Ricoh RH5RH13B - Manual (Page 5)

PWM STEP-UP DC/DC CONVERTER
1
RH5RH
××
1A/
××
2B/
××
3B SERIES
OUTLINE
The RH5RH
××
1A/
××
2B/
××
3B Series are PWM Step-up DC/DC converter ICs by CMOS process.
The RH5RH
××
1A IC consists of an oscillator, a PWM control circuit, a driver transistor (Lx switch), a refer-
ence voltage unit, an error amplifier, a phase compensation circuit, resistors for voltage detection, a soft-start cir-
cuit, and an Lx switch protection circuit. A low ripple, high efficiency step-up DC/DC converter can be constructed
of this RH5RH
××
1A IC with only three external components, that is, an inductor, a diode and a capacitor.
These RH5RH
××
1A/
××
2B/
××
3B ICs can achieve ultra-low supply current (no load) –TYP. 15µA –by a new-
ly developed PWM control circuit, equivalent to the low supply current of a VFM (chopper) Step-up DC/DC con-
verter.
Furthermore, these ICs can hold down the supply current to TYP. 2µA by stopping the operation of the oscil-
lator when the input voltage > (the output voltage set value + the dropout voltage by the diode and the inductor).
These RH5RH
××
1A/
××
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 RH5RH
××
2B/
××
3B Series ICs use the same chip as that employed in the RH5RH
××
1A IC and are pro-
vided 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 RH5RH
××
2B/
××
3B Series ICs
are recommendable to the user who need a current as large as several tens mA to several hundreds mA.
The RH5RH
××
3B IC also includes an internal chip enable circuit so that it is possible to set the standby sup-
ply current at MAX. 0.5µA.
These RH5RH
××
1A/
××
2B/
××
3B ICs are suitable for use with battery-powered instruments with low noise
and low supply current.
• 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 is 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 Packages
...................................................
SOT-89 (RH5RH
××
1A, RH5RH
××
2B),
SOT-89-5 (RH5RH
××
3B)
FEATURES
APPLICATIONS
• Power source for battery-powered equipment.
• Power source for cameras, camcorders, VCRs, PDAs, electronic data banks,and hand-held communication
equipment.
• Power source for instruments which require low noise and low supply current, such as hand-held audio equip-
ment.
• Power source for appliances which require higher cell voltage than that of batteries used in the appliances.