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LP2957/LP2957A 5V Low-Dropout Regulator for µP Applications
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1FEATURES DESCRIPTION
The LP2957 is a 5V micropower voltage regulator
2• 5V Output within 1.4% Over Temperature (A with electronic shutdown, error flag, very low
Grade) quiescent current (150 µA typical at 1 mA load), and
• Easily Programmed for Snap-On/Snap-Off very low dropout voltage (470 mV typical at 250 mA
Output load current).
• Ensured 250 mA Output Current Output can be wired for snap-on/snap-off operation to
• Extremely Low Quiescent Current eliminate transition voltage states where µP operation
may be unpredictable.
• Low Input-Output Voltage Required for
Regulation Output crowbar (50 mA typical pull-down current) will
• Reverse Battery Protection bring down the output quickly when the regulator
snaps off or when the shutdown function is activated.
• Extremely Tight Line and Load Regulation The part has tight line and load regulation (0.04%
• Very Low Temperature Coefficient typical) and low output temperature coefficient (20
• Current and Thermal Limiting ppm/°C typical).
• Error Flag Signals when Output is out of The accuracy of the 5V output is ensured at room
Regulation temperature and over the full operating temperature
range.
APPLICATIONS The LP2957 is available in the five-lead TO-220 and
• High-Efficiency Linear Regulator DDPAK/TO-263 packages.
• Battery-Powered Regulator
Package Outline
Top View Top View
Figure 1. Bent, Staggered Leads Figure 2. Plastic Surface Mount Package
5-Lead TO-220 Package 5-Lead DDPAK/TO-263 Package
See Package Number NDH0005D See Package Number KTT0005B
Side View
Figure 3. See Package Number KTT0005B
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 1998–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
using: Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator
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Absolute Maximum Ratings(1)(2)
Operating Junction Temperature Range −40°C to +125°C
Storage Temperature Range −65°C to +150°C
Lead Temperature (Soldering, 5 Seconds) 260°C
Power Dissipation(3) Internally Limited
Input Supply Voltage −20V to +30V
Shutdown Input −0.3V to +30V
ESD Rating 2 kV
(1) Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply
when operating the device outside of its rated operating conditions.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/Distributors for availability and
specifications.
(3) The maximum allowable power dissipation is a function of the maximum junction temperature, T J(MAX), the junction-to-ambient thermal
resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated
will go into thermal shutdown. The junction-to-ambient thermal resistance of the TO-220 (without heatsink) is 60°C/W and 73°C/W for
the DDPAK/TO-263. If the DDPAK/TO-263 package is used, the thermal resistance can be reduced by increasing the P.C. board copper
area thermally connected to the package: Using 0.5 Square inches of copper area, θJA is 50°C/W, with 1 square inch of copper area,
θJA is 37°C/W; and with 1.6 or more square inches of copper area, θJA is 32°C/W. The junction-to-case thermal resistance is 3°C/W. If
an external heatsink is used, the effective junction-to-ambient thermal resistance is the sum of the junction-to-case resistance (3°C/W),
the specified thermal resistance of the heatsink selected, and the thermal resistance of the interface between the heatsink and the
LP2957 (see Application Hints).
Electrical Characteristics
Limits in standard typeface are for TJ= 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, VSD = 3V. LP2957AI LP2957I
Symbol Parameter Conditions Typical Units
Min Max Min Max
VO5.0 4.975 5.025 4.950 5.050
Output Voltage(1) 4.940 5.060 4.900 5.100 V
1 mA ≤IL≤250 mA 5.0 4.930 5.070 4.880 5.120
Output Voltage See(2) 20 100 150 ppm/°C
Temperature Coefficient
VIN = 6V to 30V 0.03 0.10 0.20
Line Regulation %
0.20 0.40
IL= 1 mA to 250 mA 0.16 0.20
Load Regulation 0.04 %
IL= 0.1 mA to 1 mA(3) 0.20 0.30
VIN–VOIL= 1 mA 60 100 100
150 150
IL= 50 mA 240 300 300
420 420
Dropout Voltage(4) mV
IL= 100 mA 310 400 400
520 520
IL= 250 mA 470 600 600
800 800
(1) When used in dual-supply systems where the regulator load is returned to a negative supply, the output voltage must be diode-clamped
to ground.
(2) Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
(3) Regulation is measured at constant junction temperature using low duty cycle pulse testing. Parts are tested separately for load
regulation in the load ranges 0.1 mA–1 mA and 1 mA–250 mA. Changes in output voltage due to heating effects are covered by the
thermal regulation specification.
(4) Dropout voltage is defined as the input to output voltage differential at which the output voltage drops 100 mV below the value
measured with a 1V input to output differential.
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Electrical Characteristics (continued)
Limits in standard typeface are for TJ= 25°C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, VSD = 3V. LP2957AI LP2957I
Symbol Parameter Conditions Typical Units
Min Max Min Max
IGND IL= 1 mA 150 200 200 µA
230 230
IL= 50 mA 1.1 2 2
2.5 2.5
Ground Pin Current(5) IL= 100 mA 3 6 6 mA
8 8
IL= 250 mA 16 28 28
33 33
IGND IL= 0 130 180 180 µA
Ground Pin Current in
Shutdown(5) VSD = 0.4V 200 200
IGND VIN = 4.5V 180 230 230 µA
Ground Pin Current at
Dropout(5) IL= 0.1 mA 250 250
IO(Sink) VIN = 5.3V 50 30 30
Off-State Output Pulldown mA
Current VO= 5V, VSD = 0.4V 20 20
IO(Off) I(SD IN) ≥1 µA 3 10 10
Output Leakage in µA
Shutdown VIN = 30V, VOUT = 0V 20 20
ILIMIT RL= 1Ω400 500 500
Current Limit mA
530 530
See(6)
Thermal Regulation 0.05 0.2 0.2 %/W
enOutput Noise Voltage CL= 2.2 µF 500
(10 Hz to 100 kHz) µV RMS
CL= 33 µF 320
IL= 100 mA
SHUTDOWN INPUT
VSD (ON) 1.155 1.305 1.155 1.305
Output Turn-On Threshold V
Voltage 1.140 1.320 1.140 1.320
HYST Hysteresis 6 mV
IBVIN(SD) = 0V to 5V 10 −30 30 −30 30
Input Bias Current nA
−50 50 −50 50
DROPOUT DETECTION COMPARATOR
IOH VOH = 30V 0.01 1 1
Output “HIGH” Leakage µA
2 2
VOL VIN = 4V 150 250 250
Output “LOW” Voltage mV
IO(COMP) = 400 µA 400 400
VTHR (Max) See(7) −240 −320 −150 −320 −150
Upper Threshold Voltage mV
−380 −100 −380 −100
VTHR (Min) See(7) −350 −450 −230 −450 −230
Lower Threshold Voltage mV
−640 −160 −640 −160
HYST Hysteresis See(7) 60 mV
(5) Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the load current plus the
ground pin current.
(6) Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load
or line regulation effects. Specifications are for a 200 mA load pulse at VIN = 20V (3W pulse) for T = 10 ms.
(7) Voltages are referenced to the nominal regulated output voltage.
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Typical Performance Characteristics
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, V SD = 3V, TA= 25°C
Ground Pin Current Ground Pin Current
Figure 4. Figure 5.
Ground Pin Current
vs Load Ground Pin Current
Figure 6. Figure 7.
Ground Pin Current Output Noise Voltage
Figure 8. Figure 9.
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Typical Performance Characteristics (continued)
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, V SD = 3V, TA= 25°C
Ripple Rejection Ripple Rejection
Figure 10. Figure 11.
Ripple Rejection Line Transient Response
Figure 12. Figure 13.
Line Transient Response Output Impedance
Figure 14. Figure 15.
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Typical Performance Characteristics (continued)
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, V SD = 3V, TA= 25°C
Load Transient Response Load Transient Response
Figure 16. Figure 17.
Dropout Characteristics Enable Transient
Figure 18. Figure 19.
Short-Circuit Output Current
Enable Transient and Maximum Output Current
Figure 20. Figure 21.
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Typical Performance Characteristics (continued)
Unless otherwise specified: VIN = 6V, IL= 1 mA, CL= 2.2 µF, V SD = 3V, TA= 25°C
Thermal Regulation Error Output Sink Current
Figure 22. Figure 23.
Dropout Detection
Threshold Voltages Maximum Power Dissipation (DDPAK/TO-263)(1)
Figure 24. Figure 25.
Error Output Voltage Dropout Voltage
Figure 26. Figure 27.
(1) The maximum allowable power dissipation is a function of the maximum junction temperature, T J(MAX), the junction-to-ambient thermal
resistance, θJA, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated
will go into thermal shutdown. The junction-to-ambient thermal resistance of the TO-220 (without heatsink) is 60°C/W and 73°C/W for
the DDPAK/TO-263. If the DDPAK/TO-263 package is used, the thermal resistance can be reduced by increasing the P.C. board copper
area thermally connected to the package: Using 0.5 Square inches of copper area, θJA is 50°C/W, with 1 square inch of copper area,
θJA is 37°C/W; and with 1.6 or more square inches of copper area, θJA is 32°C/W. The junction-to-case thermal resistance is 3°C/W. If
an external heatsink is used, the effective junction-to-ambient thermal resistance is the sum of the junction-to-case resistance (3°C/W),
the specified thermal resistance of the heatsink selected, and the thermal resistance of the interface between the heatsink and the
LP2957 (see Application Hints).
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Block Diagram
Typical Application Circuits
Figure 28. LP2957 Basic Application
*See Application Hints
Figure 29. LP2957 Application with Snap-On/Snap-Off Output
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APPLICATION HINTS
EXTERNAL CAPACITORS
A 2.2 µF (or greater) capacitor is required between the output pin and ground to assure stability (refer to
Figure 30). Without this capacitor, the part may oscillate. Most type of tantalum or aluminum electrolytics will
work here. Film types will work, but are more expensive. Many aluminum electrolytics contain electrolytes which
freeze at −30°C, which requires the use of solid tantalums below −25°C. The important parameters of the
capacitor are an ESR of about 5Ωor less and a resonant frequency above 500 kHz (the ESR may increase by a
factor of 20 or 30 as the temperature is reduced from 25°C to −30°C). The value of this capacitor may be
increased without limit. At lower values of output current, less output capacitance is required for stability. The
capacitor can be reduced to 0.68 µF for currents below 10 mA or 0.22 µF for currents below 1 mA.
A 1 µF capacitor should be placed from the input pin to ground if there is more than 10 inches of wire between
the input and the AC filter capacitor or if a battery input is used. This capacitor may have to be increased if the
regulator is wired for snap-on/snap-off output and the source impedance is high (see Snap-On/Snap-Off
Operation section).
SHUTDOWN INPUT
A logic-level signal will shut off the regulator output when a “LOW” (< 1.2V) is applied to the Shutdown input.
To prevent possible mis-operation, the Shutdown input must be actively terminated. If the input is driven from
open-collector logic, a pull-up resistor (20 kΩto 100 kΩrecommended) must be connected from the Shutdown
input to the regulator input.
If the Shutdown input is driven from a source that actively pulls high and low (like an op-amp), the pull-up resistor
is not required, but may be used.
If the shutdown function is not to be used, the cost of the pull-up resistor can be saved by tying the Shutdown
input directly to the regulator input.
IMPORTANT: Since the Absolute Maximum Ratings state that the Shutdown input can not go more than 0.3V
below ground, the reverse-battery protection feature which protects the regulator input is sacrificed if the
Shutdown input is tied directly to the regulator input.
If reverse-battery protection is required in an application, the pull-up resistor between the Shutdown input and the
regulator input must be used.
MINIMUM LOAD
It should be noted that a minimum load current is specified in several of the electrical characteristic test
conditions, so the value listed must be used to obtain correlation on these tested limits. The part is parametrically
tested down to 100 µA, but is functional with no load.
DROPOUT VOLTAGE
The dropout voltage of the regulator is defined as the minimum input-to-output voltage differential required for the
output voltage to stay within 100 mV of the output voltage measured with a 1V differential. The dropout voltages
for various values of load current are listed under Electrical Characteristics.
If the regulator is powered from a transformer connected to the AC line, the minimum AC line voltage and
maximum load current must be used to measure the minimum voltage at the input of the regulator. The
minimum input voltage is the lowest voltage level including ripple on the filter capacitor . It is also advisable to
verify operation at minimum operating ambient temperature , since the increasing ESR of the filter capacitor
makes this a worst-case test due to increased ripple amplitude.
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HEATSINK REQUIREMENTS
A heatsink may be required with the LP2957 depending on the maximum power dissipation and maximum
ambient temperature of the application. Under all possible operating conditions, the junction temperature must be
within the range specified under Absolute Maximum Ratings.
To determine if a heatsink is required, the maximum power dissipated by the regulator, P(max), must be
calculated. It is important to remember that if the regulator is powered from a transformer connected to the AC
line, the maximum specified AC input voltage must be used (since this produces the maximum DC input
voltage to the regulator), and the maximum load current must also be used. Figure 30 shows the voltages and
currents which are present in the circuit. The formula for calculating the power dissipated in the regulator is also
shown in Figure 30.
PTOTAL = (VIN −5)I L+ (VIN)IG
*See EXTERNAL CAPACITORS
Figure 30. Basic 5V Regulator Circuit
The next parameter which must be calculated is the maximum allowable temperature rise, TR(Max). This is
calculated by using the formula:
TR(Max) = TJ(Max) −TA(Max)
where
• TJ(Max) is the maximum allowable junction temperature
• TA(Max) is the maximum ambient temperature (1)
Using the calculated values for TR(Max) and P(Max), the required value for junction-to-ambient thermal
resistance, θ(JA), can now be found:
θ(JA) = TR(Max)/P(Max) (2)
If the calculated value is 60°C/W or higher , the regulator may be operated without an external heatsink. If the
calculated value is below 60°C/W, an external heatsink is required. The required thermal resistance for this
heatsink, θ(HA), can be calculated using the formula:
θ(HA) =θ(JA) − θ (JC) − θ(CH)
where
•θ(JC) is the junction-to-case thermal resistance, which is specified as 3°C/W for the LP2957
•θ(CH) is the case-to-heatsink thermal resistance, which is dependent on the interfacing material
(see Table 1 and Table 2) (3)
Typical TO-220 Case-To-Heatsink
Thermal Resistance in °C/W
Table 1. (From AAVID)
Silicone Grease 1.0
Dry Interface 1.3
Mica with Grease 1.4
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Table 2. (From Thermalloy)
Thermasil III 1.3
Thermasil II 1.5
Thermalfilm (0.002) with Grease 2.2
θ(HA) is the heatsink-to-ambient thermal resistance. It is this specification (listed on the heatsink manufacturers
data sheet) which defines the effectiveness of the heatsink. The heatsink selected must have a thermal
resistance which is equal to or lower than the value of θ(HA)calculated from the above listed formula.
ERROR COMPARATOR
This comparator produces a logic “LOW” whenever the output falls out of regulation by more than about 5%. This
figure results from the comparator's built-in offset of 60 mV divided by the 1.23V reference. An out-of-regulation
condition can result from low input voltage, current limiting, or thermal limiting.
Figure 31 gives a timing diagram showing the relationship between the output voltage, the ERROR output, and
input voltage as the input voltage is ramped up and down to the regulator without snap-on/snap-off output.
The ERROR signal becomes low at about 1.3V input. It goes high at about 5V input, where the output equals
4.75V. Since the dropout voltage is load dependent, the input voltage trip points will vary with load current. The
output voltage trip point does not vary.
The comparator has an open-collector output which requires an external pull-up resistor. This resistor may be
connected to the regulator output or some other supply voltage. Using the regulator output prevents an invalid
“HIGH” on the comparator output which occurs if it is pulled up to an external voltage while the regulator input
voltage is reduced below 1.3V. In selecting a value for the pull-up resistor, note that while the output can sink
400 µA, this current adds to battery drain. Suggested values range from 100k to 1 MΩ. The resistor is not
required if the output is unused.
*In shutdown mode, ERROR will go high if it has been pulled up to an external supply. To avoid this invalid response,
pull up to regulator output.
**Exact value depends on dropout voltage, which varies with load current.
Figure 31. ERROR Output Timing
If a single pull-up resistor is connected to the regulator output, the error flag may briefly rise up to about 1.3V as
the input voltage ramps up or down through the 0V to 1.3V region.
In some cases, this 1.3V signal may be mis-interpreted as a false high by a µP which is still “alive” with 1.3V
applied to it.
To prevent this, the user may elect to use two resistors which are equal in value on the error output (one
connected to ground and the other connected to the regulator output).
If this two-resistor divider is used, the error output will only be pulled up to about 0.6V (not 1.3V) during power-up
or power-down, so it can not be interpreted as a high signal. When the regulator output is in regulation (4.8V to
5V), the error output voltage will be 2.4V to 2.5V, which is clearly a high signal.
OUTPUT ISOLATION
The regulator output can be connected to an active voltage source (such as a battery) with the regulator input
turned off, as long as the regulator ground pin is connected to ground. If the ground pin is left floating,
damage to the regulator can occur if the output is pulled up by an external voltage source.
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SNAP-ON/SNAP-OFF OPERATION
The LP2957 output can be wired for snap-on/snap-off operation using three external resistors:
*Minimum value (increase as required for smooth turn-on characteristic).
Figure 32. Snap-On/Snap-Off Output
When connected as shown, the shutdown input holds the regulator off until the input voltage rises up to the turn-
on threshold (V ON), at which point the output “snaps on”.
When the input power is shut off (and the input voltage starts to decay) the output voltage will snap off when the
input voltage reaches the turn-off threshold, VOFF.
Figure 33. Snap-On/Snap-Off Input and Output Voltage Diagram
It is important to note that the voltage VOFF must always be lower than VON (the difference in these voltage levels
is called the hysteresis).
Hysteresis is required when using snap-on/snap-off output, with the minimum amount of hysteresis required for
a specific application being dependent on the source impedance of whatever is supplying VIN.
Caution: A type of low-frequency oscillation can occur if VON and VOFFare too close together (insufficient
hysteresis). When the output snaps on, the regulator must draw sufficient current to power the load and
charge up the output capacitor (in most cases, the regulator will briefly draw the maximum current allowed
by its internal limiter).
For this reason, it is best to assume the LP2957 may pull a peak current of about 600 mA from the source
(which is the listed maximum short-circuit load current of 530 mA plus the ground pin current of 70 mA).
This high peak current causes VIN to drop by an amount equal to the source impedance multiplied by the current.
If V IN drops below VOFF, the regulator will turn off and stop drawing current from the source. This will allow VIN to
rise back up above VON, and the cycle will start over. The regulator will stay in this oscillating mode and never
come into regulation.
HYSTERESIS IN TRANSFORMER-POWERED
APPLICATIONS:
If the unregulated DC input voltage to the regulator comes from a transformer, the required hysteresis is easily
measured by loading the source with a resistive load.
Figure 34. Transformer Powered Input Supply
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If the regulator is powered from a battery, the source impedance will probably be low enough that other
considerations will determine the optimum values for hysteresis (see Design Example #2).
For best results, the load resistance used to test the transformer should be selected to draw about 600 mA for
the maximum load current test, since this is the maximum peak current the LP2957 could be expected to draw
from the source.
The difference in input voltage measured at no load and full load defines the amount of hysteresis
required for proper snap-on/snap-off operation (the programmed hysteresis must be greater than the
difference in voltages).
CALCULATING RESISTOR VALUES:
The values of R1, R2 and R3 can be calculated assuming the designer knows the hysteresis.
In most transformer-powered applications, it can be assumed that VOFF (the input voltage at turn-off) should be
set for about 5.5V, since this allows about 500 mV across the LP2957 to keep the output in regulation until it
snaps off. VON (the input voltage at turn on) is found by adding the hysteresis voltage to VOFF.
R1, R2 and R3 are found by solving the node equations for the currents entering the node nearest the shutdown
pin (written at the turn-on and turn-off thresholds).
The shutdown pin bias current (10 nA typical) is not included in the calculations:
Figure 35. Turn-ON Transition - Equivalent Circuit Figure 36. Turn-OFF Transition - Equivalent
Circuits
(4)
Since these two equations contain three unknowns (R1, R2 and R3) one resistor value must be assumed and
then the remaining two values can be obtained by solving the equations.
The node equations will be simplified by solving both equations for R2, and then equating the two to generate an
expression in terms of R1 and R3.
(5)
Setting these equal to each other and solving for R1 yields:
(6)
The same equation solved for R3 is:
(7)
A value for R1 or R3 can be derived using either one of the above equations, if the designer assumes a value for
one of the resistors.
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The simplest approach is to assume a value for R3. Best results will typically be obtained using values between
about 20 kΩand 100 kΩ(this keeps the current drain low, but also generates realistic values for the other
resistors).
There is no limit on the minimum value of R3, but current should be minimized as it generates power that drains
the source and does not power the load.
SUMMARY: TO SOLVE FOR R1, R2 AND R3:
1. Assume a value for either R1 or R3.
2. Solve for the other variable using the equation for R1 or R3.
3. Take the values for R1 and R3 and plug them back into either equation for R2 and solve for this value.
DESIGN EXAMPLE #1:
A 5V regulated output is to be powered from a transformer secondary which is rectified and filtered. The voltage
VIN is measured at zero current and maximum current (600 mA) to determine the minimum allowable hysteresis.
VIN is measured using an oscilloscope (both traces are shown on the same grid for clarity):
Figure 37. VIN VOLTAGE WAVEFORMS
The full-load voltage waveform from a transformer-powered supply will have ripple voltage as shown. The correct
point to measure is the lowest value of the waveform.
The 1.2V differential between no-load and full-load conditions means that at least 1.2V of hysteresis is required
for proper snap-on/snap-off operation (for this example, we will use 1.5V).
As a starting point, we will assume:
VOFF = 5.5V VON = V OFF + HYST = 5.5 + 1.5 = 7V R3 = 49.9k
Solving for R1:
(8)
Solving for R2:
(9)
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DESIGN EXAMPLE #2:
A 5V regulated output is to be powered from a battery made up of six NiCad cells. The cell data is:
cell voltage (full charged): 1.4V
cell voltage (90% discharged): 1.0V
The internal impedance of a typical battery is low enough that source loading during regulator turn-on is not
usually a problem.
In a battery-powered application, the turn-off voltage VOFF should be selected so that the regulator is shut down
when the batteries are about 90% discharged (over discharge can damage rechargeable batteries).
In this case, the battery voltage will be 6.0V at the 90% discharge point (since there are six cells at 1.0V each).
That means for this application, VOFF will be set to 6.0V.
Selecting the optimum voltage for VON requires understanding battery behavior. If a Ni-Cad battery is nearly
discharged (cell voltage 1.0V) and the load is removed, the cell voltage will drift back up. The voltage where the
regulator turns on must be set high enough to keep the regulator from re-starting during this time, or an on-off
pulsing mode can occur.
If the regulator restarts when the discharged cell voltage drifts up, the load on the battery will cause the cell
voltage to fall below the turn-off level, which causes the regulator to shut down. The cell voltage will again float
up and the on-off cycling will continue.
For NiCad batteries, a good cell voltage to use to calculate VON is about 1.2V per cell. In this application, this will
yield a value for VON of 7.2V.
We can now find R1, R2 and R3 assuming:
VOFF = 6.0V V ON = 7.2V R3 = 49.9k
Solving for R1:
(10)
Solving for R2:
(11)
Copyright © 1998–2013, Texas Instruments Incorporated Submit Documentation Feedback 15
Product Folder Links: LP2957 LP2957A
LP2957, LP2957A
www.ti.com
SNVS102C –JUNE 1998–REVISED APRIL 2013
REVISION HISTORY
Changes from Revision B (April 2013) to Revision C Page
• Changed layout of National Data Sheet to TI format .......................................................................................................... 16
Copyright © 1998–2013, Texas Instruments Incorporated Submit Documentation Feedback 17
Product Folder Links: LP2957 LP2957A
PACKAGE OPTION ADDENDUM
www.ti.com 27-Oct-2016
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead/Ball Finish
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
LP2957AISX/NOPB ACTIVE DDPAK/
TO-263 KTT 5 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP2957AIS
LP2957AIT/NOPB ACTIVE TO-220 NDH 5 45 Green (RoHS
& no Sb/Br) CU SN Level-1-NA-UNLIM -40 to 125 LP2957AIT
LP2957ISX/NOPB ACTIVE DDPAK/
TO-263 KTT 5 500 Pb-Free (RoHS
Exempt) CU SN Level-3-245C-168 HR -40 to 125 LP2957IS
(1) The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
PACKAGE OPTION ADDENDUM
www.ti.com 27-Oct-2016
Addendum-Page 2
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
LP2957AISX/NOPB DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
LP2957ISX/NOPB DDPAK/
TO-263 KTT 5 500 330.0 24.4 10.75 14.85 5.0 16.0 24.0 Q2
PACKAGE MATERIALS INFORMATION
www.ti.com 23-Sep-2013
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
LP2957AISX/NOPB DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
LP2957ISX/NOPB DDPAK/TO-263 KTT 5 500 367.0 367.0 45.0
PACKAGE MATERIALS INFORMATION
www.ti.com 23-Sep-2013
Pack Materials-Page 2
MECHANICAL DATA
NDH0005D
www.ti.com
MECHANICAL DATA
KTT0005B
www.ti.com
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