FAQ Frequently Asked Questions

[S-8520/21] How to Take a Measure against Large Rush Current Flowing from VIN at Startup?

This problem is inherent to series S-8520/8521.
This IC has a soft start circuit that ensures slow startup of the output voltage by gradually increasing the Vref voltage from 0 V to the reference voltage and minimizes rush current at startup. However, the Vref voltage and VOUT pin voltage go 0 V the moment voltage starts dropping. Any rise in the output voltage is controlled until the Vref voltage keeps a certain level of voltage because normal control of the output voltage is not available. This enables the output voltage to start up at a certain Vref voltage, to be instantaneously increased. At this time rush current flows. As one of measures, it is recommended that TR2, 3, R1 to 4 and C1 be added.

Basically, the same effect as soft start can be obtained by charging CL from VIN via R4 while the ON/OFF switch is forcibly turning off TR1 in the UVLO circuit when LO→HI.
Configure the IC so that off time is obtained in the UVLO circuit using C1 and R1 (when the configuration is achieved by microcomputer, use it.) or design the IC so that gradient of a rise in the OUT voltage can meet soft start via R4 In addition, rush current can be decreased by turning on TR2 and TR3, flowing current of (Vin-Vout)/R4 through OUT and charging CL.

[S-8520/21] Merit or Demerit of the PWM Method and the PWM/PFM Switching Method?

Different from the PWM/PFM switching method, the PWM method ensures stable switching frequency and gives easy determination of frequency of external noise and also easy assembly of the filter. On the contrary, the PWM/PFM switching method is extremely superior in efficiency during moderate and light load. The following is efficiency data of PWM/PFM based S-8521B50 and PWM based S-8520B50 for your reference.

[S-8340] Maximum Ability of the Current Limit Circuit to Retain 100 mA to 200 mA max. Generated at 3.3 V to 5.6 V When Output is Shorted in Series S-8340A56?

The current limit circuit is to protect external FETs against breakage due to overheat. When output is shorted and external FETs are off, current passes from the input pin via the external coil and the Schottky diode as well to the output pin. In other words, DC current flows.

Theoretically, as you know, when output is shorted, the S-8340 stops its operation and turns the Tr off. Then, nearly the same input voltage is applied to both external coil and Schottky diode and large current exceeding the power dissipation. This may damage these elements because of overheat.

Actually, however, any of the following elements such as
· Input power supply resistor,
· Diode resistor, and
· Output short resistor (contact resistance and wiring resistance)

is involved in inevitable overheat. Voltage (loss) to be applied to each element varies depending upon the ratio

among resistances. Because of it, the most sensitive element will be thermally damaged.

[S-8353/54] When the VDD pin is turned on and off by using a transistor in the S-8353D reverse output circuit, does current flow from the battery side to the S-8353D when VDD is turned off?

Only leakage current may flow. The IC current consumption when the VDD pin is open causes VDD to be equal to VSS and CONT to be open. There is a several MΩ routes from VOUT to VDD via a parasitic diode, however, current does not flow to the VDD pin because of the voltage relationship VOUT < VDD.

[S-8355/56/57/58] Can +5 V output be obtained by inputting a −5 V input (with an output current of 20 mA)?

+5 V output can be obtained by using the S-8357E. The input voltage, however, must be fixed to 5 V. Figure 1 shows an example of a circuit to convert voltage from positive to negative.

A process opposite that shown in Figure 1 must be done to convert voltage from negative to positive.

A configuration shown in Figure 2 can be achieved with the S-8357E, but a positive voltage must be set as the negative voltage reference. Output voltage = (S-8357E set voltage) − | Input voltage | , so resistance must be set such that the set voltage of the S-8357E is 10 V. The input voltage must be fixed for this reason.

[S-8355/56/57/58] Output Amplitude at EXT Pin of VDD Discrete Type S-8355/56 and 8357/8 (E,J,G,P)?

The EXT amplitude ranges from GND to the power supply voltage of the internal circuit of series S-8355/56/57/58.
Power supply of the internal circuit in normal types B,H,F and N for series S-8357/8 is supplied from the VOUT pin.
Hence, the EXT output amplitude ranges from GND to VOUT; whereas the power supply of the internal circuit in VDD discrete types E, J, G and P for series S-8357/8 and S-8355/6 is supplied from VDD pin. Hence the EXT output amplitude ranges from GND to VDD. For instance, when VIN voltage is supplied to the VDD pin, the EXT output amplitude ranges from GND to VIN.

External Transistor Peripheral Circuit

[S-8355/56/57/58] How to Discharge Output to GND during Power Off in the Output Voltage Adjustment Curcuits Listed in the Datasheet?

i. When rush current that flows from the input power supply results in no problem during power on:
Cut off SWR from VIN during power off.
Then, turn on TR3 and discharge Cout on RC because the TR2 is turned off during power off.

ii. When rush current that flows from the input power supply results in a problem during power on:
Cut off VDD of the IC and GND side of the external resistor during power off.
Then, turn on Tr5 and discharge Cout2 on RC because Tr3 and Tr4 are turned off during power off.
Dual input of power ON positive logic and negative logic is needed.
2 transistors and 1 capacitor are added to the circuit configured in Figure 2.

[S-8353/54/55/56/57/58] The Soft Start Mechanism in Series S-8353/54/57/58?

Any soft start function is added to prevent overshoot of the output voltage at startup of boosting and rush current during boosting. The soft start method adopted in this IC is designed to slowly increase the reference voltage. Waveform obtained at the time of soft start in series S-8357B30 is shown below. As the figure shows, output voltage Vout is slowly increased in connection with the gradual rise in the reference voltage Vref inside the measurement circuit from 0 V. The rise time is determined inside the IC per oscillating frequency [Note: the dotted line Vref given in the waveform graph is the value calculated by converting reference voltage Vref to output voltage Vout level (Vref=VREF´(R1+R2)¸R2)].

The rise in Vout near Vin is attributed to supply of current from VIN to VOUT via L and SD of the measurement circuit.

Measurement Circuit

[S-8353/54/55/56/57/58] Kinds of Switching Regulator’s Soft Start Function?

Any soft start function is added to prevent overshoot of the output voltage at startup of boosting and rush current during boosting. Soft start methods are as follows:

i. establish a current limit in switching current.
ii. slowly increase the reference voltage (series S-8353/54/57/58).
iii. impose “ON duty” limits at the time of startup.

S-8353/54/55/56/57/58 adopts the method of ii.

[S-8353/54] Malfunction of the IC Even When Input Side Voltage Vin Goes 0 V While the Output Side Voltage Vout Retains 5 V In a Standard Circuit Configuration on Series S-8354A50MC?

There is no problem.
In series S-8353/4, the power of the IC is supplied from Vout side. Basically, any fluctuation of Vin voltage does not directly affect the IC.

[Reference]
Both S-8353D and S-8354D are equipped with power supply pin VDD and called VDD discrete regulators. These ICs are not equipped with a diode that is forward connected from VOUT to VDD. Hence, each IC is free of a malfunction you questioned.

[S-8357] Measures against Generation of Ripple of 100 mV or more at Output in the S-8357B-based Booster (peak to peak)?

Effective measures are as follows:

i. Increase the output capacitance (Cout).
ii. Use series S-8357N (600 kHz-products).
iii. Insert an LC filter after the SWR. This leads to an increase cost because a coil of DCR of several tens of m ohm higher than Ioutmax 500 mA is needed.

[S-8351/52] How to Eliminate Noise Generating During Light Load?

A method to increase value “L” of the coil from 22µH to 1mH is introduced here. This method ensures that the switching frequency is higher than the audio frequency. Be sure that the increased value “L” decreases the maximum load current to be obtained by the switching regulator. If noise remains, replace the current coil with a new one that deadens noise.

Use a large capacitance coil;

Use a coil with unshielded construction.

Coil noise results from any shrinkage of ferrite due to any variation in the magnetic field and is amplified with resonance of the coil and PCB. Coil noise can be minimized by enhancing the coil mount design.

[Switching Regulator] The elctronic volume does not seem to have 8-bit resolution in full range, though it is said to have 8-bit resolution. Is it correct ?

As you have indicated, it is true that the resolution of the electronic volume does not satisfy 8 bits when the S8330A26FS runs at 14 to 26 V.
Linear Error Aspect:
There are 3 definitions of a linear error used in ABLIC’s specifications. To facilitate your understanding, brief and clear explanation is given to each definition as follows.

(1) Specifications covering 0 to 127 of the electronic volume data (at ±23.5 mV)
This is a linear error obtained by connecting the actually-measured output voltage when electronic volume data is 0 and the actually-measured output voltage when electronic volume data is 127, respectively, with a straight line. It corresponds to the difference between the measured value and the calculated output value in any bit of 0 to 127 of the electronic volume.

  

(2) Specifications covering 128 to 255 of the electronic volume data (at ±23.5 mV) This is a linear error obtained by connecting the actually-measured output voltage when electronic volume data is 128 and the actually-measured output voltage when electronic volume data is 255, respectively, with a straight line. It corresponds to the difference between the measured value and the calculated output value in any bit of 128 to 255 of the electronic volume.

(3) Specifications covering 0 to 255 of the electronic volume data (at ±93.8 mV) This is a linear error obtained by connecting the actually-measured output voltage when electronic volume data is 0 and the actually-measured output voltage when electronic volume data is 255, respectively, with a straight line. It corresponds to the difference between the measured value and the calculated output value in any bit of 0 to 255 of the electronic volume.

[Switching Regulator] Models of Inverted Switching Regulators Capable of Creating Negative Voltage?

A switching regulator specifically for use in creating negative voltage is not available. However, negative voltage can be output using a step-up switching regulator.

Inverting Switching Regulator Circuit

The start circuit is not needed because power supply is supplied from VDD pin to the IC. Set voltage VIN to 9V-|V CC. When VCC is -2 V, -3 V and -5 V, be sure to connect VOUT of S-8353D20MC, S8353D30MC and S-8353D50MC to GND without attaching RA, and RB. The external resistor Rb must be 60 ohm or more and RE must be 6 k ohm or less. The larger RE becomes, the smaller the invalid current flowing RE and Rb and also the better the efficiency. A large value for RE raises efficiency due to the reduction of reactive current for RE and Rb. Too large value of RE lowers efficiency due to the large switching loss of the external transistor(Tr). Choose a suitable value of RE under the operating conditions.

[Switching Regulator] Reasons that Duty Ratio Does Not Go up to the Maximum Duty at Heavy Load?

It may be attributed to the continuous mode the IC is entered. Conditions to enter the continuous mode are determined by input voltage and output voltage. Once the continuous mode is entered, the duty ratio does not go up at heavy load.

Figure 1: Continuous Mode Based On the PWM Method

[Switching Regulator] The Reasons That Output Voltage Drops of the Switching Regulator?

One of possible reasons is marginal setting of output current drive, in particular, when a drop appears at low Vin. This drop greatly affects hFE(small) and base resistance Rb value(large) of an external bipolar transistor. In addition, the drop affects value L (large) of the inductor and frequency (high) of the switching regulator to a certain extent. If output voltage drops at large output current despite sufficient output current drive, it results from the load stability characteristic in itself. The following are probable reasons:
(1)PCB patterns
It is known that any drop in output voltage at large output current range greatly differs depending upon PCB patterns. So, you are asked to check whether or not the drop depends on PCB patterns.
(2)Output capacitance
When (1) is deemed ideal, another probable reason is due to output capacitance. If improper output capacitance is selected and used, there may be an apparent drop in output voltage at large output current. For instance, the drop is attributable to (2) if parallel connection of two additional output capacitors allows the drop to be minimized. Control of the switching regulator is extremely affected by, especially, ESR of output capacitor. As you are well aware of, it is experientially effective to minimize the drop in output voltage at large output current by adopting a low ESR tantalum electrolytic capacitor and increasing the output capacitance value.

[Switching Regulator] Problem When Voltage (about 10 V) Higher Than the Output Voltage (about 3.5 V) is Constantly Impressed to the IC?

Basically, up to 9 V can be impressed to input voltage (CONT) pin and output voltage (VOUT) pin, respectively, without causing a problem because voltage of up to 9 V is within the voltage range that warrants normal functions of the IC.
[Reference]
Absolute maximum rating voltage of 11 V warrants that it can safeguard the IC against its breakage even when DC is impressed to the IC. However, operation of the IC is out of the warranty.
In other words, impression of 11 V would lead to an abnormal flow of current or an ON error (EXT=VDD) in the external transistors.

[Switching Regulator] Problem When Forcedly Using a Boosting-Enabled Switching Regulator Incapable of Controlling the Output Voltage by Resistance Division?

When it is used as resistance division, gate charge current will flow from VOUT to EXT to FET in popular FETs. This affects voltage at the VOUT pin. Please avoid this type of use.

[Switching Regulator] Models of Step-up Switching Regulator Capable of Controlling the Output Voltage by Resistance Division?

The following ABLIC’s switching regulators equipped with their own power supply pins allow the output voltage to be controlled by resistance division:

• Types D and J for S-8353 series
• Types D and J for S-8354 series
• All of S-8355 series
• All of S-8356 series
• Types E, J, G and P for S-8357 series
• Types E, J, G and P for S-8358 series
• Types B and D for S-8340 and S-8341 series

[Switching Regulator] How to Decrease Peak Current Flowing through the Coil with ABLIC’s Switching Regulators Contorollers?

Increase inductance value of the coil you use, increase the switching frequency and decrease the “Iout” value. Check the peak current using the GTSCAT Note* (circuit simulation).
Note* : GTSCAT simulates a plurality of characteristics of ABLIC’s switching regulator peripheral circuits. Please download it from ABLIC homepage.
URL: http//www.ABLIC.co.jp/compo/compo.htm

[Switching Regulator] What is the function and influence of an LC filter added to the input side of a switching regulator in a switching power supply circuit?

An LC filter suppresses voltage variation of the power supply.
When there is no LC filter, ripple voltage variation of the magnitude equal to the series resistance of the power supply multiplied by the on-current appears at the power supply.
But if an LC filter is added to the circuit, it suppresses the ripple voltage variation, since the on-currnt of the switching regulator is provided from the capacitor which is charged by rather tranquil current, which reslts from the nature of a inductor.
However please pay atention to the following points.

· The input voltage, which is taken after the LC filter, to the switching regulator becomes easy to vary.

· When the equivalent series resistance “L” is several hundreds of mW or more, efficiency may worsen due to overheat caused by the equivalent resistance and input current.

· This is because the RC filter is formed by the equivalent series resistance and “C,” the input voltage of the switching regulator (after LC filtering) is lower than the power supply voltage (before LC filtering) and eventually output amperage will be decreased.

[Switching Regulator] Use of an Aluminum Electrolytic Capacitor in Cin and Cout?

An aluminum electrolytic capacitor can be used as Cin without causing a problem. Select a large capacitance capacitor (Cout) with low ESR (Equivalent Series Resistance) to level and smoothen the ripple voltage output capacitor. The capacitance is 10mF min. It is recommended to use a tantalum electrolytic capacitor that is superior in low temperature and leak current characteristics. For example, series F93 is deemed ideal.
When the aluminum electrolytic capacitor is used as Cout, the IC may malfunction depending upon its operation conditions and wiring. It is recommended to use a tantalum electrolytic capacitor as practical as possible. When an aluminum electrolytic capacitor is used, be sure to validate influence of ripple and spike noise on your actual product according to the precautions listed in ABLIC’s datasheet. In addition, please note that attaching a ceramic capacitor of 0.1 mF or thereabouts between VOUT-VSS in the vicinity of the IC may avoid a malfunction.

[Switching Regulator] How to Choose a Value for External Parts to be Added to ABLIC’s Switching Regulator Controllers?

Choose a value for external parts by GTSCAT Note* simulation.
Note* GTSCAT simulates several characteristics of ABLIC’s switching regulator peripheral circuits. Please
download it from ABLIC homepage.
URL: http//www.ABLIC.co.jp/compo/compo.htm

[Switching Regulator] How to Select External Parts to Minimize Ripple Voltage of ABLIC’s Switching Regulator Controllers?

Refer to the following table showing the relationship between major characteristics of switching regulators and external parts.

[Switching Regulator] How to Select External Parts to Enhance the Efficiency of ABLIC’s Switching Regulator Controllers?

Refer to the following table showing the relationship between major characteristics of switching regulators and external parts.

[Switching Regulator] How to Select External Parts to be Added to ABLIC’s Switching Regulator Controllers to Obtain Large Output Amperage?

Refer to the following table showing the relationship between major characteristics of switching regulators and external parts.

[Switching Regulator] How to Obtain High Efficiency?

Follow the procedures given below:

– Check the maximum rated current of the coil you use and be sure that it is more than its peak current (failure to do so may lead to magnetic saturation resulting in worsening efficiency).

– Select an external diode with low VF characteristic and speedy first-recovery time.

– Select low ESR of the output capacitance COUT that greatly affects the efficiency.

– Please note that the ON resistance of an external switching transistor differs depending on the value of base resistance RB (resistance between EXT pin and external transistor base) and high RB value worsens efficiency.
Also please note that low RB value leads to an increase in current consumption and may worsen the efficiency

[Product Reliability] How is the product life judged?

Acceleration tests, which are included in periodic reliability tests, are performed for a time equivalent to the product life, to judge the endurance of the product.
Voltage acceleration and temperature acceleration are included in the acceleration tests. ABLIC adopts temperature acceleration tests based on the Arrhenius model.
The acceleration factor conforms to JEITA standard EIAJ ED-4701 and is calculated by the following formula.

(Acceleration factor calculation formula) L = exp(Ea/kT2)/exp(Ea/kT1)
L: Acceleration factor
Ea: Energy of activation
k: Boltzmann coefficient
T2: Actual use temperature (absolute temperature)
T1: Acceleration test temperature (absolute temperature)

Specifically, the following conditions are substituted.
Energy of activation 0.5 eV
Boltzmann coefficient 8.617 × 10-5 eV/K
Actual use temperature 40°C
As a result of the above substitution, the acceleration factor at 125°C is shown to be 52 times that at 40°C. In sum,
1,000 hours are equivalent to 5.9 years
2,000 hours are equivalent to 11.8 years.

As shown above, successfully performing reliability tests at 125°C for 2,000 hours assures that the product life is judged to be at least 10 years at the actual use temperature.

[Package] Does the mold resin contain phosphorus?

Inorganic phosphorus is not used in ABLIC products. Organic phosphorus is used in some packages as a resin hardness accelerator.

[Package] Can packages be used when the power dissipation is momentarily exceeded due to rush current?

The power dissipation is the average power per second.
Packages can be used when the average power is within the power dissipation range, even if a large current momentarily flows due to rush current.

[Package] How should the potential of a radiation pad on the rear of a package be kept constant?
HSON(A), SNB(B), SON(B), PLP

Radiation pads on the rear side are affixed to the IC die substrate via silver paste (conductive paste). Radiation pads, therefore, must be used with the potential of the pads being the same as that of the IC die substrate or floating.

*Caution Radiation pads cannot be used as electrodes.

Product Name Subject Package Name Potential of Radiation Pad
S-1131 6-pin HSON(A) VSS or open
S-1170 6-pin HSON(A) VSS or open
S-8355/56/57/58 6-pin SNB(B) VOUT (VDD for VDD separate type) or open
S-8821 6-pin SNB(B) VSS or open
S-8261 6-pin SNB(B) VDD or open
S-8242 6-pin SNB(B) VDD or open
S-8424A 8-pin SON(B) VSS or open
S-8425 8-pin SON(B) VSS or open
S-83M355/356 PLP-8B See the data sheet.
  • Tips and hints described herein are for your reference only. ABLIC shall not be liable for any warranty and responsibility of use or application of ABLIC's ICs in or to your product regardless of description herein.
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  • Information described herein is subject to revision or change without notice.