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BD87A34FVM-TR Datasheet(PDF) 8 Page - Rohm

Part # BD87A34FVM-TR
Description  Voltage Detector ICs with Watchdog Timer
Download  19 Pages
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Manufacturer  ROHM [Rohm]
Direct Link  http://www.rohm.com
Logo ROHM - Rohm

BD87A34FVM-TR Datasheet(HTML) 8 Page - Rohm

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BD37Axx Series
BD87Axx Series
BD99A41F
Datasheet
Timing Chart
Figure 15. Timing Chart
Explanation
The RESET pin voltage (RESET) switches to low when the power supply voltage (VDD) falls to 0.8 V.
The external capacitor connected to the CT pin begins to charge when VDD rises above the reset detection voltage
(VDETH). The RESET signal stays low until VDD reaches the VDETH voltage and switches to high when VDD reaches or
exceeds the VDETH voltage. The RESET transmission delay time tPLH allowed to elapse before RESET switches from
low to high is given by the following equation:
tPLH (s)
≈ 0.69 × Rrst × CCT (µF)   [1]
Rrst denotes the IC's built-
in resistance and is designed to be 10 MΩ (Typ). CCT denotes the external capacitor
connected to the CT pin.
The external capacitor connected to the CTW pin begins to charge when RESET rises, triggering the watchdog timer.
The CTW pin state switches from charge to discharge when the CTW pin voltage (VCTW) reaches VthH, and RESET
switches from high to low. The watchdog timer monitor time tWH is given by the following equation:
tWH (s)
≈ (0.5 × CCTW (µF))/(ICTWC)   [2]
ICTWC denotes the CTW charge current and is designed to be 0.50 µA (Typ). CCTW denotes the external capacitor
connected to the CTW pin.
The CTW pin state switches from charge to discharge when VCTW reaches VthL, and RESET switches from low to
high. The watchdog timer reset time tWL is given by the following equation:
tWL (s)
≈ (0.5 × CCTW (µF))/(ICTWO)   [3]
ICTWO denotes the CTW discharge current and is designed to be 1.50 µA (Typ).
The CTW pin state may not switch from charge to discharge when the CLK input pulse width tWCLK is short. Use a
tWCLK input pulse width of at least 500 ns.
tWCLK
≥ 500 ns (Min)
When a pulse (positive edge trigger) of at least 500 ns is input to the CLK pin while the CTW pin is charging, the CTW
state switches from charge to discharge. Once it discharges to VthL, it will charge again.
Watchdog timer operation is forced off when the INH pin switches to low (L: BD37Axx Series. BD99A41F, H:
BD87AxxSeries). At that time, only the watchdog timer is turned off. Reset detection is performed normally.
The watchdog timer function turns on when the INH pin switches to high(H: BD37Axx Series. BD99A41F, L:
BD87AxxSeries). The external capacitor connected to the CTW pin begins to charge at that time.
RESET switches from high to low when VDD falls to the RESET detection voltage (VDET) or lower.
When VDD falls to 0 V, the RESET signal stays low until VDD reaches 0.8 V.
*2
(BD37AxxFVM/BD99A41F)
④ ⑤⑧
⑤ ⑩ ②
④ ⑤
INH
VCTW
CLK
RESET
①② ③
0
0
0
0
0
WDT circuit turns off when INH is high
tWCLK
*4 tWCLK
VthH
VthL
*1
TPLH
*3
TWL
TWH
VCT
VCTH
INH
VDD
VDETH
VDET
WDT circuit turns off when INH is low
0
0
VDETH=VDET+Vrhys
(BD87AxxFVM)
8/15
TSZ02201-0G1G0AN00130-1-2
© 2013 ROHM Co., Ltd. All rights reserved.
05.Sep.2014 Rev.003
www.rohm.com
TSZ22111・15・001


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