BU48XXG_11 Datasheet, PDF (5/9 Pages) Rohm – Low Voltage Standard CMOS Voltage Detector ICs

BU48□□G Series, BU48□□F Series, BU48□□FVE Series,
BU49□□G Series, BU49□□F Series, BU49□□FVE Series
Technical Note
●Reference Data
Examples of Output rising value(TPLH)and Output falling value(TPHL)
Part Number
TPLH[µs]
TPHL[µs]
BU4845G/F/FVE
23.3
275.9
BU4945G/F/FVE
3.5
354.3
VDD=4.3V5.1V
VDD=5.1V4.3V
* This data is for reference only.
This figure will vary with the application, so please confirm actual operation conditions before use.
●Explanation of Operation
For both the open drain type(Fig.12)and the CMOS output type(Fig.13), the detection and release voltages are used as
threshold voltages. When the voltage applied to the VDD pins reaches the applicable threshold voltage, the Vout terminal
voltage switches from either “High” to “Low” or from “Low” to “High”. Because the BU48□□G/F/FVE series uses an open
drain output type, it is possible to connect a pull-up resistor to VDD or another power supply [The output “High” voltage
(VOUT) in this case becomes VDD or the voltage of the other power supply].
VDD
VDD
VDD
R1
Vref
R2
R3
GND
VOUT
Q1
RL
RESET
R1
Vref
R2
R3
GND
Q2
VOUT RESET
Q1
Fig.12 (BU48□□ type internal block diagram)
Fig.13 (BU49□□ type internal block diagram)
●Timing Waveforms
Example:The following shows the relationship between the input voltage VDD, the CT Terminal Voltage VCT and the output
voltage VOUT when the input power supply voltage VDD is made to sweep up and sweep down (The circuits are those in
Fig.12 and 13).
①When the power supply is turned on, the output is unsettled
from after over the operating limit voltage (VOPL) until TPHL.
VDD
Therefore it is possible that the reset signal is not outputted
VDET+ΔVDET
VDET
when the rise time of VDD is faster than TPHL.
⑤
②When VDD is greater than VOPL but less than the reset release
voltage (VDET + VDET), output (VOUT) voltages will switch to L.
VOPL
0V
③If VDD exceeds the reset release voltage (VDET + VDET), then
VOUT switches from L to H (with a delay of TPLH).
VOUT
④If VDD drops below the detection voltage (VDET) when the
VOH
power supply is powered down or when there is a power
TPHL
TPLH
TPLH
supply fluctuation, VOUT switches to L (with a delay of TPHL).
⑤The potential deference between the detection voltage and the
VOL
TPHL
release voltage is known as the hysteresis width (VDET). The
system is designed such that the output does not flip-flop with
①②③ ④
power supply fluctuations within this hysteresis width,
preventing malfunctions due to noise.
Fig.14
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2011.03 - Rev.D