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Voltage Regulators

Technical Information on Ricoh Voltage Regulators.

The Fold-Back Protection Circuit shown in the blue ellipse as “Current Limit” protects the regulator from damage by limiting the output current if the output pin (VOUT) and the ground pin (GND) are shorted.
In the datasheet it is shown as a short circuit current (Ilim). The protection circuit limits the current to this value. In Ricoh regulators this is usually set within a range of about 30mA to 70mA. (For the 2A LDO regulator R1171J it is set to 200mA.)
In the typical characteristic, the short circuit current (Ilim) is shown by the blue circle on the “Output Voltage vs Output Current” graph.

R1131x26xx

Products with the Fold-Back Protection Circuit

The Thermal Shutdown Circuit shown in the blue ellipse, detects overheating of the regulator if the output pin (VOUT) is shorted to the ground pin (GND) etc. and stops regulator operation to protect it from damage.
The Thermal Shutdown Circuit stops regulator operation if the junction temperature of the regulator becomes higher than 150°C. Additionally, if the junction temperature after the regulator being stopped decreases to a level below 125°C (120°C for some products), it restarts regulator operation.
As a result the operation of the Thermal Shutdown Circuit causes the regulator repeatedly to turn OFF and ON till the causes of overheating are removed. As a consequence a pulse shaped output voltage occurs. Please prevent this situation.
In the datasheet it is shown as a thermal shutdown detection temperature (TTSD) and a thermal shutdown release temperature (TTSR).

Products with the Thermal Shutdown Circuit

When you switch the regulator from the active mode to the standby mode with the CE pin, the VOUT pin voltage would not immediately fall to the ground level in case an output capacitor took time to discharge. To prevent this, Ricoh added N-channel transistor has been added the output circuit (shown in blue circles in the diagram below) in regulators having this function, so that any output capacitor can be promptly discharged.
This Auto Discharge Function can be combined with the system shutdown sequence.

When the CE pin is in the active mode, the regulator is operating. The P-channel transistor circled in light blue is ON.The N-channel transistor circled in blue that provides the auto discharge function is OFF.

When the CE pin is in the inactive mode, the regulator is in the standby mode. When in standby mode the P-channel transistor circled in light blue turns OFF and stops the regulator output from the VOUT pin. The N-channel transistor circled in blue that provides the auto discharge function turns ON and the charge in the output capacitor connected to the VOUT pin is rapidly discharged to the ground pin. It is called the “Auto Discharge Function”.

This Auto Discharge Function ensures that output rapidly drops when the regulator enters standby mode, but it also effectively prevents problems that might occur if the output capacitor connected to the VOUT pin was to discharge via the system side.

Products with the Auto Discharge Function

How to define which products have an Auto Discharge Function from the Product Name
	Single LDO (Low Drop Out) regulator products include an Auto Discharge Function if the 10th character of product name is a “D”. (Example : R1114N281D-TR-F)
	Multi LDO (Low Drop Out) regulator products include an Auto Discharge Function if the 10th character of product name is a “B”. ( Example : R5322N001B-TR-F RP150K001B-TR)

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An increasing number of devices such as mobile phones, do not have only a talk mode (active mode) and Off mode state, but also a standby mode (sleep mode) etc. However during the active mode and sleep mode the regulator must satisfy very different requirements.
The regulators are required to have a fast response and a high ripple rejection in the active mode, but consume low supply current in the sleep mode. To satisfy these conflicting requirements, Ricoh's regulators include an ECO Function that allows switching between a fast response mode and a low power mode.

Compared to the low power mode, the fast response mode has a load transient response that is more than 100 times faster and output voltage variations are suppressed to 1/10 times smaller.
R1162x28x

Compared to fast response mode, the low power mode supply current is only one tenth.
R1162x28x

During fast response mode, the ripple rejection at 1kHz is about 75dB but during low power mode it drops to about 35dB.
R1162x28x

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There are three methods of switching the ECO Function and Ricoh offers three types of products utilizing each method.

Manual Mode Shift Type (With ECO pin)
	The mode is switched by sending a control signal to the ECO pin. The user can set the switching conditions but a CPU control pin is required.

Automatic Mode Shift Type
	The ECO pin is eliminated and the regulator automatically switches mode depending on system load. A CPU I/O pin can be omitted but the user cannot set the switching conditions.

Seamless Type
	Instead of switching between two modes, a smooth transition is made between modes. Seamless means “no step” so the transition is made without a step.

Manual Mode Shift Type
Automatic Mode Shift Type
Seamless Type

The mode is switched by sending a control signal to the ECO pin.

Switching occurs between low power mode and fast response mode depending on system load (output current).

The supply current smoothly decreases as the system load (output current) decreases.

Products According to Mode Switching Type

Manual Mode Shift Type

Automatic Mode Shift Type

Seamless Type

The Reverse Current Protection Circuit protects the regulator from being damaged by a reverse current from the VOUT pin. If the Reverse Detector detects that the VOUT pin voltage has become higher than the VDD pin voltage, it switches the circuit to prevent a reverse current.
In the R1163 series the reverse current (IREV) is restricted to Max 0.1µA. (When VOUT >= 0.5V and 0V <= VIN <= 6V)

Reverse Current Protection Circuit

Products with Reverse Current Protection Circuit

R1163x

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	PCB Layout
	Ensure the VDD and GND lines are sufficiently robust. If their impedance is too high, noise pickup or unstable operation may result. Connect a capacitor with a suitable value between the VDD and GND pins, and as close as possible to the pins.

Phase Compensation

In LDO (Low Drop Out) regulators, phase compensation is provided to secure stable operation even when the load current is varied. For this purpose, use a capacitor COUT with good frequency characteristics and proper ESR (Equivalent Series Resistance), value in the hatched area.
If you use a tantalum type capacitor and the ESR value of the capacitor is large, the output might be unstable. Evaluate your circuit including consideration of frequency characteristics.
Depending on the capacitor size, manufacturer, and part number, the bias characteristics and temperature characteristics are different. Evaluate the circuit taking actual characteristics into account.

Equivalent Series Resistance vs. Output Current R1116x Series Example The relations between IOUT (Output Current) and ESR of an output capacitor are shown below. The conditions when the white noise level is under 40mV (Avg.) are shown by the hatched area in the graph.
	VIN=VOUT+1V
	C21GRM155B30J105KE18B(Murata)
	Noise Frequency Band: 10Hz～1MHz
	Measurement Temperature: 25°C
	Hatched Area : Noise level below 40mV (average value)

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