R1245x Series
1.2 A, 30 V Step-Down DC/DC Converter
No. EA-269-201022
OUTLINE
The R1245x is a CMOS-based Step-down DC/DC converter with internal N-channel high side Tr. The ON
resistance of the built-in high-side transistor is 0.35 and the R1245x can provide the maximum 1.2 A output
current. Each of the ICs consists of an oscillator, a PWM control circuit, a voltage reference unit, an error
amplifier, a phase compensation circuit, a slope compensation circuit, a soft-start circuit, protection circuits, an
internal voltage regulator, and a switch for bootstrap circuit. The ICs can make up a step-down DC/DC
converter with an inductor, resistors, a diode, and capacitors.
The R1245x is a current mode operating type DC/DC converter without an external current sense resistor, and
realizes fast response and high efficiency. As an output capacitor, a ceramic type capacitor can be used with
the R1245x. The options of the internal oscillator frequency are preset at 330 kHz for version A and B, 500
kHz for version C and D, 1000 kHz for version E and F, 2400 kHz for version G and H.
As for protection, an Lx peak current limit circuit cycle by cycle, a thermal shutdown function and an under
voltage lockout (UVLO) function are built in. Furthermore, there are two types for short protection, for A/C/E/G
version, a latch protection function which makes the output latch off if the output voltage keeps lower than the
set output voltage for a certain time after detecting current limit is built in, for B/D/F/H version, a fold-back
protection function which changes the oscillator frequency slower after detecting short circuit or equivalent.
As for the packages of the R1245x, HSOP-8E, DFN(PLP)2020-8, SOT23-6W are available.
FEATURES
Operating Voltage
ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ 4.5 V to 30 V
Internal N-channel MOSFET Driver ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Typ. RON = 0.35
Adjustable Output Voltage with External Resistor ꞏꞏꞏꞏ 0.8 V or more
Feedback Voltage and Tolerance ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ 0.8 V1.0%
Peak Current Limit ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Typ. 2.0 A
UVLO Function Released Voltage ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Typ. 4.0 V
Operating Frequency ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ 330 kHz (Ver. A/B), 500 kHz (Ver. C/D),
1000 kHz (Ver. E/F), 2400 kHz (Ver. G/H)
Fold-back Protected Frequency ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ 170 kHz (Ver. B/D), 250 kHz (Ver. F), 400 kHz (Ver. H)
Latch Protection Delay Time ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Typ. 4 ms (Ver. A/C/E/G)
Ceramic Capacitors Recommended for Input and Output.
Stand-by Current ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Typ. 0 A
Packages ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ SOT-23-6W, DFN(PLP)2020-8, HSOP-8E
1
R1245x
No. EA-269-201022
APPLICATIONS
Digital Home Appliances: Digital TVs, DVD Players
Office Equipment: Printers, Faxes
5V PSU or 2-cell or more Li-ion Battery Powered Communication Equipment, Cameras, VCRs, Camcorders
High Voltage Battery-powered Equipment
SELECTION GUIDE
In the R1245x, the package, type of short protection (Latch or Fold-back), and the oscillator frequency can be
selected with the user’s request.
Selection Guide
Product code
Package
Quantity per Reel
Pb Free
Halogen Free
R1245S003-E2-FE
HSOP-8E
1,000 pcs
Yes
Yes
DFN(PLP)2020-8
5,000 pcs
Yes
Yes
SOT-23-6W
3,000 pcs
Yes
Yes
R1245K003-TR
R1245N001-TR-FE
: Designation of the oscillator frequency and the protection function option.
Latch
Fold-back
Oscillator
Symbol
Protection
Protection
Frequency
A
330 kHz
B
330 kHz
C
500 kHz
D
500 kHz
E
1000 kHz
F
1000 kHz
G
2400 kHz
H
2400 kHz
2
R1245x
No. EA-269-201022
BLOCK DIAGRAM
R1245x Block Diagram
*1
Version
A
B
C
D
E
F
G
H
Oscillator Frequency
330 kHz
330 kHz
500 kHz
500 kHz
1000 kHz
1000 kHz
2400 kHz
2400 kHz
Short Protection Type
330 kHz
330 kHz
500 kHz
500 kHz
1000 kHz
1000 kHz
2400 kHz
2400 kHz
3
R1245x
No. EA-269-201022
PIN DESCRIPTIONS
Top View
Bottom View
8
7
6
5
5
6
7
8
1
2
3
4
4
3
2
1
DFN(PLP)2020-8 Pin Configuration
Top View
8
1
7
2
6
3
Top View
Bottom View
5
4
5
4
6
3
7
2
HSOP-8E Pin Configuration
8
6
5
4
1
2
3
1
SOT-23-6W Pin Configuration
* Connect the backside heat radiation tub to GND or same as GND level (recommendation). The tub is
connected to the GND pin.
4
R1245x
No. EA-269-201022
R1245S Pin Description
Pin No.
Symbol
Description
1
Lx
Lx Switching Pin
2
VIN
Power Supply Pin
3
CE
Chip Enable Pin, Active with ”H”
4
TEST
TEST pin (must be open for user side.)
5
GND
Ground Pin
6
FB
Feedback Pin
7
NC
No connection
8
BST
Bootstrap Pin
* Connect the backside heat radiation tub to GND or same as GND level (recommendation). The tub is connected to the
GND pin.
R1245K Pin Description
Pin No.
Symbol
Description
1
Lx
Lx Switching Pin
2
VIN
Power Supply Pin
3
VIN
Power Supply Pin
4
CE
Chip Enable Pin, Active with ”H”
5
GND
6
FB
7
TEST
8
BST
Ground Pin
Feedback Pin
Test Pin (must be open for user side.)
Bootstrap Pin
* Connect the backside heat radiation tub to GND or same as GND level (recommendation). The tub is connected to the
GND pin.
R1245N Pin Description
Pin No.
Symbol
Description
1
BST
Bootstrap Pin
2
GND
Ground Pin
3
FB
Feedback Pin
4
CE
Chip Enable Pin, Active with ”H”
5
VIN
Power Supply Pin
6
Lx
Lx Switching Pin
5
R1245x
No. EA-269-201022
INTERNAL EQUIVALENT CIRCUIT FOR EACH PIN
Regulator
VIN
BST
LX
LX
Regulator
Regulator
6
VIN
CE
FB
TEST
R1245x
No. EA-269-201022
ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings
(GND = 0 V)
Symbol
VIN
Item
Rating
Unit
−0.3 V to 32 V
V
VLX −0.3 V to VLX + 6 V
V
Input Voltage
VBST
BST Pin Voltage
VLX
Lx Pin Voltage
−0.3 V to VIN + 0.3
V
VCE
CE Pin Input Voltage
−0.3 V to VIN + 0.3
V
VFB
Feedback Pin Voltage
−0.3 V to 6 V
V
PD
Power
Dissipation*
HSOP-8E
Ultra High Wattage
Land Pattern
2900
DFN(PLP)2020-8
Standard Land Pattern
880
SOT-23-6W
Standard Land Pattern
430
mW
Tj
Junction Temperature Range
−40 to 125
ºC
Tstg
Storage Temperature Range
−55 to 125
ºC
* Refer to POWER DISSIPATION for detailed information.
ABSOLUTE MAXIMUM RATINGS
Electronic and mechanical stress momentarily exceeded absolute maximum ratings may cause the permanent
damages and may degrade the lifetime and safety for both device and system using the device in the field.
The functional operation at or over these absolute maximum ratings is not assured.
RECOMMENDED OPERATING CONDITIONS
Recommended Operating Conditions
Symbol
Item
Rating
VIN
Operating Input Voltage
Ta
Operating Temperature Range
Unit
4.5 to 30
V
−40 to 105
°C
RECOMMENDED OPERATING CONDITIONS
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.
7
R1245x
No. EA-269-201022
ELECTRICAL CHARACTERISTICS
Electrical Characteristics
Symbol
Item
Min.
Typ.
Max.
Unit
0.5
VUVLO2
−0.2
1.0
VUVLO2
−0.1
mA
IIN
Consumption Current
VIN = 30 V, VFB = 1.0 V
VUVLO1
UVLO Detect Voltage
Specified VIN falling edge
3.6
VUVLO2
UVLO Released Voltage
Specified rising edge
3.8
4.0
4.2
V
0.792
0.800
0.808
V
ppm/
ºC
VFB
ΔVFB/ΔTa
fosc
fFLB
Maxduty
tstart
VFB Voltage Tolerance
VFB Voltage Temperature
Coefficient
Oscillator Frequency
Fold back Frequency
Oscillator Maximum
Duty Cycle
−40ºC ≤ Ta ≤ 105ºC
±100
Ver. A/B
300
330
360
Ver. C/D
450
500
550
Ver. E/F
900
1000
1100
Ver. G/H
2200
2400
2600
VF B < 0.56 V
Ver. B/D
170
Ver. F
250
Ver. H
400
Ver. A/B/C/D
92
Ver. E/F
88
Ver. G/H
76
V
kHz
kHz
%
VFB = 0.72 V
1
ms
Ver. A/C/E/G
4
ms
0.35
VCEL
Soft-start Time
Delay Time for Latch
Protection
Lx High Side Switch ON
Resistance
Lx High Side Switch
Leakage Current
Lx High Side Switch Limited
Current
CE “L” Input Voltage
VIN = 30 V
VCEH
CE “H” Input Voltage
VIN = 30 V
1.6
IFB
VFB Input Current
VIN = 30.0 V, VFB = 1.0 V
−1.0
1.0
μA
ICEL
CE “L” Input Current
VIN = 30 V, VCE = 0 V
−1.0
1.0
μA
ICEH
CE “H” Input Current
VIN = 30 V, VCE = 30 V
−1.0
1.0
μA
tDLY
RLXH
ILXHOFF
ILIMLXH
TTSD
Istandby
8
(Unless otherwise noted, VIN = 12 V, Ta = 25ºC)
Conditions
Thermal Shutdown Detect
Temperature
Standby Current
VBST − VLX = 4.5 V
VIN = 30 V, VCE = 0 V
VBST − VLX = 4.5 V
Hysteresis 30ºC
VIN = 30 V
1.5
0
5
μA
2.0
2.7
A
0.3
V
V
160
0
ºC
5
μA
R1245x
No. EA-269-201022
OPERATING DESCRIPTIONS
OPERATION OF THE BUCK CONVERTER AND THE OUTPUT CURRENT
The DC/DC converter charges energy in the inductor when the switch turns on, and discharges the energy
from the inductor when the switch turns off and controls with less energy loss, so that a lower output voltage
than the input voltage is obtained. Refer to the following figures.
ILmax
IL
ILmin
i1
VIN
Switch
L
Diode
i2
topen
VOUT
COUT
GND
ton
toff
t=1/fosc
Basic Circuit
Current flowing through the Inductor
Step 1: The switch turns on and current IL (= i1) flows, and energy is charged into COUT. At this moment, IL
increases from ILmin (= 0) to reach ILmax in proportion to the on-time period (ton) of the switch.
Step 2: When the switch turns off, the diode turns on in order to maintain IL at ILmax, and current IL (= i2)
flows.
Step 3: IL (= i2) decreases gradually and reaches IL = ILmin = 0 after a time period of topen, and the diode
turns off. This case is called as discontinuous mode. If the output current becomes large, next switching cycle
starts before IL becomes 0 and the diode turns off. In this case, IL value increases from ILmin (> 0), and this
case is called continuous mode.
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.
9
R1245x
No. EA-269-201022
TYPICAL APPLICATION CIRCUIT
R1245x00xA/B Typical Application Circuit, 330 kHz, VOUT = 1.2 V, VIN = 24 V
R1245x00xC/D Typical Application Circuit, 500 kHz, VOUT = 3.3 V, VIN = 24 V
* TEST pin must be open.
10
R1245x
No. EA-269-201022
R1245x00xE/F Typical Application Circuit, 1000 kHz, VOUT = 3.3 V VIN = 12 V
R1245x00xG/H Typical Application Circuit, 2400 kHz, VOUT = 5. 0 V, VIN = 12 V
* TEST pin must be open.
11
R1245x
No. EA-269-201022
OUTPUT CURRENT AND SELECTION OF EXTERNAL COMPONENTS
The relation between the output current and external components is as follows:
When the switch of Lx turns on:
(Wherein, the peak to peak value of the ripple current is described as IRP, the ON resistance of the switch is
described as RONH, and the diode forward voltage as VF, and the DC resistance of the inductor is described as
RL, and on time of the switch is described as ton)
VIN = VOUT + (RONH + RL) IOUT + L IRP / ton ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 1
When the switch turns off (the diode turns on) as toff:
L IRP / toff = VF + VOUT + RL IOUT ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 2
Put Equation 2 to Equation 1 and solve for ON duty of the switch, ton / (toff + ton) = DON,
DON = (VOUT + VF + RL IOUT) / (VIN + VF - RONH IOUT)ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 3
Ripple Current is as follows:
IRP = (VIN −VOUT −RONH IOUT −RL IOUT) DON / fosc / L ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 4
wherein, peak current that flows through L, and the peak current ILmax is as follows:
ILmax = IOUT + IRP / 2 ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 5
As for the valley current ILmin,
ILmin = IOUT - IRP / 2 ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 6
If ILmin < 0, the step-down DC/DC converter operation becomes current discontinuous mode.
Therefore the current condition of the current discontinuous mode, the next formula is true.
IOUT < IRP / 2 ꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏꞏ Equation 7
Consider ILmax and ILmin, conditions of input and output and select external components.
*The above explanation is based on the calculation in an ideal case in continuous mode.
12
R1245x
No. EA-269-201022
Ripple Current and Lx Current Limit
The ripple current of the inductor may change according to the various reasons. In the R1245x, as an Lx
current limit, Lx peak current limit is used. Therefore the upper limit of the inductor current is fixed.
The peak current limit is not the average current of the inductor (output current). If the ripple current is large,
peak current becomes also large. The characteristic is used for the fold-back current limit of version B/D/F/H.
In other words, the peak current limit is maintained and the switching frequency is reduced, as a result, the
average current of the inductor is reduced. To release this condition, at 170 kHz for version B/D, at 250 kHz
for version F, at 400 kHz for version H must not be beyond the peak current limit. In the figure1, the sequence
of the Lx current limit function is described.
Figure 1. LX Limit function sequence
13
R1245x
No. EA-269-201022
Latch Protection Function for Version A/C/E/G
The latch function works after detecting current limit and if the output voltage becomes low for a certain time,
the output is latched off. Refer to the TECHNICAL NOTES.
Fold-back Protection Function for Version B/D/F/H
If FB voltage becomes lower than approximately 0.56 V, the fold-back protection function limits the oscillator
frequency to typically 170 kHz for version B/D, typically 250 kHz fir version F, typically 400 kHz for version
H. By reducing frequency, the ripple current increases. The R1245x has the peak current limit function,
therefore as in the equation 8, the Lx average current decreases by the increase of the ripple current.
IOUT = ILmax + IRP / 2………………………………………………………………………………………..Equation 8
If FB voltage becomes less than 0.56 V, the oscillator frequency is reduced. At heavy load, if the R1245x
becomes into the fold-back protection mode, the situation may not be released by increase the ripple current.
In terms of other notes on this protection function, refer to the TECHNICAL NOTES.
14
R1245x
No. EA-269-201022
MAXIMUM OUTPUT CURRENT
The output current of the R1245x is limit by the power dissipation PD of the package and the maximum
specification 1.2 A. The loss of the IC includes the switching loss, and it is difficult to estimate. To estimate
the maximum output, using the efficiency data is one method.
By using the efficiency data, the loss including the external components can be calculated with the equation,
(100 / efficiency (%) - 1) x (VOUT (V) x IOUT (A)). From this equation, by reducing the loss of external
components, the loss of the IC can be estimated. The main loss of the external components is composed
by the rectifier diode and DCR of the inductor. Supposed that the forward voltage of the diode is described
as VF, the loss of the diode can be described as follows:
(VIN (V) - RON () x IOUT (A) - VOUT (V) - VF (V))) / VIN (V) x VF (V) x IOUT (A)
The loss by the DCR of the inductor can be calculated by the formula DCR () x IOUT2 (A).
Thus,
The loss of the IC = (100 / efficiency (%) - 1) x (VOUT (V) x IOUT (A) - (VIN (V) - RON () x IOUT (A) - VOUT (V) -VF
(V)) / VIN (V) x VF (V) x IOUT (A) – DCR () x IOUT2 (A)
The efficiency of the R1245x at Ta = 25C, VIN = 12 V, VOUT = 3.3 V, IOUT = 600 mA is approximately 89.5%
for version A/B (Oscillator frequency: 330 kHz). Supposed that the On resistance of the internal driver is
0.35 , the DCR of the inductor is 65 m, the VF of the rectifier diode is 0.3 V and applied to the formula
above,
The loss of the IC = (100% / 89.5% - 1) x (3.3 V x 0.6 A) - (12 V - 0.35 x 0.6 A - 3.3 V - 0.3 V) / 12 V x 0.3
V x 0.6 A - 0.065 x 0.62 A = 86 mW
The power dissipation PD of the package is specified at Ta = 25C based on the Tjmax = 125C. Thus the
thermal resistance of the package ja = (Tjmax (C) - Ta(C)) / PD (W), therefore the thermal resistance of
the each available package is as follows:
HSOP-8E: (125C - 25C) /2.9 W = 34.5C/W
DFN(PLP)2020-8: (125C - 25C) / 0.88 W = 114C/W
SOT-23-6W: (125C - 25C) / 0.43 W = 233C/W
Due to the loss of the IC is 86mW for this example, therefore Tj increase of the each package is as follows:
HSOP-8E: 34.5C/W x 86 mW = 2.96C
DFN(PLP)2020-8: 114C/W x 86 mW = 9.80C
SOT-23-6W: 233C/W x 86 mW = 20.0C
For all the packages, even if the ambient temperature is at 105C, Tj can be suppressed less than 125C.
By the increase of the temperature, on resistance and switching loss increases, therefore, temperature
margin is not enough, measure the efficiency at the actual maximum temperature and recalculation is
necessary.
At the same condition, if the preset frequency is 2400 kHz, the efficiency will be down to approximately 81%.
The result of the loss calculation is 310 mW, therefore the Tj increase of each package is,
HSOP-8E: 34.5C/W x 310 mW = 11C
DFN(PLP)2020-8: 114C/W x 310 mW = 35C
SOT-23-6W: 233C/W x 310 mW = 72C
15
R1245x
No. EA-269-201022
HSOP-8E can be used at the ambient temperature 105C, DFN(PLP)2020-8 can be used at the ambient
temperature up to 90C, SOT-23-6W can be used at the ambient temperature up to 53C. Note that the
result is different by the frequency.
The next graphs are the output current and estimated ambient temperature limit.
Maximum Output Current
VIN = 12 V, VOUT = 3.3 V, fosc = 330 kHz
-40°C
105°C
1400
1200
IOUT[mA]
1000
800
SOT-23-6W
DFN2020-8
HSOP-8E
600
400
200
0
-50
0
50
100
150
Ta[°C]
Maximum Output Current
VIN = 12 V, VOUT = 3.3 V, fosc = 2400 kHz
-40°C
105°C
1400
1200
IOUT[mA]
1000
SOT-23-6W
DFN2020-8
HSOP-8E
800
600
400
200
0
-50
0
50
Ta[°C]
16
100
150
R1245x
No. EA-269-201022
TECHNICAL NOTES
External components must be connected as close as possible to the ICs and make wiring as short as
possible. Especially, the capacitor connected in between VIN pin and GND pin must be wiring the shortest.
If their impedance is high, internal voltage of the IC may shift by the switching current, and the operating
may be unstable. Make the power supply and GND lines sufficient. In the wiring of the power supply, GND,
LX, VOUT and the inductor, large current by switching may flow. To avoid the bad influence, the wiring
between the resistance, “RUP” for setting the output voltage and loading, and the wiring between the inductor
and loading must be separated.
The ceramic capacitors have low ESR (Equivalent Series Resistance) and recommended for the ICs. The
recommendation of CIN capacitor between VIN and GND is 10 F or more for A/B/C/D version, 4.7 F or
more for E/F version, and 2.2 F or more for G/H version. Verify the bias dependence and the
temperature characteristics of the ceramic capacitors. Recommendation conditions are written based on
the case which the recommendation parts are used with the R1245x.
The R1245x is designed with the recommendation inductance value and ceramic capacitor value and
phase compensation has been made. If the inductance value is large, due to the lack of current sensing
amount of the current mode, unstable operation may result. On the contrary, if the inductance value is
small, the current sensing amount may increase too much, low frequency oscillation may occur when the
on duty ratio is beyond 50%. Not only that, if the inductance value is small, according to the increase of
the load current, the peak current of the switching may increase, as a result, the current may reach the
current limit value and the current limit may work.
As for the diode, use the Schottky diode with small capacitance between terminals. The reference
characteristic of the capacitance between terminals is around 100 pF or less at 10 V. If the capacitance
between terminals is large, excess switching current may flow and the operation of the IC may be
unstable. If the capacitance between terminals of the Scottky diode is beyond 100 pF at 10 V or unknown,
verify the load regulation, line regulation, and the load transient response.
Output voltage can be set by adjustment of the values of R1 and R2. The equation of setting the output
voltage is VOUT = VFB (R1 + R2) / R2. If the values of R1 and R2 are large, the impedance of FB pin
increases, and pickup the noise may result. The recommendation value range of R2 is approximately
between 1.0 kΩ to 16 kΩ. If the operation may be unstable, reduce the impedance of FB pin.
For the CE pin, as an ESD protection element, a diode to VIN pin is formed internal of the IC. If CE pin
voltage may become higher than VIN pin voltage, to prevent flowing large current from CE pin to VIN pin,
connect 10 k or more resistor between CE and VIN pin.
Connect the backside heat radiation tub of the DFN(PLP)2020-9/HSOP-8E to the GND. As for multi-layered
boards, to make better power dissipation, putting some thermal via on the thermal pad in the land pattern
and radiation of the heat to another layer is effective.
After the soft-start operation, the latch function is enabled for version A/C/E/G. The latch protection starts
the internal counter when the internal current limit protection circuit detects the current limit. When the
internal counter counts up to the latch timer limit, typically 4 ms, the output is latched off. To reset the latch
function, make the CE pin “L”, or make VIN pin voltage lower than UVLO detector threshold. Then in the
case that the output voltage or FB voltage becomes setting voltage within the latch timer preset time,
counter is initialized. If the slew rate of the power supply is too slow and after the soft-start time, the output
voltage does not reach the set output voltage even if the latch timer preset time is over, the latch function
may work unexpectedly.
17
R1245x
No. EA-269-201022
After the soft-start operation, fold-back protection function is enabled for version B/D/F/H. The fold-back
function will limit the oscillator frequency if the FB pin voltage becomes lower than typically 0.56 V. For B/D
version, the oscillator frequency will be reduced typically into 170 kHz, for F version, into 250 kHz, for H
version, into 400 kHz.
If the slew rate of the power supply is too slow, and even after the soft-start time, the output voltage is still
less than 70% of the set output voltage, or FB pin voltage is less than typically 0.56 V, then this function
may work unexpectedly.
The performance of power circuit using this IC largely depends on external components. Selection of
external components is very important, especially, do not exceed each rating value (voltage/current/power).
Table 1. Recommended Values for Each Output Voltage
R1245x00xA/B: 330 kHz
VOUT (V)
0.8 to 1.2
R1245x00xC/D: 500 kHz
VOUT (V)
0.8 to 1.2
R1 (RUP) (kΩ)
R2 (RBOT) (kΩ)
16
CSPD (pF)
open
100
COUT (F)
4.7
L (H)
R1245x00xE/F: 1000 kHz
VOUT (V)
0.8 to 1.0
R1 (RUP) (kΩ)
R2 (RBOT) (kΩ)
16
CSPD (pF)
open
100
COUT (F)
2.2
L (H)
R1245x00xG/H: 2400 kHz
VOUT (V)
R1 (RUP) (kΩ)
R2 (RBOT) (kΩ)
CSPD (pF)
COUT (F)
L (H)
18
2.5 to 5.0
5.0 ≤
= (VOUT / 0.8 − 1) × R2
R1 (RUP) (kΩ)
R2 (RBOT) (kΩ)
CSPD (pF)
COUT (F)
L (H)
1.2 to 2.5
16
open
47
4.7
1.2 to 1.5
16
100
100
4.7
1.0 to 1.2
16
100
100
2.2
1.2 to 1.8
16
100
10
1.0
12
470
47
10
1.5 to 2.0
1.20
2200
22
15
2.0 to 5.0
1.20
1000
22
33
5.0 to 12.0
12.0 ≤
1.2
1000
22
15
1.2
470
22
15
2.5 to 5.0
5.0 ≤
1.2
470
10
4.7
1.2
470
10
10
= (VOUT / 0.8 − 1) × R2
16
1.2
100
1000
22
22
10
10
1.2 to 1.5
1.5 to 2.5
= (VOUT / 0.8 − 1) × R2
16
16
100
100
47
22
2.2
2.2
1.8 to 2.5
2.5 to 5.0
= (VOUT / 0.8 − 1) × R2
12
1.2
100
470
10
4.7
1.5
2.2
5.0 ≤
1.2
470
4.7
4.7
R1245x
No. EA-269-201022
*1 Divider Resisters Values and Possible Setting Range of Input/ Output
VOUT
[V]
0.8
1
1.2
1.5
1.8
2
2.5
3.3
5
R1 (RUP)
[kΩ]
R2 (RBOT)
[kΩ]
0
open
0
16
4
16
8
16
6
12
10.5
12
14
16
Input Voltage Range [V]
Ver. A/B
Ver. C/D
Ver. E/F
Ver. G/H
4.5 to 20
4.5 to 13.5
4.5 to 7
-
4.5 to 25.5
4.5 to 17
4.5 to 8.5
-
4.5 to 30
4.5 to 20
4.5 to 10
-
4.5 to 30
4.5 to 25
4.5 to 12.5
4.5 to 5.5
4.5 to 30
4.5 to 30
4.5 to 15
4.5 to 6.5
4.5 to 30
4.5 to 30
4.5 to 17
4.5 to 7
4.5 to 30
4.5 to 30
4.5 to 21
4.5 to 9
4.5 to 30
4.5 to 30
4.5 to 27.5
4.5 to 12
20
16
15
12
24
16
1.8
1.2
34
16
25.5
12
2.55
1.2
3.75
1.2
6.3
1.2
5.5 to 30
5.5 to 30
6 to 30
7 to 18.5
6.5 to 30
7 to 30
8 to 20
6
7.8
1.2
6.5 to 30
9
12.3
1.2
10 to 30
10 to 30
11 to 30
12 to 30
12
16.8
1.2
13 to 30
13 to 30
14 to 30
16 to 30
15
21.3
34.8
1.2
16.5 to 30
16.5 to 30
17 to 30
20 to 30
1.2
26.5 to 30
26.5 to 30
27.5 to 30
30
24
19
R1245x
No. EA-269-201022
Table 2. Recommended External Components Examples (Considering All the Range)
Symbol
Condition
Value
Parts Name
CIN
50 V/ X5R
50 V/ X5R
50 V/ X7R
50 V/ X7R
10 F
10 F
4.7 F
2.2 F
UMK325BJ106MM-P
CGA6P3X7S1H106K
GRM31CR71H475KA12L
GRM31CR71H225KA88L
COUT
50 V/ X5R
50 V/ X5R
50 V/ X7R
25 V/ X7R
10 V/ X7R
16 V/ B
10 V/ X7R
10 F
10 F
10 F
10 F
22 F
47 F
47 F
CBST
16 V/ X7R
0.47 F
UMK325BJ106MM-P
TAIYO YUDEN
CGA6P3X7S1H106K
TDK
KTS500B106M55N0T00
Nippon Chemi-Con
GRM31CR71E106K
Murata
GRM31CR71A226M
Murata
GRM32EB31C476KE15
Murata
GRM32ER71A476KE15
Murata
NOTE: The value of COUT depends on
the setting output voltage.
EMK212B7474KD-T
TAIYO YUDEN
L
D
RCE
20
MFR
TAIYO YUDEN
TDK
Murata
Murata
SLF6045T-100M1R6-3PF
TDK
10 H
SLF7045T-4R7M2R0-PF
TDK
4.7 H
NR4018T-4R7M2R0-PF
TDK
4.7 H
NR6020T4R7N
TAIYO YUDEN
4.7 H
NR6028T100M
TAIYO YUDEN
10 H
NR6045T150M
TAIYO YUDEN
15 H
NR6045T220M
TAIYO YUDEN
22 H
NR8040T330M
TAIYO YUDEN
33 H
VLCF4020T-2R2N1R7
TDK
2.2 H
NR4012T2R2M
TAIYO YUDEN
2.2 H
NR3015T1R5N
TAIYO YUDEN
1.5 H
NR4010T1R0N
TAIYO YUDEN
1.0 H
30 V/ 2.0 A
0.37 V
CMS06
TOSHIBA
40 V/ 2.0 A
0.55 V
CMS11
TOSHIBA
An up diode is formed between the CE pin and the VIN pin as an ESD protection element.
If the CE pin may become higher than the voltage of the VIN pin, connect the 10 kΩ resistance
between the CE pin and VIN pin, to prevent a large current from flowing into the VIN pin from
the CE pin.
1.8 A
1.65 A
1.7 A
2.4 A
1.9 A
2.3 A
1.9 A
1.9 A
1.7 A
1.65 A
1.8 A
1.8 A
R1245x
No. EA-269-201022
APPLICATION INFORMATION
TO IMPROVE THE PERFORMANCE
The R1245 can make its performance better, by adding components as shown below.
Cspd: Speed up capacitor
Cspd has two roles, one is to improve the stability, and the other is to improve the transient speed.
The transfer function from VOUT (-which is made of Cspd and feedback resisters, R1(Rup) and
R2(Rbot)) to FB will make a forward bump by low frequency zero and high frequency pole, and
improve the stability of feedback loop. Cspd can improve the gain and make the transient speed fast
at high frequency.
Figure 2. Transfer function BODE plot from VOUT to FB (R1=3.75kΩ, R2=1.2kΩ, Cspd=470pF)
21
R1245x
No. EA-269-201022
To improve the stability
If the resistance values of the R1 and R2 have to be changed, make the value of R1*Cspd be
constant.
(For example, with the R1245x00xA/B and making VOUT=1.2V, if R1=0.6kΩ, R2=1.2kΩ are used,
Cspd=4700pF. By making the values of R1 and R2 increase, the impedance of FB pin also increases,
as a result, the influence by noise must be cared. To avoid this, recommendation value range of R2 is
from 1.0kΩ to 16kΩ. If the operation becomes unstable by increasing the impedance, choose low
resistance value.
If COUT and L are necessary to be changed, or unusual voltage setting is necessary, the Cspd value
must be adjusted. The instruction of the adjustment is as follows:
1. Without Cspd, measure the output under-shoot amount by load transient response.
2. Further, with using a small value Cspd, measure the output under-shoot amount by load transient
response. The appropriate initial value is about 1/10 of the recommendation Cspd value. If Cspd is too
small, the under-shoot amount is almost same as the one without Cspd. If the value of Cspd is changed
bigger gradually, the under-shoot amount will be less. Supposed that this new good Cspd as Cspd1, and
continue to make it bigger, and finally, the under-shoot amount becomes unchanged, at this point,
supposed that the maximum Cspd as Cspd2.
3. Select an appropriate value according to the formula, Cspd=√(Cspd1*Cspd2).
To improve the transient response speed
If the stability is enough, (for example, in the case that COUT is big enough), make Cspd value bigger.
The stability will be same, but the gain at high frequency will be large, and improve the transient
response speed. However, if Cspd value is set Cspd2 value or more, the result will not be improved, not
only that, due to the high gain at high frequency, compared with the result without Cspd, the stability will
be worse.
22
R1245x
No. EA-269-201022
①R1=3.75kΩ, R2=1.2kΩ, Cspd: none, VOUT=3.3V
VOUT
ILX
IOUT
Due to no Cspd, the stability is not good enough, and under-shoot amount is big during the load transient.
②R1=3.75kΩ, R2=1.2kΩ, Cspd=2200pF, VOUT=3.3V
VOUT
ILX
IOUT
Cspd value is appropriate, and stability and response speed is adjusted properly.
③R1=3.75kΩ, R2=1.2kΩ, Cspd=33000pF, VOUT=3.3V
VOUT
ILX
IOUT
Cspd value is too big, the response speed is fast, but the stability decreases slightly.
23
R1245x
No. EA-269-201022
Rspd: Noise reduction filter for speed up capacitor
Cspd can improve the high frequency characteristics due to its differential function. In other words, the
high frequency component is passed through without change, therefore the spike noise of VOUT is
transferred to FB pin as it is. If the spike noise is too big, by its noise of FB pin, the output voltage may
be changed especially at heavy load. To avoid this situation, by setting an Rspd which inserts in series in
Cspd and making a pole at high frequency, filtering is possible and effective. The appropriate value range
of Rspd is from 10Ω to 30Ω. If the resistance value is too big, the effect of Cspd is cancelled by the
lowering pole at high frequency by Rspd. By removing FB pin noise, using low R1 and R2 resistance
value.
24
R1245x
No. EA-269-201022
VOLTAGE BETWEEN Lx PIN AND BST PIN
In the boot-strap style switching regulator, when the Lx pin voltage becomes lower than the regulator
which supplies BST voltage, CBST is charged.
By this charge, while the Lx pin voltage is "H", high side switch can be turned on continuously. Therefore,
if Lx pin voltage does not become lower than the BST voltage supply regulator, switching may be
abnormal. In the R1245, the output voltage of the BST voltage supply regulator is set at 5V. The abnormal
switching may be caused by the following conditions:
・VOUT>5V, the difference between VIN and VOUT is small, inductor current is discontinuous by light
load
When the inductor current is continuous, or load current is big enough even if the discontinuous mode,
the forward current of the diode will make Lx pin voltage down and CBST is charged, but at light load, Lx
pin voltage does not become low enough against the BST voltage supply regulator output(5V). The
voltage of CBST is not high enough and drive capability will be down. (Figure 3-①) Due to the lack of the
drive capability, VOUT cannot be maintained, and under-shoot happens to VOUT, Lx pin voltage may become
lower than the BST voltage supply regulator output (5V), but the error amplifier operation may be
abnormal. When the charge of CBST is recovered and normal switching starts, VOUT becomes back to set
output voltage. However, after recovering the VOUT, to recover the error amplifier's operation, some
response time is necessary, during this response time, VOUT may be over-shoot. (Figure 3-②) As a result,
LX pin voltage cannot be low enough against the BST voltage supply regulator output voltage (5V), undershoot and over-shoot may be repeated. (Figure 4)
25
R1245x
No. EA-269-201022
Abnormal waveforms are shown in the next figures. Figure 3: VIN voltage start-up is slower than the softstart time Figure 4: The voltage difference between input and output is small and load current is small
In both cases, the voltage between Lx pin and BST pin is not enough.
①
②
VIN
VOUT
VBST
VLX
Figure 3. VIN slow start-up (R1245S003A: VIN=30V, VOUT=24V, IOUT=0mA)
VIN
VOUT
VBST
VLX
Figure 4. The voltage difference between input and output is small
(R1245S003A VIN=5.5V, VOUT=5V, IOUT=500uA)
26
R1245x
No. EA-269-201022
To avoid these situations, please refer to the countermeasures shown below:
If start-up with VOUT>5V is necessary, avoid the extremely low load, and start up should be done
by CE pin control after VIN becomes high enough.
・ If VOUT>5V at low load operation is necessary, make the inductance value bigger and assure the
"L" time of Lx.
・ If start-up with VIN=CE is necessary, avoid very slow VIN setting and low load current condition.
・
During the output overshoot while the normal transient response, even the no-switching condition
happens, the operation keeps normal. Other than that, low load condition with VOUT
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