Copyright © 2013 Microsemi Page 1
Rev. 1.1a 1/28/2014 Analog Mixed Signal Group
One Enterprise Aliso Viejo, CA 92656 USA 1-800-713-4113, 1-949-380-6100, fax 1-949-215-4996
LX7176A
4A Step-Down-Regulator
Production Datasheet
Description
The LX7176A is a 4A step-
down regulator with
integrated MOSFETs packaged in a space saving QFN12
2mm x 2mm for today’s mobile devices. It uses an ultra
fast, constant frequency hysteretic control method to
minimize external filter components while maintaining
excellent regulation. The LX7176A reference voltage is
0.6V.
The LX7176A operates from 3V to 5.5V rails and outputs
0.6V to 100% of the input voltage.
Cycle-by-cycle current limiting protects against over-
current conditions. Hiccup mode provides protection for
heavy over-load or short-
circuit faults. Thermal
protection shuts down the regulator under over-
temperature conditions. Over voltage conditions will
immediately shut off the output to protect against
permanent damage. The LX7176A automatically restarts
when all fault conditions are cleared. Internal soft start
circuitry limits start up inrush currents.
Features
♦ 0-4A Step-down Regulator
♦ Operational Input Supply Voltage Range:
3V-5.5V (short durations to 6.5V.)
♦ Hysteretic control offers best transient
response
♦ CCM switching at a constant 1.65MHz
♦ Automatically switches to DCM switching
under light loads to improve efficiency
♦ 100% Duty Ratio Operation
♦ Input under voltage and over voltage
protection
♦ Enable and Power Good Function
♦ Internal soft-start
♦ Cycle-by-Cycle Over Current Protection
♦ Hiccup Mode protects against short circuit
faults
♦ RoHS Compliant
Applications
• High Performance HDD
• LCD TV
• Notebook/Netbook
• Server and Workstations
• Video Cards
• PoE Powered Devices Smart Phone
Figure 1: Typical Application Diagram
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Pin Configuration and Pinout
• 76A
YWWL
• Pin 1 Indicator, YWWL = Year/Week/Lot Code
RoHS / Pb-free Matte Tin Pin Finish
Figure 2: Pinout
Ordering Information
Thermal Properties
Thermal Resistance(θJA) Typ Units
QFN 2x2mm 12L 30 °C/W
Note: The θJA number assumes no forced airflow. Junction Temperature is calculated using TJ = TA + (PD x θJA). 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).
Ambient
Temperature Type Package Part Numbe r Packaging
Type
0°C to 85°C RoHS compliant, Pb-free QFN 2x2mm 12L LX7176ACLQ Bulk
LX7176ACLQ-TR Tape and Reel
Copyright © 2013 Microsemi Page 3
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Pin Description
Pin Number Pin Designator Description
1, 10 PVIN Supply Voltage. Bypass PVIN to ground plane as close as possible to
the IC.
2, 11 SW Switch Output. Drives the external L-C filter.
3, 12 PGND Power Ground. Connect to ground plane.
4 AGND Analog Ground. Connect to ground plane.
5 NC No connect pin. Leave floating. Serves as SCL when accessing the
serial port.
6 OUT
Output Voltage Sense Pin – This pin monitors the output voltage.
Serves as SDA when accessing the serial port. Digital signals at this
pin will be capacitively coupled onto FB and disturb the output
voltage.
7 FB Feedback – Analog input, monitors the output voltage either directly
or through a resistor divider.
8 EN Enable – Digital input. Force high to enable the IC.
9 PG
Power Good – Open drain digital output. Pulls low to indicate a fault
condition. Requires an external pull up resistor. Also used to
monitor selected internal signals.
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Block Diagram
Figure 3: Block Diagram
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Absolute Maximum Ratings
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.
Parameter Min Max Units
PVIN, EN, PG, OUT, FB, SW to PGND -0.3 7 V
AGND to PGND -0.3 0.3 V
SW to PGND (Shorter than 50ns) -2 7 V
Junction Temperature Range 0 150 °C
Storage Temperature Range -65 150 °C
Peak Lead Soldering Temperature (40s, reflow) 260 (+0, -5) °C
Operating Ratings
Performance is generally guaranteed over this range as further detailed below under Electrical
Characteristics.
Parameter Min Max Units
Input Voltage 3.0 5.5 V
Output Voltage 0.6 5.5 V
Output Current (VIN = 3V to 5V) 0 4 A
Ambient Temperature 0 85 °C
Note: Corresponding Max Junction Temperature is 125°C
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Electrical Characteristics
Unless otherwise specified, the following specifications apply over the operating ambient temperature
of 0°C ≤ TA ≤ 85°C with the following test conditions: PVIN = 5V. Typical parameters refers to TJ = 25°C.
VOUT = 0.9V. VOUT is disconnected from FB for open loop tests. Iload = 0,. EN=high, GBD specifications are
guaranteed by design and/or characterization and are not tested on a production basis.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
PVIN
I
QPSM
PSM Bias Current
Enable PSM
280
µA
ISLEEP
Input Current at
Shutdown EN = low, TJ = 25°C 0.1 3 µA
UVLORISING
Under Voltage
Rising Threshold PVIN rising 2.8 V
UVLOHYST
UVLO Hysteresis
PVIN falling
0.2
V
OVPR
Over Voltage
Rising Threshold
PVIN rising. Will also trigger on
DV/DT > 1V/µs 6.1 V
OVPF
Over Voltage
Falling Threshold PVIN falling 5.5 5.85 V
VREF
VREF
Reference Voltage
0.6
V
T
SS
V
REF
Slew Rate
3.75
mV/µs
THICCUP
Hiccup Time
1.2
ms
VOUT
VOUT VOUT Accuracy
V
OUT
is set to 0.9V with 0.1%
feedback resistors. PVIN = 5V, ,
0°C to 85°C.
0.891 0.9 0.909 V
Line Regulation
VIN from 3V to 5V,
VOUT = 0.9V. Note
1
ILOAD = 0.1A
(in DCM)
0.01
%/V
ILOAD = 2.5A
(in CCM) 0.06
VOUTLR Load Regulation
V
OUT
= 0.9V, I
OUT
= 0A to 4A .
Note 1 -0.06 %/A
FB
IL
FB Input Current
1
µA
FBUV
FB Under Voltage
Threshold
V
OUT
below this threshold will
initiate a hiccup sequence. 80 %VREF
RDISC
Output Discharge
Resistance EN = low 80 314 500 Ω
SW
RDSON_H
High Side On
Resistance 46 mΩ
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Symbol
Parameter
Conditions
Min
Typ
Max
Units
RDSON_L
Low Side On
Resistance 21 mΩ
IRATED
Rated Output
Current PVIN = 3V to 5V. Note 1 4 A
ICL Current Limit
Peak inductor current. PVIN = 3V
to 5V . Note 1 6.3 7.4 9 A
TSH
Thermal
Shutdown
Threshold¹
Note 1 150 °C
TH
Thermal
Shutdown
Hysteresis¹
Note 1 20 °C
FSW PWM Switching
Frequency VOUT / VIN ≥ 35%, T=25°C, Note 1 1.55 1.65 1.75 MHz
EN
V
IH
Input High
1.2
V
VIL
Input Low
0.4
V
I
IN
Input Current
0.01
1
µA
PG
VPG90
PGOOD V
OUT
Lower Threshold VOUT rising, percentage of VREF 90 %
VPG110
PGOOD V
OUT
Upper Threshold VOUT falling, percentage of VREF 110 %
V
PGHY
Hysteresis
Percentage of V
REF
5
%
PGRDSON
PGOOD Pull-down
Resistance 13 50 Ω
PGILEAK
PGOOD Leakage
Current TJ = 25°C 0 1 µA
Note 1: These parameters are not tested, but guaranteed by design and characterization.
Copyright © 2013 Microsemi Page 8
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Typical Performance Curves (Efficiency)
Figure 4: LX7176A Efficiency with VIN = 5V, L = 0.47µH, COUT = 22µF
30%
40%
50%
60%
70%
80%
90%
100%
1 10 100 1000
Efficiency
Load Current (mA)
VOUT = 0.9V
VOUT = 1.8V
VOUT = 3.3V
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Step Response(Load Current = 1.5A to 4A, L = 0.47μH, COUT = 22μF)
Typical Performance Curves
Figure 5. Step Load Figure 6. Step Load Rising Edge
Figure 7. Step Load Falling Edge
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Theory of Operation
LX7166
Basic Operation
The LX7176A compares the FB voltage to an
internal reference, VREF. When FB is lower than
Vref, the upper switch turns on and the lower
switch turns off. When FB is higher than VREF, the
upper switch turns off and the lower switch turns
on. An internal ramp and a frequency control loop
keep the switching frequency constant when in
constant conduction mode (CCM) over a wide
range of output capacitor values and parasitic
components (i.e. ESR, ESL).
At light loads, the converter automatically reduces
the switching frequency to optimize conversion
efficiency.
Startup
The LX7176A is enabled when EN is high and PVIN
rises above the UVLO threshold. At start up, after
all the internal bias voltages and currents stabilize,
VREF ramps up from 0V to the target voltage at the
defined slew rate. While VREF ramps, PGOOD is
held low. At the end of the ramp time, PGOOD is
allowed to go high if the FB has reached the
PGOOD rising threshold.
Over Current Protection
The LX7176A protects against all types of short
circuit conditions. Cycle by cycle over current
protection turns off the upper switch when the
current exceeds the ICL threshold. When this
occurs, the upper switch is kept off for about
360ns before being allowed to turn on again. After
startup, if FB drops below the FBUV threshold,
a hiccup sequence will be initiated where both
output switches are shut off for 1.2ms before
initiating another soft start. This protects against a
crowbar short circuit. FB under voltage detection is
not active during startup.
Setting the Output Voltage
The reference voltage is 0.6V
REFOUT V
R
R
V⋅
+= 1
2
1
(1)
Where R1 is high side feedback divider resistor, R2 is
low side feedback divider resistor, VREF is 0.6V.
Copyright © 2013 Microsemi Page 11
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Recommended Output Filter Components
The following tables show recommended feedback
component values (RHIGH, RLOW, Cff) for different
input/output voltages, power inductor (L), and
output capacitance (C) values that result in
optimum closed loop response of the regulator in
each case. The estimated crossover frequency is
also shown in the table in each case. If the L*C
factor exceeds a certain number
the regulator
would run with low phase margin, or become
unstable. The L and C range provided in the table
provides 30°, or higher of phase margin. Therefore,
it is not recommended to increase L*C factor
beyond what is given in the table.
It is a good practice to determine L such that the
peak-to-peak inductor ripple current in continuous
conduction mode operation is roughly equal to 30%
of converter’s rated output current. In general,
increasing the inductance slows down the closed
loop response of the regulator.
Hence, for
applications that require fast line/load transient
response, lower inductance values should be
preferred over larger ones. Output capacitance can
be determined based on desired output ripple
voltage staying within the limits provided in the
table depending on the inductance value.
VIN
(V)
VOUT
(V)
L
(µH)
COUT
(µF)
RHIGH
(kΩ)
RLOW
(kΩ)
Cff
(pF)
F
crossover
(kHz)
5.0 0.9
2.2
4x22
60 120
47 70
3x22 83
2x22 33 100
1x22 12 150
1.5
5x22
27
73
4x22 84
3x22 100
2x22 12 120
1x22 200
1.0
5x22
22
92
4x22 110
3x22 130
2x22 12 170
1x22 300
0.47
5x22
10
140
4x22 170
3x22 220
2x22 0 280
1x22 575
0.33
5x22
6.8
180
4x22 220
3x22 280
2x22 0 400
1x22 7.5 15 625
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Recommended Output Filter Components - Continued
VIN
(V)
VOUT
(V)
L
(µH)
COUT
(µF)
RHIGH
(kΩ)
RLOW
(kΩ)
Cff
(pF)
F
crossover
(kHz)
3.0 0.9
2.2 2x22
60 120
33 76
1x22 12 110
1.5
3x22 27 74
2x22 12 90
1x22 140
1.0
5x22
22
68
4x22 78
3x22 93
2x22 12 120
1x22 190
0.47
5x22
10
100
4x22 120
3x22 150
2x22 0 180
1x22 325
0.33
5x22
6.8
130
4x22 150
3x22 190
2x22 0 240
1x22 475
VIN
(V)
VOUT
(V)
L
(µH)
COUT
(µF)
RHIGH
(kΩ)
RLOW
(kΩ)
Cff
(pF)
F
crossover
(kHz)
5.0 1.8
2.2
5x22
240 120
12
49
4x22 57
2x22 70
3x22 6.8 85
1x22 150
1.5
5x22
6.8
58
4x22 68
3x22 84
2x22 120
1x22 200
1.0
5x22
6.8
77
4x22 92
3x22 120
2x22 0 130
1x22 260
0.47
5x22
0
110
4x22 130
3x22 180
2x22 120 60 190
1x22 475
0.33
5x22
240 120
0
150
4x22 190
3x22 260
2x22 60 30 220
1x22 500
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Recommended Output Filter Components - Continued
VIN
(V)
VOUT
(V)
L
(µH)
COUT
(µF)
RHIGH
(kΩ)
RLOW
(kΩ)
Cff
(pF)
F
crossover
(kHz)
3.0 1.8V
2.2
5x22
240 120
12
36
4x22 42
3x22 50
2x22 6.8 60
1x22 100
1.5
5x22
6.8
42
4x22 49
3x22 60
2x22 79
1x22 140
1.0
5x22
6.8
55
4x22 64
3x22 79
2x22 0 87
1x22 150
0.47
5x22
0
76
4x22 89
3x22 110
2x22 160
1x22 350
0.33
5x22
0
97
4x22 120
3x22 150
2x22 240
1x22 525
VIN
(V)
VOUT
(V)
L
(µH)
COUT
(µF)
RHIGH
(kΩ)
RLOW
(kΩ)
Cff
(pF)
F
crossover
(kHz)
5.0 3.3
2.2
5x22
540 120
22
58
4x22 67
2x22 81
3x22 110
1x22 170
1.5
5x22 75
4x22 87
3x22 100
2x22 140
1x22 240
1.0
5x22
33
100
4x22 120
3x22 140
2x22 190
1x22 325
0.47
5x22
33
170
4x22 200
3x22 240
2x22 350
1x22 225 50 0 450
0.33
5x22
540 120 22
220
4x22 260
3x22 325
2x22 475
1x22 135 30 0 525
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LX7176A
4A Step-Down-Regulator
Production Datasheet
Package Dimensions
Recommended Footprint
QFN 2x2mm 12L Package
Dim
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
0.80
1.00
0.031
.039
A3
0.20 REF
0.008 REF
B
0.20
0.30
0.008
0.012
D 1.90 2.10 0.075 0.083
D2
0.50BSC
0.02BSC
E
1.90
2.10
0.075
0.083
e
0.50 BSC
0.020 REF
L 0.30 0.45 0.012 0.018
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.
2. Dimensions are in millimeters, inches for
reference only.
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LX7176A
4A Step-Down-Regulator
Production Datasheet
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 pre-production data and is
proprietary to Microsemi. It may not be modified in any way without the express written
consent of Microsemi. Product referred to herein is offered in pre-production form only and
ma
y not have completed Microsemi’s Quality Assurance process for Release to Production.
Microsemi reserves the right to change or discontinue this proposed product at any time.
