Texas Instruments TPS3801 User manual

TPS3801/09 - Smallest SVS
for Monitoring DSPs and
Processors
September 1999 Mixed Signal Products
Application
Report
SLVA075

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iii
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
Contents
1 Introduction 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Circuit Description 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1 Overview of Features 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2 Supervised Supply Voltages 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3 Terminals 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.4 Terminal Functions 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.5 Block Diagram 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.6 Basic Timings 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Voltage Supervision at the VDD Terminal 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Functional Description 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 Measurement of a Voltage Drop on the Supply Line 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3 Threshold Overdrive Versus Pulsewidth 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4 Making the Supervisor Circuit Less Sensitive 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Manual Reset 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1 Functional Description 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2 A Measurement of Low Pulse at the Manual Reset Input 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3 Minimum Conditions for Triggering a Manual Reset 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4 Saving Current While Using the Manual Reset Function 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.1 Current Flow Off the Manual Reset Input 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.2 Lateral Current From VDD to GND 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 Applications 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.1 A TPS3801 Supervises a DSP 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.2 Switching the Power Supply With a TPS3801 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.3 Keeping a Low Signal at Reset Output for Voltages Below 1.1 V 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4 Supervising a Customer Defined Threshold Voltage 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.1 Threshold Voltage Change Application 1 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.2 Worst Case Considerations for Application 1 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.3 Threshold Voltage Change Application 2 19. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5.4.4 Worst Case Considerations for Application 2 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Mechanical Data and Layout Considerations 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1 Mechanical Data 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2 Layout Considerations 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Summary 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8 References 23. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Figures
iv
SLVA075
List of Figures
1 A Simple Reset Solution 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Features Overview 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Terminal Assignment 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 Block Diagram of TPS3801 and TPS3809 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5 Timing Diagram of TPS3801 5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6 Relations Between VIT+, VIT–, and Vhys 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7 Measurement Circuit for Measuring the Reaction of a Voltage Drop 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8 Measurement of the Voltage Drop at VDD 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9 Breakdown Voltage versus Pulsewidth at a TPS380xI50 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10 Breakdown Voltage versus Pulsewidth at a TPS380xJ25 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
11 TPS3801 With a Low Pass Filter at VDD Terminal 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
12 Breakdown Voltage versus Pulsewidth With a Low Pass Filter 10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
13 Reset Pulse, Triggered by Manual Reset 11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
14 Minimum Conditions for Triggering a Reset at Manual Reset Input 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
15 Internal Realization of the Manual Reset Circuit 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
16 Lateral Current in Dependence of the Voltage at a CMOS Input Stage 13. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17 TPS3801 Supervises the TMS320LC542-DSP 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18 System Power Control With the TPS3801 15. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19 Measurements of Switching Power With A TPS2051 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20 An Additional Resistor Ensures a Valid Reset Down to 0 V 16. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21 Higher Accuracy Supervision of 3.6 V 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
22 Measurement Plot of the 3.6 V Voltage Supervision 18. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
23 Supervision of 3.6 V With Less Current Consumption 20. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
24 Linear Dimensions of SOT323 Package 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
25 Linear Dimensions of SOT23-3 Package 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
26 Layout Suggestion Using a TPS3801 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
27 Layout Suggestion Using a TPS3809 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
List of Tables
1 The Nominal Supply Voltages and Their Threshold Voltages 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 Terminal Functions 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 Typical Values of Internal Voltage Divider 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 The Specified Values of VIT– and the Hysteresis, Vhys 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
Bernd Kornmeier
ABSTRACT
This application report describes the TPS3801 and TPS3809 supply voltage supervisor
(SVS) families of devices. The report gives a general introduction to reset generators
followed by an overview of the technical parameters and the special features of the
TPS380x. Each feature is discussed separately. Measurements make it easy to
understand SVS principles of operation. Typical applications that increase system
reliability are included. Layout considerations and design issues help in the system
integration of the TPS3801 and TPS3809.
1 Introduction
After power-on, a digital system must be forced into a definite initial state. Digital
signal processors (DSPs), microcontrollers, and microprocessors have a reset
inputforthispurpose.InthesimpleapplicationshowninFigure1,anRCnetwork
is connected to the RESET input to deliver the necessary reset pulse. After
switchingonthepowersupply,thiscircuitkeepsthelogiclevelattheRESETinput
low for a time determined by the capacitor and resistor values. This delay time,
required by the system to complete the initialization, allows the power supply to
become stable.
However, this circuit has some disadvantages. In cases of brief reductions of the
supply voltage, it does not work correctly. It does not recognize spikes, because
the voltage at the RESET input does not decrease as fast as the supply voltage
duetothecapacitor.Malfunctionisthuspossible.OnlyifVDD decreasesbymore
than 0.7 V, the capacitor can be discharged quickly through the diode. Because
of tolerances of discrete components (especially capacitors), the delay time can
not be calculated very precisely.
The problem is that this solution does not deliver a proper low to high transition
at reset input. It is a charge curve of a capacitor, which is for a certain period of
time undefined between low and high.
VCC
RESET
GND
VDD
VRES
Figure 1. A Simple Reset Solution

Circuit Description
2 SLVA075
Thereliabilityofacomputersystemisveryimportant,severalfeaturesareoffered
to prevent errors: power-fail interrupts can signal dangerous conditions in time,
a battery back-up can protect the content of the memory, and so on. In smaller
systems this may be too expensive, and, in most applications, it is not required.
It is usually sufficient to force the microcomputer into a defined state after a
serious voltage drop.
To implement these functions while preventing problems, the following circuit
features are required:
•Accurate detection of a voltage drop below the critical voltage
•Generation of a reset signal when the supply voltage is below the device
specific threshold voltage
•Keepingthe reset signalactivefora definedtimeafterthe supplyvoltagehas
returned to its nominal value to ensure proper initialization of the
microprocessor or DSP
The Texas Instruments TPS3801 and TPS3809 families of integrated circuits
fulfill the requirements described above without requiring additional external
components.
2 Circuit Description
This section describes the TPS3801 and TPS3809 devices and features.
2.1 Overview of Features
Figure 2 is an overview of the features of TPS3801 and TPS3809.
TPS3801 TPS3809
Manual Reset
Function Voltage
Supervision Low-Active Reset
Figure 2. Features Overview
2.2 Supervised Supply Voltages
Table 1 gives an overview of the nominal supply voltages, which can be
supervisedbytheTPS3801andTPS3809.Thevaluesinthecolumnofthreshold
voltage are the negative-going threshold voltages. The differences between
positive-going and negative-going threshold voltage is explained in Chapter 3.

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 1Negative 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
voltagebya comparator. If thedividedvoltageisbelow the thresholdvoltage,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 kΩ. 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.

Circuit Description
4 SLVA075
Table 3. Typical Values of Internal Voltage Divider
DEVICES R1TYPICAL R2TYPICAL
TPS3801I50, TPS3809I50 165 kΩ495 kΩ
TPS3801K33, TPS3809K33 256 kΩ404 kΩ
TPS3801L30, TPS3809L30 284 kΩ376 kΩ
TPS3801J25, TPS3809J25 334 kΩ326 kΩ
TheTPS3801hasinadditiontotheTPS3809amanualresetinput.Thisinputhas
an internal pullup resistor of 30 kΩto VDD. Therefore an external resistor is not
necessary if the function is not used.
The oscillator clocks the reset logic to generate the delay time of about 200ms.
_
+
RESET
Logic
+
Timer
Oscillator
30 kΩ
R1
R2
Reference
Voltage
or 1.137 V
TPS3809
TPS3801
MR
VDD
GND
RESET
TPS3801
Only!
Figure 4. Block Diagram of TPS3801 and TPS3809
2.6 Basic Timings
Figure 5 summarizes the two reasons for an active reset at a TPS3801. The
behavior of the TPS3809 is the same without the manual reset input.
If the supply voltage is below 1.1 V, there is no defined reset signal. If the supply
voltageincreasesabove1.1V,thereset output has astable low signal.The reset
gets inactive one delay time after the supply voltage has increased the threshold
voltage.
A logical zero at the manual reset input triggers the same as a breaking-in of the
supply voltage: the reset becomes active. One delay time after the manual reset
input gets a logical high signal again, the reset output becomes inactive.

Circuit Description
5
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
For VDD < 1.1 V Undefined
Behavior of RESET Output
tdtdtd
t
t
t
VDD
MR
RESET
Vnom
VIT
1.1 V
‘1‘
‘0‘
‘1‘
‘0‘
Figure 5. Timing Diagram of TPS3801

Voltage Supervision at the V
DD
Terminal
6 SLVA075
3 Voltage Supervision at the VDD Terminal
3.1 Functional Description
ThemainfunctionofanSVSistosuperviseasupplyvoltageandtotriggerareset
signal if necessary.
If the supply voltage falls below the negative-going threshold voltage VIT–,the
devicehas to assertareset.The resetreturnstothe inactivestate, about200ms
after the voltage again exceeds the positive-going threshold voltage VIT+. This
delay time tdof 200 ms is necessary to ensure that the crystal oscillator works
stable after a power-on reset and that the processor initialization could be
completed.
The difference between the negative-going and the positive-going threshold
voltage is called hysteresis Vhys:
V
IT )+
V
I T–
) V
hys
Thereason forthe hysteresisis to avoidtoggling ofthe resetoutput ifthe voltage
is noisy.
For a better understanding, a timing diagram with these parameters is given:
RESET Goes High After Delay
Time of Typical 200 ms
RESET Goes Low
VSENSE
VCC
VIT+
VIT–
t
Vhys
Figure 6. Relations Between VIT+, VIT–, and Vhys
The devices are specified in a temperature range of –40°C to +85°C and for an
input voltage range of 2 V to 6 V. Due to the wide range of temperature and input
voltageandbecauseofprocessvariationsthethresholdvoltagesvaryalittle.The
minimum, typical and maximum values of the negative-going threshold voltages
and the typical hysteresis can be taken from Table 4.
(1)

Voltage Supervision at the V
DD
Terminal
7
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
Table 4. The Specified Values of VIT– and the Hysteresis, Vhys
DEVICES VIT– – MIN VIT– – TYP VIT– – MAX Vhys – TYP
TPS3801I50
TPS3809I50 4.45 V 4.55 V 4.65 V 60 mV
TPS3801K33
TPS3809K33 2.87 V 2.93 V 2.99 V 40 mV
TPS3801L30
TPS3809L30 2.58 V 2.64 V 2.70 V 35 mV
TPS3801J25
TPS3809J25 2.20 V 2.25 V 2.30 V 30 mV
3.2 Measurement of a Voltage Drop on the Supply Line
To demonstrate the typical operation of an SVS the following measurement has
been made. The measurement circuit of Figure 7 has been used.
Waveform
Generator
100 nF VDD GND
MR
RES
TPS3801–50
Oscilloscope
39 nF
1 MΩ
Figure 7. Measurement Circuit for Measuring the Reaction of a Voltage Drop
Thewaveform generator suppliesthesupervisor andgeneratesthe voltage drop
totriggeraresetpulse.The1MΩresistorandthe39pFcapacitoraretosimulate
a CMOS load. The 100 nF capacitor at the VDD pin of the TPS3801 is
recommended for all applications. The oscilloscope records the measurement
data for the plot.

Voltage Supervision at the V
DD
Terminal
8 SLVA075
VDD and RESET VDD and
RESET
RESET
Figure 8. Measurement of the Voltage Drop at VDD
Adelaytime of232msismeasured.Thisparameterisspecifiedbetween120ms
minimum value and 280 ms maximum value with a typical value of 200 ms. This
wide range is because of variations in the process. The oscillator is built up
internally with an RC network.
3.3 Threshold Overdrive Versus Pulsewidth
The datasheet specifies, that a voltage drop of 3 µs to at least 200 mV below the
negative-going threshold voltage VIT– must trigger a reset pulse. But what
happens with a shorter, but deeper drop? This question is answered with the
measurements shown in Figure 9 and Figure 10.
The x-axis shows the duration of the voltage drop, the y-axis shows the
breakdown voltage of the drop down from 5 V respectively 2.5 V.

Voltage Supervision at the V
DD
Terminal
9
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
0.0
1.0
2.0
3.0
4.0
5.0
012345678910
Voltage – V
VIT = 4.55 V
t – Time – µs
1.1
Figure 9. Breakdown Voltage versus Pulsewidth at a TPS380xI50
0.0
0.5
1.0
1.5
2.0
2.5
012345678910
Voltage – V
1.1
t – Time – µs
VIT = 2.25 V
Figure 10. Breakdown Voltage versus Pulsewidth at a TPS380xJ25

Voltage Supervision at the V
DD
Terminal
10 SLVA075
3.4 Making the Supervisor Circuit Less Sensitive
Supplyvoltage supervisorsaredesigned todetectsmall voltagedropsbelow the
threshold voltage. The datasheet of TPS380x specifies, that a reset pulse from
200 mV above the threshold voltage VIT to 200 mV below VIT with a duration of
3 µs suffices to trigger a reset pulse. But not every system requires the detection
of such small spikes, because these spikes do not influence the functionality of
thesystem.In thiscase,itispossibletoreducethesensitivityoftheundervoltage
recognition.
AsimplesolutiontothisproblemistoaddalowpassfilterinfrontoftheVDDinput.
The recommended capacitor at VDD works as a part of the RC network.
VDD RESET
GND
TPS3801J25
C = 100 nF
R
Figure 11. TPS3801 With a Low Pass Filter at VDD Terminal
Care has to be so taken that the additional resistor does not alter the threshold
voltage too much. The threshold voltage is determined by the internal voltage
divider, like shown in the block diagram in Chapter 2. A resistor of R1= 10 kΩin
the RC combination raises the threshold voltage by 1.5% independent of the
voltage version of the device. A R =1 kΩresistor causes a rise in the threshold
voltage of 0.15%, so that it can be ignored.
Figure 12 shows a measurement with different RC networks. The value of the
capacitorisC=100nF,theresistorvaluesare100Ω,1kΩ,and10kΩ.Thedevice
is a TPS3801J25 with a threshold voltage of 2.25 V.
0.00
0.50
1.00
1.50
2.00
2.50
1.0 10.0 100.0 1000.0
Voltage – V
30.09.01.5
t – Time – µs
100 Ω
1 kΩ
10 kΩC = 100 nF = constant
VIT = 2.25
Figure 12. Breakdown Voltage versus Pulsewidth With a Low Pass Filter

Manual Reset
11
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
4 Manual Reset
4.1 Functional Description
The manual reset is an input for triggering a reset by an external component. As
an example, a pushbutton switch or a microcontroller or a DSP port can provide
themanual reset. Theresetwill beassertedfor the timeofa lowsignalatmanual
reset input plus delay time td.
An internal pullup resistor of 30 kΩbetween manual reset input and VDD makes
an external pullup resistor unnecessary. This input can be left floating, if it is not
used.
4.2 A Measurement of Low Pulse at the Manual Reset Input
For a better illustration, a measurement of a low pulse of 100 ms at manual reset
and the resulting reset pulse is shown in Figure 13. The measurement has been
made at a TPS3801I50.
MR and RESET MR and RESET
RESET
Figure 13. Reset Pulse, Triggered by Manual Reset
4.3 Minimum Conditions for Triggering a Manual Reset
As specified in the datasheet, a high-to-low transition from 0.7×VDD to 0.3×VDD
with a duration of at least 100ns is enough to trigger a reset. For shorter signals
at manual reset input, the triggering of a reset can not be assured.

Manual Reset
12 SLVA075
100 ns
VMR
VDD
0.7 ×VDD
0.3 ×VDD
0 V t
Figure 14. Minimum Conditions for Triggering a Reset at Manual Reset Input
4.4 Saving Current While Using the Manual Reset Function
4.4.1 Current Flow Off the Manual Reset Input
Figure 15 illustrates the internal structure of the manual reset input. It shows
the internal pullup resistor of 30 kΩ, which causes a steady current flow, if
VMR ≠VDD. If it is important to keep the current consumption as low as possible,
the following two points are important to considerate:
•In normal operation VMR should be equal to VDD. Thereby a steady current
flow can be avoided.
•If a reset should be triggered with a low pulse at manual reset, it should be
a short pulse.
Reset
Logic
30 kΩ
VDD
MR
VMR
Voltage
Source
TPS3801
IMR
Figure 15. Internal Realization of the Manual Reset Circuit
The current out of the manual reset terminal depends on the difference between
VDD and VMR and can be easily calculated with equation 2.
I MR +
V DD * V MR
30 k W
4.4.2 Lateral Current From V
DD
to GND
Thereisanotherpossibilitytoreduce powerconsumptionwhileusingthemanual
reset. During a transition at MR from high-to-low or low-to-high, there is a lateral
currentofmorethan300µAatavoltageof2.5V.Powerconsumptionisimportant
inabatterypoweredsystemandasteepedgeinbothdirectionshelpstominimize
power consumption. The following Figure 16 shows the lateral current in
dependence of the voltage at manual reset input.
(2)

Manual Reset
13
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
–50.0
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
0.00 1.00 2.00 3.00 4.00 5.00
VMR – V
Ilat –µA
Figure 16. Lateral Current in Dependence of the Voltage at a CMOS Input Stage

Applications
14 SLVA075
5 Applications
5.1 A TPS3801 Supervises a DSP
The standard task of a supply voltage supervisor is supervising a processor
supply voltage and triggering a reset, if this voltage falls below the threshold
voltage. The application example of Figure 17 shows a TPS3801K33, which
supervises the 3.3 V power line of the DSP TMS320LC542. This DSP has the
samesupplyvoltageforthecore and theI/Opart.Ifthesupplyvoltagefallsbelow
2.93 V, which is the typical threshold voltage of a TPS3801K33, a reset is
asserted. The reset output keeps active until the supply voltage increases again
above the threshold voltage plus 200 ms of delay time.
A push button can be used to trigger a reset manually, a pullup resistor is not
needed. A capacitor of 100 nF between the VDD terminal of the supervisor and
GND ensures proper operation of the supervisor and is recommended.
VDD
MR
TPS3801K33
RESET
GND
VDD
TMS320LC542
RESET
GND
100 nF
VDD 3.3 V
Figure 17. TPS3801 Supervises the TMS320LC542-DSP
5.2 Switching the Power Supply With a TPS3801
Figure 18 illustrates an application to turn system power on and off with a
TPS3801. The TPS2051, a power distribution switch of Texas Instruments has
a high-active enable input, so that it can be directly connected to the reset output
of the supervisor.
Typically, the TPS2051 has RDSon of less than 100 mΩ. To keep the on-state
resistance low, the device has two input terminals and three output terminals.
Themanualresetinputof theTPS3801allowsaremotepowercontrol.Thisinput
canbe connectedwith an outputof aDSP,which turnsthe power ofa subsystem
on (⇒with a logical high signal) and off (⇒with a logical low signal). The
low-active OC terminal signals overcurrent or overtemperature conditions. The
output will remain asserted until the overcurrent or overtemperature condition is
removed. Due to the open-drain output, a resistor must be placed between the
OC terminal and the supply voltage.
When Vin is below VIT, the reset output of the TPS3801is low and the power
distributionswitchisdisabled.WhenVinisaboveVIT,the resetoutputishigh and
the TPS2051 is enabled.

Applications
15
TPS3801/09 – Smallest SVS for Monitoring DSPs and Processors
VDD
MR
TPS3801
RESET
GND
TPS2051
GND
EN
IN
IN
OUT
OUT
OUT
OC
100 kΩ
VO
Vin
ILOAD
RLOAD
VEN
From a Digital Output To a Digital Input
Figure 18. System Power Control With the TPS3801
Technical Data of the TPS2051
MIN MAX UNIT
Input voltage Vin 2.7 5.5 V
Continuous output current 500 mA
On-state-resistance, rDSon (Vin=5 V; TJ=25°C) 95 mΩ
Turnon time, ton 20 ms
Turnoff time, toff 40 ms
Standby current 10 µA
For more detailed information:
The datasheet can be found on the WWW at the address:
http://www–s.ti.com/sc/psheets/slvs172a/slvs172a.pdf
An application report with the title TPS202x/3x and TPS204x/5x USB Power
Distribution
is available at http://www–s.ti.com/sc/psheets/slva049/slva049.pdf
Figure 19 shows the three most important voltages of the application example.
Theloadwasa3.3kΩresistor.Normallya resistor up to10 Ωcanbe used, which
causesacurrentflowof500mA.Forthemeasurement,afunctiongeneratorwith
a limited output current was used to generate the shape of input voltage.
Therefore the output current was limited to 1.5 mA with the 3.3 kΩresistor .

Applications
16 SLVA075
Figure 19. Measurements of Switching Power With A TPS2051
5.3 Keeping a Low Signal at Reset Output for Voltages Below 1.1 V
The reset output is defined for supply voltages above 1.1 V. Below this voltage,
a low level at RESET cannot be assured, because the internal transistors need
acertainvoltageleveltopulldowntheoutputtoground.Whenthesupplyvoltage
is below this voltage level, the reset input of the connected device is floating and
this state should be avoided. Although most microcontrollers and DSPs do not
work at voltages below 1.1 V, there are systems, that requires a correct reset
signal down to 0 V.
To solve this problem, a pulldown resistor of 100 kΩis placed between the reset
output and ground. The disadvantage of this solution is a steady current flow
during inactive state. At a supply voltage of 2.5 V, a current of 25 µA has to be
taken into the account.
VDD
TPS3801J25
RESET
GND
VDD
DSP
RESET
GND
100 nF 100 kΩ
Vin
Figure 20. An Additional Resistor Ensures a Valid Reset Down to 0 V