PWM STEP-UP DC/DC CONVERTER
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.
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 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)
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.
1
RH5RH
BLOCK DIAGRAM
Lx
Vss
LxSW
PWM control
EXT
OSC
Chip Enable
–
+
Error Amp.
V
LX
limiter
Buffer
Slow start
Phase Comp.
Vref
OUT
CE
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.
(Note) Lx Pin ............only for RH5RH
××
1A and RH5RH
××
3B
EXT Pin .........only for RH5RH
××
2B and RH5RH
××
3B
CE Pin ...........only for RH5RH
××
3B
SELECTION GUIDE
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
↑ ↑
↑
a b
c
}
}
}
Code
Description
a
Setting Output Voltage (V
OUT
):
Stepwise setting with a step of 0.1V in the range of 2.7V to 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. SOT-89 : T1, T2
SOT-89-5 : T1, T2
(refer to Taping Specifications)
“T1” is prescribed as a standard.
b
c
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.
2
RH5RH
ABSOLUTE MAXIMUM RATINGS
Symbol
Item
Rating
Unit
Vss=0V
Note
V
OUT
V
LX
V
EXT
V
CE
I
LX
I
EXT
P
D
Topt
Tstg
Tsolder
Output Pin Voltage
Lx Pin Voltage
EXT Pin Voltage
CE Pin Voltage
Lx Pin Output Current
EXT Pin Current
Power Dissipation
Operating Temperature Range
Storage Temperature Range
Lead Temperature(Soldering)
+12
+12
– 0.3 to V
OUT
+0.3
–0.3 to V
OUT
+0.3
250
±50
500
–30 to +80
–55 to +125
260˚C,10s
(Note 2) Applicable to RH5RH
××
2B and RH5RH
××
3B.
V
V
V
V
mA
mA
mW
˚C
˚C
Note1
Note2
Note3
Note1
Note2
(Note 1) Applicable to RH5RH
××
1A and RH5RH
××
3B.
(Note 3) Applicable to RH5RH
××
3B.
ABSOLUTE MAXIMUM RATINGS
Absolute Maximum ratings are threshold limit values that must not be exceeded even for an instant under any
conditions. Moreover, such values for any two items must not be reached simultaneously. Operation above
these absolute maximum ratings may cause degradation or permanent damage to the device. These are stress
ratings only and do not necessarily imply functional operation below these limits.
4
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