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MC33066DW Fiches technique(PDF) 8 Page - Motorola, Inc |
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MC33066DW Fiches technique(HTML) 8 Page - Motorola, Inc |
8 / 12 page MC34066 MC33066 8 MOTOROLA ANALOG IC DEVICE DATA Figure 6. Undervoltage Lockout and Reference VCC 15 9 Enable/ UVLO Adjust 7k 50k 7k 50k Reference Regulator 5.1V Vref UVLO 8.0V VCC UVLO UVLO 4.2V/4.0V Vref 5 Gnd 4 – + – + The Enable/UVLO Adjust terminal allows the power supply designer to select the VCC UVLO threshold voltages. When this pin is open, the comparator switches the controller on at 16 V and off at 9.0 V. If this pin is connected to the VCC terminal, the upper and lower thresholds are reduced to 9.0 V and 8.6 V, respectively. Forcing the Enable/UVLO Adjust pin low will pull the VCC UVLO comparator input low (through an internal diode) turning off the controller. The Reference Regulator provides a precise 5.1 V reference to internal circuitry and can deliver up to 10 mA to external loads. The reference is trimmed to better than 2% initial accuracy and includes active short circuit protection. Fault Detector The high–speed Fault Comparator and Latch illustrated in Figure 7 can protect a power supply from destruction under fault conditions. The Fault Input pin connects to the input of the Fault Comparator. If this input exceeds the 1.0 V threshold of the comparator, the Fault Latch is set and two logic signals simultaneously disable the primary control path. The signal labeled Fault at the output of the Fault Comparator is connected directly to the output drivers. This direct path reduces the propagation delay from the Fault Input to the A and B outputs to typically 70 ns. The Fault Latch output is OR’d with UVLO output from the Vref UVLO comparator to produce the logic output labeled UVLO + Fault. This signal disables the Oscillator and One–Shot by forcing both the COSC and CT capacitors to be continually charged. Fault Comparator Q R S Fault Fault Latch 1V 9 µA 10 Fault Input UVLO UVLO + Fault EA Clamp Soft–Start Buffer CSoft– Start 11 – + Figure 7. Fault Detector and Soft–Start The Fault Latch is reset during startup by a logic one at the UVLO output of the Vref UVLO comparator. The latch can also be reset after startup by pulling the Enable/UVLO Adjust pin momentarily low to disable the Reference Regulator. Soft–Start Circuit The Soft–Start circuit shown in Figure 7 forces the variable frequency Oscillator to start at the minimum frequency and ramp upward until regulated by the feedback control loop. The external capacitor at the CSoft–Start terminal is initially discharged by the UVLO + Fault signal. The low voltage on the capacitor pass through the Soft–Start Buffer to hold the Error Amplifier output low. After UVLO + Fault switches to a logic zero, the soft–start capacitor is charged by a 9.0 µA current source. The buffer allows the Error Amplifier output to follow the soft–start capacitor until it is regulated by the Error Amplifier inputs (or reaches the 2.5 V clamp). The soft–start function is generally applicable to controllers operating below resonance and can be disabled by simply opening the CSoft–Start terminal. APPLICATIONS The MC34066 can be used for the control of series, parallel or higher order half/full bridge resonant converters. The IC is designed to provide control in discontinuous conduction mode (DCM) or continuous conduction mode (CCM) or a combination of the two. For example, in a parallel resonant converter (PRC) operating in the DCM, the IC is programmed to operate in fixed on–time, variable frequency mode of operation. For a PRC operating in the CCM, the IC can be programmed to operate in the variable frequency mode with a fixed off–time. When operating with a wide input voltage range, such as a universal input power supply, a PRC can operate in the DCM for high input voltage and in the CCM for low input voltage. In this particular case, on–time is programmed corresponding to DCM. The deadtime of the chip is programmed to provide the desired off–time in the CCM. The frequency range is chosen to cover the complete frequency range from the DCM to the CCM. When programmed as such, the controller will operate in the fixed on–time, variable frequency mode at low frequencies. At the frequency which causes the Oscillator to retrigger the One–Shot, the control law changes to variable frequency with fixed off–time. At higher frequencies the supply will operate in the CCM with this control law. Although the IC is designed and optimized for double ended push–pull type converters, it can also be used for single ended applications, such as forward and flyback resonant converters. |
Numéro de pièce similaire - MC33066DW |
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Description similaire - MC33066DW |
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