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Important Points in the Design of a Power Supply Using a Linear RegulatorTypical Application Circuit Examples of Linear Regulator ICs

2025.01.27

table of contents

・About the Linear Regulator IC Used as an Example
・Typical Application Circuit Examples of Linear Regulator ICs
・Method for Setting the Output Voltage of an Adjustable Output Linear Regulator IC
・Kelvin Connections to Linear Regulator ICs
・Output Voltage Errors of a Linear Regulator IC

About the Linear Regulator IC Used as an Example

The linear regulator ICs used in the explanations of this section are the BDxxIC0 series with an output current of 1.0 A. This is one series in a family of linear regulator ICs constituting a broad lineup of devices. The BDxxIC0 series includes both adjustable-output and fixed-output devices; each model is available in two different packages. HTSOP-J8 package models are available in three grades, for consumer, industrial, and automotive. When the “xx” in a part number is “00”, the output voltage is adjustable; in the case of a fixed output device, the “xx” is a two-digit code that indicates the output voltage. Further details can be found on the data sheets linked to the part numbers. Here we essentially describe examples of consumer-grade devices with adjustable and fixed output voltages.

Package Types	Adjustable Output Devices	Fixed Output Devices
HTSOP-J8	BD00IC0WEFJ（Consumer） BD00IC0MEFJ-LB（Industrial） BD00IC0MEFJ-M（Automotive）	BDxxIC0WEFJ（Consumer） BDxxIC0MEFJ-LB（Industrial） BDxxIC0MEFJ-M（Automotive）
HVSOF6	BD00IC0WHFV（Consumer）	BDxxIC0WHFV（Consumer）

■Block Diagrams

Block Diagrams

■Basic Application Circuits

Basic Application Circuits

The BDxxIC0 series is highly versatile, and as the basic application circuits presented above indicate, this series devices have widely used pin configurations that include input, output, FB/VO_S (adjustable/fixed output types), and EN (output on/off switching) pins. (FIN represents an exposed pad on the rear surface.)

The devices are (low-saturation) LDOs that adopt P-channel MOSFETs as output-stage transistors. The output current is 1A, and both the reference voltage (adjustable type) and output voltage (fixed type) have high precisions of ±1%. The adjustable output devices use external resistors R₁ and R₂, allowing a desired output voltage to be set between 0.8 V and 4.5 V There are nine fixed output models available, with output voltages from 1.0 V to 3.3 V.

Overcurrent protection circuits and thermal shutdown circuits to prevent IC destruction are provided internally; an EN pin to turn the output on and off is also present. Ceramic capacitors can be used as the output capacitors.

Below are listed the features of the BDxxIC0 series.

・Input power supply voltage range: 2.4 V to 5.5 V
・Output current: 1.0 A （Max.）
・Internal high-precision reference voltage circuit: ±1%
・Output voltage range (Adjustable output type): 0.8 V to 4.5 V
・Output voltage (Fixed output type): 1.0 V/1.2 V/1.25 V/1.5 V/1.8 V/2.5 V/2.6 V/3.0 V/3. 3V (1.25 V/2.6 V: HVSOF6 only)
・Shutdown current:：0 µA（Typ.）
・Built-in overcurrent protection circuit（OCP）
・Built-in thermal shutdown circuit（TSD）
・Output on/off (EN) pin
・Halogen-free design (HVSOF6 package)
・Operating temperature range: -25 to +85℃

Typical Application Circuit Examples of Linear Regulator ICs

Adjustable Output Devices

We begin by presenting application circuit examples of adjustable output linear regulators. The pin configurations and pin functions of the two types of packages are also shown. Adjustable output devices require external voltage dividing resistors to set the output voltage in addition to the other external components, which are an input capacitor and an output capacitor.
Even though the packages and pin configurations are different, pins with the same names have the same functions. What is different from fixed output devices, described later, is the presence in adjustable output devices of an FB pin.

Adjustable output device, HTSOP-J8 package BD00IC0WEFJ, BD00IC0MEFJ-LB, BD00IC0MEFJ-M	Adjustable output device, HVSOF6 package BD00IC0WHFV

*The circuit example for the HTSOP-J8 package shows an example in which the EN pin is used to turn output on and off. The example for the HVSOF6 package shows an example in which the EN pin is connected to V_CC and the on/off function is not used. The EN pin function is the same for both packages.
*The pin configuration diagram is a top view.

HTSOP-J8 pin number	HVSOF6 pin number	Pin name	Function
1	1	V_O	Output pin Supplies power to the load. In order to prevent oscillation, a capacitor must be connected between V_O and GND.
2	2	FB	Output voltage setting pin Output voltage feedback pin. Since the IC operates such that the FB pin is at 0.8 V, a resistor divider is connected to obtain a desired output voltage. The settable output voltage range is 0.8 V to 4.5 V.
3	3	GND	Ground pin Ground for the regulator circuit.
4	–	N.C	Unconnected pin The N.C pin is not connected to the internal circuit. It should either be connected to GND or left open.
5	4	EN	Enable pin When this pin is set to high level, the output is turned on, and when set to low, the output is turned off.
6, 7	5	N.C	Unconnected pin The N.C pin is not connected to the internal circuit. It should either be connected to GND or left open.
8	6	V_CC	Input pin Power supply input to the IC. In order to keep the input stable, a ceramic capacitor must be connected between V_CC and GND. The capacitor should be located close to the pin.
E-Pad	E-Pad	FIN	Exposed pad The exposed pad on the rear surface is connected to the die via the lead frame. It is recommended that it be soldered to a ground plane with a broad copper foil area in order to increase heat dissipation efficiency. The exposed pad is electrically connected to GND via a substrate within the package.

Fixed Output Devices

Next, application circuit examples of fixed output linear regulator as well as the pin configurations and pin functions for two types of packages are described. Fixed output devices do not require external voltage dividing resistors to set the voltage, and so the only required external components are an input capacitor and an output capacitor. Fixed output devices do not have an FB pin to set the output voltage as with adjustable output devices, but instead are provided with a V_{O_S} pin. This pin is used to detect the output voltage at the load. Details are described in the separate article “Kelvin connections”. Similarly to the adjustable output devices, in the case of the fixed output devices also, pins with the same name have the same functions even if the packages and pin configurations are different.

Fixed output device, HTSOP-J8 package BDxxIC0WEFJ, BDxxIC0MEFJ-LB, BDxxIC0MEFJ-M	Fixed output device, HVSOF6 package BDxxIC0WHFV

HTSOP-J8 pin number	HVSOF6 pin number	Pin name	Function
1	1	V_O	Output pin Supplies power to the load. In order to prevent oscillation, a capacitor must be connected between V_O and GND.
2	2	V_{O_S}	Output voltage detection pin This pin is used to cancel the voltage drop occurring in the wiring resistance between the regulator output and the load.
3	3	GND	Ground pin Ground for the regulator circuit.
4	–	N.C	Unconnected pin The N.C pin is not connected to the internal circuit. It should either be connected to GND or left open.
5	4	EN	Enable pin When this pin is set to high level, the output is turned on, and when set to low, the output is turned off.
6, 7	5	N.C	Unconnected pin The N.C pin is not connected to the internal circuit. It should either be connected to GND or left open.
8	6	V_CC	Input pin Power supply input to the IC. In order to keep the input stable, a ceramic capacitor must be connected between V_CC and GND. The capacitor should be located close to the pin.
E-Pad	E-Pad	FIN	Exposed pad The exposed pad on the rear surface is connected to the die via the lead frame. It is recommended that it be soldered to a ground plane with a broad copper foil area in order to increase heat dissipation efficiency. The exposed pad is electrically connected to GND via a substrate within the package.

Method for Setting the Output Voltage of an Adjustable Output Linear Regulator IC

We begin with an application circuit example for an adjustable-output IC. The pin configurations and pin functions for the two packages are also shown.

\(V_\text{out} = 0.8 \times \displaystyle \frac{R_1 + R_2}{R_2} \, [\text{V}]\)

It is recommended that R₁ and R₂ be set such that the sum of the two values is between 1 kΩ and 90 kΩ.

Method for Setting the Output Voltage of an Adjustable Output Linear Regulator IC

As shown in the figure above, this IC outputs to the V_O pin a voltage such that the FB pin is at 0.8 V with reference to ground. The current I₂ in R₂ can be calculated as 0.8 V/ R₂, and the current in R₁ is equal to the current in R₂ with the bias current I_FB through the FB pin added. However, the internal circuit (error amplifier) at the FB pin is a MOSFET gate input, and so the bias current I_FB is extremely small, and can be neglected. The output voltage V_OUT is equal to 0.8 V plus the voltage equal to the product of R₁ and I₂, as shown in the equation:

\(V_\text{out} = 0.8 + R_1 I_2 = 0.8 + R_1 \displaystyle \frac{0.8}{R_2} = 0.8 \times \left(1 + \displaystyle \frac{R_1}{R_2}\right)\)

As a note of caution, in the PCB layout, the lower side of the output voltage setting resistor R₂ should be connected directly to the GND pin in order to obtain the optimum load regulation performance.

Next, resistor values used to set typical output voltages are shown in tables. Of course, the equation shown above can be used to compute resistor values, but tables such as these can be used as well. In this example, the E24 series is used for nominal resistor values. The “Set with minimum number of components” table is used to select the two resistances closest to the calculated values from the E24 series nominal values, with a certain amount of output voltage tolerance. The “High precision setting” table is an option for obtaining the output voltage with precision by combining a plurality of resistors to obtain the calculated value.

The same resistor types should be used for the resistors R₁ and R₂. If the types are different, differences in the tolerances and temperature characteristics will result in changes in the ratio of R₁ and R₂, and there is an increased possibility that the output voltage precision will be worsened. Also, when using chip resistors of size 0402 mm (01005 inch) or smaller, resistors must be selected with attention paid to the resistor rated power and rated voltage, and to the maximum usable voltage.

Setting with minimum number of components,High precision setting

Kelvin Connections to Linear Regulator ICs

By using Kelvin connections at the output of a linear regulator IC, the voltage drop from the output pin to the load is compensated, and the preset output voltage can be supplied to the load. This is sometimes called remote sensing. Different methods are used for adjustable-output ICs and for fixed-output ICs, so they are explained separately.

Kelvin Connections for Adjustable Output Devices

Normally, optimal regulation is obtained when an output voltage setting resistor is connected to the V_O pin. However, during use under such conditions as a large load current, narrow wiring width to the load, or a long distance to the load, there is the possibility that a voltage drop may occur due to the resistance of the thin film wiring of the PCB. For this reason, the actual voltage at the load end is lower than the preset voltage.

This voltage drop can be compensated for by connecting the upper side of the output voltage setting resistor divider as close as possible to the load. Noise tolerance is obtained by placing a high-impedance resistor divider close to the IC and extending the low-impedance wiring on the upper side of the resistors to the load. The IC ground is likewise connected by independent ground wiring up to the load so that it is not affected by voltage drop due to the load current (see the diagram below).

Kelvin Connections for Adjustable Output Devices
* I_LARGE is a large current flowing in the board wiring; the resistance symbols appearing in the V_O and GND lines represent wiring resistances.

The output capacitor C_OUT for the IC should be placed near the load. When dealing with sharp load responses, a large value capacitor C_BULK should be added.

Kelvin Connection for Fixed-Output Devices

Fixed-output ICs have internal resistors to set the output voltage. In the case of standard 3-terminal regulators and the like, the upper side of the resistor divider is connected to the output within the IC (there is no V_{O_S} pin which is shown in the block diagram below, and the upper side is internally connected to V_O). ICs configured in this way do not allow Kelvin connections. In the BDxxIC0 series devices, the upper side of the resistor divider is exposed externally as the V_{O_S} pin, so that Kelvin connections can be made as with the adjustable output devices (see the diagram below).

Kelvin Connection for Fixed-Output Devices
* I_LARGE is a large current flowing in the board wiring; the resistance symbols appearing in the V_O and GND lines represent wiring resistances.

In cases where a regulator IC that does not have a V_{O_S} pin or a pin with a similar function is being used and the voltage drop up to the load is a problem, it can be resolved by switching to a regulator IC that does have such a pin.

Output Voltage Errors of a Linear Regulator IC

The maximum error in the output voltage of a fixed output device is the sum total of the output voltage tolerance, the line regulation tolerance, and the load regulation tolerance. This is a combination of three parameters based on the maximum and minimum values for each, and so is slightly complicated; but the matter must be examined in order to be able to infer the worst-case value.

In the case of an adjustable output device, the product of the reference voltage (V_FB) tolerance and the tolerance of the external resistors used to set the output voltage (see the formulas below) is combined with the line regulation tolerance and the load regulation tolerance.

Output voltage tolerance for an adjustable output device

Minimum value

\( V_{\text{OUT(MIN)}} = V_{\text{C(MIN)}} \times \displaystyle \frac{R_{\text{1(MIN)}} + R_{\text{2(MAX)}}}{R_{\text{2(MAX)}}} \, [\text{V}] \)

Maximum value

\( V_{\text{OUT(MAX)}} = V_{\text{C(MAX)}} \times \displaystyle \frac{R_{\text{1(MAX)}} + R_{\text{2(MIN)}}}{R_{\text{2(MIN)}}} \, [\text{V}] \)

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