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OUTLINE
PRELIMINARY
2001.10.18
PWM/VFM step-down DC/DC Converter
R1224N Series
The R1224N Series are CMOS-based PWM step-down DC/DC Converter controllers with low supply current.
Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a
phase compensation circuit, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable
circuit, resistors for output voltage detect, and input voltage detect circuit. A low ripple, high efficiency step-down
DC/DC converter can be easily composed of this IC with only several external components, or a power-transistor, an
inductor, a diode and capacitors. Output Voltage is fixed or can be adjusted with external resistors (Adjustable types
are without PWM/VFM alternative circuit).
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. Several types of
the R1224N XXX, which are without a PWM/VFM alternative circuit, are also available.
If the term of maximum duty cycle keeps on a certain time, the embedded protection circuit works. The protection
circuit 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. When the cause of large load current or something else is removed, the
operation is automatically released and returns to normal operation.
Further, built-in UVLO function works when the input voltage is equal or less than UVLO threshold, it makes this IC
be standby and suppresses the consumption current and avoid an unstable operation.
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FEATURES
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Range of Input Voltage
• • • • • • • • • • • • •2.3V∼18.5V
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Built-in Soft-start Function and Protection Function (Reset type protection)
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Three options of Oscillator Frequency
• • • • • •180kHz,
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 1.2V to 6.0V as
fixed voltage type. Reference Voltage of Adjustable Type is 1.0V
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Standby Current
• • • • • • • • • • • • • • • • •TYP.
0.0µA
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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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SELECTION GUIDE
In the R1224N 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 with designating the part number as shown below;
R1224NXX2X-XX
↑ ↑↑ ↑
a
b c
Code
a
d
Contents
b
c
d
Setting Output Voltage(V
OUT
):
Stepwise setting with a step of 0.1V in the range of 1.2V to 6.0V is possible.
Adjustable type; a=10 means Reference voltage=1.0V Optional Function is G/H/M.
Designation of Oscillator Frequency
2 : fixed
Designation of Optional Function
E : 300kHz, with a PWM/VFM alternative circuit
F : 500kHz, with a PWM/VFM alternative circuit
G : 300kHz, without a PWM/VFM alternative circuit
H : 500kHz, without a PWM/VFM alternative circuit
L : 180kHz, with a PWM/VFM alternative circuit
M : 180kHz, without a PWM/VFM alternative circuit
Designation of Taping Type; Ex. :TR,TL(refer to Taping Specification)
”TR” is prescribed as a standard.
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PIN CONFIGURATION
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SOT-23-5
5
4
V
IN
EXT
(mark side)
V
OUT
CE GND (V
FB
)
1
2
3
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PIN DESCRIPTION
Pin No.
1
2
3
4
5
Symbol
CE
GND
V
OUT
/(V
FB
)
EXT
V
IN
Description
Chip Enable Pin (Active with “H”)
Ground Pin
Pin for Monitoring Output Voltage(Feedback Voltage)
External Transistor Drive Pin(CMOS Output)
Power Supply Pin
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