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参数资料
| 型号： | R5220D321B-TR |
| 厂商： | RICOH COMPANY LTD |
| 元件分类： | 稳压器 |
| 英文描述： | 0.8 A SWITCHING REGULATOR, 1440 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | 0.85 MM HEIGHT, TSON-6 |
| 文件页数： | 22/22页 |
| 文件大小： | 627K |
| 代理商： | R5220D321B-TR |
R5220D
9
TIMING CHART
1) IC start-up
The timing chart as shown in the next describes the operation starting the IC is enabled with CE. When the CE
pin voltage becomes higher than the threshold voltage, the IC’s operations starts. At first, only the voltage
regulator (VR) starts. The threshold level of the CE pin is between CE “H” input voltage and CE “L” input voltage.
After starting the operation, the output capacitor (COUT) is charged with the output current of the VR, and the
output level becomes the set VR output voltage. At this moment, the output of Lx is “off”, (“Hi-Z”), the pin voltage,
VLX
=VOUT through the external inductor L.
Secondly, the Mode pin voltage is higher than the threshold voltage, internal operation of DC/DC starts. The
threshold level is between Mode “H” input voltage and Mode “L” input voltage. The soft-start circuit inside the
DC/DC converter’s operation is as follows:
(Case 1) DC/DC output voltage < VR output voltage
After the soft-start time, while the output voltage level is down from the VR output voltage to DC/DC output
voltage, the circuit is waiting for the start of DC/DC operation. When the output voltage reaches so set DC/DC
output voltage level, the actual DC/DC operation starts.
(Case 2) DC/DC output voltage> VR output voltage
The soft-start circuit of DC/DC converter makes the voltage reference unit of the IC rise gradually and be
constant. After the voltage reference unit reaches the constant level which the output voltage of DC/DC
converter can balance becomes the output voltage of VR, the set output voltage of DC/DC converter may be
realized.
Therefore, the soft-start time means the time range of starting to the time when the voltage reference unit
reaches the constant level, and the soft-start time is different from turning on speed in some cases. The
operation starting time depends on the ability of the power supply, the load current, the inductance value, the
capacitance value, and the voltage difference between the set VR output and the set DC/DC output.
If CE and Mode are on at once, the same operation as above is happened except the VR start-up and
Soft-start operation start at the same time.
If Mode signal is forced earlier than CE signal, this IC is stand-by until CE signal comes. Therefore when the
CE signal is set, the IC operation starts as above.
VOUT voltage rising speed at start-up with power supply is affected by the next conditions:
1.The turning on speed of VIN voltage limited by the power supply to the IC and the input capacitor CIN.
The output capacitor, COUT value and load current.
DC/DC operation starting time
If the VR output >
= DC/DC output, the operation starting time of the DC/DC converter is approximately equal to
the next formula.
TDCDC_ACT
=TSS+ (VOUT_VRVOUT_DC/DC+15mV) ×COUT / (load current at mode change + 1A)
TSS: Soft-start time
VOUT_VR: VR output voltage
VOUT_DC/DC: DC/DC Output Voltage
*1
A is the supply current of the IC itself for the output.
If the VR output < DC/DC output, the operation starting time is the soft-start time
+ starting operation time
which depends on the power supply, the load current, and the external components.
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