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CS8120YTHA5 データシート(PDF) 7 Page - ON Semiconductor |
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CS8120YTHA5 データシート(HTML) 7 Page - ON Semiconductor |
7 / 14 page CS8120 http://onsemi.com 7 functionally independent of the rest of the IC, thereby guaranteeing that the RESET signal is valid for VOUT as low as 1.0 V. Figure 12. RC Network for RESET Delay Circuitry VOUT CS8120 5.0 V to mP and System Power RESET RRST to mP RESET Port CRST C2 22 mF An external RC network on the RESET lead (Figure 12) provides a sufficiently long delay for most microprocessor based applications. RC values can be chosen using the following formula: RTOT CRST + −tDelay ln VT*VOUT VRST*VOUT where: RTOT = RRST in parallel with RIN, RIN = mP port impedance, CRST = RESET delay capacitor, tDelay = desired delay time, VRST = VSAT of RESET lead (0.7 V @ turn − ON), and VT = mP logic threshold voltage. APPLICATION NOTES The circuit depicted in Figure 13 lets the microprocessor control its power source, the CS8120 regulator. An I/O port on the mP and the SWITCH port are used to drive the base of Q1. When Q1 is driven into saturation, the voltage on the ENABLE lead falls below its lower threshold. The regulator’s output is switched out. When the drive current is removed, the voltage on the ENABLE lead rises, the output is switched off and the IC moves into Sleep mode where it draws 250 mA. By coupling these two controls with the ENABLE, the system has added flexibility. Once the system is running, the state of the SWITCH is irrelevant as long as the I/O port continues to drive Q1. The microprocessor can turn off its own power by withdrawing drive current, once the SWITCH is open. This software control at the I/O port allows the microprocessor to finish key housekeeping functions before power is removed. The logic options are summarized in Table 1. Table 1. Logic Control of CS8120 Output Microprocessor I/O Drive SWITCH ENABLE Output ON Closed LOW ON Open LOW ON OFF Closed LOW ON Open HIGH OFF The I/O port of the microprocessor typically provides 50 mA to Q1. In automotive applications the SWITCH is connected to the ignition switch. VBAT SWITCH Q1 500 k W 0.1 mF 500 k W 100 k W 100 k W CRST 22 mF RRST VCC RESET I/O Port mP VOUT RESET ENABLE VIN Figure 13. Microprocessor Control of CS8120 Using External Switching Transistor Q1 CS8120 GND C1 C2 |
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