R1250V301A Datasheet, PDF (13/14 Pages) RICOH electronics devices division – Negative Output Charge Pump Regulator(100mA)

R1250V××1A
OPERATION
1) Basic Operation
The R1250V××1A Series make SW1 through SW4 ON and OFF by the clock generated by internal oscillator (OSC)
with fixed frequency, and operate as a inverting charge pump with the capacitor CP and the capacitor COUT.
The Output Voltage is feedback and the voltage between the Output Voltage and Reference Voltage (Vref =VOUT
V) is divided half, and it is compared with the GND (=0V) level by an internal operational amplifier.
By this action, the impedance of SW3 is controlled to correspond with its load current and Output Voltage keeps
“Set VOUT” level.
2) Status of Internal Circuits at Standby mode and Standby Current
At Standby mode, R1250V Series keep the voltage of CP as shown below:
VIN
CIN
CP
RO
up to 5kΩ
ROUT
COUT
R1250V××1A
VOUT
When you design a system with using this IC, consider the following subjects;
2-(1) If very small leakage current would be a critical, the leakage current of both CIN and CP should be considered.
2-(2) Because the voltage level of CP keeps as much as VDD level, the speed for start-up from stand-by mode is faster
than the start-up by power-on.
2-(3) VOUT is internally pulled down through 5kΩ to GND. Time constant “τ” of transient response (turn-off speed) of
VOUT can be calculated as follows:
τ ≅ (5[kΩ]  ROUT) × COUT (ROUT: Output load resistance)
2-(4) Load current should be OFF synchronously with this IC if the load is electronic or connected between VIN and
VOUT. If some charge is continuously flown to the Output VOUT at the “OFF” state, the voltage level of VOUT will
rise and could be beyond 0V. And if the voltage will be +0.3V (that is designated as absolute maximum rating.),
this IC might be break down.
3) Ripple Voltage
Ripple voltage of Output waveform can be roughly calculated as follows:
Vripple [mVp-p] ≅ 0.5× (IOUT [mA] + Supply Current at no load [mA]) / (Oscillator Frequency: 280000 [Hz])
/ COUT [F]
Supply Current at no load [mA] ≅ Supply Current 1 [mA]
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