Bay Linear LP2951AM-3, LP2951AM, LP2951BM-5, LP2951BM-3.3, LP2951BM-3 Datasheet

Bay Linear, Inc

2478 Armstrong Street, Livermore, CA 94550 Tel: [phone], Fax: [phone] www.baylinear.com

100mA Low Dropout Voltage Regulator

LP2950/LP2951

Pin Connection

TO-92 (Z)

Ordering Information

8SOIC (M)

Package Tolerance

0.5% 1%

TO-92

LP2950AZ-XX LP2950-BZ-XX

8SOIC

LP2951AM-XX LP2951BM-XX

“XX” Voltage Selection Guide

Vout XX Code

5.0V

5

3.3V

3.3

3.0V

3

Adjustable

Left Blank

Description

The Bay Linear LP2950 and LP2951 are low power voltage
regulators. They are excellent choice for use in Battery
Powered applications such notebooks computers. The LP2950
and LP2951 feature low quiescent current ( 75µA Typ.) and
low dropout of 40mV at light loads 380mV (typ.) at 100mA.
With a tight initial tolerance of 0.5% typ., extremely good load
and line regulation of 0.05% typ. And very low output
temperature coef ficien t makin g th e LP 2950 an d LP2 95 1 u seful
as a low power reference.

The Bay Linear LP2950 is available in fixed voltages of 3.0V,

3.3V, and 5.0V in a TO-9 2 package.

The Bay Linear LP2951 co mes in an 8SOIC package and h as
an adjustable output voltage from 1.24V to 29V programmed
with a pair of external resistor. It also features pin-strap
capability providing the fixed voltage of 3.0, 3.3V or 5V for
convenience. The LP29 51 has an error flag ou tpu t feature used
as power-on reset for warning of low output voltage due to
falling battery voltages. Also, the logic compatible shutdown
input enables the regulator to be switched ON and OFF.

Features

•

Guaranteed 100mA Output

•

5.0V, 3.3V and 3.0V Versions

•

Very Low Quiescent Current

•

Low Dropout Voltage

•

Extremely Tight Load and Line
Regulation

•

Very Low Temperature Coefficient

•

Needs only 1µµµµF for Stability

•

Error Flag warns of output dropout

•

Logic-Controlled Electronic Shutdow n

•

Output programmable from 1.24V to 29V

Applications

• Battery Powered Systems

• Portable instrumentation

• Notebooks Computers

• Potable Consumer Equipment

• Automotive electronics

• SMPS Post-Regulator

Bay Linear

Bay LinearBay Linear

Bay Linear

Linear Excellenc e

1

2

4

3

5

6

7

8

Output

Input

Shutdown

Sense

-XX V tap

Feedback

Ground

Error

Vout

Vin

Grd

Bay Linear, Inc

2478 Armstrong Street, Livermore, CA 94550 Tel: [phone], Fax: [phone] www.baylinear.com

LP2950/LP2951

Absolute Maximum Rating

Parameter

Power Dissipation Internally Limited
Lead Temperature ( Soldering 5 seconds )

260 °C

Storage Temperature Range

-65 °C to +150 °C

Operating Junction Temperature

-55 °C to +150 °C
Input Supply Voltage -0.3V to +30V
Feedback Input Voltage -1.5V to +30V
Shutdown Input Voltage -0.3V to +30V
Error Comparator Output -0.3V to +30V

Electrical Characteristics

(VS = 15V, TA = 25°C , unless otherwise specified)

Parameter Conditions MIN TYP MAX UNIT

Output Voltage

-25 °C ≤ T

j

≤

85 °C

Full Operating Temperature

0.985 [ V

o

]

0.98 [ V

o

]

V

o

1.015 [ Vo ]

1.02 [ V

o

]

V

Output Voltage

100µA ≤ I

L

≤

100mA, T

j

≤ T

jmax

0.976 [Vo ] Vo 1.024 [ Vo ]

V

Output Voltage Temperature
Coefficient

(Note 1) 50 150

ppm / ° C

Line Regulation (Note 3)

V

O

+ 1V ≤ VIN ≤ 30V (Note 4)

0.04 0.4 %

Load Regulation (Note 5)

100µA ≤ I

L

≤

100mA

0.1 0.3 %

Dropout Voltage

I

L

= 100µA

IL = 100mA

50

380

80

450

mV

Ground Current

I

L

= 100µA

IL = 100mA

75 8 120

12

µ

A

mA

Dropout Ground Current

V

IN

= VO - 0.5V, IL = 100µA

110 170

µ

A

Current Limit V

OUT

= 0 160 200 mA
Thermal Regulation 0.05 0.2 % / W
Output Noise,

10Hz to 100KHz

C

L

= 1µF

C

L

= 200µF

C

L

= 3.3µF
(Bypass = 0.01 µF pins 7 to 1 for
LP2951-XX)

430

160
100

µ

Vrms

8 pin Versions only (LP2951)

Reference Voltage

Over temperature

1.21

1.185

1.235 1.26

1.285

V

Feedback Pin Bias Current 20 40

η

A

Reference Voltage Temperature
Coefficient

(Note 7) 50

ppm/°C

Feedback Pin Bias Current
Temperature Coefficient

0.1 100

ηA/°

C

Error Comparator

Output Leakage Current VOH = 30V 0.01 1.0

µ

A

Output Low Voltage

V

IN

4.5V, IOL = 400µA

150 250 mV
Upper Threshold Voltage (Note 8) 40 60 mV
Lower Threshold Voltage (Note 8) 75 95 mV
Hysteresis (Note 8) 15 mV

Bay Linear, Inc

2478 Armstrong Street, Livermore, CA 94550 Tel: [phone], Fax: [phone] www.baylinear.com

LP2950/LP2951

Parameter Conditions MIN TYP MAX UNIT

Shutdown Input

Input Logic Vol tage Low (Regulator ON)

High (Regulator OFF)

2

1.3 0.7 V

Shutdown Pin Input Current VS = 5V

V

S

=30V

30

450

50

600

µ

A

Regulator Output Current
in Shutdown

(Note 9)
V

OUT

= 5.0V

3.3V ≤ V

OUT

≤

5.0V

2.0V ≤ V

OUT

≤

3.3V

3

10
20
30

µ

A

Note 1:

Output or reference voltage temperature coefficient s defined as the worst case voltage change di vided by the total temperature range.

Note 2:

Unless otherwise sp ecified all limits guaranteed for T

J

= 25°C, VIN = VO +1V, IL = 100µA and CL = 1µF. Additional conditions for the 8-

pin versions are feedback tied to –XX Voltage tap and output tied to output Sense pin ( V

OUT

= XX V) and V

SHUTDOWN

≤ 0.8V

Note 3:

Regulation is meas ured at constant junction temperat ure , using pulse testing with a low dut y cycle. Changes in output voltage due to

heating effects are covered under sp ecification for therm al regulation.

Note 4:

Line regulation for LP2951-XX is tested at 150°C for I

L

= 1mA. For IL = 100µA and TJ = 125°C, line regulation is guaranteed by design

to 0.2%. See typical performance characteristics for line regulation versus temperature and load current.

Note 5:

Dropout voltage is defi ned as the input to output differential at which the output voltage drops 100mV below its nominal value measured
at 1V differenti al. At very low values of programmed output voltage, the minimum input supply voltag e of 2V (2.3V over tempera ture) must be
taken into account.

Note 6:

V

REF

≤ V

OUT

≤ (V

IN

–1V), 2.3V ≤ VIN ≤ 30V, 100µA ≤ IL ≤100mA, T

J

≤ T

JMAX

Note 7:

Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range

Note 8:

Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference voltage
measured at V

O

+ 1V input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = V

OUT

/ V

REF

=
(R1 + R2)/R2. For example, at a programmed output voltage of 5V, the error output is guaranteed to go low when the output drops by 95mV X
5V / 1.235V = 384mV. Thresholds remain constant as a percent of V

OUT

as V

OUT

is varied, with the dropout warning oc curring at typically 5%

below nominal, 7.5% guaranteed.

Note 9:

V

SHUTDOWN

≥ 2V, VIN ≤ 30V, V

OUT

= 0, Feed-back pin tied to –XX Voltage Tap.

Block Diagram

FEEDBACK

INPUT

OUTPUT

UNREGULATED DC

SHUTDOWN

GROUND

ERROR

______

5V TAP

SENSE

5V @ 150mA

MAX

TO CMOS OR
TTL

REFERENCE

ERROR DETECTION
COMPARATOR

ERROR
AMPLIFIER

1.23V

FROM
CMOS OR
TTL

+

+

+

+

+

+

60 mV

3

7

8

1

2

6

5

4

Ω

..

60k

330k

180k

Ω

..

Ω

..

µ

..1F

_

_

LP2950 and LP2951 Block Diagram

FEEDBACK

INPUT

OUTPUT

UNREGULATED DCUNREGULATED DC

SHUTDOWN

GROUND

ERROR

______

5V TAP

SENSE

5V @ 150mA

MAX

5V @ 150mA

MAX

TO CMOS OR
TTL

TO CMOS OR
TTL

REFERENCE

ERROR DETECTION
COMPARATOR

ERROR DETECTION
COMPARATOR

ERROR
AMPLIFIER

ERROR
AMPLIFIER

1.23V

FROM
CMOS OR
TTL

FROM
CMOS OR
TTL

+

+

+

+

+

+

60 mV

3

7

8

1

2

6

5

4

Ω..Ω

..

60k

330k

180k

Ω..Ω

..

Ω..Ω

..

µ..µ

..1F

_

_

LP2950 and LP2951 Block Diagram

Bay Linear, Inc

2478 Armstrong Street, Livermore, CA 94550 Tel: [phone], Fax: [phone] www.baylinear.com

LP2950/LP2951

APPLICATION HINTS
EXTERNAL CAPACITORS

The stability of the LP2950/LP2951 requires a 1.0µF or greater
capacitor between output and ground. Oscillation could occur
without this capacitor. Most types of tantalum or aluminum
electrolytic works fine here. For operations below -25°C solid
tantalum is recommended since many aluminum types have
electrolytes that freez e at about -30°C. The ESR of about 5Ω or
less and resonant frequency above 500kHz are the most important
parameters in the value of th e capacitor. The capaci tor value can
be increased without limit.
At lower values of output current, less output capacitance is
required for stability. For the currents below 10mA the value of
the capacitor can be reduced to 0.5µF and 0.15µF for 1mA. More
output capacitance is needed for the 8-pin version at voltages
below 5V since it runs the error amplifier at lower gain. At worst
case 5µF or greater must be used for the condition of 150mA load
at 1.23V output.
The LP2950, unlike other low dropout regulators will remain
stable in regulation with no load in addition to the internal voltage
divider. This feature is especially important in applications like
CMOS RAM keep-alive. When setting the output volt age of the
LP2951 version with external resistors, a minimum load of 1uA is
recommended.
If there is mor e than 10 inches of wire between the input and the
AC filter cap acitor or if a battery is used as th e input then a 1µA
tantalum or aluminum electrolytic capacitor should be placed from
the input to the ground.
Instability can occur if there is stray capacitance to the LP2951
feedback terminal (pin 7). This could cause more problems when
using a higher va lue of extern al resis tors to set the ou tput volt age.
This problem can be fixed by adding a 100pF capacitor between
output and feedb ack and in creas ing the outpu t capac itor to at least

3.3µF.

ERROR DETECTION COMPARATOR
OUTPUT

The Comparator produces a logic low output whenever the
LP2951 output fa lls out of regulation by more than around 5%.

This is around 60mV offset divi ded by t he 1.23 5 referen ce volt age.
This trip level remains 5% below normal regardless of the
programmed outp ut voltage of the regulator. Figure 1 shows the
timing diagram depicting the ERROR signal and the regulator.
output voltage as the LP2951 input is ramped up and down. The
ERROR signal becomes low at around 1.3V input, and goes high
around 5V input (input voltage at which V

OUT

= 4.75 ). Since the
LP2951’s drop out voltage is loa d dependent, the input volta ge trip
point (around 5V) will vary with the load current. The output
voltage trip poin t (approx. 4.75V) does not vary with load

The error comparator has an open-collector output which requires
an external pull-up resistor. Depending on the system requirements
the resistor ma y be retu rned to 5 V output or oth er supp ly volta ge in
determining the value of this resistor, note that the output is rated to
sink 400µA, this value adds to battery drain in a low battery
condition. Suggested values range from 100K to 1MΩ. If the
output is unused this resistor is not required.

PROGRAMMING THE OUTPUT VOLTAGE OF
LP2951

The LP2951 may be pin-strapped for 5V using its internal voltage
divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback)
to Pin 6 (5V Tap). Also it may be programmed for any output
voltage between i ts 1.235 V referenc e and it s 30V maximu m ratin g .
As seen in Figure 2, an external pair of resistors is required.
Refer to the below equation for the programming of the output
voltage.

V

OUT

= V

REF

× ( 1 + R1/R2 )+ IFBR

1

The V

REF

is 1.235 and IFB is the feedback bias current, nominally

-20 nA. The minimum recommended load current of 1µA forces an
upper limit of 1.2 MΩ on value of R

2

. If no load presented the IFB

produces an error of typi call y 2% in V

OUT

which may be eliminated

at room temperature by trimming R

1

. To improve the accuracy

choose the valu e of R

2

= 100k this reduces th e error by 0.17% and

increases the resistor program current by 12µA. Since the LP2951
typically draws 60µA at no load with Pin 2 open-circuited this is a
small price to pay.

REDUCING OUTPUT NOISE

It may be an advantage to reduce the AC noise present at the output.
One way is to reduce the regulator bandwidth by increasing the size
of the output capacitor. This is the only way that noise can be
reduced on the LP2950 but is relatively inefficient, as increasing the
capacitor from 1µF to 220 µF only decreases the noise f rom 4 30µV
to 160µV

RMS

. for a 100kHz bandwidth at 5V output.
Noise could also be reduced fourfold by a bypass capacitor across
R

1

, since it reduces the high frequency gain from 4 to unity. Pick

C

BYPASS

≅ 1 / 2πR

1

× 200 Hz

or choose 0.01 µF. When doing this, the output capacitor must be
increased to 3.3µF to maintain st ability. Th ese chan ges reduc e the
output noise from 4 30µV to 100µV

RMS

. for a 100kHz bandwidth at
5V output. With the bypass capacitor added, noise no longer scales
with output voltage so that improvements are more dramatic at
higher output volt ages.

+

+

+

+

4.75V

OUTPUT

VOLTAGE

ERROR*

_______

INPUT

VOLTAGE 1.3V

5.0V

Figure 1. ERROR Output Timing

_______

* See Application Info.