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R1221N33AA-TR Datasheet(PDF) 7 Page - RICOH electronics devices division |
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R1221N33AA-TR Datasheet(HTML) 7 Page - RICOH electronics devices division |
7 / 21 page 12345 Rev. 1.11 - 7 - n n n n TYPICAL APPLICATIONS AND APPLICATION HINTS Vcc Reset/ CPU EXT VIN VOUT GND VDOUT CE SD1 L COUT CIN PMOS R1 CE CONTROL PMOS: HAT1020R (Hitachi), Si3443DV (Siliconix) L : CD105(Sumida, 27 mH) SD1 : RB491D (Rohm) COUT : 47 mF(Tantalum Type) CIN :10 mF(Tantalum Type) R1 : 100k W When you use these ICs, consider the following issues; l As shown in the block diagram, a parasitic diode is formed in each terminal, each of these diodes is not formed for load current, therefore do not use it in such a way. When you control the CE pin by another power supply, do not make its "H" level more than the voltage level of VIN pin. l Detector threshold hysteresis is set at 3 percent of detector threshold voltage. (Min. 1 percent, Max. 5 percent) l Setting Detector threshold voltage range depends on Output voltage of DC/DC converter. Release Voltage from Reset condition must not be more than Output voltage of DC/DC converter. (Detector Threshold Voltage ´1.07 < Output Voltage of DC/DC converter´0.98 l When the R1221NXXXX is on stand-by mode, the output voltage of VDOUT is GND level, therefore if the pull-up resistor for VDOUT pin is pulled up another power supply, a certain amount of current is loading through the resistor. l The operation of Latch-type protection circuit is as follows; When the maximum duty cycle continues longer than the delay time for protection circuit, (Refer to the Electrical Characteristics) the protection circuit works to shut-down the external Power MOS with its latching operation. Therefore when an input/output voltage difference is small, the protection circuit may work even at small load current. To release the protection state, after disable this IC with a chip enable circuit, enable it again, or restart this IC with power-on. However, in the case of restarting this IC with power-on, after the power supply is turned off, if a certain amount of charge remains in CIN, or some voltage is forced to VIN from CIN, this IC might not be restarted even after power-on. If rising transition speed of supply voltage is too slow, or the time which is required for VIN voltage to reach Output Voltage of DC/DC converter is longer than soft-starting time plus delay time for protection circuit, protection circuit works before VIN voltage reaches Output Voltage of DC/DC converter. To avoid this condition, make this IC disable(CE=”L”) first, then force VIN voltage, and after VIN voltage becomes equal or more than VOUT, make this IC enable(CE=“H”). l Set external components as close as possible to the IC and minimize the connection between the components and the IC. In particular, a capacitor should be connected to VOUT pin with the minimum connection. And make sufficient grounding and reinforce supplying. A large switching current flows through the connection of power supply, an inductor and the connection of VOUT. If the impedance of power supply line is high, the voltage level of power supply of the IC fluctuates with the switching current. This may cause unstable operation of the IC. |
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