June 2013 Rev. 1.0 www.microsemi.com 1
© 2013 Microsemi Corporation
3MHz, 2.4A Constant Frequency
Hysteretic Synchronous Buck Regulator
VOUT
R1
1%
R2
1%
PGOOD
COUT
C1
0.47µH
100k
PVIN
EN
PG
SW
PGND
FB
GND
LX7167A
VIN
CIN
8
5
3
1
4
2
6
VCC
7
Figure 1 · Typical Application of LX7167A
Features
2.4A Step-down Regulator
Operational Input Supply Voltage Range:
3V-5.5V
Integrated PMOS and NMOS
Load Current from Zero to 2.4A
3MHz Switching Frequency
SKIP Pulse to Improve Light Load
Efficiency
Input UVLO and OV Protection
Enable Pin
Power Good
Internal Soft-start
Cycle-by-Cycle Over Current Protection
Hiccup Mode Operation Under FB UVLO
RoHS Compliant for Pb Free
Applications
HDD
Set-Top Box
LCD TV’s
Notebook/Netbook
Routers
Video Cards
PC Peripherals
PoE Powered Devices Smart Phone
Description
LX7167A is a step-down PWM Switching Regulator
IC with integrated high side P-CH and low side N-
CH MOSFETs. The IC operates using a hysteretic
control topology with a full load operating switching
frequency of 3MHz allowing small output filter
components while maintaining excellent dynamic
load response.
The operational input voltage range of LX7167A is
from 3V to 5.5V. The part has a Power Save Mode
(PSM) that automatically transitions between PWM
and PSM mode depending on the load current. This
allows the converter’s efficiency to remain high
when load current drops. There is a Power Good
function to indicate the status of the IC.
In the shutdown mode, the IC’s current consumption
is reduced to less than 1µA and the output capacitor
is discharged.
Other features of the part are: a) Cycle-by-cycle
current limit followed by HICCUP mode which
reduces the overall power dissipation of the internal
MOSFETs, b) thermal protection and internal digital
soft start.
The LX7167A is available in a 2mm x 2mm 8 pin
exposed pad DFN package.
LX7167A
3MHz 2.4A Synchronous Buck Regulator
2
Pin Configuration and Pinout
PGND
SW
GND
FB EN
PG
VCC
PVIN
1
2
3
45
6
7
8
67A
xxxx
Figure 2 · Pinout DFN 2mmx2mm 8L Top View
Marking: First Line 67A
Second Line YWWA (Year/Work Week/Lot Code)
Ordering Information
Pin Description
Pin
Number
Description
1
Ground pin for the power stage.
2
Switch-node pin. Connect the output inductor between this pin and output capacitor.
When the chip is DISABLED, the internal discharge resistor will be enabled to discharge
the output capacitance. The current will flow into this pin.
3
Ground pin.
4
Voltage feedback pin. Connect to the output terminal through a resistor divider network
to set the output voltage of the regulator to the desired value.
5
Pull this pin higher than 1V will enable the controller. When pulled low, the IC will turn
off and the Internal discharge FET will turn on to discharge the output capacitor through
the SW pin.
6
Power-good pin. This is an open-drain output and should be connected to a voltage
rail with an external pull-up resistor. During the power on, this pin switches from
LOW to HI state when FB voltage reaches above the power good threshold and the
internal soft start has finished its operation. It will be pulled low when the FB falls
below the power-good threshold minus the hysteresis. It will turn back on when the
pull FB rises above the threshold.
7
Analog input voltage terminal. Connect this pin to PVIN directly.
8
Input voltage terminal of the regulator. A minimum of 10µF, X5R type ceramic
capacitor must be connected as close as possible from this pin to PGND plane to
insure proper operation.
For good thermal connection, this PAD must be connected using thermal VIAs to the
GND plane and to the LAND pattern of the IC.
Ambient Temperature
Type
Package
Part Number
Packaging Type
-10°C to 85°C
RoHS Compliant,
Pb-free
DFN 2mmx2mm 8L
LX7167ACLD
Bulk / Tube
LX7167ACLD-TR
Tape and Reel
Block Diagram
3
Block Diagram
Freq Correction
Lo
Co Rl
VOUT
R1
R2
VFB
VIN
-
Vref
+
Hysteresis = XmV
Delay = Xns
Freq
Ref
Hysteretic
Engine
ramp
Figure 3 · Simplified Block Diagram of LX7167A
3MHz 2.4A Synchronous Buck Regulator
4
Absolute Maximum Ratings
Parameter
Min
Max
Units
PVIN, VCC, EN, FB, PG to GND
-0.3
7
V
SW to GND
-0.3
7
V
SW to GND ( Shorter than 50ns)
-2
7
V
Junction Temperature
-10
150
°C
Storage Temperature
-65
150
°C
Peak Package Solder Reflow Temperature (40s, reflow)
260 (+0,-5)
°C
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
Operating Ratings
Parameter
Min
Max
Units
PVIN
3
5.5
V
VOUT
0.6
VIN – 0.5
V
Ambient Temperature
-10
85
°C
Output Current
0
2.4
A
Thermal Properties
Thermal Resistance
Typ
Units
θJA
75
°C/W
Note: The JA number assumes 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: Unless otherwise specified, the following specifications apply over the operating ambient temperature of
-10°C ≤ TA ≤ 85°C except where otherwise noted with the following test conditions: PVIN = 5V. Typical
parameter refers to TJ = 25°C.
Symbol
Parameter
Test Condition
Min
Typ
Max
Units
Operating Current
IQ
Input Current
ILOAD = 0
350
500
µA
ISHDN
Input Current at Shut Down
VEN = GND
0.1
2
µA
PVIN Input UVLO
PVIN
Under Voltage Lockout
PVIN rising
2.4
2.8
V
UVLO Hysteresis
260
mV
Electrical Characteristics
5
Symbol
Parameter
Test Condition
Min
Typ
Max
Units
FEEDBACK
VREF
Feedback Voltage
TA = 25°C
0.594
0.600
0.606
V
TA = -10°C to 85°C
0.591
0.609
IFB
FB Pin Input Current
10
nA
Line Regulation
PVIN from 3V to 5.5V
0.70
%
Load Regulation
ILOAD = 0 to 2A. Note 1
1.0
%/A
FB UVLO
VFBUVLO
FB UVLO Threshold
63
70
79
%VREF
OUTPUT DEVICE
RDSON_H
RDSON of High Side
95
150
mΩ
RDSON_L
RDSON of Low Side
75
100
mΩ
IL
Peak Current Limit
2.6
3.5
4.5
A
TSH
Thermal Shutdown
Threshold
150
°C
TH
Thermal Shutdown
Hysteresis
20
°C
PVIN OVP
OVPR
Rising Threshold
5.8
6.1
6.3
V
OVPF
Falling Threshold
5.5
6.1
V
OSCILLATOR FREQUENCY
f
Switching Frequency
2.6
3
3.4
MHz
SOFT START
TSS
Soft Start Time
From EN High to VOUT reach
regulation
380
500
800
µs
THICCUP
Hiccup Time
VFB = 0.2V
1.2
2.5
ms
EN INPUT
ENVIN
Input High
1
V
ENVIL
Input Low
0.4
V
ENH
Hysteresis
0.1
V
ENII
Input Bias
0.01
1
µA
PG ( Power Good)
VPG
Power Good Transition
High Threshold
73
83
93
%
VPGHY
Hysteresis
Either VFB rising or falling
40
mV
PGRDSON
Power Good Internal FET
RDSON
PVIN = 5V
100
300
Ω
PG FET Leakage Current
0.01
1
µA
PG internal Glitch Filter
Note 1
5
µs
OUTPUT DISCHARGE
Internal Discharge Resistor
80
200
1400
Ω
Note 1: Guaranteed by design, not tested during production.
3MHz 2.4A Synchronous Buck Regulator
6
Typical Performance Curves -- (Efficiency)
Figure 4 · Efficiency vs. Output Current with 3.3V Input
Figure 5 · Efficiency vs. Output Current with 5V Input
40
50
60
70
80
90
100
110 100 1000
Efficiency (%)
Load Current (mA)
VOUT = 0.9V
VOUT = 1.2V
VOUT = 1.8V
50
60
70
80
90
100
110 100 1000
Efficiency (%)
Load Current (mA)
VOUT = 0.9V
VOUT = 1.2V
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
Typical Performance Curves -- (Step Load Response.)
7
Typical Performance Curves -- (Step Load Response.)
Figure 6 · Step Response (VIN = 5V, VOUT = 3.3V, L = 0.47µH, COUT = 22µF, Rising Slew Rate: 1A/µs, Falling Slew
Rate: 1A/µs)
3MHz 2.4A Synchronous Buck Regulator
8
Theory of Operation / Application Information
Basic Operation
The operation of the controller consists of comparing the VFB voltage to an internal reference. When
the VFB voltage is lower than the VREF, the upper switch turns on. When the VFB voltage is higher
than VREF, the upper switch turns off and the lower switch turns on. An internal ramp is used to
stabilize the switching frequency and keep the VFB immune to the output capacitor, CO, value or
parasitic components (i.e. ESR, ESL). In addition, a frequency control loop ensures the switching
frequency is constant under continuous conduction mode of operation.
At light load, the converter automatically reduces the switching frequency to optimize efficiency while
ensuring the ripple voltage is low.
Setting of the Output Voltage
The LX7167A develops a 0.6V reference voltage between the feedback pin, FB, and the signal
ground. The output voltage is set by a resistive divider according to the following formula:
  

The output component values are recommended below.
VOUT
L
R1
R2
COUT
C1
5V input
3.3V input
1V
0.47μH
&
0.68μH
66.5kΩ
100kΩ
22μF
10pF
2x22μF
15pF
4x22μF
22pF
1.0μH
22μF
15pF
12pF
2x22μF
22pF
22pF
4x22μF
27pF
27pF
1.8V
0.47μH
&
0.68μH
100kΩ
49.9kΩ
22μF
10pF
2x22μF
15pF
4x22μF
22pF
1.0μH
22μF
15pF
2x22μF
22pF
4x22μF
27pF
2.5V
0.47μH
&
0.68μH
158kΩ
49.9kΩ
22μF
15pF
2x22μF
22pF
4x22μF
33pF
1.0μH
22μF
10pF
22pF
2x22μF
15pF
27pF
4x22μF
22pF
33pF
3.3V
0.47μH
&
0.68μH
158kΩ
34.8kΩ
22μF
22pF
-
2x22μF
33pF
-
4x22μF
47pF
-
1.0μH
22μF
22pF
-
2x22μF
33pF
-
4x22μF
47pF
-
Theory of Operation / Application Information
9
Start Up
The reference (VREF) is ramped up from zero voltage to 0.6V in 500µs. During this time, the PG is
pulled low. When the reference reaches 0.6V, signaling the end of the soft start cycle, the PG pin will
go high within 5µs.
Over Current Protection
The IC has the ability to protect against all types of short circuit protection. It has cycle-by-cycle short
protection that turns off the upper MOSFET and ends the cycle when the current exceeds the OCP
threshold, when this occurs; the off-time is at least 200ns before the upper FET is turned on again.
After startup, if the FB pin drops below the Feedback UVLO threshold, the chip will go into a hiccup
mode of operation. This helps to protect against a crowbar short circuit. The FB UVLO Alarm is not
active during startup.
Hiccup Mode of Operation
Hiccup mode of operation will protect the IC during a short of the output. After startup, it will be
triggered when the FB UVLO is exceeded.
Input Over Voltage Protection
The IC is protected against damage when the input voltage rapidly rises to the absolute maximum
level. When the input voltage rises over the PVIN OVP rising threshold, the IC will turn off switching.
It will resume switching when the input voltage drops below the PVIN OVP falling threshold with
hysteresis.
Typical Application Diagram
VOUT
R1
100k
1%
R2
49.9k
1%
PGOOD
22µF
X5R
0.47µH
100k
22µF
X5R
PVIN
EN
PG
SW
PGND
FB
GND
LX7167A
VIN
0.01µF
8
5
3
1
4
2
6
C1
10pF
VCC
7
Figure 7 · LX7167A Typical Application Diagram
3MHz 2.4A Synchronous Buck Regulator
10
Package Outline Dimensions
Dim
MILLIMETERS
INCHES
MIN
MAX
MIN
MAX
A
0.70
0.80
0.0276
0.0315
A1
0
0.05
0
0.0020
A3
0.20 ref
0.0079 ref
b
0.18
0.30
0.0071
0.0118
D
2.00 BSC
0.0787 BSC
D2
1.55
1.80
0.0610
0.0709
e
0.50 BSC
0.0197 BSC
E
2.00 BSC
0.0787 BSC
E2
0.75
1.00
0.0295
0.0394
L
0.20
0.40
0.0079
0.0157
Figure 8 · 8 Pin Plastic DFN 2x2mm Dual Exposed Pad 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.
D
e
E
AA3
A1
E2
D2
b
L
top bottom
side
Land Pattern Recommendation
11
Land Pattern Recommendation
2.4
0.28
1.4
1.7
0.5
R 2x0.3
0.8
6x0.5
Center Thermal Pad
PCB Land Pattern
Defined Pad
63% Printed
solder coverage
on thermal pad
0.9
Figure 9 · 8 Pin Plastic DFN 2x2mm Dual Exposed Pad Package Footprint
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.
LX7167A-4/1.0
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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