High Efficiency Conversion from 5V or 3. The device integrates a main switch and a synchronous rectifier for high efficiency without an external Schottky diode. The output voltage can be regulated as low as 0. This device offers two operation modes, PWM control and PFM Mode switching control, which allows a high efficiency over the wider range of the load. Must be closely decoupled to GND with a 22? F or greater ceramic capacitor.
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With internal? Adjustable Output from 0. The output voltage is? Accurate Reference: 0. They are halogen-free,? Applications Pin Configuration? Battery-Powered Portable Devices? Digital Still Cameras? Wireless and DSL Modems? Personal Information Appliances? Laptop, Palmtops, Notebook Computers? Power Supply Input. Input voltage that supplies current to the output voltage and powers the 2 VIN internal control circuit.
Connect this pin to the output inductor. Ground of the buck converter. This pin is the inverting input of the error amplifier. FB senses the switcher output through an external resistor divider network. This pin is output of the error amplifier. The current comparator threshold 6 COMP increases with this control voltage. Connect an RC network to ground for control loop compensation.
Buck Converter Enable Active High. A logic low forces the converter into shutdown mode 7 EN reducing the supply current. Connect a softstart capacitor CSS to this pin. Leave open for no softstart application. The softstart capacitor is discharged to ground when EN pin is low. Exposed Pad Power Ground. The exposed pad is the mainly path for heat convection and should be well soldered to the PCB for best thermal performance.
With internal low RDS ON switches, it is capable of delivering 3A output current over a wide input voltage range from 4. The output voltage is adjustable from 0. Other features include Programmable softstart, chip enable, overvoltage, under-voltage, overtemperature and over-current protections. The supply voltage range is from 4. A power on reset POR continuously monitors the input supply voltage. The POR level is typically 4. The buck converter draws pulsed current with sharp edges each time the upper switch turns on, resulting in voltage ripples and spikes at supply input.
A minimum 10uFx2 ceramic capacitor with shortest PCB trace is highly recommended for bypassing the supply input. In the shutdown mode, both upper and lower switches are turned off. Pulling EN pin higher than 2. The uPS features programmable soft start function to limit the inrush current from supply input by a soft start capacitor CSS connected to SS pin as shown in Figure 1. The error amplifier is a tri-input device.
During normal operation, the uPS operates at PWM mode to regulate output voltage by transferring the power to the output voltage cycle by cycle at a constant frequency. The uPS turns on the upper switch at each rising edge of the internal oscillator allowing the inductor current to ramp up linearly. The switch remains on until either the current limit is tripped or the PWM comparator turns off the switch for regulating output voltage. The lower switch turns on with optimal dead time and picks up the inductor current after the upper switch turns off allowing the inductor current to ramp down linearly.
The switch remains on until the next rising edge of oscillator turns on the upper switch. The high frequency switching ripple is easily smoothed by the output filter.
The upper switch current is sensed, slope compensated and compared with the error amplifier output COMP to determine the adequate duty cycle. The feedback voltage VFB is sensed through a resistive voltage divider and regulated to internal 0. The error amplifier amplifies and compensates voltage variation to get appropriate COMP pin voltage. When the load current increases, it causes a slight decrease in the feedback voltage relative to the 0. In real applications, a 22pF feed-forward ceramic capacitor is recommended in parallel with R1 for better transient response.
Current Limit Function The uPS continuously monitors the inductor current for current limit by sensing the voltage drop across the upper switch when it turns on. When the inductor current is higher than current limit threshold 5A typical , the current limit function activates and forces the upper switch turning off to limit inductor current cycle by cycle.
When the output is shorted to ground, the current limit function activates immediately, and VOUT will be pulled down very fast. Eventually the under voltage protection will be triggered, and the IC will shut down to protect external components. The IC will restart after the UVP retry delay, and the above behavior may repeat if the output short condition is not released. The OTP is a non-latch type protection. The uPS automatically initiates another soft start cycle if the junction temperature drops below OC.
Stresses listed as the above Absolute Maximum Ratings may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may remain possibility to affect device reliability.
Note 2. Devices are ESD sensitive. Handling precaution recommended. Note 3. Note 4. The device is not guaranteed to function outside its operating conditions. Output Current 0. Output Current 3. The inductance is chosen based on the desired ripple current. Large value inductors result in lower ripple currents and small value inductors result in higher ripple currents. For most applications, the value of the inductor will fall in the range of 1uH to 10uH. Make sure that the inductor will not saturate over the operation conditions including temperature range, input voltage range, and maximum output current.
If possible, choose an inductor with rated current higher than 5. The size requirements refer to the area and height requirement for a particular design. For better efficiency, choose a low DC resistance inductor. DCR is usually inversely proportional to size. The choice of which style inductor to use often depends on the price vs. Input Capacitor Selection The buck converter draws pulsed current with sharp edges from the input capacitor resulting in ripple and noise at the input supply voltage.
The input capacitor should be placed as near the device as possible to avoid the stray inductance along the connection trace. Y5V dielectrics, aside from losing most of their capacitance over temperature, they also become resistive at high frequencies.
This reduces their ability to filter out high frequency noise. The capacitor with low ESR equivalent series resistance provides the small drop voltage to stabilize the input voltage during the transient loading. For input capacitor selection, the ceramic capacitor larger than 10uFx2 is recommend. The capacitor must conform to the RMS current requirement. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief.
This makes it advisable to further derate the capacitor, or choose a capacitor rated at a higher temperature than required. Always consult the manufacturer if there is any question. The ESR of the output capacitor determines the output ripple voltage and the initial voltage drop following a high slew rate load transient edge.
The ceramic capacitor with low ESR value provides the low output ripple and low size profile. Using Ceramic Capacitors Higher value, lower cost ceramic capacitors are now available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN.
At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN, large enough to damage the part. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. Checking Transient Response The regulator loop response can be checked by looking at the load transient response.
Switching regulators take several cycles to respond to a step in load current.
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