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OUTLINE
‘99.12.8
PWM/VFM step-down DC/DC Converter
R1223N Series
The R1223N Series are PWM step-down DC/DC Converter controllers with low supply current by CMOS
process.
Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier,
a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, and resistors for
voltage detection. A low ripple, high efficiency step-down DC/DC converter can be easily composed of this IC
with only four external components, or a power-transistor, an inductor, a diode and a capacitor.
With a PWM/VFM alternative circuit, when the load current is small, the operation is automatically switching
into the VFM oscillator from PWM oscillator, therefore the efficiency at small load current is improved. The
R1223N XXXB type, which is without a PWM/VFM alternative circuit, is also available.
If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. There are
two types of protection function. One is latch-type protection circuit, and it works to latch an external Power
MOSFET with keeping it disable. To release the condition of protection, after disable this IC with a chip enable
circuit, enable it again, or restart this IC with power-on. The other is Reset-type protection circuit, and it works to
restart the operation with soft-start and repeat this operation until maximum duty cycle condition is released.
Either of these protection circuits can be designated by users’ request.
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FEATURES
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Range of Input Voltage
· · · · · · · · · · · · ·2.3V~13.2V
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Built-in Soft-start Function and Two choices of Protection Function (Latch-type or Reset type)
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Two choices of Oscillator Frequency
· · · · · ·300kHz,
500kHz
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High Efficiency
· · · · · · · · · · · · · · · · · ·TYP.
90%
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Output Voltage
· · · · · · · · · · · · · · · · ·
Stepwise Setting with a step of 0.1V
in the range of 1.5V
~
5.0V
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Standby Current
· · · · · · · · · · · · · · · · ·TYP.
0µA
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High Accuracy Output Voltage
· · · · · · · · · ·±2.0%
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Low Temperature-Drift Coefficient of Output Voltage
· · · · ·
TYP. ±100ppm/°C
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APPLICATIONS
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Power source for hand-held communication equipment, cameras, video instruments such as VCRs,
camcorders.
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Power source for battery-powered equipment.
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Power source for household electrical appliances.
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Rev. 1.11
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BLOCK DIAGRAM
V
IN
OSC
V
OUT
Vref
EXT
PWM/VFM
CONTROL
Protection
Soft Start
Chip Enable
CE
GND
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SELECTION GUIDE
In the R1223N Series, the output voltage, the oscillator frequency, the optional function, 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;
R1223NXXXX-XX
- -- -
a
b c
Code
a
b
c
d
Contents
d
Setting Output Voltage(V
OUT
):
Stepwise setting with a step of 0.1V in the range of 1.5V to 5.0V is possible.
Designation of Oscillator Frequency
2 : fixed
Designation of Optional Function
A : 300kHz, with a PWM/VFM alternative circuit, Latch-type protection
B : 500 kHz, with a PWM/VFM alternative circuit, Latch-type protection
C : 300kHz, without a PWM/VFM alternative circuit, Latch-type protection
D : 500kHz, without a PWM/VFM alternative circuit, Latch-type protection
E : 300kHz, with a PWM/VFM alternative circuit, Reset-type protection
F : 500 kHz, with a PWM/VFM alternative circuit, Reset-type protection
G : 300kHz, without a PWM/VFM alternative circuit, Reset-type protection
H : 500kHz, without a PWM/VFM alternative circuit, Reset-type protection
Designation of Taping Type; Ex. :TR,TL(refer to Taping Specification)
”TR” is prescribed as a standard.
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Rev. 1.11
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PCB Design
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