|Description||PWM Step-up Dc/dc Converter|
|Datasheet||Download RH5RH321A-T2 datasheet
The 2B/ 3B Series are PWM Step-up DC/DC converter ICs by CMOS process. The 1A IC consists of an oscillator, a PWM control circuit, a driver transistor (Lx switch), a reference voltage unit, an error amplifier, a phase compensation circuit, resistors for voltage detection, a soft-start circuit, and an Lx switch protection circuit. A low ripple, high efficiency step-up DC/DC converter can be constructed of this 1A IC with only three external components, that is, an inductor, a diode and a capacitor. These 2B/×× 3B ICs can achieve ultra-low supply current (no load) TYP. 15µA by a newly developed PWM control circuit, equivalent to the low supply current of a VFM (chopper) Step-up DC/DC converter. Furthermore, these ICs can hold down the supply current to TYP. 2µA by stopping the operation of the oscillator when the input voltage > (the output voltage set value + the dropout voltage by the diode and the inductor). These 2B/×× 3B Series ICs are recommendable to the user who desires a low ripple PWM DC/DC converter, but cannot adopt a conventional PWM DC/DC converter because of its too large supply current. The 2B/×× 3B Series ICs use the same chip as that employed in the 1A IC and are provided with a drive pin (EXT) for an external transistor. Because of the use of the drive pin (EXT), an external transistor with a low saturation voltage can be used so that a large current can be caused to flow through the inductor and accordingly a large output current can be obtained. Therefore, these 2B/×× 3B Series ICs are recommendable to the user who need a current as large as several tens mA to several hundreds mA. The 3B IC also includes an internal chip enable circuit so that it is possible to set the standby supply current at MAX. 0.5µA. These 2B/×× 3B ICs are suitable for use with battery-powered instruments with low noise and low supply current.FEATURES
Small Number of External Components..........Only an inductor, a diode and a capacitor (RH5RH 1A) Low Supply Current...........................................TYP. 15µA (RH5RH301A) Low Ripple and Low Noise Low Start-up Voltage (when the output current 1mA)..................MAX. 0.9V High Output Voltage Accuracy..........................±2.5% High Efficiency...................................................TYP. 85% Low Temperature-Drift Coefficient of Output Voltage......................TYP. ±50 ppm/°C Soft-Start.............................................................MIN. 500µs Small RH5RH 2B),APPLICATIONS
Power source for battery-powered equipment. Power source for cameras, camcorders, VCRs, PDAs, electronic data banks,and hand-held communication
Power source for instruments which require low noise and low supply current, such as hand-held audio equip-
Power source for appliances which require higher cell voltage than that of batteries used in the appliances.
Lx Vss LxSW PWM control EXT OSC Chip Enable + Error Amp. VLX limiter Buffer Slow start Phase Comp. Vref OUT
Error Amp. (Error Amplifier) has a DC gain of 80dB, and Phase Comp. (Phase Compensation Circuit) provides the frequency characteristics including the 1st pole (fp=0.25Hz) and the zero point (fz=2.5kHz). Furthermore, another zero point (fz=1.0kHz) is also obtained by the resistors and a capacitor connected to the OUT pin.
In RH5RH Series, the output voltage, the driver, and the taping type for the ICs can be selected at the user's request. The selection can be made by designating the part number as shown below RH5RH Part Number b cDescription
Setting Output Voltage (VOUT): Stepwise setting with a step 0.1V in the range 7.5V is possible. Designation of Driver: 1A: Internal Lx Tr. Driver (Oscillator Frequency 50kHz) 2B: External Tr. Driver (Oscillator Frequency 100kHz) 3B: Internal Tr./External Tr. (selectively available) (Oscillator Frequency 100kHz, with chip enable function) Designation of Taping Type : Ex. T1, T2 (refer to Taping Specifications) "T1" is prescribed as a standard.
For example, the product with Output Voltage 5.0V, the External Driver (the Oscillator Frequency 100kHz) and Taping Type T1, is designated by Part Number RH5RH502B-T1.
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