3-terminal Regulator

Output voltage
This is the most important characteristic of a 3-terminal regulator. The upper-limit and lower-limit values of the output voltage (i.e., accuracy of the output voltage) are specified under given conditions of junction temperature, input voltage, and output current (load current) .
When designing your system using a 3-terminal regulator, make sure that the conditions of the output voltage of the regulator are satisfied. The output voltage of NEC Electronics' 3-terminal regulators is indicated in their part number.
Example uPC2405AHF: uPC2400AHF Series with output voltage of 5 V
Reference:Usage of Three-Terminal Regulators

Line regulation
This is the maximum value of changes in the output voltage when the input voltage varies in a specific range at constant conditions of junction temperature (normally T_j=125°C) and output current. The lower the Line regulation, the higher the stability of the output voltage of an IC.
Reference: Usage of Three-Terminal Regulators

load regulation (output stability)
This is the maximum value of changes in the output voltage when the output current (load current) varies in a specific range at constant conditions of junction temperature (normally T_j=125°C) and input current. The lower the load regulation, the higher the stability of the output voltage of an IC.
Reference: Usage of Three-Terminal Regulators

Quiescent current
This is the current necessary for an IC to operate, which is specified as a current flowing from an input pin to a GND pin.

Ripple rejection
This is the ratio expressed in dB at which the alternate current (AC) component included in an input voltage attenuates before it is produced as an output voltage. The higher the ripple rejection, the better the performance as changes in the input voltage do not appear as the output voltage.

Ripple rejection =20log (ΔV_IN/ΔV_O) [dB]

The ripple rejection is dependent on the frequency of the AC component. NEC Electronics usually specifies the ripple rejection of its products at 120 Hz.

Output noise voltage
When an IC operates, noise is internally generated. The output noise voltage is noise generated inside an IC and appears as an output and is expressed as an effective value. The lower the output noise voltage, the more suitable the IC is for the voltage for a circuit that handles audio signals or minute voltages.

Dropout voltage
This is the difference between the input voltage and output voltage required for an IC to produce a stable output voltage. The product of the input and output voltage difference and the output current is the input-output loss of the 3-terminal regulator. Therefore, the lower this value is, the lower the loss of the 3-terminal regulator.
Reference: Usage of Three-Terminal Regulators

Total loss
The total loss of a 3-terminal regulator is the sum of the input-output loss and the circuit loss.
In other words, total loss P_d can be expressed by the following equation.
P_d= (V_IN-V_O) ·I_O+V_IN·(I_bias+ΔI_bias1)
(V_IN-V_O) : Input-output voltage difference
I_O: Output current
I_bias: Quiescent current
ΔI_bias1: Quiescent current change

Peak output current
A 3-terminal regulator has an internal overcurrent restriction circuit. The peak output current is an output current value at which the overcurrent restriction circuit starts operating. If an attempt is made to flow a current exceeding the peak output current, the output voltage drops.
Usually, the overcurrent restriction circuit is used in combination with a stable operation area restriction circuit, and the overcurrent is restricted at the lower peak output current if the voltage difference between the input and output is great (if the input voltage is high) or if the chip temperature is high. Take the uPC2900 Series with an output current of 1 A, for example. If the input voltage is high or if the chip temperature is high, the restriction circuits may operate, lowering the output voltage, even when the output current is less than 1 A.
Reference: Usage of Three-Terminal Regulators

Short circuit current
This is the current output from the output pin if the output short-circuited with ground by accident. This value is determined by the characteristics of the overcurrent restriction circuit. That is, the higher the input voltage and the higher the chip temperature, the more the current is restricted.

Caution This parameter does not guarantee the reliability. Do not short-circuit the output continuously. If continuous output short-circuiting must be guaranteed, use external circuits.

Temperature coefficient of output voltage
The output voltage changes depending on the chip temperature. The temperature change of output voltage is a change in the output voltage when the chip temperature is in a range of 0 to 125°C. The lower this value, the better. However, because this parameter is not a guaranteed value, it usually cannot be used for an application where changes in the output voltage with temperature are required. For applications where changes in the output voltage with temperature must be guaranteed, the following products are recommended.

uPC1060: 2.5 V reference voltage source
uPC1093: Variable output shunt regulator
uPC1943, 1944, 1945: Low-voltage shunt regulator

Startup quiescent current
Low dropout regulators like the uPC2400 Series use a PNP transistor in their output stage. When the input voltage is low, therefore, this transistor saturates and a high current flows from the input to GND. At startup operation, the circuit operating current is at the maximum value of this current. Unless a current exceeding this value flows, the regulator does not operate correctly.

Fold-back type drooping (fold-back type load) characteristics
These are the changes in the output voltage expressed as load characteristics when the output current is gradually increased. The output current immediately before the output current decreases because the internal overcurrent restriction circuit of the IC operates is called a peak output current (I_Opeak) . The output current at which the output voltage is decreased to 0 V by action of the overcurrent restriction circuit is called an output short-circuit current (I_Oshort).
If the peak output current is higher than the output short-circuit current, the output voltage vs. output current characteristic has a fold-back shape. If the peak output current is equal to the output short-circuit current, the characteristic curve shows "constant current drooping characteristics" in a shape like reversed letter "L".

Can a negative voltage be output when a positive voltage is input (for example, "+5 V → -12 V") ?

No, it cannot.
The 3-terminal regulator can output only a positive voltage when a positive voltage is input.

Can a positive voltage be output when a negative voltage is input (for example, "-12 V → +5 V") ?

No.
The 3-terminal regulator can output only a negative voltage when a negative voltage is input.

Can a higher voltage be output when a lower voltage is input (for example "+3 V → +5 V" or "-3 V → -5 V") ?

No.
The output voltage of the 3-terminal regulator must be less than the input voltage in absolute value.

In what conditions does the overheat protection circuit operate?

It operates when the junction temperature (T_j) exceeds the absolute maximum rating (generally, 150°C) . It shuts off the output of the IC where T_j is 150 to 200°C.

In what conditions is the overheat protection circuit deactivated?

It is automatically deactivated when the junction temperature (T_j) drops below the overheat protection circuit operating temperature (150 to 200°C) .

Isn't the product degraded if the overheat protection circuit operates?

The overheat protection circuit operates because the junction temperature (T_j) exceeds the absolute maximum rating. There is a high possibility that the product is degraded.

Which is the purpose of the overheat protection circuit, to protect the regulator IC itself or the peripheral circuits?

There are cases where the IC overruns immediately before it breaks down, affecting the peripheral circuits. The overheat protection circuit is to secure safety of the peripheral circuit as well by protecting the IC itself.

What are variations of the overcurrent restriction circuit?

The peak output current (I_Opeak) indicates the operation starting point of the overcurrent restriction circuit. Refer to the variations of the peak output current.

I can't find a specification for the junction-case thermal resistance in the case of a self-standing package product (e.g. uPC78L05J).

The uPC78L05J is housed in a self-standing package, but this is a TO-92 package, which doesn't have a heat sink attached. We therefore ask you to design your product based on the value of the thermal resistance between the junction and ambient air. Note that self-standing packages with a heat sink attached do have a specification for the junction-case thermal resistance.

(2006/03)

Output Noise Voltage (V_n) Conditions column in Electrical Characteristics for the uPC7800A Series has "10 Hz ≤ f ≤ 100 kHz", but what does this indicate?

[Output Noise Voltage] uPC7805A

Parameter	Symbol	Condition	MIN.	TYP.	MAX.	Unit
Output noise voltage	Vn	TJ=25°C,10 Hz ≤ f ≤ 100 kHz		40	200	µVrms

The output noise voltage is measured under the condition of setting a bandpass filter to the output pin and the measured result is expressed as the effective (root mean square) voltage value. "10 Hz ≤ f ≤ 100 kHz" indicates the bandwidth of this bandpass filter. The unit is usually µVrms.

[Related FAQ]
Please explain the meanings of the units used to measure electricity.

(2006/12)

3-pin regulator: The overcurrent restriction circuit, thermal shut down circuit, and stable operation area restriction circuit are described in the UPC29M10T Data Sheet, but is a shutdown function for circuit protection not provided?
Also, does only the overcurrent restriction circuit operate in the output shorted state?

[UPC29M00 Series Block Diagram]

A protection circuit that completely nullifies the output current (shutdown function) is not incorporated (refer to the Vo-Io characteristic in the data sheet: A fold-back type drooping load characteristic can be verified, and a slight output current flows even when the output voltage is 0 V.)

[Vo-Io Characteristic: UPC29M03]


When an output shorts, the overcurrent restriction circuit operates, and if no measure is taken, the overheating protection circuit, stable operation area restriction circuit, etc., begin operating as the temperature rises. For this reason, it cannot be said that "only the overcurrent restriction circuit operates in the output shorted state."

[Related FAQ]
Terminology

(2007/02)

A reference voltage (V_REF) is defined in the electrical specifications of the three-terminal positive adjustable regulator (uPC317). What is the meaning of this voltage?
How is the reference voltage (V_REF) used?

Although the uPC317 is a three-terminal voltage regulator IC, any output voltage can be set externally. Therefore, the reference voltage (V_REF) is defined and publicized.

The desired output voltage can be easily calculated by using R₁ and R₂, based on the reference voltage (V_REF). The following diagram and description below explains the operation.

[Block diagram]


The operating circuit current necessary for each block is output from the OUTPUT pin and flows through R₁ and R₂ into external GND.
The current (I_ADJ) flowing out of the ADJ pin is 100 uA at the most, but the current ratio of I_ADJ to V_REF/R₁ must be sufficiently large in order to obtain a stable output voltage.
The recommended value of R₁ is 240 Ω and, therefore, V_REF / R₁ = 1.25 V /240 Ω = 5.2 mA. In this case, its current ratio to I_ADJ is about 52. Although the details are explained later, a stable output voltage can be set with only the external resistance ratio if a current ratio as much as this is obtained.

When the output voltage is stabilized, the voltage between both ends of R₁ is equal to V_REF (when imaginary short-circuiting of the error amplifier is established).
If the voltage of OUTPUT drops for some reason in this status, the voltage between both ends of R₁ falls below V_REF. Consequently, a positive voltage is applied to the non-inverted pin of the error amplifier, raising the bias voltage of Tr1 and forcing the voltage of OUTPUT to rise. Conversely, if OUTPUT increases, the voltage between both ends of R₁ rises above V_REF, lowering the bias voltage of Tr1 and forcing the voltage of OUTPUT to lower.

In this way, V_REF serves as a reference in the above control action to keep the voltage of OUTPUT constant.

In addition, any output voltage can be set by the external circuit, by using the operation that keeps the output voltage constant. An example of a standard connection for this is given below.



The voltage between the ADJ pin and OUTPUT pin is kept the same as the reference voltage (V_REF) if the ADJ pin is used as a common point. Since the current flowing between these pins (1.25 V / 240 Ω = 5.2 mA) ends up to be kept constant, by changing the resistance of R₂, the voltage between the ADJ pin and ground can be changed.
The output voltage is determined by the following expression.
V_O = R₂ (I_ADJ + V_REF / R₁) + V_REF
≈ R₂ × V_REF / R₁ + V_REF (I_ADJ: Current flowing out of ADJ pin is ignored.)
= (1 + R₂ / R₁) × V_REF
From this expression, it can be learned that the output voltage can be changed by the rate of R₁ and R₂ while V_REF serves as a reference voltage.

Related FAQ: How should the resistors (R₁ and R₂) for the output voltage setting circuit of the three-terminal positive adjustable regulator (uPC317) be set?

(2007/04)

How can I calculate the total dissipation (P_T) of the uPC317?
I know that the total dissipation of a 3-terminal regulator is the sum of the dissipation between the input and output and the circuit dissipation. Can I therefore use the following equation to calculate the total dissipation of the uPC317?

The uPC317 is different from an ordinary 3-terminal regulator in circuit configuration. Specifically, most of the circuit operating current (I_bias<1>) (shown in the block diagram) flows out from the OUTPUT pin as the output current (I_O).
The rest of the circuit operating current (I_bias<2>) flows out from the ADJ pin as IADJ. Therefore, total dissipation P_T is calculated as follows.

P_T = (V_IN - V_O)•I_O + V_IN•IADJ, where I_O includes I_bias<1>.

However, IADJ can be ignored because it is at the micro ampere (µA) level as described in the electrical specifications, and therefore, the total dissipation (P_T) can be calculated by this expression.

P_T = (V_IN - V_O)•I_O

(2007/08)

Is a capacitor necessary at the input side and output side?

Yes.
The low-saturation regulator and negative output regulator are likely to oscillate depending on the capacitance and type of the capacitor. Therefore, be sure to use the capacitor introduced in the Data Sheet. As the input capacitor, the one with good temperature characteristics and frequency characteristics is recommended.

Using a tantalum capacitor or a film capacitor is recommended as an external capacitor. Can any other capacitor be used?

Any capacitor can do as long as it has good temperature characteristics and frequency characteristics.
Some capacitors have poor temperature characteristics and frequency characteristics.
Therefore, be careful about the characteristics of the capacitor to be used.

1. Some electrolytic capacitors substantially decrease in capacitance at a low temperature (0 °C or lower). The specified capacitance must be secured at the temperature at which you use the capacitor. 2. Generally, the capacitance of an electrolytic capacitor is measured at a frequency as low as 100 to 120 Hz. If the frequency rises, the capacitance of some electrolytic capacitors substantially drops. The 3-terminal regulator oscillates in the vicinity of 1 to 3 MHz. Therefore, the specified capacitance must be secured at 1 to 3 MHz. If a capacitor with poor frequency characteristics is used, oscillation must be suppressed by connecting a capacitor with good high-frequency characteristics in parallel.

Particular caution is required regarding the characteristics of electrolytic capacitors.
In addition, some ceramic capacitors also have poor characteristics. Exercise care in selecting capacitors.
Generally, the characteristics of a tantalum capacitor are stable.
Therefore, use of a tantalum capacitor is recommended in the Data Sheet.
Note that oscillation could also occur when using a capacitor with low ESR (equivalent series resistance) or ESL (equivalent series inductance). It is therefore very important to sufficiently evaluate your system with the capacitor to be used, because the ESR and ESL are affected by temperature and frequency.

(2007/11)

Can the driving current be increased by parallel connection?

No.
If the current is insufficient, dissipates the heat or connect a transistor to the output.
Reference:Usage of Three-Terminal Regulators

Can the output voltage be increased by inserting a resistor to GND of a low dropout regulator?

No.
A circuit operating current at startup that is higher than the normal circuit operating current flows through a low dropout regulator. If such a circuit is used, the output voltage increases at startup or stopping the regulator.
Reference:Usage of Three-Terminal Regulators

Is there any problem if the recommended output current shown in the Data Sheet is exceeded?

It is considered that the 3-terminal regulator does not break down even if the maximum value of the output current (1 A for the uPC2900 Series) is exceeded.
An output current is not specified for the 3-terminal regulator. The 3-terminal regulator has an internal overcurrent restriction circuit to restrict the overcurrent under overload condition. If the output current exceeds the recommended condition, however, the characteristic values are not guaranteed. We recommend choosing another IC.

What are the drooping characteristics of the output?

They can be easily calculated from the I_Opeak-(V_IN-V_O) characteristics.

What will happen if the regulator is kept used with V_IN lower than the recommended condition?

An output voltage almost equal to the input voltage is output.
Under such a condition, however, the electrical specifications and the operation of the protection circuits are not guaranteed. When a 3-terminal low dropout regulator is used, a high circuit current flows and the temperature rises if V_IN is lower than the regulation start voltage.

What will happen if the regulator is kept used with V_IN higher than the recommended condition?

The regulator will not break down as long as the absolute maximum rating is not exceeded. However, the voltage difference between input and output increases and therefore, consideration must be given to a temperature rise. Also note that there is little margin of the input voltage of absolute maximum rating.

Do problems, such as breakdown and temperature rise, occur if the regulator is used without load?

Generally, there is no problem even if the regulator is used without load. However, the possibility that oscillation occurs increases. Thoroughly evaluate the characteristics of the regulator in the application set.
Do not use variable output type regulators without load because the variable output types are prescribed to be used with the minimum output current (refer to Troubleshooting).

Is there any problem as the junction temperature does not exceed the absolute maximum rating, even if the ambient operating temperature exceeds the absolute maximum rating?

Yes. The reliability cannot be guaranteed.
The value of even one parameter of the absolute maximum ratings must not be exceeded.

Can a variable output type 3-terminal regulator output the voltage from 5 to 3.3 V?

No.
The uPC317 and uPC7800 Series requires 3 V or more voltage difference between input and output. Use the uPC2933 (3.1 V output) of the uPC2900 Series that operates with 1 V or more voltage difference between input and output.

There are three parameters of V_O for the uPC7805A.
The temperature conditions of two are shown but those of the third are not.
Is it all right to consider that T_j of the parameter whose temperature conditions are not shown is 0 to 125°C?

That is correct; T_j is 0 to 125°C.
The conditions (common conditions) shown in the margin are applied to a parameter whose conditions are not shown.
These conditions are also applied to the parameter in question.

What kind of diode should I use for D1 in the Standard Circuit Connection section (assuming a connection whereby the OUTPUT pin has a higher voltage than the INPUT pin)?

With the aim of mitigating damage to the power supply IC, we would recommend using a Schottky barrier diode. Note that the withstanding voltage of the diode must be equal to or higher than the voltage differential between INPUT and OUTPUT.

(2006/03)

What withstanding voltage of a reverse current protection diode (which passes current flowing from the output to input) should I use when the voltage of the output pin of my 3-terminal regulator (for a positive power supply) becomes higher than the input pin's voltage?

The withstanding voltage of the diode in this case must be higher (at least 1.2 to 1.3 times higher) than the absolute maximum rating of the 3-terminal regulator IC's input voltage.

Example: uPC29xxB series

(2006/09)

I would like to use the uPC7805AHF with the input voltage set to 30 V, but the recommended operating conditions list the input voltage as 25 V max. What problems would occur if the uPC7805AHF is used with the input voltage set to 30 V?

The uPC7805AHF can be used safely at 30 V without degradation of characteristics or damage. However, caution is required for the absolute maximum rating for the internal power dissipation (P_T). Be sure to use the uPC7805AHF in a range that does not exceed absolute maximum rating P_T.

(2006/11)

Which points regarding the quiescent current (I_BIAS) specification should one be careful of during circuit design using the uPC2933A?

I_BIAS is a current necessary for each internal block of the power IC to operate in the steady state, and defines a current that flows from an input pin to a GND pin.
In addition, the startup quiescent current (I_BIAS(S)) must also be noted.
A low dropout voltage regulator such as the uPC2900 series uses a PNP transistor as the output-stage transistor. This transistor is saturated and a high current flows from the input pin to the GND pin when the input voltage is low at startup. The startup quiescent current is the maximum value of this current. The regulator does not operate correctly unless the startup quiescent current flows.

[Example of uPC2933A]

Item	Symbol	Conditions	MIN.	TYP.	MAX.	Unit
Quiescent current	IBIAS	Io=0A		2.0	3.0	mA
Startup quiescent current	IBIAS(s)	VIN=3.1V,Io=0A		10	30	mA

The quiescent current in this example indicates that ICs require I_BIAS of 2.0 mA on average to operate in the steady state, and that ICs through which up to 3.0 mA flows are included.
Similarly, it indicates that ICs through which a startup quiescent current of up to 30 mA flows are included.
Therefore, an external power supply that can supply a current of at least 30 mA to the input pins of the ICs is necessary, in addition to the current that flows into the circuit load.

(2006/12)

How should the resistors (R₁ and R₂) for the output voltage setting circuit of the three-terminal positive adjustable regulator (uPC317) be set?

Basically, a 240 Ω resistor is recommended for R₁ in the above standard connection.
Output voltage Vo is calculated by the following expression and is shown in the table below, where R₁ is 240 Ω.

Vo = (1+R₂/R₁) × V_REF


If R₁ is a value higher than 240 Ω, the following points must be noted.
If R₁ is at 240 Ω, 1.25 V/240 Ω = 5.2 mA flows through R₁, even without load. In the meantime, the current (I_ADJ) flowing out from the ADJ pin is defined to be 100 uA (max.) in the electrical specifications, which is considerably lower than 5.2 mA and is negligible.
If R₁ is increased to a value higher than 240 Ω (1 kΩ, for example), the value of the current flowing through R₁ decreases. Consequently, the value of I_ADJ may no longer be negligible, resulting in deterioration of the output accuracy.

(2007/04)

If a 3-terminal regulator is used in a dual power supply circuit, only one of the power supplies operates.Why?

The IC does not operate if a power is supplied to its output pin from an external source.
In the case of a dual power supply circuit, a reverse voltage is supplied to one IC with the load if the other is activated first.
In this state, the IC does not operate.

Once the IC has fallen in this condition, it does not recover until the voltage applied to all the pins reaches zero.
Protect the IC with a diode (such as Schottky barrier diode) with a low forward voltage so that a reverse current does not flow through the output pin.

The operation becomes unstable when the output pin is pulled up with a resistor.

The 3-terminal regulator is designed on the assumption that a current is supplied to the load.
If a current is supplied to its output pin from an external source, the regulator becomes uncontrollable and cannot operate normally.

Once the regulator has become uncontrollable, it may not recover until the power is turned off. Therefore, do not pull up the output pin.

With the variable output type uPC317, the output voltage exceeds the rated value if the output is opened.

The output of a variable output type must not be opened because the minimum output current is specified.
The uPC317 does not start at a load current of 3 mA or less at room temperature. When it does not start, the output voltage exceeds the rated value.

The output voltage does not rise if a positive-negative power supply is created.

If the positive power supply rises slower than the negative power supply, a current flows from GND of the positive power supply to OUTPUT, and consequently, the positive power supply does not rise. Bypass the current by connecting a diode between GND and OUTPUT.

The output voltage drops when a load is connected.

The possible causes and actions are as follows.

Cause: The output oscillates.
Action: Check connection of the capacitor connected between input and output.

Cause: A current exceeding the peak output current flows.
Action: Lower the input voltage. Effectively dissipate the heat to lower the chip temperature.
Caution A high current is required for starting the regulator when a motor or a lamp is connected as the load.

Cause: The chip temperature exceeds 150°C.
Action: Lower the input voltage. Effectively dissipate the heat to lower the chip temperature.

Cause: The input and output are connected in reverse.
Action: Check the pin connection.

Cause: The capacitance of the previous-step power supply is insufficient (in the case of a low-saturation regulator).
Action: When a low-saturation regulator is used, prepare a power supply that can supply a circuit operating current at startup, as well as an output current.

The output oscillates.

The possible causes and actions are as follows.

Cause: A capacitor not specified in the Data Sheet is connected between the input and output.
Action: If only an aluminum electrolytic capacitor is connected to the input side, connect the specified capacitor. If a (laminated) ceramic capacitor is connected, replace it with the specified capacitor.

Cause: The distance between the capacitor and IC is too long.
Action: Keep the wiring length to within 1 cm.

Note For the 3-terminal low dropout regulator type or negative output type, connect a capacitor with a low series equivalent resistance (low impedance) to the output.

The base metal is exposed at the roots of a pin.

There is no problem. If the lead is plated up to the thinner part, the product is good.