R1224N SERIES
PWM/VFM step-down DC/DC Controller
NO.EA-096-181004
OUTLINE
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 R1224Nxxx, 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.
FEATURES
• Supply Current ................................................................ Typ. 20µA (R1224Nxx2E/F/M/L, R1224N102M)
Typ. 30µA (R1224Nxx2G, R1224N102G)
Typ. 40µA (R1224Nxx2H, R1224N102H)
• Standby Current .............................................................. Typ. 0µA
• Input Voltage Range ....................................................... 2.3V to 18.5V
• Output Voltage Range..................................................... 1.2V to 6.0V (0.1V steps; R1224Nxx2x)
1.0V to VIN (R1224N102x)
• Output Voltage Accuracy................................................. ±2.0%
• Oscillator Frequency ....................................................... Typ. 180kHz (R1224Nxx2L/M, R1224N102M)
Typ. 300kHz (R1224Nxx2E/G, R1224N102G)
Typ. 500kHz (R1224Nxx2F/H, R1224N102H)
• Efficiency ......................................................................... Typ. 90%
• Low Temperature-Drift Coefficient of Output Voltage ..... Typ. ±100ppm/°C
• Package .......................................................................... SOT-23-5
• Built-in Soft-start Function............................................... Typ. 10ms
• Built-in Current Limit Circuit
APPLICATIONS
• Power source for hand-held communication equipment, cameras, video instruments such as VCRs,
camcorders.
• Power source for battery-powered equipment.
• Power source for household electrical appliances.
1
R1224N
NO.EA-096-181004
BLOCK DIAGRAM
Fixed Output Voltage Type
VIN
5
EXT
4
OSC
3 VOUT
Amp
Vref
PWM/VFM
CONTROL
Soft Start
Chip Enable
Protection
1 CE
Vref
UVLO
2
GND
Adjustable Output Voltage Type
VIN
5
EXT
4
OSC
3 VFB
Amp
Vref
Soft Start
Protection
UVLO
2
GND
2
Chip Enable
Vref
1 CE
R1224N
NO.EA-096-181004
SELECTION GUIDE
The output voltage, the oscillator frequency, the modulation method and the output voltage adjustment for the
ICs can be selected at the user’s request.
Product Name
R1224Nxx2∗-TR-FE
Package
Quantity per Reel
Pb Free
Halogen Free
SOT-23-5
3,000 pcs
Yes
Yes
xx : The output voltage can be designated in the range from 1.2V(12) to 6.0V(60) in 0.1V steps.
(For externally adjustable output voltage type, feedback voltage of 1.0V(10).)
∗ : The oscillator frequency, the modulation method and the output voltage adjustment are options as
follows.
Code
Oscillator frequency
PWM/VFM
alternative circuit
Output voltage
adjustment
E
300kHz
Yes
No
F
500kHz
Yes
No
G
300kHz
No
Yes
H
500kHz
No
Yes
L
180kHz
Yes
No
M
180kHz
No
Yes
PIN CONFIGURATION
•
SOT-23-5
5
4
(mark side)
1
2
3
PIN DESCRIPTION
Pin No
Symbol
1
CE
2
GND
3
VOUT (VFB)
4
EXT
5
VIN
Pin Description
Chip Enable Pin ("H" Active)
Ground Pin
Pin for Monitoring Output Voltage (Feedback Voltage)
External Transistor Drive Pin (CMOS Output)
Power Supply Pin
3
R1224N
NO.EA-096-181004
ABSOLUTE MAXIMUM RATINGS
Symbol
Item
GND=0V
Rating
Unit
−0.3 to 20
V
VIN
VIN Supply Voltage
VEXT
EXT Pin Output Voltage
−0.3 to VIN+0.3
V
VCE
CE Pin Input Voltage
−0.3 to VIN+0.3
V
VOUT/VFB Pin Input Voltage
−0.3 to VIN+0.3
V
± 50
mA
420
mW
VOUT/VFB
IEXT
EXT Pin Inductor Drive Output Current
∗
PD
Power Dissipation (SOT-23-5)
Topt
Operating Temperature Range
−40 to 85
°C
Tstg
Storage Temperature Range
−55 to 125
°C
∗) For Power Dissipation, please refer to PACKAGE INFORMATION.
ABSOLUTE MAXIMUM RATINGS
Electronic and mechanical stress momentarily exceeded absolute maximum ratings may cause the
permanent damages and may degrade the life time and safety for both device and system using the device
in the field. he functional operation at or over these absolute maximum ratings is not assured.
4
R1224N
NO.EA-096-181004
ELECTRICAL CHARACTERISTICS
•
R1224Nxx2x (x=E/F/G/H/L/M) except R1224N102x
Symbol
VIN
Item
Conditions
Operating Input Voltage
Topt=25°C
Min.
Typ.
2.3
Max.
Unit
18.5
V
VSET
×1.02
V
VOUT
Step-down Output Voltage
VIN=VCE=VSET+1.5V, IOUT=−100mA
When VSET≤1.5V, VIN=VCE=3.0V
∆VOUT/
∆Topt
Step-down Output Voltage
Temperature Coefficient
−40°C≤Topt≤85°C
Oscillator Frequency
VIN=VCE=VSET+1.5V, IOUT=−100mA
L/M Version
E/G Version
F/H Version
Oscillator Frequency
Temperature Coefficient
−40°C≤Topt≤85°C
IDD1
Supply Current 1
VIN=VCE=VOUT=18.5V
E/F/L/M Version
G version
H version
20
30
40
50
60
80
µA
Istandby
Standby Current
VIN=18.5V, VCE=0V, VOUT=0V
0
0.5
µA
IEXTH
EXT "H" Output Current
VIN=8V, VEXT=7.9V, VOUT=8V,
VCE=8V
−17
−10
mA
IEXTL
EXT "L" Output Current
VIN=8V, VEXT=0.1V, VOUT=0V,
VCE=8V
ICEH
CE "H" Input Current
VIN=VCE=VOUT=18.5V
ICEL
CE "L" Input Current
VIN=VOUT=18.5V, VCE=0V
−0.5
VCEH
CE "H" Input Voltage
VIN=8V, IOUT=−10mA
1.5
VCEL
CE "L" Input Voltage
VIN=8V, IOUT=−10mA
Maxduty
Oscillator Maximum
Duty Cycle
VFMdty
VFM Duty Cycle
E/F/L Version
VUVLO1
UVLO Voltage
VIN=VCE=2.5V to 1.5V, VOUT=0V
VUVLO2
UVLO Release Voltage
VIN=VCE=1.5V to 2.5V, VOUT=0V
tstart
Delay Time by Soft-Start function
VIN=VSET+1.5V, IOUT=−10mA
VCE=0V→VSET+1.5V
tprot
Delay Time for protection circuit
VIN=VCE=VSET+1.5V
VOUT=VSET+1.5V→0V
fosc
∆fosc/
∆Topt
VSET
×0.98
VSET
±100
144
240
400
180
300
500
ppm/°C
216
360
600
±0.2
20
%/°C
30
0
mA
0.5
µA
µA
0
V
0.3
100
V
%
35
1.8
kHz
%
2.0
2.2
V
VUVLO1
+0.1
2.3
V
5
10
20
ms
5
15
30
ms
RECOMMENDED OPERATING CONDITIONS (ELECTRICAL CHARACTERISTICS)
All of electronic equipment should be designed that the mounted semiconductor devices operate within the
recommended operating conditions. The semiconductor devices cannot operate normally over the
recommended operating conditions, even if when they are used over such conditions by momentary
electronic noise or surge. And the semiconductor devices may receive serious damage when they continue
to operate over the recommended operating conditions.
5
R1224N
NO.EA-096-181004
•
R1224N102x (x=G/H/M)
Symbol
Item
Topt=25°C
Conditions
Min.
Typ.
Unit
18.5
V
1.02
V
VIN
Operating Input Voltage
VFB
Feedback Voltage
VIN=VCE=3.0V, IOUT=−100mA
Feedback Voltage
Temperature Coefficient
−40°C≤Topt≤85°C
Oscillator Frequency
VIN=VCE=2.5V, IOUT=−100mA
M Version
G Version
H Version
Oscillator Frequency
Temperature Coefficient
−40°C≤Topt≤85°C
IDD1
Supply Current 1
VIN=VCE=VFB=18.5V
M Version
G Version
H Version
20
30
40
50
60
80
µA
Istandby
Standby Current
VIN=18.5V, VCE=0V, VFB=0V
0
0.5
µA
IEXTH
EXT "H" Output Current
VIN=8V, VEXT=7.9V, VFB=8V,
VCE=8V
−17
−10
mA
IEXTL
EXT "L" Output Current
VIN=8V, VEXT=0.1V, VFB=0V,
VCE=8V
ICEH
CE "H" Input Current
VIN=VCE=VFB=18.5V
ICEL
CE "L" Input Current
VIN=VFB=18.5V, VCE=0V
−0.5
VCEH
CE "H" Input Voltage
VIN=8V, IOUT=−10mA
1.5
VCEL
CE "L" Input Voltage
VIN=8V, IOUT=−10mA
∆VFB/
∆Topt
fosc
∆fosc/
∆Topt
Maxduty
2.3
Max.
Oscillator Maximum Duty Cycle
0.98
1.00
±100
144
240
400
180
300
500
ppm/°C
216
360
600
±0.2
20
%/°C
30
0
mA
0.5
UVLO Voltage
VIN=VCE=2.5V to 1.5V, VFB=0V
V
0.3
VUVLO2
UVLO Release Voltage
VIN=VCE=1.5V to 2.5V, VFB=0V
tstart
Delay Time by Soft-Start function
VIN=2.5V, IOUT=−10mA
VCE=0V→2.5V
tprot
Delay Time for protection circuit
VIN=VCE=2.5V
VFB=2.5V→0V
1.8
µA
µA
0
100
VUVLO1
kHz
V
%
2.0
2.2
V
VUVLO1
+0.1
2.3
V
5
10
20
ms
5
15
30
ms
RECOMMENDED OPERATING CONDITIONS (ELECTRICAL CHARACTERISTICS)
All of electronic equipment should be designed that the mounted semiconductor devices operate within the
recommended operating conditions. The semiconductor devices cannot operate normally over the
recommended operating conditions, even if when they are used over such conditions by momentary
electronic noise or surge. And the semiconductor devices may receive serious damage when they continue
to operate over the recommended operating conditions.
6
R1224N
NO.EA-096-181004
TYPICAL APPLICATION AND APPLICATION HINTS
(1) Fixed Output Voltage Type (R1224Nxx2E/F/G/H/L/M except xx=10)
L
PMOS
C1
4
R1
EXT
5 VIN
VOUT 3
R1224N
1 CE
C3
SD
GND
C2
LOAD
2
CE CONTROL
PMOS: uPA1914 (Renesas)
SD1 : CMS06 (TOSHIBA)
C1
: 10µF (Ceramic Type)
R1
: 10Ω
L : CR105NP-270MC (Sumida, 27µH)
C3 : 47µF (Tantalum Type)
C2 : 0.1µF (Ceramic Type)
(2) Adjustable Output Type (R1224N102G/H/M) Example: Output Voltage=3.2V
L
PMOS
C1
C4
R4
4
R1
5 VIN
EXT
R3
VFB 3
R1224N
1 CE
C2
GND
2
C3
SD
R2
LOAD
CE CONTROL
PMOS: uPA1914 (Renesas)
L : CR105NP-270MC (Sumida, 27µH)
SD1 : CMS06 (TOSHIBA)
C3 : 47µF (Tantalum Type)
C1
: 10µF (Ceramic Type)
C2 : 0.1µF (Ceramic Type) C4: 1000pF (Ceramic Type)
R1
: 10Ω, R2=22kΩ, R3=2.7kΩ, R4=33kΩ
7
R1224N
NO.EA-096-181004
When you use these ICs, consider the following issues;
⋅As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed
for load current, therefore do not use it in such a way. When you control the CE pin by another power supply, do
not make its “H” level more than the voltage level of VIN pin.
⋅Set external components as close as possible to the IC and minimize the connection between the components
and the IC. In particular, a capacitor should be connected to VIN pin with the minimum connection. Make sufficient
ground and reinforce supplying. A large switching current could flow through the connection of power supply, an
inductor and the connection of VIN. If the impedance of the connection of power supply is high, the voltage level
of power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC.
⋅Protection circuit may work if the maximum duty cycle continue for the time defined in the electrical characteristics.
Once after stopping the output voltage, output will restart with soft-start operation. If the difference between input
voltage and output voltage is small, the protection circuit may work.
⋅Use capacitors with a capacity of 22µF or more for VOUT pin, and with good high frequency characteristics such
as tantalum capacitors. We recommend you to use output capacitors with an allowable voltage at least twice as
much as setting output voltage. This is because there may be a case where a spike-shaped high voltage is
generated by an inductor when an external transistor is on and off.
⋅Choose an inductor that has sufficiently small D.C. resistance and large allowable current and is hard to reach
magnetic saturation. And if the value of inductance of an inductor is extremely small, the ILX may exceed the
absolute maximum rating at the maximum loading.
Use an inductor with appropriate inductance.
⋅Use a diode of a Schottky type with high switching speed, and also pay attention to its current capacity.
⋅Do not use this IC under the condition with VIN voltage at equal or less than minimum operating voltage.
⋅When the threshold level of an external power MOSFET is rather low and the drive-ability of voltage supplier is
small, if the output pin is short circuit, input voltage may be equal or less than UVLO detector threshold. In this
case, the devise is reset with UVLO function that is different from the reset-protection function caused by
maximum duty cycle.
⋅With the PWM/VFM alternative circuit, when the on duty cycle of switching is 35% or less, the R1224N alters
from PWM mode to VFM mode (Pulse skip mode). The purpose of this circuit is raising the efficiency with a light
load by skipping the frequency and suppressing the consumption current. However, the ratio of output voltage
against input voltage is 35% or less, (ex. VIN>8.6V and VOUT=3.0V) even if the large current may be loaded, the
IC keeps its VFM mode. As a result, frequency might be decreased, and oscillation waveform might be unstable.
These phenomena are the typical characteristics of the IC with PWM/VFM alternative circuit.
⋅If the input voltage is equal or more than 6V, R1 and C2 in the typical application are necessary as a VIN filter to
prevent unstable operation.
The performance of power source circuits using these ICs extremely depends upon the peripheral circuits.
Pay attention in the selection of the peripheral circuits. In particular, design the peripheral circuits in a way that
the values such as voltage, current, and power of each component, PCB patterns and the IC do not exceed their
respected rated values.
8
R1224N
NO.EA-096-181004
How to Adjust Output Voltage and about Phase Compensation
As for Adjustable Output type, feedback pin (VFB) voltage is controlled to maintain 1.0V.
Output Voltage, VOUT is as following equation:
VOUT: R2+R4=VFB: R2
VOUT=VFB×(R2+R4)/R2
Thus, with changing the value of R2 and R4, output voltage can be set in the specified range.
In the DC/DC converter, with the load current and external components such as L and C, phase might be behind
180 degree. In this case, the phase margin of the system will be less and stability will be worse. To prevent this,
phase margin should be secured with proceeding the phase. A pole is formed with external components L and
C3.
Fpole ~ 1/2π L × C3
A zero (signal back to zero) is formed with R4 and C4.
≅Fzero~1/(2π×R4×C4)
For example, if L=27µH, C3=47µF, the cut off frequency of the pole is approximately 4.5kHz.
To make the cut off frequency of the pole as much as 4.5kHz, set R4=33kΩ and C4=1000pF.
If VOUT is set at 2.5V, R2=22kΩ is appropriate.
R3 prevents feedback of the noise to VFB pin, about 2.7kΩ is appropriate value.
L
PMOS
C1
C4
R4
4
R1
5 VIN
EXT
R3
VFB 3
R1224N
1 CE
C2
GND
2
C3
SD
R2
LOAD
CE CONTROL
9
R1224N
NO.EA-096-181004
OPERATION of step-down DC/DC converter and Output Current
The step-down DC/DC converter charges energy in the inductor when Lx transistor is ON, and discharges the
energy from the inductor when Lx transistor is OFF and controls with less energy loss, so that a lower output
voltage than the input voltage is obtained. The operation will be explained with reference to the following
diagrams:
i1
IL
ILmax
IOUT
VIN
Lx Tr
SD
L
VOUT
ILmin
topen
i2
CL
GND
toff
ton
T=1/fosc
Step 1: Lx Tr. turns on and current IL (=i1) flows, and energy is charged into CL. At this moment, IL increases
from ILmin. (=0) to reach ILmax. in proportion to the on-time period (ton) of Lx Tr.
Step 2: When Lx Tr. turns off, Schottky diode (SD) turns on in order that L maintains IL at ILmax, and current IL
(=i2) flows.
Step 3: IL decreases gradually and reaches ILmin. after a time period of topen, and SD turns off, provided that
in the continuous mode, next cycle starts before IL becomes to 0 because toff time is not enough. In this
case, IL value is from this ILmin (>0).
In the case of PWM control system, the output voltage is maintained by controlling the on-time period (ton), with
the oscillator frequency (fosc) being maintained constant.
Discontinuous Conduction Mode and Continuous Conduction Mode
The maximum value (ILmax) and the minimum value (ILmin) current which flow through the inductor is the
same as those when Lx Tr. is ON and when it is OFF.
The difference between ILmax and ILmin, which is represented by ∆I;
∆I=ILmax-ILmin=VOUT×topen/L=(VIN-VOUT)×ton/L ................................... Equation 1
wherein, T=1/fosc=ton+toff
duty (%)=ton/T×100=ton×fosc×100
topen <
= toff
In Equation 1, VOUT×topen/L and (VIN-VOUT)×ton/L are respectively shown the change of the current at ON, and
the change of the current at OFF.
When the output current (IOUT) is relatively small, topen0). The
former mode is referred to as the discontinuous mode and the latter mode is referred to as continuous mode.
10
R1224N
NO.EA-096-181004
In the continuous mode, when Equation 1 is solved for ton and assumed that the solution is tonc,
tonc=T×VOUT/VIN ..................................................................................... Equation 2
When ton
工商网监
湘ICP备2023018690号
