Texas Instruments TPS3801, Application Report

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Circuit Description
3 TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
Table 1. The Nominal Supply Voltages and Their Threshold Voltages
DEVICES
NOMINAL SUPPLY
VOLTAGE
THRESHOLD
VOLTAGE
TPS3801J25, TPS3809J25 2.5 V 2.25 V
TPS3801L30, TPS3809L30 3.0 V 2.64 V
TPS3801K33, TPS3809K33 3.3 V 2.93 V
TPS3801I50, TPS3809I50 5.0 V 4.55 V
2.3 Terminals
The TPS3801 is available in a 5-pin SOT323 package, the TPS3809 in a 3-pin SOT23
package. More information about the package dimensions are in Chapter 6.
3
2
4
5
TPS3801
1
GND
GND
RESET
MR
VDD 2
3
TPS3809
1
GND
RESET
VDD
Figure 3. Terminal Assignment
2.4 Terminal Functions
Terminal functions lists and describes the functions of the TPS3801 and
TPS3809 terminals.
Table 2. Terminal Functions
TERMINAL
NAME
NO. I/O Description
NAME
TPS3801 TPS3809
GND 1, 2 1 Negative power supply
Ground. Connects the circuit with ground and zero-volt reference for manual
reset input MR.
MR 5 – Digital input, low-active
Manual reset. Input to trigger a Reset pulse by an external component or an
external signal source.
RESET 3 2 Digital output, low-active
Output for triggering a reset at the connected controller or DSP, shows the
state of the internal reset logic.
VDD 4 3 Positive power supply Supplies the circuit with voltage and input for the voltage supervision.
2.5 Block Diagram
Figure 4 shows a block diagram of the TPS3801 and TPS3809. One important
block is the stable voltage reference which has a voltage of 1.137 V. The supply
voltage is divided by two internal resistors and compared with the reference
voltage by a comparator. If the divided voltage is below the threshold voltage, the
reset logic lets the reset output become active. Otherwise the reset output is
inactive.
The values of the two internal resistors depend on the nominal supply voltage.
In sum the resistors have a typical value of 660 k
Ω
. The ratio of the resistors is
fixed, but the absolute values of the resistors vary up to 20% because of process
variations. The typical resistor values are shown in Table 3.