BD48xx/BD49xx series: 10k-1MΩ (VDET=2.3-6.0V) BU48xx/BU49xx series: 10k-1MΩ (VDET=1.5-4.8V) BU48xx/BU49xx series: 100k-1MΩ (VDET=0.9-1.4V) However, this value may vary depending on board layout. Therefore, please verify under actual operating conditions.
In applications where voltage is input to the VDD terminal via a voltage divider (resistance), a pass-through current will momentarily flow during output logic switching. This current may cause malfunctions. (Pass-through current: Instantaneous current that flows from VDD to ground during output H←→L switching.) Configuring a capacitor at the VDD terminal will reduce voltage drop, while connecting one to the output terminal will prevent output reset chatter, suppressing output vibration. However, the capacitance value will affect the reaction time, making it imperative to consider the set conditions when selecting a capacitor. The BD48xx series is recommended when introducing a resistor (including resistance divider circuits).
Regarding reset output during power supply startup, the power supply rise time will vary depending on the external load. Because of this the minimum rated value cannot be specified. Please ensure that sufficient margin is included for transient response based on external circuitry or conditions.
Reference data regarding the specifications for reset recovery time is contained in the technical notes. With the BU4845, the rise time (tPLH) is 23.3µs and the fall time (tpHL) is 275.9µs, while for the BU4945 the rise and fall times are 3.5µs and 354.3µs, respectively. (VDD=4.3V←→5.1V) For cases where the power supply fluctuation is faster than this time the output will become delayed. If within this reaction time the power supply recovers no reaction from the output will occur. The output behavior may differ depending on power supply voltage fluctuations or changing conditions. Therefore, ROHM recommends that the customer ensures sufficient margins in their designs.
For the BU49xx series with CMOS output, the output will be based on the surge voltage, while in the BU48xx series with open drain output the pull-up voltage will be output continously. Regarding the reaction time in response to surges, please refer to the reference data for tPHL and tPLH on page 5 of the technical notes.
No. The output switching time can be calculated using the discharge of the input capacitor through the IC current consumption. Please estimate using the circuit current given in the electrical characteristics in the technical notes (Pg. 4, Figs. 3, 9, and 10). However, please note that if the power supply is connected to devices other than the reset IC, the total sum of all components must be taken into account when considering the discharge current.