Fujitsu MB39A104 manual Functions

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MB39A104

■FUNCTIONS

1.DC/DC Converter Functions

(1)Reference voltage block (REF)

The reference voltage circuit generates a temperature-compensated reference voltage (5.0 V Typ) from the voltage supplied from the power supply terminal (pin 7). The voltage is used as the reference voltage for the IC’s internal circuitry.

The reference voltage can supply a load current of up to 1 mA to an external device through the VREF terminal (pin 17).

(2) Triangular-wave oscillator block (OSC)

The triangular wave oscillator incorporates a timing capacitor and a timing resistor connected respectively to the CT terminal (pin 13) and RT terminal (pin 12) to generate triangular oscillation waveform amplitude of 1.5 V to 2.5 V.

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

(3) 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 CS1 terminal (pin 11) and CS2 terminal (pin 14) which are 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.

(4) 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 remain higher than the triangular wave voltage.

(5) Output block

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

(6) Bias voltage block (VH)

This bias voltage circuit outputs VCC − 5 V(Typ) as minimum potential of the output circuit. In standby mode, this circuit outputs the potential equal to VCC.

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Contents Package FeaturesDescription PIN Assignments MB39A104PIN Description Pin No Symbol DescriptionsBlock Diagram Recommended Operating Conditions Parameter Symbol Condition Rating Unit Min MaxParameter Symbol Condition Value Unit Min Typ Absolute Maximum RatingsMin Typ Max Electrical CharacteristicsParameter Pin No ConditionsPin No Conditions Value Unit Min Parameter SymbolReference Voltage vs. Ambient Temperature Typical CharacteristicsTriangular Wave Oscillation Frequency Power Dissipation vs. Ambient Temperature Functions Operating circuit Timer-latch overcurrent protection circuit block OCPUnder voltage lockout protection circuit Uvlo Protection circuit operating function tableSetting the Triangular Oscillation Frequency Setting the Output VoltageSetting the SOFT-START and Discharge Times MB39A104 Without Setting Soft-Start Time Treatment Without Using CS TerminalOvercurrent detection circuit About TIMER-LATCH Protection CircuitMethod to detect by mean current Overcurrent Protection Circuit Range of OperationTimer-latch short-circuit protection circuit Resetting the Latch of Each Protection Circuit Treatment Without Using Cscp TerminalEquivalent Circuit On Power on OFF Standby mode Component Specification Vendor Parts ListCH1 Selection of ComponentsCH2 = 3 2 ⋅ 0.05 ⋅ 0.174 = 0.078 W Example Peak-to-peak value ΔIL Di ≥ I O ⋅ 1 − ESR ≤ ΠfC L 050 491 ESR ≤ ΠfC L 033 364 Total Efficiency vs. Input Voltage Reference DataSwitching Wave Form CH1 Part number Package Remarks Usage PrecautionOrdering Information Do not apply negative voltagesIndex Package DimensionsFujitsu Limited
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