LM4121
Precision Micropower Low Dropout Voltage Reference
LM4121 Precision Micropower Low Dropout Voltage Reference
General Description
The LM4121 is a precision bandgap voltage reference available in a fixed 1.25V and adjustable version with up to 5 mA
current source and sink capability.
This series reference operates with input voltages as low as
1.8V and up to 12Vconsuming 160 µA (Typ.) supply current.
In power down mode, device current drops to less than 2 µA.
The LM4121 comes in two grades A and Standard. The best
grade devices (A) have an initial accuracy of 0.2%, while the
standard have an initial accuracy of 0.5%, both with a
tempco of 50ppm/˚C guaranteed from −40˚C to +125˚C.
The very low operating voltage, low supply current and
power-down capability of the LM4121 makes this product an
ideal choice for battery powered and portable applications.
The device performance is guaranteed over the industrial
temperature range (−40˚C to +85˚C), while certain specs are
guaranteed over the extended temperature range (−40˚C to
+125˚C). Please contact National for full specifications over
the extended temperature range. The LM4121 is available in
a standard 5-pin SOT-23 package.
Features (LM4121-1.2)
n Small SOT23-5 package
n Low voltage operation
n High output voltage accuracy:0.2%
n Source and Sink current output:
n Supply current:160 µA Typ.
n Low Temperature Coefficient:50 ppm/˚C
n Enable pin
n Output voltages:1.25V and Adjustable
n Industrial temperature Range:−40˚C to +85˚C
n (For extended temperature range, −40˚C to 125˚C,
contact National Semiconductor)
±
5mA
Applications
n Portable, battery powered equipment
n Instrumentation and process control
n Automotive & Industrial
n Test equipment
n Data acquisition systems
n Precision regulators
n Battery chargers
n Base stations
n Communications
n Medical equipment
Block DiagramConnection Diagrams
DS101291-2
Refer to the Ordering Information Table in this Data Sheet for Specific
Part Number
Only four fields of marking are possible on the SOT-23’s small surface. This
table gives the meaning of the four fields.
Field Information
First Field:
R = Reference
Second and third Field:
19 = 1.250V Voltage Option
20 = Adjustable
Fourth Field:
A-B = Initial Reference Voltage Tolerance
±
A=
0.2%
±
B=
0.5%
LM4121 Supplied as
3000 Units, Tape and
Reel
Top
Marking
www.national.com2
LM4121
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The
guaranteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed
test conditions.
Note 2: Without PCB copper enhancements. The maximum power dissipation must be de-rated at elevated temperatures and is limited by T
junction temperature), θ
=(T
JMAX−TA
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.
Note 5: Limits are 100% production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control
(SQC) methods. The limits are used to calculate National’s Averaging Outgoing Quality Level (AOQL).
Note 6: Output noise for 1.25V option. Noise is proportional to V
Note 7: Bias Current flows out of the Adjust pin.
Note 8: Thermal hysteresis is defined as the change in +25˚C output voltage before and after exposing the device to temperature extremes.
Note 9: Long term stability is change in V
)/θ
J-A
Unless otherwise specified VIN= 3.3V, V
= 25˚C, and limits in boldface type apply over the −40˚C ≤ TA≤ +85˚C temperature
LM4121-1.25 Typical Operating Characteristics Unless otherwise specified, V
= 1.25V, I
Typical Temperature Drift
Line Regulation
LOAD
=0,C
= 0.022µF, TA= 25˚C and VEN=VIN.
OUT
DS101291-28
Long Term Drift
Load Regulation
= 3.3V, V
IN
DS101291-29
OUT
DS101291-30
DS101291-31
www.national.com9
LM4121-ADJ Typical Operating Characteristics Unless otherwise specified, V
= 1.2V, I
LM4121
Typical Temperature Drift
LOAD
=0,C
= 0.022µF, TA= 25˚C and VEN=VIN.
OUT
Long Term Drift
= 3.3V, V
IN
OUT
Dropout Voltage vs Output Error
DS101291-16
DS101291-47
DS101291-36
Dropout Voltage vs Load Current
DS101291-48
www.national.com10
LM4121
LM4121-ADJ Typical Operating Characteristics Unless otherwise specified, V
= 1.2V, I
Line Regulation
Adjust Pin Bias Current
LOAD
=0,C
= 0.022µF, TA= 25˚C and VEN=VIN. (Continued)
OUT
Load Regulation
DS101291-37
Change In Reference Voltage vs Output Voltage
= 3.3V, V
IN
DS101291-38
OUT
DS101291-39
DS101291-40
www.national.com11
LM4121-ADJ Typical Operating Characteristics Unless otherwise specified, V
= 1.2V, I
LM4121
LOAD
=0,C
= 0.022µF, TA= 25˚C and VEN=VIN. (Continued)
OUT
= 3.3V, V
IN
OUT
Bode Plot
DS101291-41
Bode Plot
DS101291-42
www.national.com12
Pin Functions
Output (Pin 5): Reference Output.
Input (Pin 4):Positive Supply.
Ground (Pin 2):Negative Supply or Ground Connection.
Enable (Pin 3):Pulled to input for normal operation. Forcing
this pin to ground will turn-off the output.
REF (Pin 1):REF Pin (1.25V option only). This pin should be
left unconnected for 1.25V option.
Adj (Pin 1):V
Adj Pin (Adjustable option only). See Ap-
OUT
plication Hints section.
Application Hints
The standard application circuit for the LM4121 is shown in
Figure 1
resistors, according to the following formula:
Values for R1 and R2 should be chosen to be less than 1
MΩ.I
and I
table. For best accuracy, be sure to take into account the
variation of V
The LM4121 is designed to be stable with ceramic output
capacitors in the range of 0.022µF to 0.047µF. Note that
0.022µF is the minimum required output capacitor. These
capacitors typically have an ESR of about 0.1 to 0.5Ω.
Smaller ESR can be tolerated, however larger ESR can not.
The output capacitor can be increased to improve load transient response, up to about 1µF. However, values above
0.047µF must be tantalum. With tantalum capacitors, in the
1µF range, a small capacitor between the output and the
reference (Adj) pin is required. This capacitor will typically be
in the 50pF range. Care must be taken when using output
capacitors of 1µF or larger. These application must be thoroughly tested over temperature, line and load. Also, when
the LM4121 is used as a controller, with external active
components, each application must be carefully tested to
ensure a stable design. The adjust pin is sensitive to noise
and capacitive loading. The trace to this pin must be as short
as possible and the feedback resistiors should be close to
this pin. Also, a single point ground to the LM4121 will help
ensure good accuracy at high load currents.
An input capacitor is typically not required. However, a 0.1µF
ceramic can be used to help prevent line transients from
entering the LM4121. Larger input capacitors should be
tantalum or aluminium.
The enable pin is an analog input with very little hysteresis.
About 6µA into this pin is required to turn the part on, and it
must be taken close to GND to turn the part off (see spec.
table for thresholds). There is a
pin of about 0.003V/µS to prevent glitches on the output. All
of these conditions can easily be met with ordinary CMOS or
TTL logic. If the shutdown feature is not required, then this
pin can safely be connected directly to the input supply.
Floating this pin is not recommended.
. The output voltage is set with the two feedback
V
=[V
OUT
typically flows out of the adjust pin. Values for V
bias
are found in the Electrical Characteristics Spec.
bias
REF
(1+ R1/R2] − I
ref
with input voltage, load and output voltage.
minimum
R1
•
bias
slew rate on this
LM4121
DS101291-32
DS101291-43
ref
Printed Circuit Board Layout Consideration
The mechanical stress due to PC board mounting can cause
the output voltage to shift from its initial value. References in
SOT packages are generally less prone to assembly stress
than devices in Small Outline (SOIC) package.
To reduce the stress-related output voltage shifts, mount the
reference on the low flex areas of the PC board such as near
to the edge or the corner of the PC board.
LM4121 Precision Micropower Low Dropout Voltage Reference
LIFE SUPPORT POLICY
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
Email: support@nsc.com
www.national.com
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.
National Semiconductor
Asia Pacific Customer
Response Group