RN5RK SERIES
VFM STEP-UP DC/DC CONVERTER
NO.EA-045-0602
OUTLINE
The RN5RKxx1A/xx1B/xx2A Series are CMOS-based VFM (Chopper) Step-up DC/DC converter ICs with ultra
low supply current and high output voltage accuracy.
Each of the RN5RKxx1A/xx1B consists of an oscillator, a VFM control circuit, a driver transistor to have low
ON resistance (Lx switch), a reference voltage unit, a high speed comparator, resistors for voltage detection, an
Lx switch protection circuit and an internal chip enable circuit. A low ripple, high efficiency step-up DC/DC
converter can be composed of this RN5RKxx1A/xx1B with only three external components: an inductor, a diode
and a capacitor.
The RN5RKxx2A uses the same chip as what is employed in the RN5RKxx1A/1B IC and has a drive pin (EXT)
for an external transistor instead of an Lx pin. As it is possible to load a large output current with a power
transistor which has a low saturation voltage, RN5RKxx2A IC is recommendable to users who need an output
current as large as between several tens mA and several hundreds mA.
Using the chip enable function, it is possible to make the supply current on standby minimized.
Since the package for these ICs is SOT-23-5 (Mini-mold), high density mounting of the ICs on board is
possible.
FEATURES
•
Small Number of External Components .............................. Only an inductor, a diode and a capacitor
(RN5RKxx1A/xx1B)
•
Standby Current ................................................................... Typ. 0µA
•
High Output Voltage Accuracy .............................................
±2.5%
•
Low Ripple and Low Noise
•
Low Start-up Voltage............................................................ Max.0.9V
•
High Efficiency ..................................................................... Typ. 80%
•
Including a Driver Transistor with Low ON Resistance........ Only RN5RKxx1A/xx1B
•
Two Kinds of Duty Ratio....................................................... 77% (xx1A, xx2A)/ 55% (xx1B)
•
Output Voltage Range.......................................................... 2.0V to 5.5V
•
Low Temperature-Drift Coefficient of Output Voltage........... Typ.
±100ppm/°C
•
Small Packages ................................................................. SOT-23-5 (Mini-Mold)
APPLICATIONS
•
Power source for battery-powered equipment.
•
Power source for cameras, camcorders, VCRs, and hand-held communication equipment.
•
Power source for those appliances which require higher cell voltage than that of batteries.
1
RN5RK
OUTLINE DIAGRAM
RN5RKxx1x
Vref
V
LX
limiter
Buffer
LxSW
VFM Control
OSC 100kHz
Chip Enable
－
＋
Error Amp.
RN5RKxx2A
Vref
Buffer
VFM Control
－
＋
Lx 5
2 V
OUT
EXT 5
2 V
OUT
OSC 100kHz Error Amp.
Chip Enable
4 GND
1
CE
1
CE
4 GND
SELECTION GUIDE
The output voltage, the driver type, the duty cycle 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:
RN5RKxxxx-xx
↑ ↑↑ ↑
a bc d
Code
a
b
←Part
Number
Contents
Setting Output Voltage (V
OUT
) :
Stepwise setting with a step of 0.1V in the range of 2.0V to 5.5V is possible.
Designation of Driver
1: Internal Lx Tr. Driver
2: External Tr. Driver
Designation of Duty Cycle
A: 77%
B: 55%
Designation of Taping type
Ex. TR, TL (refer to Taping Specifications, TR type is prescribed as a standard.)
c
d
2
RN5RK
PIN CONFIGURATIONS
•
5
SOT-23-5
4
(mark side)
1
2
3
PIN DISCRIPTION
•
RN5RKxx1x
Pin No.
1
2
3
4
5
Symbol
CE
V
OUT
NC
GND
L
X
Description
Chip Enable Pin
Step-up Output Monitoring Pin,
Power Supply (for device itself)
No Connection
Ground Pin
Switching Pin
(Nch Open Drain)
•
RN5RKxx2x
Pin No.
1
2
3
4
5
Symbol
CE
V
OUT
NC
GND
EXT
Description
Chip Enable Pin
Step-up Output Monitoring Pin,
Power Supply (for device itself)
No Connection
Ground Pin
External Tr. Drive Pin
(CMOS Output)
ABSOLUTE MAXIMUM RATINGS
Symbol
V
OUT
V
LX
V
EXT
V
CE
I
LX
I
EXT
P
D
Topt
Tstg
LX Pin Voltage
EXT Pin Voltage
CE Pin Voltage
Lx Pin Output Current
EXT Pin Output Current
Power Dissipation (SOT-23-5)*
1
Operating Temperature Range
Storage Temperature Range
Item
Step-up Output Pin Voltage
Rating
9.0
9.0
–0.3
to V
OUT
+0.3
–0.3
to V
OUT
+0.3
500
±30
420
–40
to +85
–55
to +125
Unit
V
V
V
V
mA
mA
mW
°C
°C
*1)For Power Dissipation, please refer to PACKAGE INFORMATION to be described.
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.
3
RN5RK
Symbol
Item
2.0V
2.5V
3.0V
I
LX
Lx Switching Current
3.5V
4.0V
4.5V
5.0V
<
=
<
=
<
=
<
=
<
=
<
=
<
=
Conditions
V
OUT
V
OUT
V
OUT
V
OUT
V
OUT
V
OUT
V
OUT
<
=
<
=
<
=
<
=
<
=
<
=
<
=
Min.
80
100
120
140
160
180
200
Typ.
Max.
Unit
2.4V, V
LX
=0.4V
2.9V, V
LX
=0.4V
3.4V, V
LX
=0.4V
3.9V, V
LX
=0.4V
4.4V, V
LX
=0.4V
4.9V, V
LX
=0.4V
5.5V, V
LX
=0.4V
mA
*1)Condition: An Output load resistor R
L
is connected between V
OUT
and GND.
Note that the resistor R
L
has a resistance which makes an output current 1mA after step-up operation.
*2)The Supply Current 1 (I
DD1
) for IC itself is measured when the internal oscillator works continuously.
If the oscillator works intermittently, the supply current becomes smaller than the value which is written on
the above table.
Measurement condition: V
OUT
=V
CE
=Setting
Output Voltage×0.96
5
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