R1271x Series
30 V, 1 A Synchronous PWM Step-down DC/DC Converter
No. EA-517-201127
OVERVIEW
The R1271x is a synchronous step-down DC/DC converter with a maximum input voltage rating of 42V. This device is
suitable for small inductors with the switching frequency of 2 MHz. The external components are only an inductor and
several capacitors and a resistance. The tiny DFN package option makes the power circuit compact .
KEY BENEFITS
● High efficiency 85% is realized with switching frequency of 2 MHz
● The output voltage is maintained at cranking by reducing a switching frequency to minimum 1/4 of normal frequency.
● EMI noise reduction by using a spread spectrum clock generator. (Diffusion Rate: +10%).
TYPICAL APPLICATION
KEY SPECIFICATIONS
•
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Input Voltage Range (Maximum Ratings): 3.6 V to 30 V (42 V)
Start-up Voltage: 4.5 V
Standby Current: Typ. 4 µA
Operating Temperature Range: -40°C to 105°C
Output Voltage Accuracy: ±1.0% (Ta = 25°C)
Oscillator Frequency: Typ.2 MHz (Fixed inside the IC)
Spread Spectrum Clock Generator (SSCG): Diffusion Rate: Typ. +10%
Minimum On-Time: Typ. 70 ns
Minimum Off-Time: Typ. 120 ns
Duty-over: Oscillation Frequency x 1 ~ 1/4
Soft start function
Thermal Shutdown: Typ. Tj = 160°C
Undervoltage Lockout (UVLO): VCC = 3.3 V (Typ.)
Overvoltage Lockout (OVLO): VIN = 35 V (Typ.)
Overvoltage Detection (OVD): Output Voltage (VOUT) +10%
LX Current Limit: Typ. 1.8 A (LIMIT Pin Open)
High-side MOS FET On Resistance: Typ. 0.4 Ω
Low-side MOS FET On Resistance: Typ. 0.2 Ω
L
CIN
CVCC
RCE
CE Control
VIN
VCC
LIMIT
VOUT
LX
R1271x
CSS
CE
CBST
BST
GND
VOUT
COUT
PGOOD
PCB EXAMPLE
9.1 ㎜
7.6 ㎜
PACKAGES
EV Board (DFN3030-12B)
OPTIONAL FUNCTIONS
Product
Name
Set Output Voltage (VSET)
R1271x331∗
3.3 V
R1271x501∗
5.0 V
Product Name
*Wettable Flanks
DFN3030-12B
3.0 x 3.0 x 0.8 (mm)
HSOP-18
5.2 x 6.2 x 1.45 (mm)
APPLICATIONS
●
Digital Electronics: Digital TVs, DVD Players
●
R1271xxx1A
R1271xxx1B
R1271xxx1C
R1271xxx1D
Overcurrent
Protection
Hiccup-type
Latch-type
Hiccup-type
Latch-type
SSCG
Disable
Disable
Enable
Enable
Portable Communication Equipment, Cameras, Video Cameras
1
R1271x
No. EA-517-201127
SELECTION GUIDE
The set Output Voltage, the Optional functions and Quality class can be designated by user’s request.
Selection Guide
Product Name
R1271Lxx1*-TR
R1271Sxx1*-E2-FE
Package
Quantity per Reel
Pb Free
Halogen Free
DFN3030-12B
3,000 pcs
Yes
Yes
HSOP-18
1,000 pcs
Yes
Yes
xx：Select the Set Output Voltage (VSET).
xx
33
50
Set Output Voltage (VSET)
3.3 V
5.0 V
∗：Select the optional functions.
∗
A
B
C
D
Overcurrent Protection
SSCG
Hiccup-type
Latch-type
Hiccup-type
Latch-type
Disable
Disable
Enable
Enable
2
R1271x
No. EA-517-201127
BLOCK DIAGRAM
VIN
VOUT
VOUT Open
Detection
Soft_Start
Over Voltage
Detection
OVD
Under Voltage
Detection
UVD
Open_Det
VCC
VCC
Regulator
INT
Regulator
VCC
Int_Reg
OVD
SHDN
OFF_Pulse
BST
OFF_Pulse
HSMOSFET
Drive Circuit
Int_Reg
SSCG_EN
VCO
S
Q
LX
Set_Pulse
2uA
-
+
CSS
+
Soft Start
Circuit
Soft_Start
OVD
SHDN
LSMOSFET
R
GND
Rev
Slope
Reverse
Detection
OVD
SHDN
Reference
Hiccup/Latch
VIN VOUT
CE
ILIM
Hiccup
/Latch
1.2V
+
UVD
Open_Det
Peak Current
Limit
LIMIT
Hiccup/Latch
Thermal Shutdown
VCC
UVLO
VIN
OVLO
SHDN
Soft_Start
SHDN
OVD
UVD
PGOOD
R1271x Block Diagram
3
R1271x
No. EA-517-201127
PIN DESCRIPTIONS
Top View
Bottom View
R1271L (DFN3030-12B) Pin Configuration
∗ The tab on the bottom of the package is substrate level (GND). The tab must be connected to the ground plane
on the board.
R1271L (DFN3030-12B) Pin Description
Pin No.
Pin Name
(1)
Description
1
VIN
2
NC (1)
Power Supply Pin
No Connection
3
VCC
VCC Output Pin
4
LIMIT
Current Limit Adjustment Pin
5
CSS
Soft-start Adjustment Pin
6
CE
7
PGOOD
Chip Enable Pin, Active-high
8
VOUT
Output Voltage Feedback Input Pin
9
NC (1)
No Connection
10
GND
GND Pin
11
BST
Bootstrap Pin
12
LX
Switching Pin
Power Good Pin
It is recommended to set the NC pin left open to prevent failure caused by adjacent pins’ short circuit.
4
R1271x
No. EA-517-201127
Top View
Bottom View
R1271S (HSOP-18) Pin Configuration
∗ The tab on the bottom of the package is substrate level (GND). The tab must be connected to the ground plane
on the board.
R1271S (HSOP-18) Pin Description
Pin No.
Pin Name
(1)
(2)
Description
1, 2
VIN (1)
Power Supply Pin
3, 4
NC(2)
No Connection
5
VCC
VCC Output Pin
6
LIMIT
Current Limit Adjustment Pin
7
CSS
Soft-start Adjustment Pin
8
NC(2)
No Connection
9
CE
10
PGOOD
Chip Enable Pin, Active-high
Power Good Pin
11
VOUT
Output Voltage Feedback Input Pin
12
NC(2)
No Connection
13, 14, 15
GND(1)
16
BST
Bootstrap Pin
17, 18
LX(1)
Switching Pin
GND Pin
The pins with the same name should be tied together except NC pins.
It is recommended to set the NC pin left open to prevent failure caused by adjacent pins’ short circuit.
5
R1271x
No. EA-517-201127
● Equivalent Circuits for the Individual Terminals
VIN
Int_Reg
VCC
Equivalent Circuit for VCC Pin
LIMIT
Equivalent Circuit for LIMIT Pin
VIN
VIN
CSS
CE
Equivalent Circuit for CSS Pin
PGOOD
Equivalent Circuit for PGOOD Pin
VIN
Equivalent Circuit for CE Pin
VOUT
Equivalent Circuit for VOUT Pin
VCC
BST
LX
Equivalent Circuit for BST-LX Pin
6
R1271x
No. EA-517-201127
ABSOLUTE MAXIMUM RATINGS
Absolute Maximum Ratings
Symbol
Parameter
Rating
Unit
−0.3 to 42
V
−0.3 to VIN+0.3 ≤ 42
V
−0.3 ~ 3
V
VIN
VIN Pin Input Voltage
VCE
CE Pin Voltage
VCSS
CSS Pin Voltage
VOUT
VOUT Pin Voltage
−0.3 to 30
V
VCC Pin Voltage
−0.3 to 6
V
Internally Limited
mA
LX−0.3 to LX+6
V
−0.3 to VIN +0.3 ≤ 36
V
PGOOD Pin Voltage
−0.3 to 16
V
VLIMIT
LIMIT Pin Voltage
−0.3 to 6
V
PD
Power Dissipation
Tj
Junction Temperature Range
−40 to 125
°C
Tstg
Storage Temperature Range
−55 to 125
°C
VCC
VCC Pin Output Current
VBST
BST Pin Voltage
VLX
LX Pin Voltage
VPGOOD
Refer to Appendix “POWER DISSIPATION”
ABSOLUTE MAXIMUM RATINGS
Electronic and mechanical stress momentarily exceeded absolute maximum ratings may cause permanent damage
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
Parameter
VIN
Operating Input Voltage
Ta
Operating Temperature Range
VUP
PGOOD Pin Pull-up Voltage
Rating
3.6 to 30
−40 to 105
0 to 5.5
Unit
V
°C
V
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 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
R1271x
No. EA-517-201127
ELECTRICAL CHARACTERISTICS
VIN = 12 V, VCE = VIN, unless otherwise specified.
The specifications surrounded by
are guaranteed by design engineering at −40°C ≤ Ta ≤ 105°C.
R1271x Electrical Characteristics
Symbol
Parameter
Start-up Voltage
VSTART
VCC Pin Voltage (VCC-GND)
VCC
ISTANDBY
IVIN1
VUVLOF
VUVLOR
VOVLOR
VOVLOF
Standby Current
VIN Consumption Current 1
at PWM switching stop
Undervoltage Lockout (UVLO)
Threshold Voltage
Overvoltage Lockout (OVLO)
Threshold Voltage
Output Voltage (R1271x331x)
VOUT
Output Voltage (R1271x501x)
fOSC0
tSS1
tSS2
ITSS
VSSEND
RDIS_CSS
ILXLIMIT
VCEH
VCEL
ICEH
ICEL
IVOUTH
VPGOODOFF
IPGOODOFF
VOVDR
VOVDF
VUVDF
VUVDR
Oscillator Frequency 0
Soft-start Time 1
Soft-start Time 2
Soft-start Pin Charging Current
CSS Pin Voltage at soft-start
stop
CSS Pin Discharge Resistance
LX Current Limit
(High-side MOS FET)
CE ”High” Input Voltage
CE ”Low” Input Voltage
CE ”High” Input Current
CE ”Low” Input Current
VOUT ”High” Pin Current
PGOOD “Low” Output Voltage
PGOOD Pin Leakage Current
Overvoltage Detection
(OVD) Threshold Voltage
Overvoltage Release
(OVD) Threshold Voltage
Undervoltage Detection
(UVD) Threshold Voltage
Undervoltage Release
(UVD) Threshold Voltage
Conditions
Min.
Typ.
VOUT = VSET x 1.05
VCE = 0 V
VIN = 30 V, VCE = 0 V
4.75
5
4
30
VOUT = VSET x 1.05
VCC Falling
VCC Rising
VIN Rising
VIN Falling
Ta = 25°C
−40°C ≤ Ta ≤ 105°C
Ta = 25°C
−40°C ≤ Ta ≤ 105°C
8 V ≤ VIN ≤ 16 V, IOUT = 0 A
CSS = OPEN
CSS = 4.7 nF
VCSS = 0 V
VIN = 4.5 V, VCE = 0 V,
VCSS = 3 V
DC Current, LIMIT = OPEN
DC Current, LIMIT = 0V
VIN = VCE = 30 V
VIN = 30V, VCE = 0 V
3.10
4.10
33.6
32.0
3.267
3.234
4.950
4.900
1800
0.36
1.4
1.8
VOUT Rising
VOUT Falling
VOUT Falling
VOUT Rising
µA
1.0
1.35
mA
3.3
4.3
35
34
3.50
4.49
36.75
36.2
3.333
V
V
V
V
3.3
5.0
2000
0.5
2
3.366
5.050
V
5.100
2200 kHz
0.75 ms
2.0
ms
2.2
µA
0.635
0.64
0.705
V
1.8
3
5
kΩ
1.5
0.75
1.25
1.8
1.0
2.3
1.25
A
-0.1
130
1.2
0
VIN = 3.6 V, IPGOOD = 1 mA
VIN = 30V, VPGOOD = 6 V
(Ta = 25°C)
Max. Unit
4.5
V
5.25
V
-0.1
VSET
x1.06
VSET
x1.02
VSET
x0.86
VSET
x0.88
0
VSET
x1.10
VSET
x1.07
VSET
x0.90
VSET
x0.93
1.1
2.45
0.1
390
0.35
0.1
VSET
x1.14
VSET
x1.12
VSET
x0.94
VSET
x0.98
V
V
µA
µA
µA
V
µA
V
V
V
V
All test items listed under Electrical Characteristics are done under the pulse load condition (Tj ≈ Ta = 25°C).
8
R1271x
No. EA-517-201127
• TYPICAL APPRICATION CIRCUIT
CIN
LIMIT
R1271x
CE
RCE
CBST
GND
VOUT
VUP
RPG
VOUT
CSS
CSS
CE Control
BST
VCC
CVCC
L
LX
VIN
PGOOD
PGOOD
COUT
R1271x Typical Application Circuit
Recommended Ceramic Capacitors
Symbol
Capacitance
Tolerance
Voltage resistance
CIN
COUT
CBST
CVCC
10 µF
10 µF
0.1 µF
1.0 µF
±10%
±10%
±10%
±20%
50 V
50 V
25 V
16 V
Symbol
L
Inductance
2.2 µH
Tolerance
±20%
Temperature
characteristics
X7R
X7S
X7R
X7R
Rated current
3.3A
It is recommended to set 1 kΩ or higher for RCE and 10 kΩ or higher for RPG
9
R1271x
No. EA-517-201127
THEORY OF OPERATION
Operation of Step-down DC/DC Converter
The basic operation of the step-down DC/DC converter is shown in the following figures.
ILMAX
IL
L
VIN LS-MOSFET
i1
i1
HS-MOSFET
i2
0
VOUT
COUT
i2
ΔIL
IOUT
ILMIN
tONHS
t
tOFFHS
T=1/fOSC
Basic Circuit
Step1.
Current Through Inductor
When the high-side MOSFET turns on, current IL (= i1) flows through the Inductor(L) to charge COUT
and provide IOUT. At this moment, IL increases from ILMIN to reach ILMAX in proportion to the on-time
period (tON) of the high-side MOSFET.
Step2.
When the high-side MOSFET turns off, the low-side MOSFET turns on to flow current IL (= i2).
Step3.
The low-side MOSFET turns on until going to the next cycle. When IOUT is small, the low-side MOS
FET must keep “on” to meet IL = ILMIN < 0.
In the PWM mode, the output voltage is maintained constant by controlling tONHS with the constant switching
frequency (fOSC).
10
R1271x
No. EA-517-201127
Calculation of Inductor Current
The peak inductor current ILMAX can be estimated by the following equation.
ILMAX = IOUT + 1 / 2 × (VIN – VOUT) / L × VOUT / VIN / fOSC
Example: ILMAX = 1A + 1/2 × (12V – 5V) / 2.2µH × 5V / 12V / 2MHz
= 1.331 A
The above can be calculated from the equation with the inductor current in continuous mode of a general
step-down DC/DC converter. The P-P value of the inductor ripple current is “ΔIL”.
The ΔIL is calculated by Equation 1 when the high side MOS FET is ON.
ΔIL = ( VIN – VOUT ) / L × tONHS ··················································································· Equation 1
The ΔIL is calculated by Equation 2 when the high side MOS FET is OFF.
ΔIL = VOUT / L × tOFFHS ···························································································· Equation 2
Using Equation 2 to Equation 1, the ON duty of the high side MOS FET tONHS / (tONHS + tOFFHS) = DON
is solved by Equation 3.
DON = VOUT / VIN ····································································································· Equation 3
And then, the ripple current ΔIL is calculated by substituting tONHS = Don / fOSC into Equation 1.
ΔIL = (VIN − VOUT) / L × DON / fosc ·············································································· Equation 4
At this time, ILMAX flowing in the inductor and high side MOS FET is calculated by Equation 5.
ILMAX = IOUT + ΔIL / 2 ·································································································· Equation 5
Therefor ILMIN is calculated by Equation 6.
ILMIN = IOUT − ΔIL / 2 ·································································································· Equation 6
Note that the input-output conditions and peripheral components should be determined in consideration of
ILMAX and ILMIN.
The above calculations are based on the ideal operation in continuous mode.
11
R1271x
No. EA-517-201127
UVLO (Undervoltage Lockout)
When the VCC pin voltage decreases below the UVLO detection threshold voltage due to the input voltage
decrease, the R1271x turns the switching off to prevent the malfunction of the device. Due to the switching
stop, the output voltage decreases according to the load and COUT. If the VCC pin voltage increases above
the UVLO release threshold voltage, the device restarts the operation with soft-start.
Input Voltage (VIN)
Internal Regulator Voltage (VCC)
UVLO Release Voltage (VUVLOR)
UVLO Detection Voltage (VUVLOF)
LX Voltage (VLX)
Output Voltage (VOUT)
Soft-start Time (tSS)
OVLO (Overvoltage Lockout)
When the input voltage rises above the OVLO detection threshold of voltage, the R1271x turns the switching
off to prevent malfunctions of the device or damage on the high side MOS FET and low side MOS FET due
to overvoltage. Due to the switching stop, the output voltage decreases according to the load and COUT. If the
input voltage decreases below the OVLO release threshold voltage, the device restarts the operation with
soft start. Note that this function does not guarantee the operation exceeding the absolute maximum ratings.
OVLO Detection Voltage (VOVLOR)
OVLO Release Voltage (VOVLOF)
Input Voltage (VIN)
LX Voltage (VLX)
Output Voltage (VOUT)
Soft-start Time (tSS)
12
R1271x
No. EA-517-201127
Duty-over Function
When the input voltage is dropped at when the input voltage drops, the R1271x linearly changes the operating
frequency to 1/4 of the set oscillator frequency in order to maintain the output voltage. This increases the on
duty and reduce the voltage difference between input and output. The duty-over starts operating when it
detects the minimum off-time.
Input Voltage (VIN)
Output Voltage (VOUT)
Dashed line:
without duty-over function
Oscillation Frequency (fOSC)
OFFDUTY = TOFF
fOSC/4
Frequency modulation by duty over
Minimum Off-Time
The minimum off time indicates the minimum time that the high side MOS FET can be turned off within the
oscillation period. The minimum off time (Typ. 120 ns) of R1271x is determined by the internal circuit, using a
NMOS of high side MOS FET by adopting bootstrap method. Charging a voltage to drive the high side MOS
FET is needed, and the minimum off time is determined by the time required for charging.
When the input voltage is low or sudden load transient occurs, the high-side MOS FET is turned off at least
every 4 cycles by the duty over function substantially. The input / output voltage difference is decreased by
increasing the maximum duty ratio.
Minimum On-Time
The minimum on-time indicates the minimum time duration that the R1271x can turn the high-side MOS FET
on during the oscillation period. The minimum on-time (Typ. 70 ns) of the device is determined by the internal
circuit. The device cannot generate a pulse width that is less than the pulse width of minimum on-time. If the
minimum step-down ratio/ the oscillator frequency: [VOUT / VIN x (1 / fOSC)].is less than the minimum on-time, the
pulse skipping occurs, which stabilizes the output voltage but increases the ripple of current and voltage.
13
R1271x
No. EA-517-201127
Standby Function
When the CE pin voltage drops below 1.1V (“Low” threshold voltage), switching is turned off. If the CE pin
voltage rises above the 1.25 V (“High” threshold voltage), the R1271x will restart with a soft start.
In order for the VIN current to be the standby current (ISTANDBY), the CE pin voltage must be 0.4V or less.
Overvoltage Detection (OVD)
The OVD function monitors the output voltage. Switching stops even if the internal circuit is active state, when
detecting the overvoltage. The OVD detection voltage is Typ.110% of VSET, and the PGOOD pin outputs "Low"
when VOUT is over the OVD detection threshold voltage for Typ.15 μs or more. When VOUT is under 107%
(Typ.) of VSET, the PGOOD pin outputs “High” after delay time (Typ.120 µs). Then, switching is controlled by
normal operation.
Under Voltage Detection (UVD)
The UVD function monitors the output voltage. The UVD detection voltage is Typ.90% of VSET, and the
PGOOD pin outputs "Low" when VOUT is less than the UVD detection threshold voltage for Typ.15 μs or more.
When VOUT is over 93% (Typ.) of VSET, the PGOOD pin outputs “High” after delay time (Typ.120 µs.). Then, the
overcurrent protection works when detecting a current limit during the UVD detection.
Output Voltage (VOUT)
VOVDR
VOVDF
VSET
VUVDR
VUVDF
LX Voltage (VLX)
VLX
PGOOD Voltage (VPGOOD)
VUP
Typ.
15μs
Typ.
120μs
Typ.
15μs
Typ.
120μs
Overvoltage detection / undervoltage detection sequence
14
R1271x
No. EA-517-201127
PGOOD (Power Good) Function
The power good function with using a Nch open drain output pin can detect the following states of the R1271x.
The NMOS FET turns on and the PGOOD pin becomes “Low” when detecting them.
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