June 2013 Rev. 1.0 www.microsemi.com 1
© 2013 Microsemi Corporation
800mA Very High PSRR Low-Dropout
Linear Regulator
OUT
FB
GND
BIAS
IN
EN
LX8240
1
2
4
5
7
8
1.8V
1.5V @500mA
5V
C1
1µF
C3
1µF
C4
10nF
C2
10µF
Figure 1 · Typical Application of LX8240
Features
High PSRR, higher than 48 dB over all
frequency up to 100kHz
High PSRR, higher than 32 dB over all
frequency up to 1MHz
+/-2% Accuracy over Temp, Supply and
Load
Adjustable Output (0.5V reference)
Over Current Limit
Thermal Protection
Applications
Low Power Mobile Devices
Portable Devices
Post Processing for a Switching Regulator
Description
LX8240 is a low-dropout regulator offering the
highest Power Supply Rejection Ratio (PSRR),
higher than 48 dB over all frequency up to 100kHz,
and higher than 32 dB over all frequency up to
1MHz for LDO devices supplying 800mA of output
current. LX8240 also requires very low quiescent
current. It has separate Bias and Input supply rails
to improve efficiency and minimize power
dissipation. The VBIAS input includes a voltage
compliance range from 2.7V to 5.5V, and the VIN
supply range is 1.2V to 4.2V. The output voltage is
programmed by an external resistor divider utilizing
the 0.5V reference feedback (FB) pin allowing
output voltages as low as 1V.
LX8240 is an ideal selection for battery-powered
systems where the low quiescent current cannot be
compromised. It is also guaranteed to be the stable
even with only a 1µF ceramic capacitor.
To protect the device the LX8240 aso includes
internal thermal shutdown, and overcurrent limit
features.
LX8240
800mA Very High PSRR Low-Dropout Linear Regulator
2
Pin Configuration and Pinout
1
2
3
4 5
6
7
8
IN
BIAS
N/C
GND EN
N/C
FB
OUT
Figure 2 · Pinout WDFN 3mm x 2mm 8L Top View
Marking: Line 1 8240
Line 2 Date / Lot Code
Line 3 * MSC ( *Pin 1 identifier )
Ordering Information
Pin Description
Pin
Number
Pin
Designator
Description
1
IN
Power Source Input. Bypass IN to GND with a 1μF or greater capacitor.
2
BIAS
Bias Voltage. Bypass to GND with a 1μF capacitor or greater.
3, 6
NC
No Connect.
4
GND
Ground.
5
EN
Enable Input. Drive EN high to turn on, drive EN low to turn it off. For
automatic startup, connect EN to Bias.
7
FB
Feedback Input. Connect a resistive voltage divider from OUT to FB to set the
output voltage. OUT feedback threshold is 0.5V.
8
OUT
Regulator Output. OUT is the output of the linear regulator. Bypass OUT to
GND with a 1μF or greater capacitor.
Ambient
Temperature
Type
Package
Part Number
Packaging Type
-40°C to 85°C
RoHS Compliant,
Pb-free
WDFN 3mm x 2mm 8L
LX8240ILD
Bulk / Tube
LX8240ILD-TR
Tape and Reel
Block Diagram
3
Block Diagram
IN
OUT
BIAS
REF
GND
FB
EN
12
4
58
7
Figure 3 · Simplified Block Diagram of LX8240
Absolute Maximum Ratings
Parameter
Min
Max
Units
IN to GND
-0.3
7
V
BIAS to GND
-0.3
< VEN
EN, FB to GND
-0.3
7
V
OUT to GND
-0.3
7
V
Junction Temperature
-40
150
°C
Storage Temperature
-65
150
°C
Peak Solder Reflow Temperature (40 seconds)
260 (+0,-5)
°C
ESD Rating
HBM
5000
V
CDM
2000
V
Note: Performance is not necessarily guaranteed over this entire range. These are maximum stress ratings only.
Exceeding these ratings, even momentarily, can cause immediate damage, or negatively impact long-term
operating reliability
800mA Very High PSRR Low-Dropout Linear Regulator
4
Operating Ratings
Min
Max
Units
IN
1.2
4.2
V
BIAS
2.7
5.5
V
Output Voltage
1
4
V
Output Current
0
800
mA
Ambient Temperature
-40
85
°C
Note: Performance is generally guaranteed over this range as further detailed below under Electrical
Characteristics.
Thermal Properties
Thermal Resistance
Typ
Units
θJA
55
°C/W
θJC
12
°C/W
Note: The JX numbers assume no forced airflow. Junction Temperature is calculated using TJ = TA + (PD x JA). In
particular, θJA is a function of the PCB construction. The stated number above is for a four-layer board in
accordance with JESD-51 (JEDEC).
Electrical Characteristics
Note: The following specifications apply over the operating ambient temperature of -40C ≤ TA ≤ 85C except
where otherwise noted with the following test conditions: VIN = 1.8V,VBIAS = 5.0V, VOUT = 1.5V, C1 = C3 =
1µF and C2 = 10µF at TA = 25°C.
Symbol
Parameters
Test Conditions/Comments
Min
Typ
Max
Units
VBIAS
Bias Voltage Range
VBIAS > VIN + 1.3V
2.7
5.5
V
VIN
Input Voltage Range
VIN < VBIAS - 1.3V,
VIN < VOUT + 0.9V @ IOUT = 800mA
1.2
4.2
V
VIN < VBIAS - 1.3V,
VIN < VOUT + (0.727 / IOUT)V @ VOUT = 1.5V,
(Note 3)
1.2
4.2
V
IBIAS
Bias Current
IOUT = 10µA, VOUT = 1.5V
200
µA
IIN
Input Current
IOUT = 0µA, VOUT = 1.5V
20
µA
IFB
FB Biasing Current
VFB = 0.5V, TA = 25C
-0.5
0.5
µA
VFB = 0.5V, TA = 85C (Note 1)
0
µA
VREF
FB Reference
Voltage
IOUT = 1mA to 800mA
0.49
0.5
0.51
V
-40C ≤ TA ≤ 85C
0.49
0.5
0.51
VDO
Dropout Voltage
VBIAS = 4.75V, VOUT = 1.5V,
IOUT = 800mA, VIN = sweep, (Note 2)
200
mV
VOUT
Output Voltage
1
4
V
Electrical Characteristics
5
Symbol
Parameters
Test Conditions/Comments
Min
Typ
Max
Units
VBIAS Line
Regulation
IOUT = 100mA, VIN = 1.8V,
VOUT = 1.5V, VBIAS = 3.1V to 5.5V
0.07
0.4
%/V
VIN Line Regulation
IOUT = 1mA, VBIAS = 5V,
VOUT = 1.5V, VIN = 1.7V to 4.2V
0.002
0.02
%/V
Load Regulation
IOUT = 1mA to 800mA
0.0005
%/mA
PSRR
VBIAS PSRR
VIN > VOUT + 0.2V, C2 = 10µF,
VBIAS(AC) = 100mV, f = 1kHz,
ILOAD = 100mA, (Note 1)
55
dB
VIN > VOUT + 0.2V, C2 = 10µF,
VBIAS(AC) = 100mV, f = 1MHz,
ILOAD = 100mA (Note 1)
33
PSRR
VIN PSRR
VBIAS > VOUT + 1.3V, C2 = 10µF,
VIN(AC) = 100mV, f = 1kHz,
ILOAD = 100mA, (Note 1)
59
dB
VBIAS > VOUT + 1.3V, C2 = 10µF,
VIN(AC) = 100mV, f = 1MHz,
ILOAD =100mA (Note 1)
33
ICL
Output Current Limit
850
mA
IQ
Quiescent Ground
Current
EN = GND
0.1
2
µA
1.3V < EN ≤ VBIAS, ILOAD = 500mA
150
200
µA
VOUT Undershoot
Over Step Load
Transient
Load step from 20mA to 450mA with rising
time of 100ns (Note 1)
33
mV
VOUT Overshoot
Over Step Load
Transient
Load step from 450mA to 20mA with falling
time of 600ns (Note 1)
23
mV
EN Input High
Voltage
1.3
V
EN Input Low
Voltage
0.4
V
EN Input Bias
Current
VEN = 1.2V
-1
1
µA
TTHERMAL
Thermal Protection
Threshold
Rising (Note 1)
155
°C
Falling (Note 1)
125
°C
Note: 1. Guaranteed by Design
Note: 2. Dropout is defined as VIN - VOUT_LDO when VOUT_LDO is 98% of the value of VOUT_LDO for VIN = VOUT(VIN =
1.8V, VBIAS = 5V, IOUT = 800mA)
Note: 3. 0.727 is the maximum allowed power before thermal shutdown.
800mA Very High PSRR Low-Dropout Linear Regulator
6
Typical Performance Curves -- (VOUT = 1.5V)
Figure 4 · VBIAS Line Regulation, VIN = 1.8V
Figure 5 · VIN Line Regulation, VBIAS = 5V
Figure 6 · Load Regulation, VIN = 1.8V, VBIAS = 5V
Figure 7 · Voltage Dropout, VIN = 1.8V, VBIAS = 4.75V
Figure 8 · Output Voltage vs. Temperature
VIN = 1.8V, VBIAS = 4.75V, ILoad = 300mA
Figure 9 · Voltage Dropout vs. Temperature
VIN = 1.8V, VBIAS = 4.75V, ILoad = 300mA
1.5042
1.5044
1.5046
1.5048
1.505
1.5052
1.5054
1.5056
1.5058
1.506
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VOUT (V)
VBIAS (V)
Load = 100mA
Load = 50mA
Load = 500mA
1.5038
1.504
1.5042
1.5044
1.5046
1.5048
1.505
1.5052
1.5054
1.7 2.2 2.7 3.2 3.7 4.2
VOUT (V)
VIN (V)
Load = 1mA
Load = 100mA
Load = 500mA
1.5038
1.504
1.5042
1.5044
1.5046
1.5048
1.505
1.5052
1.5054
110 100 1000
VOUT (V)
Load Current (mA)
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800
Dropout (mV)
Load Current (mA)
1.486
1.488
1.49
1.492
1.494
1.496
1.498
-40 -15 10 35 60 85
VOUT (V)
Temperature (°C)
0
5
10
15
20
25
30
35
-40 -15 10 35 60 85
Dropout (mV)
Temperature (°C)
Typical Performance Curves -- (VOUT = 1.5V)
7
Typical Performance Curves -- (VOUT = 1.5V)
Figure 10 · Reference Voltage vs. Temperature
VIN = 1.8V, VBIAS = 4.75V, ILoad = 300mA
Figure 11 · VBIAS to VOUT PSRR
Figure 12 · VIN to VOUT PSRR
0.497
0.4975
0.498
0.4985
0.499
0.4995
0.5
0.5005
0.501
0.5015
-40 -15 10 35 60 85
VREF (V)
Temperature (°C)
0
10
20
30
40
50
60
110 100 1000
Gain (dB)
Frequency (kHz)
0
10
20
30
40
50
60
70
110 100 1000
Gain (dB)
Frequency (kHz)
800mA Very High PSRR Low-Dropout Linear Regulator
8
Typical Performance Curves -- (Start Up & Shut Down, VOUT = 1.5V)
Figure 13 · Power Up with 400mA Load Current
VIN = 1.8V, VBIAS = 5V
CH1: VIN, CH3: VOUT, CH4: Load Current
Figure 14 · Power Down with 400mA Load Current
VIN = 1.8V, VBIAS = 5V
CH1: VIN, CH3: VOUT, CH4: Load Current
Figure 15 · Enable Up with 400mA Load Current
VIN = 1.8V, VBIAS = 5V
CH1: VIN, CH3: VOUT, CH4: Load Current
Figure 16 · Enable Down with 400mA Load Current
VIN = 1.8V, VBIAS = 5V
CH1: VIN, CH3: VOUT, CH4: Load Current
Typical Performance Curves -- (Step Response & Over Current Limit)
9
Typical Performance Curves -- (Step Response & Over Current Limit)
Figure 17 · Dynamic Response, ILoad = 20mA to 450mA
VIN = 1.2V, VBIAS = 2.7V, VOUT = 1V
CH2: VOUT AC, CH3: VOUT DC,
CH4: Load Current
Figure 18 · Dynamic Response, ILoad = 20mA to 450mA
VIN = 1.8V, VBIAS = 5V, VOUT = 1.5V
CH2: VOUT AC, CH3: VOUT DC,
CH4: Load Current
Figure 19 · Dynamic Response, ILoad = 20mA to 450mA
VIN = 4.2V, VBIAS = 5.5V, VOUT = 4V
CH2: VOUT AC, CH3: VOUT DC,
CH4: Load Current
800mA Very High PSRR Low-Dropout Linear Regulator
10
Theory of Operation / Application Information
BIAS pin operation
The IC uses a BIAS pin to allow low RDSON. VBIAS needs to be higher than VIN by 1.3V to provide
circuit headroom since there is no internal charge pump. The VBIAS all insures the high VIN – to - VOUT
PSRR, and the low noise performance is achieved with this topology at lower cost.
Adaptive PSRR compensation
LX8240 has internal adaptive feedforward control. A typical feedforward design depends on the zero
from the external feedforward capacitance, C4 in Figure 20. In LX8240, the internal adaptive
feedforward control circuit has an automatic pole compensator to allow different frequency inputs to
experience a different zero frequency. This is equivalent to pole-zero pair in the control loop. This
method allows LX8240 to maintain high gain over a very wide frequency range. Furthermore, it
helps LX8240 sustain PSRR higher than 32dB over the entire frequency range up to 1MHz.
Setting the output Voltage
A typical LX8240 application circuit is shown in Figure 19. External component selection is driven by
the load requirement. The LX8240 develops a 0.5V reference voltage between the feedback pin and
the ground. The output voltage is set by a resistive divider according to the following formula:
OUT
FB
GND
BIAS
IN
EN
LX8240
1
2
4
5
7
8
1.8V
1.5V @500mA
5V
C1
1uF
C3
1uF
C4
10nF
C2
10uF
R1
R2
Figure 20 · Typical Application
PACKAGE OUTLINE DIMENSIONS
11
PACKAGE OUTLINE DIMENSIONS
E2
D2
L
K
e b
D
E
A1
A
A3
Pin 1
Dim
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
0.70
0.80
0.028
0.032
A1
0.00
0.05
0.000
0.002
A3
0.20 REF
0.008
D
2.00 BSC
0.079 BSC
D2
1.50
1.75
0.059
0.030
b
0.18
0.30
0.007
0.012
E
3.00 BSC
0.118 BSC
E2
1.65
1.90
0.065
0.075
e
0.50 BSC
0.020 BSC
L
0.30
0.50
0.012
0.002
K
0.20
0.008
Figure 21 · LD 8-Pin WDFN Package Dimensions
Note: 1. Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm (.006”) on any side.
Lead dimension shall not include solder coverage.
Note: 2. Dimensions are in mm, inches are for reference only.
LAND PATTERN RECOMMENDATION
1.80mm
1.75mm
0.70mm
0.20mm
0.50mm 0.30mm
Pin 1
1.80mm
3.60mm
Figure 22 · LD 8-Pin WDFN Package Land Pattern
Disclaimer:
This PCB land pattern recommendation is based on information available to Microsemi by its suppliers. The actual land pattern to be used could be different depending on the
materials and processes used in the PCB assembly, end user must account for this in their final layout. Microsemi makes no warranty or representation of performance based
on this recommended land pattern.
PRODUCTION DATA – Information contained in this document is proprietary to Microsemi and is
current as of publication date. This document may not be modified in any way without the express
written consent of Microsemi. Product processing does not necessarily include testing of all
parameters. Microsemi reserves the right to change the configuration and performance of the product
and to discontinue product at any time.
LX8240-3/1.0
Microsemi Corporation (NASDAQ: MSCC) offers a comprehensive portfolio of semiconductor
solutions for: aerospace, defense and security; enterprise and communications; and industrial
and alternative energy markets. Products include high-performance, high-reliability analog and
RF devices, mixed signal and RF integrated circuits, customizable SoCs, FPGAs, and
complete subsystems. Microsemi is headquartered in Aliso Viejo, Calif. Learn more at
www.microsemi.com
.
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One Enterprise, Aliso Viejo CA 92656 USA
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