NSC LP3878 Micropower 800ma low noise ceramic stable voltage regulator for low voltage applications designed for use with very low esr output capacitor Datasheet

LP3878
Micropower 800mA Low Noise "Ceramic Stable" Voltage
Regulator for Low Voltage Applications
Designed for Use with Very Low ESR Output Capacitors
General Description
Features
The LP3878 is a 800 mA fixed-output voltage regulator
designed to provide high performance and low noise in
applications requiring output voltages between 1.0V and
1.2V.
Output noise can be reduced to 18µV (typical) by connecting
an external 10 nF capacitor to the bypass pin.
Using an optimized VIP™ (Vertically Integrated PNP) process, the LP3878 delivers superior performance:
Ground Pin Current: Typically 5 mA @ 800 mA load, and
180 µA @ 100 µA load.
Sleep Mode: The LP3878 draws less than 2.0 µA quiescent
current when shutdown pin is pulled low.
Precision Output: Guaranteed output voltage accuracy is
1% at room temperature.
n Standard output voltage: 1.00V
n Custom voltages available from 1.0V to 1.2V (50 mV
increments)
n Input voltage: 2.2 to 6.0V
n 1% initial output accuracy
n Guaranteed 800 mA continuous output current
n Designed for use with low ESR ceramic capacitors
n Very low output noise with external capacitor
n Sense option improves load regulation
n 8 Lead LLP surface mount package
n < 2.0 µA quiescent current in shutdown
n Low ground pin current at all loads
n High peak current capability (1200 mA typical)
n Overtemperature/overcurrent protection
n 0˚C to +125˚C junction temperature range
Applications
n ASIC Power Supplies In:
- Desktops, Notebooks and Graphic Cards
- Set Top Boxes, Printers and Copiers
n DSP and FPGA Power Supplies
n SMPS Post-Regulator
Basic Application Circuit
20086803
*Capacitance values shown are minimum required to assure stability, but may be increased without limit. Larger output capacitor provides improved dynamic
response. Output capacitor must meet ESR requirements (see Application Hints).
**Shutdown must be actively terminated (see App. Hints). Tie to INPUT (Pin4) if not used.
LP3878 Micropower 800mA Low Noise "Ceramic Stable" Voltage Regulator for Low Voltage
Applications
Designed for Use with Very Low ESR Output Capacitors
November 2004
VIP™ is a trademark of National Semiconductor Corporation.
© 2004 National Semiconductor Corporation
DS200868
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LP3878
Block Diagram
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LP3878
Connection Diagram
8 Lead LLP Surface Mount Package (SD)
20086850
Top View
See NS Package Number SDC08A
Ordering Information
TABLE 1. Package Marking and Ordering Information
Output Voltage*
Grade
Order Information
Supplied as:
1.0
STD
LP3878SD-1.0
1000 Units on Tape and Reel
1.0
STD
LP3878SDX-1.0
4500 Units on Tape and Reel
8 Lead LLP
* For other voltages between 1.0V and 1.2V, contact National Semiconductor sales office.
Pin Description
PIN
NAME
1
BYPASS
Optional low noise feature. A small value capacitor connected between
BYPASS and GROUND lowers output noise voltage level (100pF 10nF).
2
N/C
DO NOT CONNECT. This pin is used for post package test and should
be left floating.
3
GROUND
4
INPUT
5
OUTPUT
6
SENSE
APPLICATION INFORMATION
Device ground.
Input source voltage.
Regulated output voltage.
Remote sense. Tie directly to output or remotely at point of load for best
regulation.
7
N/C
8
SHUTDOWN
Enabled above turn-on threshold voltage. Pull to ground to disable.
No internal connection.
LLP
DAP
SUBSTRATE
The exposed die attach pad should be connected to a thermal pad at
ground potential. For additional information on using National
Semiconductor’s No Pull Back LLP package, please refer to LLP
application note AN-1187.
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LP3878
Absolute Maximum Ratings (Note 1)
Input Supply Voltage
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Supply Voltage
(Operating)
−65˚C to +150˚C
Operating Junction
Range
Temperature
Output Voltage
(Note 4)
-40˚C to +125˚C
IOUT (Survival)
Lead Temperature
seconds)
(Soldering, 5
260˚C
Power Dissipation (Note 3)
−0.3V to +16V
2.2V to 6V
Sense Pin
Storage Temperature Range
ESD Rating (Note 2)
(Survival)
−0.3V to 6V
(Survival)
Input-Output Voltage
(Note 5)
2 kV
−0.3V to 6V
Short Circuit
Protected
(Survival)
−0.3V to +16V
Internally Limited
Electrical Characteristics
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the junction temperature range of 0˚C to
125˚C. Unless otherwise specified: VIN = 3.3V, IL = 1 mA, COUT = 10 µF, CIN = 4.7 µF, VS/D = 2V.
Symbol
VO
Parameter
Output Voltage
Tolerance
Min
(Note 6)
Conditions
1 mA < IL < 800 mA
3.0V ≤ VIN ≤ 6V
Output Voltage Line
Regulation
3.0V ≤ VIN ≤ 6V
VIN (min)
Minimum Input
Voltage Required To
Maintain Output
Regulation
IL = 800 mA
VOUT ≥ VOUT(NOM) - 1%
IGND
Ground Pin Current
IL = 100 µA
Typical
(Note 7)
Max
(Note 6)
−1.0
1.0
−2.0
2.0
−3.0
3.0
Units
%VNOM
0.014
0.005
2.2
0.032
%/V
2.75
V
180
IL = 200 mA
1
IL = 800 mA
5
IO(PK)
Peak Output Current
VOUT ≥ VO(NOM) − 5%
1200
IO(MAX)
Short Circuit Current
RL = 0 (Steady State)
(Note 8)
1400
en
Output Noise Voltage
(RMS)
BW = 100 Hz to 100 kHz
CBYPASS = 10 nF
CBYPASS = 0
Ripple Rejection
f = 1 kHz
200
225
µA
2
2.5
8
mA
10
mA
18
85
µV(RMS)
70
dB
SHUTDOWN INPUT
VS/D
S/D Input Voltage
VH = O/P ON
1.4
VL = O/P OFF
IIN ≤ 2 µA
IS/D
S/D Input Current
0.1
VS/D = 0
VS/D = 5V
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1.6
V
0.50
0.001
−1
5
15
µA
(Continued)
Note 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.
Note 2: ESD testing was performed using Human Body Model, a 100 pF capacitor discharged through a 1.5 kΩ resistor. The ESD rating of pin 8 is 1kV.
Note 3: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJ−A,
and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using:
The value θJ−A for the LLP (SD) package is specifically dependent on PCB trace area, trace material, and the number of layers and thermal vias. For improved
thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187. Exceeding the maximum allowable power dissipation will cause
excessive die temperature, and the regulator will go into thermal shutdown.
Note 4: If used in a dual-supply system where the regulator load is returned to a negative supply, the LP3878 output must be diode-clamped to ground.
Note 5: The output PNP structure contains a diode between the VIN and VOUT terminals that is normally reverse-biased. Forcing the output above the input will turn
on this diode and may induce a latch-up mode which can damage the part (see Application Hints).
Note 6: Limits are guaranteed through testing, statistical correlation, or design.
Note 7: Typical numbers reperesent the most likely parametric norm for 25˚C operation.
Note 8: See Typical Performance Characteristics curves.
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LP3878
Electrical Characteristics
LP3878
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, CIN= 4.7 µF, COUT =
10 µF, S/D is tied to VIN, VIN = 3.3V, IL = 1 mA, VOUT = 1.0V, CBYP = 0.
VOUT vs Temperature
Turn-On Characteristics
20086855
20086839
Turn-Off Characteristics
Ripple Rejection
20086807
20086808
Ripple Rejection
Ripple Rejection
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MIN VIN Over Temperature
Min VIN Over Temperature
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Load Transient Response
(1mA to 800mA)
Load Transient Response (Expanded)
(1mA to 800mA)
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20086856
Line Transient Response
Line Transient Response
20086858
20086859
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LP3878
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, CIN= 4.7 µF, COUT = 10
µF, S/D is tied to VIN, VIN = 3.3V, IL = 1 mA, VOUT = 1.0V, CBYP = 0. (Continued)
LP3878
Typical Performance Characteristics Unless otherwise specified: TA = 25˚C, CIN= 4.7 µF, COUT = 10
µF, S/D is tied to VIN, VIN = 3.3V, IL = 1 mA, VOUT = 1.0V, CBYP = 0. (Continued)
Line Transient Response
Line Transient Response
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8
Important: The output capacitor must maintain its ESR
within the stable region over the full operating temperature
range of the application to assure stability.
It is important to remember that capacitor tolerance and
variation with temperature must be taken into consideration
when selecting an output capacitor so that the minimum
required amount of output capacitance is provided over the
full operating temperature range (See Capacitor Characteristics section).
The output capacitor must be located not more than 0.5"
from the output pin and returned to a clean analog ground.
LLP PACKAGE DEVICES
The LP3878 is offered in the 8 lead LLP surface mount
package to allow for increased power dissipation compared
to the SO-8 and Mini SO-8. For details on thermal performance as well as mounting and soldering specifications,
refer to Application Note AN-1187.
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP3878 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.
Input Capacitor
Noise Bypass Capacitor
Connecting a 10 nF capacitor to the Bypass pin significantly
reduces noise on the regulator output. However, the capacitor is connected directly to a high-impedance circuit in the
bandgap reference.
Because this circuit has only a few microamperes flowing in
it, any significant loading on this node will cause a change in
the regulated output voltage. For this reason, DC leakage
current through the noise bypass capacitor must never exceed 100 nA, and should be kept as low as possible for best
output voltage accuracy.
The types of capacitors best suited for the noise bypass
capacitor are ceramic and film. High-quality ceramic capacitors with either NPO or COG dielectric typically have very
low leakage. 10 nF polypropolene and polycarbonate film
capacitors are available in small surface-mount packages
and typically have extremely low leakage current.
An input capacitor whose capacitance is at least 4.7 µF is
required between the LP3878 input and ground (the amount
of capacitance may be increased without limit).
Capacitor tolerance and temperature variation must be considered when selecting a capacitor (see Capacitor Characteristics section) to assure the minimum requirement of
input capacitance is met over all operating conditions.
The input capacitor must be located at a distance of not
more than 0.5" from the input pin and returned to a clean
analog ground. Any good quality ceramic or tantalum may be
used for this capacitor, assuming the minimum capacitance
requirement is met.
Output Capacitor
The LP3878 requires a ceramic output capacitor whose size
is at least 10 µF. Capacitance tolerance and temperature
characteristics must be considered when selecting an output
capacitor.
The LP3878 is designed specifically to work with ceramic
output capacitors, utilizing circuitry which allows the regulator to be stable across the entire range of output current with
an ultra low ESR output capacitor.
The output capacitor must meet the requirement for minimum amount of capacitance and also have an ESR (equivalent series resistance) value which is within the stable range.
Curves are provided which show the stable ESR range as a
function of load current (see ESR graph below). Because an
internal zero is built into the error amplifier, the LP3878 is
stable with output capacitor ESR values down to zero ohms.
Capacitor Characteristics
Ceramic
The LP3878 was designed to work with ceramic capacitors
on the output to take advantage of the benefits they offer: for
capacitance values in the 10 µF range, ceramics are the
least expensive and also have the lowest ESR values (which
makes them best for eliminating high-frequency noise). The
ESR of a typical 10 µF ceramic capacitor is in the range of 5
mΩ to 10 mΩ, which meets the ESR limits required for
stability by the LP3878.
One disadvantage of ceramic capacitors is that their capacitance can vary with temperature. Many large value ceramic
capacitors (≥ 2.2 µF) are manufactured with the Z5U or Y5V
temperature characteristic, which results in the capacitance
dropping by more than 50% as the temperature goes from
25˚C to 85˚C.
Another significant problem with Z5U and Y5V dielectric
devices is that the capacitance drops severely with applied
voltage. A typical Z5U or Y5V capacitor can lose 60% of its
rated capacitance with half of the rated voltage applied to it.
For these reasons, X7R and X5R type ceramic capacitors must be used on the input and output of the
LP3878.
SHUTDOWN INPUT OPERATION
The LP3878 is shut off by driving the Shutdown input low,
and turned on by pulling it high. If this feature is not to be
used, the Shutdown input should be tied to VIN to keep the
regulator output on at all times.
20086838
Stable Region For Output Capacitor ESR
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LP3878
Application Hints
LP3878
Application Hints
However, if the output is pulled above the input, this diode
will turn ON and current will flow into the regulator output.
(Continued)
To assure proper operation, the signal source used to drive
the Shutdown input must be able to swing above and below
the specified turn-on/turn-off voltage thresholds listed in the
Electrical Characteristics section under VON/OFF.
In such cases, a parasitic SCR can latch which will allow a
high current to flow into VIN (and out the ground pin), which
can damage the part.
In any application where the output may be pulled above the
input, an external Schottky diode must be connected from
VIN to VOUT (cathode on VIN, anode on VOUT), to limit the
reverse voltage across the LP3878 to 0.3V (see Absolute
Maximum Ratings).
REVERSE INPUT-OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP3878 has an inherent diode connected between the regulator output and input.
During normal operation (where the input voltage is higher
than the output) this diode is reverse-biased.
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10
inches (millimeters)
8 Lead LLP Surface Mount Package
NS Package Number SDC08A
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.
For the most current product information visit us at www.national.com.
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LP3878 Micropower 800mA Low Noise "Ceramic Stable" Voltage Regulator for Low Voltage
Applications
Designed for Use with Very Low ESR Output Capacitors
Physical Dimensions
unless otherwise noted
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