Very low drop and low noise voltage regulator low ESR
capacitors compatible, with inhibit function
Features
■ Very low dropout voltage (280 mV at 150 mA
and 7 mV at 1 mA load)
■ Very low quiescent current (2 mA typ. at 150
mA load and 80 µA at no load)
■ Output current up to 150 mA
■ Logic controlled electronic shutdown
■ Output voltage of 1.8, 2.5, 2.8, 3, 3.1, 3.3, 5 V
■ Internal current and thermal limit
■ Low output noise voltage 30 mVrms
■ Smallest package SOT23-5L
■ Temperature range: - 40°C to 125 °C
Description
LD2985Bxx
SOT23-5L
between bypass pin and GND reduce the noise
to 30 µVrms. Typical application are in cellular
phone, palmtop laptop computer, personal digital
assistant (PDA), personal stereo, camcorder and
camera.
The LD2985Bxx is a 150 mA fixed output voltage
regulator. The ultra low drop voltage and the low
quiescent current make them particularly suitable
for low noise, low power applications, and in
battery powered systems. In sleep mode
quiescent current is less than 1 µA when INHIBIT
pin is pulled low. Shutdown logic control function
is available on pin 3 (TTL compatible). This
means that when the device is used as local
regulator, it is possible to put a part of the board in
standby, decreasing the total power consumption.
An external capacitor, C
= 10 nF, connected
BYP
Table 1. Device summary
Part numbers Order codes Output voltages
LD2985BXX18 LD2985BM18R 1.8 V
LD2985BXX25 LD2985BM25R 2.5 V
LD2985BXX28 LD2985BM28R 2.8 V
LD2985BXX30 LD2985BM30R 3.0 V
LD2985BXX31 LD2985BM31R 3.1 V
LD2985BXX33 LD2985BM33R 3.3 V
LD2985BXX50 LD2985BM50R 5.0 V
February 2012 Doc ID 8189 Rev 12 1/18
www.st.com
18
Contents LD2985Bxx
Contents
1 Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5 Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6 Application notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1 External capacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.3 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4 Important . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.5 Inhibit input operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.6 Reverse current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2/18 Doc ID 8189 Rev 12
LD2985Bxx Diagram
1 Diagram
Figure 1. Schematic diagram
Doc ID 8189 Rev 12 3/18
Pin configuration LD2985Bxx
2 Pin configuration
Figure 2. Pin connections (top view)
5
12
4
3
SC12360
Table 2. Pin description
Pin n° Symbol Name and function
1 IN Input port
2 GND Ground pin
Control switch ON/OFF. Inhibit is not internally pulled-up; it cannot be left
3 INHIBIT
4Bypass
5 OUT Output port
floating. Disable the device when connected to GND or to a positive
voltage less than 0.18V
Bypass pin: capacitor to be connected to GND in order to improve the
thermal noise performances
Table 3. Thermal data
Symbol Parameter Value Unit
R
thJC
R
thJA
4/18 Doc ID 8189 Rev 12
Thermal resistance junction-case 81 °C/W
Thermal resistance junction-ambient 255 °C/W
LD2985Bxx Maximum ratings
3 Maximum ratings
Table 4. Absolute maximum ratings
Symbol Parameter Value Unit
T
V
T
V
INH
I
O
P
STG
OP
I
D
DC input voltage 16 V
INHIBIT input voltage 16 V
Output current Internally limited
Power dissipation Internally limited
Storage temperature range -65 to 150 °C
Operating junction temperature range -40 to 125 °C
Note: Absolute maximum ratings are those values beyond which damage to the device may occur.
Functional operation under these condition is not implied.
Doc ID 8189 Rev 12 5/18
Electrical characteristics LD2985Bxx
4 Electrical characteristics
TJ = 25 °C, VI = VO + 1 V, IO = 50 mA, V
Table 5. Electrical characteristics
= 2 V, CI = CO = 1 µF, unless otherwise specified.
INH
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
V
V
V
V
V
V
V
V
V
V
V
Operating input voltage 2.5 16 V
OP
V
= 2.5V 1.463 1.5 1.537
I
O
O
O
O
O
O
O
O
O
O
O
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
= 1 to 150mA 1.455 1.545
O
= 1 to 150mA, TJ= -40 to 125°C 1.440 1.560
I
O
V
= 2.8V 1.755 1.8 1.845
I
= 1 to 150mA 1.746 1.854
O
= 1 to 150mA, TJ= -40 to 125°C 1.728 1.872
I
O
V
= 3.5V 2.437 2.5 2.562
I
= 1 to 150mA 2.425 2.575
O
= 1 to 150mA, TJ= -40 to 125°C 2.4 2.6
I
O
V
= 3.5V 2.633 2.7 2.767
I
= 1 to 150mA 2.619 2.781
O
= 1 to 150mA, TJ= -40 to 125°C 2.592 2.808
I
O
V
= 3.8V 2.73 2.8 2.87
I
= 1 to 150mA 2.716 2.884
O
= 1 to 150mA, TJ= -40 to 125°C 2.688 2.912
I
O
V
= 3.85V 2.779 2.85 2.921
I
= 1 to 150mA 2.764 2.935
O
= 1 to 150mA, TJ= -40 to 125°C 2.736 2.964
I
O
V
= 4.0V 2.925 3.0 3.075
I
= 1 to 150mA 2.91 3.09
O
= 1 to 150mA, TJ= -40 to 125°C 2.88 3.12
I
O
V
= 4.1V 3.023 3.1 3.177
I
= 1 to 150mA 3.007 3.193
O
= 1 to 150mA, TJ= -40 to 125°C 2.976 3.224
I
O
V
= 4.2V 3.120 3.2 3.28
I
= 1 to 150mA 3.104 3.296
O
= 1 to 150mA, TJ= -40 to 125°C 3.072 3.328
I
O
V
= 4.3V 3.218 3.3 3.382
I
= 1 to 150mA 3.201 3.399
O
= 1 to 150mA, TJ= -40 to 125°C 3.168 3.432
I
O
V
= 4.5V 3.413 3.5 3.587
I
= 1 to 150mA 3.395 3.605
O
= 1 to 150mA, TJ= -40 to 125°C 3.360 3.640
I
O
VI
VI
VI
VI
VI
VI
VI
VI
VI
VI
VI
6/18 Doc ID 8189 Rev 12
LD2985Bxx Electrical characteristics
Table 5. Electrical characteristics (continued)
Symbol Parameter Test conditions Min. Typ. Max. Unit
V
= 4.6V 3.51 3.6 3.69
I
ΔV
V
V
V
V
V
V
I
SC
O
DROP
O
O
O
O
O
Output voltage
Output voltage
Output voltage
Output voltage
Output voltage
= 1 to 150mA 3.492 3.708
O
= 1 to 150mA, TJ= -40 to 125°C 3.456 3.744
I
O
V
= 4.8V 3.705 3.8 3.895
I
= 1 to 150mA 3.686 3.914
O
= 1 to 150mA, TJ= -40 to 125°C 3.648 3.952
I
O
V
= 5.0V 3.900 4 4.100
I
= 1 to 150mA 3.88 4.12
O
= 1 to 150mA, TJ= -40 to 125°C 3.84 4.16
I
O
V
= 5.7V 4.583 4.7 4.817
I
= 1 to 150mA 4.559 4.841
O
= 1 to 150mA, TJ= -40 to 125°C 4.512 4.888
I
O
V
= 6.0V 4.875 5 5.125
I
= 1 to 150mA 4.85 5.15
O
= 1 to 150 mA, TJ= -40 to 125°C 4.8 5.2
I
O
Short circuit current RL = 0 400 mA
VI = VO + 1V to 16V, IO = 1 mA 0.003 0.014
/ΔVILine regulation
Dropout voltage
VI = VO + 1V to 16V, IO = 1 mA,
T
= -40 to 125°C
J
I
= 0 1 3
O
= 0, TJ= -40 to 125°C 5
I
O
= 1mA 7 10
I
O
= 1mA, TJ= -40 to 125°C 15
I
O
= 10mA 40 60
I
O
= 10mA, TJ= -40 to 125°C 90
I
O
= 50mA 120 150
I
O
= 50mA, TJ= -40 to 125°C 225
I
O
= 150mA 280 350
I
O
= 150mA, TJ= -40 to 125°C 575
I
O
0.032
VI
VI
VI
VI
VI
%/V
mV
I
Doc ID 8189 Rev 12 7/18
Electrical characteristics LD2985Bxx
Table 5. Electrical characteristics (continued)
Symbol Parameter Test conditions Min. Typ. Max. Unit
IO = 0 80 100
= 0, TJ= -40 to 125°C 150
I
O
= 1mA 100 150
I
O
= 1mA, TJ= -40 to 125°C 200
I
O
= 10mA 200 300
Quiescent current
ON MODE
I
Q
OFF MODE
SVR Supply voltage rejection C
Inhibit input logic low TJ= -40 to 125°C 0.15 V
IL
Inhibit input logic high TJ= -40 to 125°C 2 V
IH
Inhibit input current
Output noise voltage
N
I
V
V
INH
e
I
O
= 10mA, TJ= -40 to 125°C 400
I
O
= 50mA 600 900
I
O
= 50mA, TJ= -40 to 125°C 1200
I
O
= 150mA 2000 3000
I
O
= 150mA, TJ= -40 to 125°C 4000
I
O
V
<0.18V 0
INH
<0.18V, TJ= -40 to 125°C 2
V
INH
= 0.01µF, CO = 10µF, f = 1kHz 45 dB
BYP
V
= 0V, TJ= -40 to 125°C 5 15
INH
= 5V, TJ= -40 to 125°C 0 -1
V
INH
B = 300 Hz to 50 kHz, C
C
= 10µF
O
= 0.01µF,
BYP
30 µV
µA
µA
8/18 Doc ID 8189 Rev 12
LD2985Bxx Typical characteristics
5 Typical characteristics
TJ = 25 °C, VI = V
O(NOM)
+1 V, CI = 1 µF(X7R), CO = 2.2 µF(X7R), V
= 2 V, unless
INH
otherwise specified.
Figure 3. Output voltage vs. temperature
= 3.5 V)
(V
Figure 5. Dropout voltage vs. output current Figure 6. Quiescent current vs. load current
I
Figure 4. Dropout voltage vs. temperature
(VO = 2.5 V)
Figure 7. Quiescent current vs. temperature Figure 8. Supply voltage rejection vs. temp.
Doc ID 8189 Rev 12 9/18
Typical characteristics LD2985Bxx
Figure 9. Supply voltage rejection vs. output
current (C
= 10 µF)
O
Figure 11. Supply voltage rejection vs.
frequency (C
= 10 µF)
O
Figure 10. Supply voltage rejection vs. output
current (CO = 1 µF)
Figure 12. Supply voltage rejection vs.
frequency (CO = 1 µF)
Figure 13. Line transient (tr = tf = 500 ns) Figure 14. Line transient (tr = tf = 1 µs)
VO = 2.5V, IO = 50mA, no CI, CO = 4.7µF, tr=tf=500ns
VO = 2.5V, IO = 50mA, no CI, CO = 4.7µF, tr=tf=1µs
10/18 Doc ID 8189 Rev 12
LD2985Bxx Typical characteristics
Figure 15. Load transient (CO = 10 µF) Figure 16. Load transient (CO = 4.7 µF)
VO = 2.5V, IO = 0 to 50mA, no CI, CO = 10µF, tr=tf=500ns
VO = 2.5V, IO = 0 to 50mA, no CI, CO = 4.7µF, tr=tf=500ns
Doc ID 8189 Rev 12 11/18
Application notes LD2985Bxx
6 Application notes
6.1 External capacitors
Like any low-dropout regulator, the LD2985 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.
6.2 Input capacitor
An input capacitor whose value is 1 µF is required with the LD2985 (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.
6.3 Output capacitor
The LD2985 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. 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 V
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.
going from 1.8 to 3.3 V, and 3.3 µF for the other versions. However,
O
6.4 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.
6.5 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 V
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 V
V
. Any slew rate can be used to drive the inhibit.
IL
12/18 Doc ID 8189 Rev 12
to keep the regulator output ON at all times. To assure
I
IH
LD2985Bxx Application notes
6.6 Reverse current
The power transistor used in the LD2985 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 V
the output, the reverse current measured flows to the GND across the two feedback
resistors. This current typical value is 160 µA. R
and R2 resistors are implanted type;
1
typical values are, respectively, 42.6 kΩ and 51.150 kΩ.
Figure 17. Reverse current test circuit
voltage is applied on
REV
Doc ID 8189 Rev 12 13/18
Package mechanical data LD2985Bxx
7 Package mechanical data
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.
14/18 Doc ID 8189 Rev 12
LD2985Bxx Package mechanical data
SOT23-5L mechanical data
mm. mils.
Dim.
Min. Typ. Max. Min. Typ. Max.
A0.90 1.45 35.4 57.1
A1 0.00 0.10 0.0 3.9
A2 0.901.30 35.4 51.2
b 0.35 0.50 13.7 19.7
C0.09 0.20 3.5 7.8
D2.80 3.00 110.2 118.1
E 1.50 1.75 59.0 68.8
e0.95 37.4
H 2.60 3.00 102.3 118.1
L 0.10 0.60 3.9 23.6
7049676D
Doc ID 8189 Rev 12 15/18
Package mechanical data LD2985Bxx
Tape & reel SOT23-xL mechanical data
Dim.
Min. Typ. Max. Min. Typ. Max.
A180 7.086
C 12.8 13.0 13.2 0.504 0.512 0.519
D 20.2 0.795
N60 2.362
T 14.4 0.567
Ao 3.133.233.33 0.123 0.127 0.131
Bo 3.07 3.17 3.27 0.120 0.124 0.128
Ko 1.27 1.37 1.47 0.050 0.054 0.0.58
Po 3.9 4.0 4.1 0.153 0.157 0.161
P 3.9 4.0 4.1 0.153 0.157 0.161
mm. inch.
16/18 Doc ID 8189 Rev 12
LD2985Bxx Revision history
8 Revision history
Table 6. Document revision history
Date Revision Changes
22-Aug-2005 4 Add new value V
02-Sep-2005 5 Mistake V
25-Jul-2006 6 Order codes updated.
13-Feb-2008 7 Added:
04-Mar-2008 8 Modified:
10-Jul-2008 9 Modified:
27-Aug-2008 10 Modified
27-Jan-2009 11 Modified
09-Feb-2012 12
Modified: pin inhibit
Removed: order codes and electrical characteristics table for type A.
O
Table 1 on page 1
Table 5 on page 6
Table 1 on page 1
: Features on page 1
: Features on page 1
==> 2.7 V on tables 5 and 6.
O
min. ==> 2.7 V on table 5.
.
.
and
Table 5 on page 6
.
.
Figure 1 on page 3
.
.
Doc ID 8189 Rev 12 17/18
LD2985Bxx
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18/18 Doc ID 8189 Rev 12
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