Applikationsnoten

Wandler+Regler+Überwachung = RICOH RP600

Der RP600 ist ein neues Produkt aus Ricohs Power Management IC Portfolio, bestehend aus drei elementaren Blöcken, mit denen spezielle Schaltungsanforderungen erfüllt werden können.

DC/DC-Wandler, Spannungsregler und Spannungsüberwachung sind in einem Chip vereint, basierend auf den früheren Produkten RS5RJ und RS5RM, jedoch mit erweiterter Funktionalität.

siehe auch: RP600-Artikel

EXAMPLES WHEN TO USE RP600

• If the input voltage varies in a range above and below the desired output voltage
• A buck-boost configuration to extend battery life.
• Using a single battery + boost converter instead of two batteries in series, saving boardspace / weight / cost.
• Obtaining 2 supply voltages from a single source
• In case the input voltage source switches between a battery and USB
• In case RP400 cannot provide enough output current, suggest RP600

The duty ratio dependence is less than RP400, in some cases, RP600 can provide more than 1.5 times the output current compared to RP400.

At 1.5V input / 300mA output, the RP600 has 5% better efficiency than the RP400.

RP600KxxxA, BUCK-BOOST CIRCUIT, fixed DC/DC Converter output voltage

RP600KxxxD BUCK-BOOST CIRCUIT, adjustable DC/DC converter output voltage

RP600 INPUT VOLTAGE VERSUS THE BEHAVIOUR OF THE OUTPUT VOLTAGES.

The X-axis represents the input voltage; the operating range is from 0.8V to 5.5V and the Y-axis shows the output voltage of the DCDC converter and LDO.

In case the application requires a supply voltage of 2.8V, the LDO need to be set to 2.8V as well. The DC/DC converter output voltage needs to be set slightly higher compared to the LDO voltage, it is to have enough margin to compensate the LDO dropout voltage and to make sure that it is able to regulate well. In some cases it is convenient to select the RP600 version with an adjustable DCDC converter voltage, to have the flexibility to adjust to the best output voltage level. For this example the DCDC output voltage is set to 3.3V.

Assume that some battery is applied to the input of the DC/DC converter with a voltage of 5.5V and discharges to 0V. At 5.5V the DC/DC is turned off since the input voltage is higher compared to the voltage setting Vout1 + diode forward voltage Vf. The output of the DC/DC converter is not regulated and follows the input voltage level, the LDO regulates to the required 2.8V. As soon the input voltage decreases to a level below the voltage setting Vout1 + Vf, the DCDC converter will start up and maintains the Vout1 voltage to 3.3V. Again the LDO regulates to the required 2.8V. The DC/DC converter continues to operate until the input voltage decreases below the minimum of 0.8V, at that moment the circuit will halt. In case the circuit had no boost DCDC converter but an LDO only, it would not be able to keep the 2.8V output voltage level if the battery voltage would drop below around 2.8V.

RP600KxxxB, TWO INDIVIDUAL OUTPUT VOLTAGES FROM A SINGLE SUPPLY

Below circuit can be used if one supply voltage above and a second supply voltage below the input voltage is required. In this way two different circuits of the application can be supplied from one power source.
It is even possible to add another external LDO to the DCDC converter output in order to obtain a similar circuit as described for the Buck-Boost circuit.

RP600KxxxB, ALTERNATIVE USE

RP600KxxxC, ENERGY HARVESTING OR ENERGY SAVING CIRCUIT

It is assumed that the buffer capacitor is fully discharged when the circuit is powered up. The voltage detector measures 0V and will provide a high level at its output VDout. As a result the Boost DCDC converter will be enabled and the output voltage will ramp up. The buffer capacitor will be charged to a level equal to the threshold voltage of the voltage detector, at that moment the output of the voltage detector will change to low and the DC/DC converter will be disabled to minimize current consumption. An LDO regulator connected to the buffer capacitor regulates to a specific voltage required for the application.

As soon the DC/DC converter is disabled, the LDO is switched to ECO mode to reduce current consumption. The voltage detector has an option to select from a wide hysteresis range from 30% to 80% of –Vdet, as a result the buffer capacitor is able to discharge until the lower threshold release voltage is reached. At that moment the DCDC converter is enabled again and this process repeats depending on the discharge rate of the buffer capacitor. Such circuit can be used when powered from a solar cell for example, collecting energy in the buffer capacitor and powering a circuit with a stable voltage level as long the solar energy is bright enough. Another example is to use such circuit in a battery operated wireless smoke detector, during standby (no alarm condition) the current consumption is reduced to a minimum but also extending battery life even if the battery voltage decreases due to discharge.