Fujitsu MB3887 manual Setting the Charging Voltage, Method of Setting the Charging Current

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MB3887

3. Soft-Start Function

Soft-start block (SOFT)

Connecting a capacitor to the CS terminal (pin 22) prevents rush currents when the IC is turned on. Using an error amplifier for soft-start detection makes the soft-start time constant, being independent of the output load of the DC/DC converter.

■SETTING THE CHARGING VOLTAGE

The charging voltage (DC/DC output voltage) can be set by connecting external voltage setting resistors (R3, R4) to the −INE3 terminal (pin 16) . Be sure to select a resistor value that allows you to ignore the on-resistor (35 Ω, 1mA) of the internal FET connected to the OUTD terminal (pin 11) . In standby mode, the charging voltage is applied to OUTD termial. Therefore, output voltage must be adjusted so that voltage applied to OUTD terminal is 17 V or less.

Battery charging voltage : VO

VO (V) =

(R3 + R4) / R4 ⋅ 4.2 (V)

 

 

B

VO

 

 

R3

 

<Error Amp3>

 

 

−INE3

−

 

 

16

 

 

 

+

 

R4

 

+

 

 

 

 

 

11

4.2 V

 

 

OUTD

 

 

 

 

 

22

 

 

 

CS

 

■METHOD OF SETTING THE CHARGING CURRENT

The charge current (output limit current) value can be set with the voltage at the +INE1 terminal (pin 9) .

If a current exceeding the set value attempts to flow, the charge voltage drops according to the set current value.

Battery charge current setting voltage : +INE1 +INE1 (V) = 20 ⋅ I1 (A) ⋅ RS (Ω)

■METHOD OF SETTING THE TRIANGULAR WAVE OSCILLATION FREQUENCY

The triangular wave oscillation frequency can be set by the timing resistor (RT) connected the RT terminal (pin 17) .

Triangular wave oscillation frequency : fOSC fOSC (kHz) =: 13630 / RT (kΩ)

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Contents Features DescriptionPackage MB3887 PIN Assignment TOP ViewPin No Symbol Descriptions PIN DescriptionBlock Diagram Parameter Symbol Conditions Rating Unit Min Max Absolute Maximum RatingsParameter Symbol Conditions Value Unit Min Typ Recommended Operating ConditionsElectrical Characteristics Parameter Sym Pin ConditionsBol Min Typ Parameter Sym Pin Conditions Value Unit Bol Min Typ Max Parameter Sym Pin Conditions Value Unit Bol Min Typ OUT = −45 mA Output block Resistor Typical Characteristics Triangular wave oscillation frequency fOSC kHz Error amplifier gain and phase vs. Frequency Gain a Power dissipation vs. Ambient temperature Functional Description Output block OUT PowerPWM comparator block PWM Comp Control block CTLMethod of Setting the Triangular Wave Oscillation Frequency Setting the Charging VoltageMethod of Setting the Charging Current Soft-start block SoftMethod of Setting the SOFT-START Time Operation Timing Diagram AC Adaptor Voltage DetectionProcessing Without Using the Current AMP Connection when Current Amp is not usedProcessing Without Using of the Error AMP Connection when Error Amp is not usedProcessing Without Using of the CS Terminal Connection when soft-start time is not specifiedApplication Example At 4 cellParts List Parts NoReference Data Batt Vbatt mV Ta = +25 C, VIN = 19 Batt = 12 Ω Usage Precautions Ordering InformationPart number Package Remarks Package Dimension IndexFujitsu Limited
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