LP2985IBPX-3.3 Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer LP2985IBPX-3.3
Beschreibung Micropower 150 mA Low-Noise Ultra Low-Dropout Regulator Designed for Use with Very Low ESR Output Capacitors
Hersteller National Semiconductor
Logo National Semiconductor Logo 

Gesamt 17 Seiten
LP2985IBPX-3.3 Datasheet, Funktion
March 2000
Micropower 150 mA Low-Noise Ultra Low-Dropout
Designed for Use with Very Low ESR Output Capacitors
General Description
The LP2985 is a 150 mA, fixed-output voltage regulator de-
signed to provide ultra low-dropout and low noise in battery
powered applications.
Using an optimized VIP(Vertically Integrated PNP) pro-
cess, the LP2985 delivers unequalled performance in all
specifications critical to battery-powered designs:
Dropout Voltage: Typically 300 mV @ 150 mA load, and
7 mV @ 1 mA load.
Ground Pin Current: Typically 850 µA @ 150 mA load, and
75 µA @ 1 mA load.
Enhanced Stability: The LP2985 is stable with output ca-
pacitor ESR as low as 5 m, which allows the use of ceramic
capacitors on the output.
Sleep Mode: Less than 1 µA quiescent current when
ON/OFF pin is pulled low.
Smallest Possible Size: SOT-23 and micro SMD packages
use absolute minimum board space.
Precision Output: 1% tolerance output voltages available
(A grade).
Low Noise: By adding a 10 nF bypass capacitor, output
noise can be reduced to 30 µV (typical).
Multiple voltage options, from 2.5V to 5.0V, are available as
standard products. Consult factory for custom voltages.
n Ultra low dropout voltage
n Guaranteed 150 mA output current
n Smallest possible size (SOT-23, micro SMD package)
n Requires minimum external components
n Stable with low-ESR output capacitor
n <1 µA quiescent current when shut down
n Low ground pin current at all loads
n Output voltage accuracy 1% (A Grade)
n High peak current capability
n Wide supply voltage range (16V max)
n Low ZOUT: 0.3typical (10 Hz to 1 MHz)
n Overtemperature/overcurrent protection
n −40˚C to +125˚C junction temperature range
n Custom voltages available
n Cellular Phone
n Palmtop/Laptop Computer
n Personal Digital Assistant (PDA)
n Camcorder, Personal Stereo, Camera
Block Diagram
VIPis a trademark of National Semiconductor Corporation.
© 2000 National Semiconductor Corporation DS100140

LP2985IBPX-3.3 Datasheet, Funktion
Electrical Characteristics (Continued)
Limits in standard typeface are for TJ = 25˚C. and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CIN = 1 µF, COUT = 4.7 µF, VON/OFF = 2V.
Typ (Note 6)
(Note 6)
Min Max Min Max
Ripple Rejection
f = 1 kHz, CBYPASS = 10 nF
COUT = 10 µF
Short Circuit Current
RL = 0 (Steady State)
(Note 9)
Peak Output Current VOUT Vo(NOM) −5%
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: The ESD rating of pins 3 and 4 is 1 kV.
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 temperture is calculated using:
Where the value of θJ-A for the SOT-23 package is 220˚C/W in a typical PC board mounting and the micro SMD package is 320˚C/W. Exceeding the maximum al-
lowable 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 LP2985 output must be diode-clamped to ground.
Note 5: The output PNP structure contains a diode between the VIN to VOUT terminals that is normally reverse-biased. Reversing the polarity from VIN to VOUT will
turn on this diode.
Note 6: 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 Average Outgoing Quality Level (AOQL).
Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential.
Note 8: The ON/OFF input must be properly driven to prevent possible misoperation. For details, refer to Application Hints.
Note 9: The LP2985 has foldback current limiting which allows a high peak current when VOUT > 0.5V, and then reduces the maximum output current as VOUT is
forced to ground (see Typical Performance Characteristics curves).

6 Page

LP2985IBPX-3.3 pdf, datenblatt
Typical Performance Characteristics Unless otherwise specified: CIN = 1µF, COUT = 4.7µF, VIN =
VOUT(NOM) +1, TA = 25˚C, ON/OFF pin is tied to VIN. (Continued)
Turn-On Time
Turn-On Time
Turn-On Time
Turn-On Time
Application Hints
Like any low-dropout regulator, the LP2985 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.
Input Capacitor
An input capacitor whose capacitance is 1 µF is required
between the LP2985 input and ground (the amount of ca-
pacitance may be increased without limit).
This capacitor must be located a distance of not more than 1
cm from the input pin and returned to a clean analog ground.
Any good quality ceramic, tantalum, or film capacitor may be
used at the input.
Important: Tantalum capacitors can suffer catastrophic fail-
ure due to surge current when connected to a
low-impedance source of power (like a battery or very large
capacitor). If a Tantalum capacitor is used at the input, it
must be guaranteed by the manufacturer to have a surge
current rating sufficient for the application.
There are no requirements for ESR on the input capacitor,
but tolerance and temperature coefficient must be consid-
ered when selecting the capacitor to ensure the capacitance
will be 1 µF over the entire operating temperature range.
Output Capacitor:
The LP2985 is designed specifically to work with ceramic
output capacitors, utilizing circuitry which allows the regula-
tor to be stable across the entire range of output current with
an output capacitor whose ESR is as low as 5 m. It may
also be possible to use Tantalum or film capacitors at the
output, but these are not as attractive for reasons of size and
cost (see next section Capacitor Characteristics).
The output capacitor must meet the requirement for mini-
mum amount of capacitance and also have an ESR (equiva-
lent 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).

12 Page

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