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. 15A 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. 2A 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. 0.5A.
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. 15A (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. 500s
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.
2
RH5RH
Part Number
a b
c
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 :
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.
Code
Description
Setting Output Voltage (V
OUT
):
a
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)
b
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 :
c
Ex. SOT-89 : T1, T2
SOT-89-5 : T1, T2
(refer to Taping Specifications)
"T1" is prescribed as a standard.
RH5RH
BLOCK DIAGRAM
Lx
Vss
EXT
LxSW
CE
Error Amp.
OUT
V
LX
limiter
Buffer
PWM control
OSC
Chip Enable
Slow start
Phase Comp.
Vref
+
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
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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
RH5RH
ABSOLUTE MAXIMUM RATINGS
Symbol
Item
V
OUT
Output Pin Voltage
V
LX
Lx Pin Voltage
V
EXT
EXT Pin Voltage
V
CE
CE Pin Voltage
I
LX
Lx Pin Output Current
I
EXT
EXT Pin Current
P
D
Power Dissipation
Topt
Operating Temperature Range
Tstg
Storage Temperature Range
Tsolder
Lead Temperature(Soldering)
Rating
Unit
Note
+12
V
+12
V
Note1
0.3 to V
OUT
+0.3
V
Note2
0.3 to V
OUT
+0.3
V
Note3
250
mA
Note1
50
mA
Note2
500
mW
30 to +80
C
55 to +125
C
260C,10s
(Note 1) Applicable to RH5RH
1A and RH5RH
3B. (Note 2) Applicable to RH5RH
2B and RH5RH
3B.
(Note 3) Applicable to RH5RH
3B.
Vss=0V
ABSOLUTE MAXIMUM RATINGS
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