LD2981

Ultra low-drop voltage regulators with inhibit

Datasheet - production data

Description
The LD2981 is a 100 mA fixed-output voltage
regulator. The low-drop voltage and the ultra low
quiescent current make them suitable for low
noise, low power applications and in battery
powered systems.
The quiescent current in sleep mode is less than
1 μA when INHIBIT pin is pulled low. Shutdown
logic control function is available on pin n° 3 (TTL
compatible). This means that when the device is
Features used as local regulator, it is possible to put a part
 Ultra low dropout voltage (0.17 V typ. at 100 of the board in standby, decreasing the total
mA load, 7 mV typ. at 1 mA load) power consumption. The LD2981 is designed to
 Very low quiescent current (80 μA typ. at no work with low ESR ceramic capacitor. Typical
load in on mode; max 1 μA in off mode) applications are in cellular phone, palmtop/laptop
 Guaranteed output current up to 100 mA computer, personal digital assistant (PDA),
 Logic-controlled electronic shutdown personal stereo, camcorder and camera.
 Output voltage of 2.5; 3.0; 3.3; 5.0 V
 Internal current and thermal limit
 ± 0.75% tolerance output voltage available
(A version)
 Output low noise voltage 160 μVRMS
 Temperature range: -40 to 125 °C
 Small package SOT23-5L and SOT-89
 Fast dynamic response to line and load
changes

April 2016 DocID6279 Rev 17 1/27

This is information on a product in full production. www.st.com
Contents LD2981

Contents
1 Diagram ............................................................................................ 5
2 Pin configuration ............................................................................. 6
3 Maximum ratings ............................................................................. 7
4 Typical application .......................................................................... 8
5 Electrical characteristics ................................................................ 9
6 Typical performance characteristics ........................................... 12
7 Application notes .......................................................................... 16
7.1 External capacitors.......................................................................... 16
7.2 Input capacitor................................................................................. 16
7.3 Output capacitor .............................................................................. 16
7.4 Important ......................................................................................... 16
7.5 Inhibit input operation ...................................................................... 16
7.6 Reverse current............................................................................... 17
8 Package information ..................................................................... 18
8.1 SOT-89 package information .......................................................... 18
8.2 SOT-89 packing information............................................................ 21
8.3 SOT23-5L package information ...................................................... 22
8.4 SOT23-5L packing information........................................................ 24
9 Ordering information..................................................................... 25
10 Revision history ............................................................................ 26

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LD2981 List of tables

List of tables
Table 1: Pin description .............................................................................................................................. 6
Table 2: Thermal data ................................................................................................................................. 6
Table 3: Absolute maximum ratings ........................................................................................................... 7
Table 4: Electrical characteristics for LD2981AB ....................................................................................... 9
Table 5: Electrical characteristics for LD2981C ........................................................................................ 10
Table 6: SOT-89 mechanical data ............................................................................................................ 19
Table 7: SOT-89 carrier tape mechanical data ......................................................................................... 21
Table 8: SOT23-5L package mechanical data ......................................................................................... 22
Table 9: SOT23-5L tape and reel mechanical data .................................................................................. 24
Table 10: Order codes .............................................................................................................................. 25
Table 11: Document revision history ........................................................................................................ 26

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List of figures LD2981

List of figures
Figure 1: Schematic diagram ...................................................................................................................... 5
Figure 2: Pin connections (top view) ........................................................................................................... 6
Figure 3: Application circuit ......................................................................................................................... 8
Figure 4: Output voltage vs temperature .................................................................................................. 12
Figure 5: Dropout voltage vs temperature ................................................................................................ 12
Figure 6: Line regulation vs temperature .................................................................................................. 12
Figure 7: Load regulation vs temperature ................................................................................................. 12
Figure 8: Dropout voltage vs temperature ................................................................................................ 13
Figure 9: Quiescent current vs temperature ............................................................................................. 13
Figure 10: Quiescent current vs output current ........................................................................................ 13
Figure 11: Off mode quiescent current vs temperature ............................................................................ 13
Figure 12: Quiescent current vs input voltage .......................................................................................... 13
Figure 13: Dropout voltage vs output current ........................................................................................... 13
Figure 14: Inhibit input current vs temperature ......................................................................................... 14
Figure 15: Inhibit voltage vs temperature ................................................................................................. 14
Figure 16: Supply voltage rejection vs frequency ..................................................................................... 14
Figure 17: Noise voltage vs frequency ..................................................................................................... 14
Figure 18: Best case: highest output version ........................................................................................... 14
Figure 19: Worst case: lowest output version ........................................................................................... 14
Figure 20: Load transient response .......................................................................................................... 15
Figure 21: Line transient response ........................................................................................................... 15
Figure 22: Reverse current test circuit ...................................................................................................... 17
Figure 23: SOT-89 package outline .......................................................................................................... 18
Figure 24: SOT-89 recommended footprint .............................................................................................. 20
Figure 25: SOT-89 carrier tape outline ..................................................................................................... 21
Figure 26: SOT23-5L package outline ...................................................................................................... 22
Figure 27: SOT23-5L recommended footprint .......................................................................................... 23
Figure 28: SOT23-5L tape and reel outline .............................................................................................. 24

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LD2981 Diagram

1 Diagram
Figure 1: Schematic diagram

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Pin configuration LD2981

2 Pin configuration
Figure 2: Pin connections (top view)

Table 1: Pin description

Pin n° Pin n°
Symbol Name and function
SOT23-5L SOT-89
1 3 VIN Input port
2 2 GND Ground pin
Control switch ON/OFF. Inhibit is not internally pulled-up; it
3 INHIBIT cannot be left floating. Disable the device when connected to
GND or to a positive voltage less than 0.18 V
4 NC Not connected
5 1 VOUT Output port

Table 2: Thermal data

Symbol Parameter SOT23-5L SOT-89 Unit
RthJC Thermal resistance junction-case 81 15 °C/W
RthJA Thermal resistance junction-ambient 255 110 °C/W

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LD2981 Maximum ratings

3 Maximum ratings
Table 3: Absolute maximum ratings
Symbol Parameter Value Unit
VI DC input voltage -0.3 to 16 V
VINH INHIBIT input voltage -0.3 to 16 V
IO Output current Internally limited
PD Power dissipation Internally limited
TSTG Storage temperature range -55 to 150 °C
TOP Operating junction temperature range -40 to 125 °C

Absolute maximum ratings are those values beyond which damage to the device
may occur. Functional operation under these condition is not implied.

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Typical application LD2981

4 Typical application
Figure 3: Application circuit

Inhibit pin is not internally pulled-up then it must not be left floating. Disable the
device when connected to GND or to a positive voltage less than 0.18 V.

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LD2981 Electrical characteristics

5 Electrical characteristics
(TJ = 25 °C, VI = VO(NOM) + 1 V, CI = 1 μF, CO = 2.2 μF, IO = 1 mA, VINH = 2 V, unless
otherwise specified).
Table 4: Electrical characteristics for LD2981AB
Symbol Parameter Test conditions Min. Typ. Max. Unit
Operating input
VOP 2.5 16 V
voltage
IO = 1 mA 2.977 3 3.023
VO Output voltage IO = 1 to 100 mA 2.97 3.03 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 2.925 3.075
IO = 1 mA 3.275 3.3 3.325
VO Output voltage IO = 1 to 100 mA 3.267 3.333 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 3.217 3.383
IO = 1 mA 4.962 5 5.038
VO Output voltage IO = 1 to 100 mA 4.95 5.05 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 4.875 5.125
VO(NOM) + 1 < VIN < 16 V, IO = 1 mA 0.003 0.014
ΔVO Line regulation %/V
TJ = -40 to 125 °C 0.032
IO = 0 80 100
IO = 0, TJ = -40 to 125 °C 150
IO = 1 mA 100 150
Quiescent IO = 1 mA, TJ = -40 to 125 °C 200
current ON
MODE IO = 25 mA 250 400
IQ µA
IO = 25 mA, TJ = -40 to 125 °C 800
IO = 100 mA 1000 1300
IO = 100 mA, TJ = -40 to 125 °C 2600
VINH < 0.3 V 0.8
OFF MODE
VINH < 0.15 V, TJ = -40 to 125 °C 2
IO = 0 1 3
IO = 0, TJ = -40 to 125 °C 5
IO = 1 mA 7 10

Dropout IO = 1 mA, TJ = -40 to 125 °C 15

VDROP mV
voltage (1) IO = 25 mA 70 100
IO = 25 mA, TJ = -40 to 125 °C 150
IO = 100 mA 180 250
IO = 100 mA, TJ = -40 to 125 °C 375
Short circuit
ISC RL = 0 150 mA
current

DocID6279 Rev 17 9/27

Electrical characteristics LD2981
Symbol Parameter Test conditions Min. Typ. Max. Unit
Supply voltage
SVR CO = 10 µF, f = 1 KHz 63 dB
rejection

Inhibit input logic LOW = Output OFF,

VINH 0.18 V
low TJ = -40 to 125 °C

Inhibit input logic HIGH = Output ON,

VINL 1.6 V
high TJ = -40 to 125 °C

Inhibit input VINH = 0 V, TJ = -40 to 125 °C 0 -1

IINH µA
current VINH = 5 V, TJ = -40 to 125 °C 5 15
Output noise
eN BW = 300 Hz to 50 KHz, CO = 10 µF 160 µVRMS
voltage

Thermal
TSHDN 170 °C
shutdown

Notes:
(1)For VO < 2.5 V dropout voltage can be calculated according to the minimum input voltage in full temperature
range.

(TJ = 25 °C, VI = VO(NOM) +1 V, CI = 1 μF, CO = 2.2 μF, IO = 1 mA, VINH = 2 V, unless

otherwise specified)

Table 5: Electrical characteristics for LD2981C

Symbol Parameter Test conditions Min. Typ. Max. Unit

Operating input
VOP 2.5 16 V
voltage

IO = 1 mA 2.468 2.5 2.531

VO Output voltage IO = 1 to 100 mA 2.45 2.55 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 2.412 2.587
IO = 1 mA 2.962 3 3.037
VO Output voltage IO = 1 to 100 mA 2.94 3.06 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 2.895 3.105
IO = 1 mA 3.258 3.3 3.341
VO Output voltage IO = 1 to 100 mA 3.234 3.366 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 3.184 3.415
IO = 1 mA 4.937 5 5.062
VO Output voltage IO = 1 to 100 mA 4.9 5.1 V
IO = 1 to 100 mA, TJ = -40 to 125 °C 4.825 5.175
VO(NOM) + 1 < VIN < 16 V, IO = 1 mA 0.003 0.014
ΔVO Line regulation %/V
TJ = -40 to 125 °C 0.032

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LD2981 Electrical characteristics
Symbol Parameter Test conditions Min. Typ. Max. Unit
IO = 0 80 100
IO = 0, TJ = -40 to 125 °C 150
IO = 1 mA 100 150
Quiescent IO = 1 mA, TJ = -40 to 125 °C 200
current
ON MODE IO = 25 mA 250 400
IQ µA
IO = 25 mA, TJ = -40 to 125 °C 800
IO = 100 mA 1000 1300
IO = 100 mA, TJ = -40 to 125 °C 2600
VINH < 0.3 V 0.8
OFF MODE
VINH < 0.15 V, TJ = -40 to 125 °C 2
IO = 0 1 3
IO = 0, TJ = -40 to 125 °C 5
IO = 1 mA 7 10

Dropout IO = 1 mA, TJ = -40 to 125 °C 15

VDROP mV
voltage (1) IO = 25 mA 70 100
IO = 25 mA, TJ = -40 to 125 °C 150
IO = 100 mA 180 250
IO = 100 mA, TJ = -40 to 125 °C 375
Short circuit
ISC RL = 0 150 mA
current
Supply voltage
SVR CO = 10 µF, f = 1 KHz 63 dB
rejection

Inhibit input LOW = Output OFF,

VINH 0.18 V
logic low TJ = -40 to 125 °C

Inhibit input HIGH = Output ON,

VINL 1.6 V
logic high TJ = -40 to 125 °C

Inhibit input VINH = 0 V, TJ = -40 to 125 °C 0 -1

IINH μF
current VINH = 5 V, TJ = -40 to 125 °C 5 15
Output noise
eN BW = 300 Hz to 50 KHz, CO = 10 µF 160 µVRMS
voltage
Thermal
TSHDN 170 °C
shutdown

Notes:
(1)For VO < 2.5 V dropout voltage can be calculated according to the minimum input voltage in full temperature
range.

DocID6279 Rev 17 11/27

Typical performance characteristics LD2981

6 Typical performance characteristics

(TJ = 25 °C, VI = VO(NOM) +1 V, CI = 1 μF, CO = 2.2 μF, VINH = 2 V, unless otherwise
specified).
Figure 4: Output voltage vs temperature Figure 5: Dropout voltage vs temperature

Figure 6: Line regulation vs temperature Figure 7: Load regulation vs temperature

12/27 DocID6279 Rev 17

LD2981 Typical performance characteristics
Figure 8: Dropout voltage vs temperature Figure 9: Quiescent current vs temperature

Figure 11: Off mode quiescent current vs

Figure 10: Quiescent current vs output current
temperature

Figure 12: Quiescent current vs input voltage Figure 13: Dropout voltage vs output current

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Typical performance characteristics LD2981
Figure 14: Inhibit input current vs temperature Figure 15: Inhibit voltage vs temperature

Figure 16: Supply voltage rejection vs frequency Figure 17: Noise voltage vs frequency

Figure 18: Best case: highest output version Figure 19: Worst case: lowest output version

14/27 DocID6279 Rev 17

LD2981 Typical performance characteristics
Figure 20: Load transient response Figure 21: Line transient response

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Application notes LD2981

7 Application notes
7.1 External capacitors
Like any low-dropout regulator, the LD2981 requires external capacitors for regulator
stability. This capacitor must be selected to meet the requirements of minimum capacitance
and equivalent series resistance. We suggest to solder input and output capacitors as
close as possible to the relative pins.

7.2 Input capacitor

An input capacitor whose value is 1 μF is required with the LD2981 (amount of capacitance
can be increased without limit). This capacitor must be located a distance of not more than
0.5" from the input pin of the device and returned to a clean analog ground. Any good
quality ceramic, tantalum or film capacitors can be used for this capacitor.

7.3 Output capacitor

The LD2981 is designed specifically to work with ceramic output capacitors. It may also be
possible to use Tantalum capacitors, but these are not as attractive for reasons of size and
cost. By the way, the output capacitor must meet both the requirement for minimum
amount of capacitance and ESR (equivalent series resistance) value. The Figure 18: "Best
case: highest output version" and Figure 19: "Worst case: lowest output version" show the
allowable ESR range as a function of the output capacitance. These curves represent the
stability region over the full temperature and IO range. Due to the different loop gain, the
stability improves for higher output versions and so the suggested minimum output
capacitor value, if low ESR ceramic type is used, is 1 μF for output voltages equal or major
than 3.8 V, 2.2 μF for output voltages from 2.85 to 3.3 V, and 3.3 μF for the other versions.
However, if an output capacitor lower than the suggested one is used, it’s possible to make
stable the regulator adding a resistor in series to the capacitor (see Figure 18: "Best case:
highest output version" and Figure 19: "Worst case: lowest output version" to choose the
right value according to the used version and keeping in account that the ESR of ceramic
capacitors has been measured @ 100 kHz).

7.4 Important
The output capacitor must maintain its ESR in the stable region over the full operating
temperature to assure stability. Also, capacitor tolerance and variation with temperature
must be considered to assure the minimum amount of capacitance is provided at all times.
This capacitor should be located not more than 0.5" from the output pin of the device and
returned to a clean analog ground.

7.5 Inhibit input operation

The inhibit pin can be used to turn OFF the regulator when pulled low, so drastically
reducing the current consumption down to less than 1 μA. When the inhibit feature is not
used, this pin must be tied to VI to keep the regulator output ON at all times. To assure
proper operation, the signal source used to drive the inhibit pin must be able to swing
above and below the specified thresholds listed in the electrical characteristics section
under VIH VIL. Any slew rate can be used to drive the inhibit.

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LD2981 Application notes
7.6 Reverse current
The power transistor used in the LD2981 has not an inherent diode connected between the
regulator input and output. If the output is forced above the input, no current will flow from
the output to the input across the series pass transistor. When a VREV voltage is applied on
the output, the reverse current measured, according to the test circuit in Figure 22:
"Reverse current test circuit", flows to the GND across the two feedback resistors. This
current typical value is 160 μA. R1 and R2 resistors are implanted type; typical values are,
respectively, 42.6 kΩ and 51.150 kΩ.
Figure 22: Reverse current test circuit

DocID6279 Rev 17 17/27

Package information LD2981

8 Package information
In order to meet environmental requirements, ST offers these devices in different grades of
ECOPACK® packages, depending on their level of environmental compliance. ECOPACK ®
specifications, grade definitions and product status are available at: www.st.com.
ECOPACK® is an ST trademark.

8.1 SOT-89 package information

Figure 23: SOT-89 package outline

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LD2981 Package information
Table 6: SOT-89 mechanical data
mm
Dim.
Min. Typ. Max.
A 1.40 1.60
B 0.44 0.56
B1 0.36 0.48
C 0.35 0.44
C1 0.35 0.44
D 4.40 4.60
D1 1.62 1.83
D3 0.90
E 2.29 2.60
e 1.42 1.57
e1 2.92 3.07
H 3.94 4.25
H1 2.70 3.10
K 1° 8°
L 0.89 120
R 0.25
β 90°

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Package information LD2981
Figure 24: SOT-89 recommended footprint

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LD2981 Package information
8.2 SOT-89 packing information
Figure 25: SOT-89 carrier tape outline

Table 7: SOT-89 carrier tape mechanical data

mm
Dim.
Value Tolerance
Ao 4.91 ± 0.10
Bo 4.52 ± 0.10
Ko 1.90 ± 0.10
F 5.50 ± 0.10
E 1.75 ± 0.10
W 12 ± 0.30
P2 2 ± 0.10
Po 4 ± 0.10
P1 8 ± 0.10
T 0.30 ± 0.10
D Ø 1.55 ± 0.05
D1 Ø 1.60 ± 0.10

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Package information LD2981
8.3 SOT23-5L package information
Figure 26: SOT23-5L package outline

Table 8: SOT23-5L package mechanical data

mm
Dim.
Min. Typ. Max.
A 0.90 1.45
A1 0 0.15
A2 0.90 1.30
b 0.30 0.50
c 0.09 0.20
D 2.95
E 1.60
e 0.95
H 2.80
L 0.30 0.60
θ 0° 8°

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LD2981 Package information
Figure 27: SOT23-5L recommended footprint

Dimensions are in mm

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Package information LD2981
8.4 SOT23-5L packing information
Figure 28: SOT23-5L tape and reel outline

A D N

T
Po

Bo
Ko Ao P

Table 9: SOT23-5L tape and reel mechanical data

mm
Dim.
Min. Typ. Max.
A 180
C 12.8 13.0 13.2
D 20.2
N 60
T 14.4
Ao 3.13 3.23 3.33
Bo 3.07 3.17 3.27
Ko 1.27 1.37 1.47
Po 3.9 4.0 4.1
P 3.9 4.0 4.1

24/27 DocID6279 Rev 17

LD2981 Ordering information

9 Ordering information
Table 10: Order codes
AB version C version
Output voltage
SOT23-5L SOT-89 SOT23-5L SOT-89
LD2981CM25TR 2.5 V
LD2981ABM30TR LD2981CM30TR 3.0 V
LD2981ABM33TR LD2981ABU33TR LD2981CM33TR LD2981CU33TR 3.3 V
LD2981ABM50TR LD2981ABU50TR LD2981CM33TR LD2981CU50TR 5.0 V

DocID6279 Rev 17 25/27

Revision history LD2981

10 Revision history
Table 11: Document revision history
Date Revision Changes
25-Jul-2006 12 Order codes updated.
14-Feb-2008 13 Added: Table 1 on page 1.
14-Jul-2008 14 Modified: Table 1 on page 1 and Table 10 on page 23.
Document name changed from LD2981ABxx and
LD2981Cxx to LD2981. Updated Table 4 and Table 5.
25-Nov-2013 15 Updated Section 8: Package information and Section
8.4: SOT-89 packing information. Minor text changes
in title, in features and description in cover page.
Updated Section 8: Package information. Minor text
16-Mar-2015 16
changes.
Updated Section 8: "Package information".
01-Apr-2016 17
Minor text changes.

26/27 DocID6279 Rev 17

LD2981

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DocID6279 Rev 17 27/27