LX12973 Datasheet

LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
KEY FEATURES
DESCRIPTION
APPLICATIONS/BENEFITS
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ƒ Internal Reference 800mv ±2%
Accuracy (Line and Temp.)
ƒ 4.5V to 5.5V Input Range
ƒ Internal Soft Start
ƒ Adj. Output From 0.8V to VIN
ƒ Output Current (I >1.5A)
ƒ Quiescent Current < 550µA, typ
at 23°C
ƒ 1.1MHz PWM Frequency
ƒ Micro Lead-frame, Thin MO229, 6-Pin Package
The regulator is capable of providing
an output load current of 1.5A, has no
minimum load current requirement for
stable operation.
Current limit is
cycle-by-cycle to protect the switch.
Power conversion efficiency is
maximized with low low regulator IQ
and PFM mode of operation
The LX12973 operational range
covers 4.0V to 6.0V, features include
power on delay; soft start to limit
inrush currents; and thermal shutdown
during fault conditions.
The 6 pin MO-229 package provides
a small form factor with excellent
power dissipation capability.
The LX12973 operates as a Current
Mode PWM Buck regulator that
switches to PFM mode with light
loads. The entire regulator function
is implemented with few external
components.
The LX12973 responds quickly to
dynamic load changes using a high
bandwidth error amplifier and
internal compensation. Tight output
voltage regulation is maintained with
the compensated 800mV, +/-2%
reference (line and temp regulation).
With two external resistors the output
voltage is easily programmed, from
800mV to 90% of Vin.
ƒ Portable Microprocessor Core
Voltage Supplies
ƒ 5V to 3V
ƒ RoHS compliant product
IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com
PRODUCT HIGHLIGHT
4.0 to 6V
EFFICIENCY vs Iout (Vin=5V)
Top Vo=3.375V, Lower Vo=1.25V
4 VINPOWER
N/C
5 VINANALOG
4.7uF
SWITCH
100%
6
3.3uH .
3
FB
90%
80%
C .
2 GND
1.2V
@ 1.5A
25K
1
10
70%
20uF
50K
C= 680p
60%
Ground
Plane
Tie-in
50%
40%
30%
1 mA
10
100
1000
10000
LX12973
Figure 1 – LX12973 Circuit Topology and Typical Efficiency Performance
PACKAGE ORDER INFO
Input Voltage Output Voltage Range
LD
Plastic MO229
6 Pin (3mm²)
RoHS Compliant / Pb-free
0 to 125
4.5V – 5.5V
Adjustable
LX12973CLD
2987
(D/C)
MSC
TJ (°C)
Note: Available in Tape & Reel. Append the letters “TR” to the part number. (i.e. LX12973CLD-TR)
Copyright © 2000
Rev. 1.1, 2005-05-05
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
FB
1
6
N/C
GND
2
5
VIN ANALOG
SW
3
4
VIN PWR
LD PACKAGE (Top View)
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to
Ground. Currents are positive into, negative out of specified terminal.
THERMAL DATA:
Note: Heatsink pad on bottom should be
connected to ground or left floating.
“ LD” PACKAGE
THERMAL RESISTANCE-JUNCTION TO AMBIENT, θJA (ASSUMES NO AMBIENT AIRFLOW)
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Input Voltage (IN)...............................................................................................................-0.3V to 7.0V
SW to GND .............................................................................................................-0.3V to (VIN + 0.3V)
VFB to GND ......................................................................................................................... -0.3V to +2V
SW Peak Current (Internally Limited) ....................................................................................... 1800mA
Operating Temperature Range.......................................................................................-40°C to +125°C
Storage Temperature Range, TA ......................................................................................-65°C to 150°C
Maximum Junction Temperature....................................................................................................150°C
Package Peak Temp. for Solder Reflow (40 seconds max. exposure) ............. 260°C (+0, -5)
25-40°C/W (PCB layout dependent)
Junction Temperature Calculation: TJ = TA + (PD x θJA). The θJA numbers are guidelines for the thermal performance of the device/pc-board system.
FUNCTIONAL PIN DESCRIPTION
NAME
VIN ANALOG
VIN PWR
FB
DESCRIPTION
Unregulated supply voltage input, ranging from +4V to 6.0V for internal analog control circuitry.
Unregulated supply voltage input (+4V to 6.0V), high current path, connects to PMOS Source of PWM switch.
Feedback input for setting programming output voltage.
GND
Circuit ground providing bias for IC operation and high frequency gate drive bias, can be connected to heatsink terminal.
SW
Inductor and commutation diode connection point. Connects to internal PMOSFET source.
ELECTRICAL CHARACTERISTICS
Specifications apply over junction temperature of: 0oC < T < 125oC for VIN = 5V (except where otherwise noted). Typical values are at TA=23°C.
Parameter
`
Symbol
Operating Range
VIN
Test Conditions
Min
Functional operation guaranteed by design
4.5
4.0V < VIN < 6.0V
784
Typ
Max
Units
5.5
V
mV
800
816
FB Input Current
IFB
VFB = 0.81V
40
75
Error Amplifier
BW
Closed Loop
100
VFB > 0.825V, Rload Switch Pin < 1K ohms
500
850
µA
Initial Power On or after Short Circuit
21
50
V/mS
0.25
0.5
Feed Back Threshold
VFBT
Quiescent Operating Current
Soft Start, Vout Slew Rate
P-Channel Switch ON Resistance
IQ (Pin 5)
Vo
RDS(ON)
ISW = 1.0A
ISW = 1.0A (assured by design, not ATE tested)
80
nA
Khz
100
Ω
%
D
SW Leakage Current
ILEAK
VFB = 0.825V
P-Channel Current Limit
ILIM
Peak Current at Switch Pin (not dc current)
1.6
1.9
FOP-PWM
PWM Mode
700
1020
Io
PFM Mode
250
1hz < Frequency Vin < 10Khz
-40
dB
VO = 1.2V, 50mA < IO < 1.2A, ckt figure 1
0.85
%VO
150
°C
PWM Frequency
PFM Mode Region
Feed Back PSRR
Closed Loop Load Regulation
Thermal Shutdown
Copyright © 2000
Rev. 1.1, 2005-05-05
Load Reg
TSD
(assured by design, not ATE tested)
0.01
135
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
5
µA
1400
KHz
ELECTRICALS
Maximum Duty Cycle
A
mA
Page 2
LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
SIMPLIFIED BLOCK DIAGRAM
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VIN
CL
Σ
CLOCK
AND RAMP
PWM
S
R
SWITCH
EA
BG REF
800MV
FEEDBACK
GROUND
Figure 2 – LX12973 Block Diagram
Vout
Cout
INDUCTOR
DIODE
Vin
Gnd
n/ c
FB
Cs
Sw
Cout
Rf
C in
Vpwr
Cout
APPLICATIONS
LX12973
Vin
Rs
Cout
Rf
Ground
Figure 3 – PCB Layout Considerations
Copyright © 2000
Rev. 1.1, 2005-05-05
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
APPLICATION NOTE
OUTPUT VOLTAGE PROGRAMMING
Resistors R1 and R2 program the output voltage. The
value of R2 (lower resistor of divider) should be less than
10KΩ. The value of R1 can be determined using the
following equation, note VREF is also referred to as VFBT.
⎡⎛ V
⎞ ⎤
R1 = R2⎢⎜⎜ OUT ⎟⎟ − 1⎥
⎣⎢⎝ VREF ⎠ ⎦⎥
INDUCTOR SELECTION
Selecting the appropriate inductor type and value ensures
optimal performance of the converter circuit for the
intended application. A primary consideration requires the
selection of an inductor that will not saturate at the peak
current level. EMI, output voltage ripple, and overall circuit
efficiency affect inductor choice. The inductor that works
best depends upon the application’s requirements and some
experimentation with actual devices in-circuit is typically
necessary to make the most effective choice.
Copyright © 2000
Rev. 1.1, 2005-05-05
CAPACITOR SELECTION
To minimize ripple voltage, output capacitors with a low
series resistance (ESR) are recommended. Multi-layer
ceramic capacitors with X5R or X7R dielectric make an
effective choice because they feature small size, very low
ESR, a temperature stable dielectric, and can be connected in
parallel to increase capacitance. Typical output capacitance
values of 10 to 30µF has proven effective. Other low ESR
capacitors such as solid tantalum, specialty polymer, or
organic semiconductor, make effective choices provided that
the capacitor is properly rated for the output voltage and
ripple current. Finally, choose an input capacitor of
sufficient size to effectively decouple the input voltage
source impedance (e.g., CIN > 4.7µF).
LAYOUT CONSIDERATIONS
The high peak currents and switching frequencies present
in DC/DC converter applications require careful attention to
device layout for optimal performance. Basic design rules
include: (1) maintaining wide traces for power components
(e.g., width > 50mils); (2) place CIN, COUT, the Schottky
diode, and the inductor close to the LX12973; (3) minimizing
trace capacitance by reducing the etch area connecting the
SW pin to the inductor; and (4) minimizing the etch length to
the FB pin to reduce noise coupling into this high impedance
sense input. Other considerations include placing a 0.1uF
capacitor between the LX12973 VOUT pin and GND pin to
reduce high frequency noise and decoupling the VIN pin
using a 0.1uF capacitor. The LX12973 Switch has fast
switching speeds which may generate noise spikes when a
high capacitance Schottky diode is selected for the catch
diode. A simple snubber circuit, as shown in Figure 1, R=10
ohms and C=680pF has proven effective to reduce the spike
voltage generated at the Switch Pin / Diode connection.
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
APPLICATIONS
DIODE SELECTION
A Schottky diode is required for switching speed and low
forward voltage. Efficiency is determined mostly by the
diode’s forward voltage. The diode conducts 1-D%, for
Vout=1.2V this becomes 76% in a 5V system.
INDUCTOR SELECTION, CONT.
The LX12973 allows for a broad selection of inductor
values and choosing a value between 2.2µH and 22µH
supports a majority of applications. The benefit of a larger
inductor value can increase efficiency at the lower output
currents and reduces output voltage ripple, thus output
capacitance related to ripple filtering. Smaller inductors
typically provide smaller package size (critical in many
portable applications) at the expense of increasing output
ripple current. Regardless of inductor value, selecting a
device manufactured with a ferrite-core produces lower
losses at higher switching frequencies and thus better overall
performance. Larger inductors may lead to diminished StepLoad response.
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FUNCTIONAL DESCRIPTION
The LX12973 is a Current Mode PWM regulator with
internal compensation.
The internal PMOS high side switch is protected with
current limit on a pulse by pulse basis and with thermal
shutdown. Thermal shutdown is activated with a junction
temperature of 160°C (typical) and has 20°C of hysteresis.
The regulator has an internal Power On Reset delay of
50-100us to ensure all circuitry is operating before enabling
the Switch output.
Soft Start is activated upon initial power-on, or
following recovery from either thermal shutdown or short
circuit. The Soft start control block generates a voltage
ramp that clamps the error amplifier non-inverting
reference voltage. As this clamp voltage rises, the duty
cycle is gradually increased, thus limiting the peak inrush
currents.
PWM / PFM mode of operation is determined by the
load current condition. The PFM mode increases system
efficiency by reducing the switching frequency thus
switching losses. During light loading, Iout < 200ma
typically, PFM mode becomes active, the switching
frequency begins to decrease, the frequency change occurs
over a continuous range, decreasing further as Iout
decreases.
LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
CHARACTERISTIC CURVES
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CH2:VOUT
CH1:SWITCH
Figure 4– Step Load Response 250ma-1.2A 3.3uH, 40uF
Blue: Vout 50mV/div AC; Green: Istep 200ma/div
Figure 5 – Switching Waveforms: PFM Mode
Regulated VOUT vs Temperature
(Iout=10ma)
0.8%
0.6%
0.4%
0.2%
0.0%
-0.2%
-0.4%
-0.6%
-0.8%
CH1:VIN
CH2:VOUT
-25
0
25
50 75 100 125 150
GRAPHS
TEMPERATURE, °C
Figure 6 – Power On and Soft Start
For Iout 10ma to 1amp
Figure 7– Vout Temperature Stability
Copyright © 2000
Rev. 1.1, 2005-05-05
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX12973
VREF @ 800mV, 1.5A, 1.1MHZ PWM
®
TM
P RODUCTION D ATA S HEET
PACKAGE DIMENSIONS
6 Pin Plastic 3 x 3 x .9 mm
D
L1
D2
Pin 1 ID
E
E2
L
K
e
b
A
or
A1
Dim
A
A1
K
e
L
b
D2
E2
D
E
L1
MILLIMETERS
MIN MAX
0.80 1.00
0.00 0.05
0.20 MIN
0.95 BSC
0.30 0.50
0.30 0.45
1.90 2.40
1.15 1.65
3.00 BSC
3.00 BSC
0.00 0.15
INCHES
MIN
MAX
0.031
0.039
0.000
0.002
0.008 MIN
0.037 BSC
0.012
0.02
0.012
0.018
0.75
0.094
0.045
0.065
0.118 BSC
0.118 BSC
0.000
0.006
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LD
or
Note:
Pin 1 ID
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.
NOTES
MECHANICALS
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.
Copyright © 2000
Rev. 1.1, 2005-05-05
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6