 1) IVos Re x1 －－－(3) －－－(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) Vout' MAX ＝VosMAX ＋Rex1MAX( VosMAX ＋IvosMAX ） Rex2MIN 24 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) Vout' MIN＝VosMIN＋Rex1MIN( VosMIN ＋IvosMIN ） Rex2MAX 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 25 SI-8000TM/TMX/TFE Series 6. 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. 26 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. 27