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TPS3850_16 Datasheet, PDF (26/44 Pages) Texas Instruments – Precision Voltage Supervisor with Programmable Window Watchdog Timer
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TPS3850
SBVS301A – OCTOBER 2016 – REVISED NOVEMBER 2016
www.ti.com
8.2 Typical Applications
8.2.1 Design 1: Monitoring a 1.2-V Rail with Factory-Programmable Watchdog Timing
A typical application for the TPS3850 is shown in Figure 32. The TPS3850G12 is used to monitor the 1.2-V,
VCORE rail powering the microcontroller.
1.8V
1.2V
TPS3850
SENSE
VDD
SET1
RESET
SET0
WDO
VCORE
VI/O
Microcontroller
RESET
NMI
CRST
WDI
0.1 µF
CWD
GND
GPIO
GND
Figure 32. Monitoring Supply Voltage and Watchdog Supervision of a Microcontroller
8.2.1.1 Design Requirements
PARAMETER
Reset delay
DESIGN REQUIREMENT
Minimum reset delay of 250 ms
Watchdog window
Output logic voltage
Monitored rail
Maximum device current
consumption
Functions with a 200-Hz pulse-width modulation
(PWM) signal with a 50% duty cycle
1.8-V CMOS
1.2 V within ±5%
200 µA
DESIGN RESULT
Minimum reset delay of 260 ms, reset delay of 322
ms (typical)
Leaving the CWD pin unconnected with SET0 = 0
and SET1 = 1 produces a window with a tWDL(max)
of 2.2 ms and a tWDU(min) of 22 ms
1.8-V CMOS
Worst-case VIT+(OV) 1.257 V (4.8%)
Worst-case VIT-(UV) 1.142 V (4.7%)
10 µA of current consumption, typical worst-case of
199 µA when WDO or RESET is asserted
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Monitoring the 1.2-V Rail
The window comparator allows for precise voltage supervision of common rails between 0.9 V and 5.0 V. This
application calls for very tight monitoring of the rail with only ±5% of variation allowed on the rail. To ensure this
requirement is met, the TPS3850G12 was chosen for its ±4% thresholds. To calculate the worst-case for VIT+(OV)
and VIT-(UV), the accuracy must also be taken into account. The worst-case for VIT+(OV) can be calculated by
Equation 9:
VIT+(OV)(Worst-Case) = VIT+(OV)typ × 1.048 = 1.2 × 1.048 = 1.257 V
(9)
The worst case for VIT-(UV) can be calculated using Equation 10:
VIT–(UV)(Worst-Case) = VIT–(UV)typ × 0.952 = 1.2 × 0.952 = 1.142 V
(10)
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