Fujitsu MB39A105 Functions, Triangular-wave oscillator block OSC, PWM comparator block PWM Comp

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MB39A105

■FUNCTIONS

1.DC/DC Converter Functions

(1)Triangular-wave oscillator block (OSC)

The triangular wave oscillator incorporates a timing resistor connected to RT terminal (pin 7) to generate triangular oscillation waveform amplitude of 0.3 V to 0.7 V.

The triangular waveforms are input to the PWM comparator in the IC.

(2) Error amplifier block (Error Amp1, Error Amp2)

The error amplifier detects the DC/DC converter output voltage and outputs PWM control signals. In addition, an arbitrary loop gain can be set by connecting a feedback resistor and capacitor from the output terminal to inverted input terminal of the error amplifier, enabling stable phase compensation to the system.

Also, it is possible to prevent rush current at power supply start-up by connecting a soft-start capacitor with the CSCP terminal (pin 2) which is the non-inverted input terminal for Error Amp. The use of Error Amp for soft-start detection makes it possible for a system to operate on a fixed soft-start time that is independent of the output load on the DC/DC converter.

(3) PWM comparator block (PWM Comp.)

The PWM comparator is a voltage-to-pulse width modulator that controls the output duty depending on the input/ output voltage.

The comparator keeps output transistor on while the error amplifier output voltage and the DTC voltage remain higher than the triangular wave voltage.

(4) Output block (Drive)

The output block is in the totem pole configuration, capable of driving an external N-channel MOS FET.

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Contents Description FeaturesPackage PIN Assignment Pin No Symbol Descriptions PIN DescriptionBlock Diagram Absolute Maximum Ratings Parameter Symbol Condition Rating Unit Min MaxParameter Symbol Condition Value Unit Min Typ Recommended Operating ConditionsParameter Electrical CharacteristicsPin Conditions Value Unit Min Typ Max Typical Characteristics ErrorTriangularwave oscillation Power Dissipation vs. Ambient Temperature Triangular-wave oscillator block OSC Error amplifier block Error Amp1, Error Amp2Functions PWM comparator block PWM CompUnder voltage lockout protection circuit Uvlo PowerTimer-latch short-circuit protection circuit SCP Short-circuit protection detection output functionSetting the Output Voltage Setting the Triangular Oscillation FrequencySetting the SOFT-START Times Timer-latch short-circuit protection circuit MB39A105 Equivalent Circuit Application Parts List Parts NoSelection of Components 2I OV O 2LV O Peak-to-peak value ESR Reference Data Do not apply negative voltages Usage PrecautionOrdering Information Part number Package RemarksPackage Dimension IndexFujitsu Limited
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