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参数资料
| 型号： | R1250V471A-E2 |
| 厂商： | RICOH COMPANY LTD |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, PDSO8 |
| 封装： | 0.65 MM PITCH, TSSOP-8 |
| 文件页数： | 4/13页 |
| 文件大小： | 127K |
| 代理商： | R1250V471A-E2 |
12345
Rev. 1.10
- 12 -
n
n OPERATION
1) Basic Operation
The R1250Vxx1A 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:
R1250V301
VIN
CP
CIN
up to 5k
W
ROUT
COUT
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 5k
W to GND. Time constant “t” of transient response (turn-off speed) of
VOUT can be calculated as follows:
t @ (5[kW] 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]
4) Power Consumption
Power Consumption at large load current of this IC can be calculated as follows:
Wchip[mW]
@ (VIN[V]-| Set Output Voltage |) (IOUT[mA])
n
n TECHNICAL NOTES
To use this IC, the following things should be considered.
1) Short Protection function for each pin is not included in this IC.
2) Use capacitors with low equivalent series resistor (ESR) for CIN, CP, COUT pins. Capacitors with large ESR make
this IC’s performance worse.
3) Make wiring of GND, VIN, CP+, CP- secure enough and decrease impedance. High impedance could be a cause of
unstable operation of this IC.
4) When this IC is used with large load current, consider its radiation of heat.
5) Basically, VREF pin can be used for soldering to the mount pad of PCB. Do not make it wiring.
6) Load type is electronic or setting between VIN and VOUT, in cases of OFF-state of this IC and start-up state of this
IC, make sure not to raise VOUT level on positive voltage side. If the voltage level is beyond +0.3V, which is
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