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SD414-100 датащи(PDF) 6 Page - Fairchild Semiconductor |
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SD414-100 датащи(HTML) 6 Page - Fairchild Semiconductor |
6 / 10 page 6 www.fairchildsemi.com FAN5330 Rev. 1.0.1 Block Diagram Figure 4. Block Diagram Circuit Description The FAN5330 is a pulse-width modulated (PWM) current-mode boost converter. The FAN5330 improves the performance of bat- tery powered equipment by significantly minimizing the spectral distribution of noise at the input caused by the switching action of the regulator. In order to facilitate effective noise filtering, the switching frequency was chosen to be high, 1.5MHz. The device architecture is that of a current mode controller with an internal sense resistor connected in series with the N-channel switch. The voltage at the feedback pin tracks the output voltage at the cathode of the external Schottky diode (shown in the test cir- cuit). The error amplifier amplifies the difference between the feedback voltage and the internal bandgap reference. The amplified error voltage serves as a reference voltage to the PWM comparator. The inverting input of the PWM comparator consists of the sum of two components: the amplified control signal received from the 30m Ω current sense resistor and the ramp generator voltage derived from the oscillator. The oscilla- tor sets the latch, and the latch turns on the FET switch. Under normal operating conditions, the PWM comparator resets the latch and turns off the FET, thus terminating the pulse. Since the comparator input contains information about the output volt- age and the control loop is arranged to form a negative feed- back loop, the value of the peak inductor current will be adjusted to maintain regulation. Every time the latch is reset, the FET is turned off and the cur- rent flow through the switch is terminated. The latch can be reset by other events as well. Over-current condition is moni- tored by the current limit comparator which resets the latch and turns off the switch instantaneously within each clock cycle. Over-Voltage Protection The voltage on the feedback pin is sensed by an OVP Compar- ator. When the feedback voltage is 15% higher than the nominal voltage, the OVP Comparator stops switching of the power tran- sistor, thus preventing the output voltage from going higher. Open-circuit protection As in any current regulator, if the feedback loop is open, the out- put voltage increases until it is limited by some additional exter- nal circuitry. In the particular case of the FAN5330, the output voltage is limited by the switching transistor breakdown at around 45V, typically (assuming that COUT and the Schottky diode rating voltage are higher). Since at such high output volt- age the output current is inherently limited by the discontinuous conduction mode, in most cases, the switching transistor enters non-destructive breakdown and the IC survives. However, to ensure 100% protection for LED disconnection, we recommend limiting VOUT with an external Zener diode or stop- ping the boost switching with an external voltage supervisory circuit. Applications Information Setting the Output Current The internal reference (VREF) is 110mV (Typical). The output current is set by a resistor divider R connected between FB pin and ground. The output current is given by Reference Oscillator n FB FB Amp Driver Comp Over Voltage Comp - - + + Σ Ramp Generator R R R Q S Current Limit Comparator 30m Ω 1.15 x VREF Shutdown Circuitry Thermal Shutdown SHDN GND SW VIN Amp Error 45 1 2 3 + + - - + - I LED V REF R -------------- = |
Аналогичный номер детали - SD414-100 |
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Аналогичное описание - SD414-100 |
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