3A, 34V Input PWM/VFM Step Down DC/DC Converter with PLL Synchronization
The R1270S is 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 0.10Ω and the R1270S can provide the maximum 3A 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 adding an inductor, resistors, a diode, and capacitors externally.
The R1270S is current mode operating type DC/DC converters without an external current sense resistor, and realizes fast response and high efficiency. As an output capacitor, a ceramic type capacitor is usable. The internal oscillator frequency is adjustable over a range of 300kHz to 2400kHz by an external resistor, and also can be synchronized externally by PLL.
The phase compensation is adjustable by using external resistor and capacitor. Thereby optimizations for the inductor and the capacitor can be done.
To improve performance under light load conditions, the R1270S can select automatically between two modes: the VFM mode when the inductor current is discontinuous and the PWM mode when the inductor current is continuous. The ripple voltage at VFM mode is 40mV (Typ.).
As for protection, the R1270S has a current limit function to control an inductor peak current every a cycle, a fold-back function to reduce the oscillator frequency under the short circuit, a thermal shutdown function, an under voltage lockout (UVLO) function, and an over voltage lockout (OVLO) function. Furthermore, the R1270S can include a latch protection function to cut off the output when the output current reaches the set current limit for a certain time. That is, the R1270S supports two types of the presence (R1270S001A) or the absence (R1270S001B) of the latch protection function.
The current limit, which is fixed at 4.5A (Typ.), is adjustable by an external resistor. And, the soft start time is fixed at 0.4ms (Typ.) internally, but is adjustable by an external resistor.
The R1270S has the FLG pin to monitor the overvoltage of the FB pin voltage and the 6V rated pin. When detecting an abnormal voltage, the R1270S outputs a flag.
The R1270S is available in HSOP-18 package.
|Operating Voltage (Maximum Rating)||3.6V to 34V (36V)|
|Consumption Current||Typ. 18µA (VIN = 12V)|
|Stand-by Current||Typ. 0µA (VIN = 34V, CE=0V)|
|Output Voltage||Externally-adjustable at 0.8V or more
(Max. step down ratio 160ns × fosc)
|Feedback Voltage and Tolerance||0.8V±1.0%|
|Operating Frequency||300kHz to 2.4MHz settable by External resistor|
|Minimum Off Time||Typ. 120ns|
|Maximum Duty||Min. 93% (fosc = 300kHz), Min. 67% (fosc = 2400kHz)|
|UVLO Function Detection Voltage||Typ. 2.6V|
|OVLO Function Detection Voltage||Min. 38V|
|Soft-start Time||Internal soft-start time (Typ. 0.4ms), as a lower limit,
Externally-adjustable by using capacitor
|High-side Switch Current Limit||Typ. 4.5A, as a upper limit,
Externally-adjustable by using resistor
|Thermal Shutdown Function||Typ. 160°C|
|CE Threshold Voltage||Typ. 1.0V|
|Latch Protection Delay Time||Typ. 2ms (R1270S001A)|
|Fold-back Protection||Fold-back for Oscillation frequency|
|VFB Voltage Temperature Tolerance (ΔVFB/ΔTa)||Typ. ±100ppm/°C (−40°C ≤ Ta ≤ 105°C)|
- *1The output current depends on external components and conditions.
- •Power source for digital home appliances such as digital TV, DVD players.
- •Power source for office equipment such as printers and fax machines.
- •Power source for 5V PSU or 2-cell or more Li-ion battery powered communication equipment, cameras, video instruments such as VCRs, camcorders.
- •Power source for high voltage battery-powered equipment.
|Data Sheet||Flyer||Design Guide||Package||Quality Assurance
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