R1275S Series
30 V, 2 A, Synchronous PWM Step-down DC/DC Converter
No. EA-370-180713
OVERVIEW
The R1275S is a 36-V synchronous step-down DC/DC converter with built-in drivers. It is designed for industrial
equipment, OA equipment and home electronics that require a 24-V input. It operates at a 2-MHz switching
frequency, which allows to use a small inductor to ensure a high transient response and to maintain a high
efficiency at heavy load condition. Using a spread spectrum clock generator, the EMI noise can be reduced.
KEY BENEFITS
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Provides a high switching frequency at 2 MHz with an efficiency of 87%.
●
Maintains the output voltage constant by reducing a switching frequency to the minimum 1/4 when an input-output
voltage difference is small.
●
Achieves the EMI noise reduction by using a spread spectrum clock generator. (Diffusion Rate: +8%).
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KEY SPECIFICATIONS
Input Voltage Range (Maximum Ratings):
3.6 V to 30 V (36 V)
Start-up Voltage: 4.5 V
Standby Current: Typ. 4 µA
Output Voltage Range: 3.3 V to 5.0 V
Feedback Voltage: 0.64 V ±1.0%
Adjustable Oscillator Frequency Using External
Resistors: 2 MHz
External Synchronous Clock Frequency:
1.8 MHz to 2.2 MHz
Spread Spectrum Clock Generator (SSCG):
Diffusion Rate: Typ. +8%
Minimum On-time: Typ. 70 ns
Minimum Off-time: Typ. 120 ns
Duty-over: Min. 1/4
Soft-start
Thermal Shutdown: Tj = 160°C
Undervoltage Lockout (UVLO): V
CC
= 3.3 V (Typ.)
Overvoltage Lockout (OVLO): V
IN
= 35 V (Typ.)
Overvoltage Detection (OVD): FB Pin Voltage (V
FB
) +10%
LX Current Limiting: Typ. 3 A
High-side Driver On Resistance:
Typ. 0.110 Ω
Low-side Driver On Resistance:
Typ. 0.045 Ω
TYPICAL CHARACTERISTICS
100
90
80
70
60
50
40
30
20
10
0
0
500
1000
Iout [mA]
Efficiency [%]
V
IN
=12V
1500
2000
Efficiency (V
OUT
= 5 V)
6.0
5.0
4.0
V
IN
V
OUT
[V]
3.0
2.0
1.0
0.0
6.0
5.5
5.0
V
IN
[V]
4.5
4.0
3.5
3.0
2.5
Dropout Voltage (I
OUT
= 1 A)
PACKAGE
HSOP-18
5.2mm x 6.2mm,
t= 1.5 mm
OPTIONAL FUNCTIONS
Choose the optional functions from below.
Overcurrent Protection
∗
A
Hiccup-type
C
Hiccup-type
SSCG
Disable
Enable
APPLICATIONS
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Digital Electronics: Digital TVs, DVD Players
OA Equipment: Printers, Facsimiles
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Portable Communication Equipment, Cameras, Video Cameras
Battery-powered Equipment
1
R1275S
No. EA-370-180713
PIN DESCRIPTION
Top View
Bottom View
R1275S (HSOP-18) Pin Configuration
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The tab on the bottom of the package is substrate level (GND). The tab must be connected to the ground plane on the
board.
R1275S Pin Description
Pin No.
Pin Name
1, 2
VIN
(1)
3
NC
4
CE
5
CSS
6
7
8
9
10
11
12
13
14, 15, 16
17
18
COMP
FB
PGOOD
VOUT
MODE
(2)
RT
VCC
BST
GND
(1)
NC
LX
Description
Power Supply Pin
Not Connected
Chip Enable Pin, Active-high
Soft-start Adjustment Pin
Capacitor Connecting Pin for Error Amplifier’s Phase
Compensation
Feedback Input Pin for Error Amplifier
Power Good Output Pin
Output Voltage Feedback Input Pin
Mode Setting Input Pin
Oscillator Frequency Adjustment Pin
VCC Output Pin
Bootstrap Pin
GND Pin
Not Connected
Switching Pin
(1)
(2)
The pins with the same name should be connected together.
This pin should be used with High or with external clock input.
3
R1275S
No. EA-370-180713
Equivalent Circuits for the Individual Terminals
VIN
Int_Reg
VIN
Int_Reg
CSS
CE
Equivalent Circuit for CE Pin
Equivalent Circuit for CSS Pin
Int_Reg
VCC
COMP
FB
Equivalent Circuit for COMP Pin
Equivalent Circuit for FB Pin
VIN
PGOOD
VOUT
Equivalent Circuit for PGOOD Pin
Equivalent Circuit for VOUT Pin
4
stm32/stm8
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