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MC33067 Folha de dados(PDF) 10 Page - ON Semiconductor |
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MC33067 Folha de dados(HTML) 10 Page - ON Semiconductor |
10 / 16 page MC34067, MC33067, NCV33067 www.onsemi.com 10 The totem−pole output drivers are ideally suited for driving power MOSFETs and are capable of sourcing and sinking 1.5 A. Rise and fall times are typically 20 ns and 15 ns respectfully when driving a 1.0 nF load. High source/sink capability in a totem−pole driver normally increases the risk of high cross conduction current during output transitions. The MC34067 utilizes a unique design that virtually eliminates cross conduction, thus controlling the chip power dissipation at high frequencies. A separate power ground pin is provided to isolate the sensitive analog circuitry from large transient currents. Figure 19. Undervoltage Lockout and Reference 8.0 V Vref 15 9 VCC 5 Vref 4.2/4.0 V Vref UVLO VCC UVLO 7.0k 50k 7.0k 50k 5.1 V Reference Enable / UVLO Adjust UVLO PERIPHERAL SUPPORT FUNCTIONS The MC34067 Resonant Controller provides a number of support and protection functions including a precision voltage reference, undervoltage lockout comparators, soft−start circuitry, and a fault detector. These peripheral circuits ensure that the power supply can be turned on and off in a controlled manner and that the system will be quickly disabled when a fault condition occurs. Undervoltage Lockout and Voltage Reference Separate undervoltage lockout comparators sense the input VCC voltage and the regulated reference voltage as illustrated in Figure 19. When VCC increases to the upper threshold voltage, the VCC UVLO comparator enables the Reference Regulator. After the Vref output of the Reference Regulator rises to 4.2 V, the Vref UVLO comparator switches the UVLO signal to a logic zero state enabling the primary control path. Reducing VCC to the lower threshold voltage causes the VCC UVLO comparator to disable the Reference Regulator. The Vref UVLO comparator then switches the UVLO output to a logic one state disabling the controller. The Enable/UVLO Adjust pin 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 Detection Converter protection from adverse operating conditions can be implemented with proper use of the Fault Comparator and Latch blocks that are illustrated in Figure 20. The Fault Comparator has an input threshold of 1.0 V and when exceeded, sets the Fault Latch and generates two logic signals that simultaneously disable the primary control path. The signal line labeled “Fault” connects directly to two gates that control the output drivers. This direct path reduces the driver turn−off propagation delay to approximately 70 ns. The Fault Latch output is OR’ed with the UVLO output that is derived from the Vref UVLO comparator, to produce the logic output labeled “UVLO+Fault”. This signal disables the Oscillator and the One−Shot by forcing both the COSC and CT capacitors to be continually charged. The Fault Latch is automatically reset during startup by a logic “1” that appears at the Vref UVLO comparator output. The latch can also be reset after startup by momentarily pulling the Enable/UVLO Adjust pin low to disable the Reference. Note that after activation, the Fault Latch will remain in a set state only as long as VCC is provided to the MC34067. Also, Drive Output B will assume a high state if the Fault input signal drops below the 1.0 V threshold level even after the Fault Latch has been set. In some applications this characteristic could be problematic but it can be easily remedied by AC coupling Drive Output B. |
Nº de peça semelhante - MC33067_15 |
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Descrição semelhante - MC33067_15 |
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