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LIN D O C #: 8940
LX8940
5V LOW D
T
HE
ROPOUT
R
E G U L ATOR
I
NFINITE
P
OWER
OF
I
N N O VAT I O N
P
RODUCTION
D
ATA
S
HEET
DESCRIPTION The LX8940 is a 5V, low dropout, low quiescent current regulator rated for 1A of output current. It can regulate with as low as 0.4V headroom between the input and output voltages, thus minimizing power dissipation. In addition, it can be used in applications where worst case supplies require a low input-output differential to maintain regulation. This feature makes it ideal for computer monitors that have to comply with energy-efficient / "Green PC" programs, where the input voltage drops to only a few tenths of a volt above the output when power supply enters sleep-mode operation.
K E Y F E AT U R E S
s 2% Internally Trimmed Output s Output Current In Excess Of 1A s Input-Output Differential Less Than 0.4V At 1A p Reverse Battery Protection p 60V Load Dump Protection p -50V Reverse Transient Protection p Short Circuit Protection p Internal Thermal Overload Protection p Available In 3-Lead Plastic TO-220 p Drops In Most lM2940 Sockets
NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com.
PRODUCT HIGHLIGHT
A P P L I C AT I O N S
5.3V 0.1F
IN
LX8940
GND
OUT 10F
5V/100mA
s Small Headroom Battery Applications s High Efficiency Linear Regulators s Post Regulators For Switching Power Supplies s Green PC Monitor Applications
LOAD TRANSIENT RESPONSE
Output Voltage
TA = 25C CO = 47F Electrolytic CIN = 1F VIN = 5.30V
5.000V
D R O P O U T VO L TA G E V S . OUTPUT CURRENT V S . TEMPERATURE
600
(20mV / Div.)
500 125C
Dropout Voltage - (mV)
400
4.980V
25C
300
Output Current
(50mA / Div.)
100mA
200 -40C
100
0mA
0
Time - (20s/Div.)
100
500
1000
Output Current - (mA)
PA C K A G E O R D E R I N F O TA (C) 0 to 125 -40 to 125
P Plastic TO-220 3-pin
LX8940CP LX8940IP
Copyright (c) 1999 Rev. 1.3 3/99
LINFINITY MICROELECTRONICS INC.
11861 WESTERN AVENUE, GARDEN GROVE, CA. 92841, 714-898-8121, FAX: 714-893-2570
1
PRODUCT DATABOOK 1996/1997
LX8940
5V LOW D
P
ROPOUT
R
E G U L ATOR
RODUCTION
D
ATA
S
HEET
A B S O L U T E M A X I M U M R AT I N G S
(Note 1)
PACKAGE PIN OUTS
Tab is GROUND
3 2 1
Input Voltage (VIN) .......................................................................................... -15V to 26V Operating Junction Temperature Plastic (P Package) ................................................................................................ 150C Storage Temperature Range ...................................................................... -65C to 150C Lead Temperature (Soldering, 10 seconds) ............................................................. 300C
Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. Pin numbers refer to DIL packages only.
OUTPUT GND INPUT
P PACKAGE (Top View)
T H E R MAL DATA
P PACKAGE: THERMAL RESISTANCE-JUNCTION TO TAB, JT THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA 3.0C/W 60C/W
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
BLOCK D IA GR A M
* Required if regulator is located far from power supply filter. INPUT VOLTAGE
C1* 0.1F
1 (INPUT)
LX8940
OVERVOLTAGE THERMAL SHUTDOWN
3 (OUTPUT)
C2 10F
OUTPUT VOLTAGE
REGULATOR BIAS 1.23V REFERENCE
2 (GND)
2
Copyright (c) 1999 Rev. 1.3 3/99
PRODUCT DATABOOK 1996/1997
LX8940
5V LOW D
P
ROPOUT
R
E G U L ATOR
RODUCTION
D
ATA
S
HEET
R E C O M M E N D E D O P E R AT I N G C O N D I T I O N S Parameter
Input Voltage Load Current (with adequate heatsinking) Maximum Line Transient (Load Dump), VO 5.5V Input Capacitor (VIN to GND) Output Capacitor with ESR of 10 max., (VOUT to GND & VSB to GND) Note 2. VIN (MIN) = 1.2V(MAX). See Dropout Voltage maximum limit.
Symbol
VIN
Recommended Operating Conditions Min. Typ. Max.
Note 2 5 0.1 10 26 1000 60
Units
V mA V F F
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, these specifications apply over the operating ambient temperatures of -40C to +125C for LX8940IP, and 0C to +125C for LX8940CP; VIN = 10V, IO = 1A, COUT = 22F, and are for DC characteristics only. (Low duty cycle pulse testing techniques are used which maintains junction and case temperatures equal to the ambient temperature.)
Parameter
Output Voltage Line Regulation Load Regulation Output Impedance (Note 3) Quiescent Current
Symbol
VO VOI VOL rO IQ
Test Conditions
IO = 0A, TA = 25C 7V VIN 26V, IO = 5mA 50mA IO 1A 100mADC and 20mARMS, fO = 120Hz IO 5mA, 7 VIN 26V IO = 500mA IO = 1000mA 10Hz - 100kHz, IO = 5mA fO = 120Hz, 1VRMS, IO = 100mA IO = 100mA IO = 500mA IO = 1A VIN = 26V RO = 100, T 100ms
Min.
4.85
LX8940 Typ. Max.
5 1 10 200 3 30 115 150 20 66 150 275 400 1.2 31 60 5.15 50 50 15 50 180
Units
V mV mV m mA mA mA VRMS mV/1000hr dB mV mV mV A V V
Output Noise Voltage (Note 3) Long Term Stability (Note 3) Ripple Rejection (Note 3) Dropout Voltage
VO RMS RR V
300 500 800
Current Limit Maximum Operational Input Voltage Maximum Line Transient
I CL VIN (MAX) VIN (TR)
1 26
Note 3. These parameters, although guaranteed, are not tested in production.
Copyright (c) 1999 Rev. 1.3 3/99
3
PRODUCT DATABOOK 1996/1997
LX8940
5V LOW D
P
ROPOUT
R
E G U L ATOR
RODUCTION
D
ATA
S
HEET
A P P L I C AT I O N N O T E S The advantages of using a low-dropout regulator such as the LX8940 is the need for less "headroom" for full regulation, and the inherent reverse polarity protection provided by the PNP output device. A typical NPN regulator design requires an input to output differential of approximately two volts minimum. This is due to the 2Vbe + Vcesat of the NPN Darlington used in the output, coupled with the voltage drop across the current limit resistor. In contrast, the "PNP Regulator" uses a single series pass transistor with its single Vcesat, thus the lower input to output voltage differential or dropout voltage. In some applications the regulator output voltage is used not only as a power supply but also as a voltage reference for control systems. In such cases not just the temperature stability of the output is important but also the initial accuracy. LX8940 fills this need as the internal bandgap reference is trimmed allowing a typical output voltage tolerance of 1%. EXTERNAL CAPACITORS To stabilize the outputs and prevent oscillation (perhaps by many volts) external capacitors are required. The minimum recommended value for the output capacitors is 10F, although the actual size and type will likely vary according to the particular application, e.g., operating temperature range and load. Another consideration is the effective series resistance (ESR) of the capacitor. Capacitor ESR will vary by manufacturer. Consequently, some evaluation may be required to determine the minimum value of the output capacitors. Generally worst case occurs at the maximum load and minimum ambient temperature. The size of the output capacitor can be increased to any value above the minimum. One possible advantage of this would be to maintain the output voltage during brief periods of negative input transients The output capacitors chosen should be rated for the full range of ambient temperature over which the circuit will be exposed and expected to operate. For example, many aluminum type electrolytic capacitors change values at cold temperatures. The effective capacitance is reduced and regulator stability is effected. Tantalum capacitors are a good choice for these types of environments. OUTPUT PROTECTION The output features fault protection against overvoltage as well as a thermal shutdown feature. If the input voltage rises above 33V (load dump), the output shuts down automatically. The internal circuitry is thus protected and the IC is able to survive higher voltage transients than might otherwise be expected. The thermal shutdown output effectively guards against overheating of the die and protects the device from being damaged.
PRODUCTION DATA - Information contained in this document is proprietary to Lin Finity, and is current as of publication date. This document may not be modified in any way without the express written consent of LinFinity. Product processing does not necessarily include testing of all parameters. Linfinity reserves the right to change the configuration and performance of the product and to discontinue product at any time.
4
Copyright (c) 1999 Rev. 1.3 3/99

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