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LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
KEY FEATURES Internal Reference 1.17V 2% Accuracy (Line and Temperature) 4V to 6.0V Input Range Adj. Output From 1.17V to VIN Output Current (IDC >850mA) Quiescent Current < 300A 1MHz Operation Frequency MSOP 8-Pin APPLICATIONS/BENEFITS Portable Microprocessor Core Voltage Supplies 5V to 3V
DESCRIPTION
The LX1910 PWM buck regulator achieves very high efficiencies over a broad range of operating load conditions. The LX1910 implements a load-detection architecture and enters a power-saving PFM mode when driving small load currents ensuring optimal regulator efficiency over the entire output current range thus maximizing battery life. The PWM operating mode implements a fixed frequency of 1MHz (typ), the transconductance error amplifier has 12A of drive with an output voltage swing rail to rail. Compensation is external for maximum user flexibility.
The LX1910 does not require a minimum load current for stable operation. There is no Under Voltage Lockout for the input voltage, operational range includes 4V to 6V. The regulator is capable of providing an output dc load current of 850mA. The SHDN pin places the device in a sleep-mode drawing less than 1A of quiescent current. The LX1910 comes in space-saving MSOP package allowing a complete application circuit to occupy a very small PCB area. These features make the LX1910 ideal for use in SmartPhones, PDAs, or other batteryoperated devices
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IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com
PRODUCT HIGHLIGHT
LX1910 Efficiency @ Vout=1.5V
90%
LX1910
VIN
CIN
80% CONVERSION EFFICIENCY
PVIN AVIN SHDN COMP
RC CC
L
SW
D CX R1
VOUT
COUT
70% 60% 50% 40% 30% 20% 10% 0 100 200 300 400 500 600 700 OUTPUT CURRENT, mA
FB PGND
R2
AGND
Figure 1 - LX1910 Circuit Topology and Typical Efficiency Performance
PACKAGE ORDER INFO TJ(C) 0 to 85 Input Voltage 4.5V - 6.0V Output Voltage Range 1.17V to VIN
DU
Plastic MSOP 8-PIN
LX1910 LX1910
RoHS Compliant / Pb-free
LX1910CDU
Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. LX1910-13016CDU-TR)
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
PACKAGE PIN OUT
ABSOLUTE MAXIMUM RATINGS
Input Voltage (IN) or SHDN to GND .............................................................................-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) ....................................................................................... 1000mA Operating Temperature Range.......................................................................................-40C to +125C Storage Temperature Range, TA ...................................................................................... -65C to 150C Maximum Junction Temperature.................................................................................................... 150C RoHS / Pb-free Peak Package Solder Reflow Temperature (40 seconds maximum exposure) ......................................................................................260C (+0, -5) 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.
PVIN AVIN SHDN COMP
1 2 3 4
8 7 6 5
SW PGND AGND FB
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DU PACKAGE
(Top View)
RoHS / Pb-free 100% Matte Tin Lead Finish
THERMAL DATA
DU
Plastic MSOP 8-Pin 206C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
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.
FUNCTIONAL PIN DESCRIPTION
NAME SW AGND FB DESCRIPTION Inductor and commutation diode connection point. Connects to internal MOSFET drain. Analog circuit ground providing bias for IC operation. Feedback input for setting adjustable output voltage Enable control input. Reduces quiescent current to 1A. Pin 8, Output becomes high impedance. Unregulated supply voltage input connected to PMOS Source. Input range from +2.7V to 6.0V Frequency Compensation of the overall loop is effected by placing a series R/C combination between COMP pin and GND. Unregulated supply voltage input. Input range from +4V to 6.0V Power ground (return path for internal PMOS gate driver).
SHDN
PVIN COMP AVIN PGND
PACKAGE DATA PACKAGE DATA
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
ELECTRICAL CHARACTERISTICS
Specifications apply over junction temperature of: 0oC < T < 85oC for VIN = 5V (except where otherwise noted). Typical values are at TA=25C.
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Parameter Operating Range Output Voltage Range Feed Back Threshold FB Input Current EA Drive Current (COMP Pin)
Symbol VIN VOUT VFBT IFB ISOURCE ISINK
Test Conditions Functional operation guaranteed by design Closed loop operating range 4V < VIN < 6V VFB = 1.2V VFB -125mV of Overdrive, VCOMP = 2.5V VFB +125mV of Overdrive, VCOMP = 2.5V VOL, Sinking 10A VOH, Sourcing 10A Pin 2 Supply Current VSHDN = 0V, SW Pin open VSHDN = 0V, SW grounded
SHDN = GND or SHDN = 5V Device Off Device On ISW = 0.5A ISW = 0.5A (assured by design, not ATE tested)
Min 3.5 VFB 1.146
Typ
Max 6.0 0.95*VIN
Units V V V nA A A mV V
1.170 300
1.193 500
10 10
16 16 95 4.86 250 400 1 2 5
100 0.2*VIN
EA Output Swing (COMP Pin) Quiescent Operating Current Sleep (Shutdown Mode) Current Shutdown Input Bias Current
Shutdown Voltage Threshold P-Channel Switch ON Resistance Maximum Duty Cycle SW Leakage Current P-Channel Current Limit Frequency Closed Loop Load Regulation Thermal Shutdown
VEA OUT IQ IQVINSD IQVINSD ISD_IB
VSD RDS(ON) D ILEAK ILIM FOP Load Reg TSD
A A A
nA V V
-100
0.8*VIN 0.53 80 900 0.80 100 1 950 1.07 0.35 125 150 5 1.2 0.5 0.8
%
A mA
MHz % VO C
VO = 1.5V, 5mA < IO < 700mA, ckt figure 3
E ELECTRICALS
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
SIMPLIFIED BLOCK DIAGRAM
AVIN
PVIN
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Ramp
comparator
+
avin
SW
Logic
+
bg
PWM
FB
Skip Mode Shutdown
COMP
Thermal Sense
AGND
Figure 2 - LX1910 Block Diagram
LX1910
5.0V PVIN AVIN
4.7F 4.7H
SHDN COMP
30K
AGND
3300pF
Figure 3 - Circuit for 1.5V Output Voltage
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
agnd OSC
pgnd ilimit
SHDN
LX1910
PGND
SW
3300pF D 14K 10F 51K
1.5V
FB PGND
BLOCK DIAGRAM
Microsemi
Page 4
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
APPLICATION NOTE
FUNCTIONAL DESCRIPTION The LX1910 implements a PFM / PWM architecture that improves power management efficiency across the output load range. OUTPUT VOLTAGE PROGRAMMING Resistors R1 and R2 program the output voltage. An optional capacitor CX may be inserted across R1 to improve the transient response (see Figure 1). The value of R2 should be less than 100K. The value of R1 can be determined using the following equation, note VREF is also referred to as VFBT.
V R1 = R2 OUT - 1 V REF
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 capacitance values of 4.7 to 30F have 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 > 4.7F). 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 LX1910; (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 LX1910 VOUT pin and GND pin to reduce high frequency noise and decoupling the VIN pin using a 0.1F capacitor.
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DESIGN EXAMPLE: Let R2 equal 50K and the required VOUT equal to 3.0V.
R1 = 50K
3V - 1 1.17
= 78K
DIODE SELECTION A Schottky diode is recommended for use with the LX1910 because it provides fast switching and superior reverse recovery performance. The Microsemi UPS5817 (20V @ 1A) makes an effective choice for most applications. INDUCTOR SELECTION Selecting the appropriate inductor type and value ensures optimal performance of the converter circuit for the intended application. This selection process requires the designer to make trade-offs between circuit performance and cost. A primary consideration requires the selection of an inductor that will not saturate at the peak current level. Other considerations that affect inductor choice include EMI, output voltage ripple, and overall circuit efficiency. The inductor that works best depends upon the application's requirements. Further, some experimentation with actual devices in-circuit is typically necessary to make the most effective choice. The LX1910 allows for a broad selection of inductor values and choosing a value between 2.2H and 30H supports a majority of applications. Selecting a larger inductor value can increase efficiency and reduce output voltage ripple. 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.
APPLICATIONS APPLICATIONS
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
CHARACTERISTIC CURVES
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LX1910 LOAD REGULATION (Vout=1.5V)
0.15% 0.10% 0.05% 0.00% -0.05% -0.10% -0.15% -0.20% -0.25% -0.30% -0.35% 0 100 200 300 400 500 600 700 IOUT, ma
CONVERSION EFFICIENCY 80% 70% 60% 50% 40% 30% 20% 10% 0 10
LX1910 Efficiency @ Vout=1.5V
OUTPUT DEVIATION, %
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT, ma
Figure 4
Figure 5
1910 LINE REG (Vout=1.5V, Rload=15 ohms)
1.55 1.45 1.35 1.25 Vo VOLT 1.15 1.05 0.95 0.85 0.75 0.65 0.55 1 1.5 2 2.5 3 3.5 4 Vin, volts 4.5 5 5.5 6 Vo Vout Error 0.5% 0.4% 0.3% 0.2% 0.1% 0.0% -0.1% -0.2% -0.3% -0.4% -0.5%
Vfb (Pin 5), Volts 1.180 1.175 1.170 1.165 1.160 1.155 -10 1.185
Feedback Voltage Thermal Stability
0
10
20
30
40
50
60
70
80
Temperature, C
Figure 6
Figure 7
GRAPHS GRAPHS
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
CHARACTERISTIC CURVES
WWW .Microsemi .C OM
Figure 9- Output Load Step Response: CH1: VOUT and CH4: IOUT; Condition: VIN = 5.0V; ISTEP = 50 to 600mA
Figure 10 - Switching Waveforms: PFM Mode CH3: VSW (pin 8) and CH1: VOUT; ( VIN = 5.0V; IOUT = 1mA)
Figure 11 - Switching Waveforms: PWM Mode CH3: VSW (pin 8) and CH1: VOUT; (VIN = 5.0V; IOUT = 10mA)
GRAPHS
Copyright (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1910
TM (R)
Step-Down Regulator
PRODUCTION DATA SHEET
PACKAGE DIMENSIONS
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DU
8-Pin Miniature Shrink Outline Package (MSOP)
A
Dim A B C D G H J K L M N P
B
H
G P C N K M
D
L
MILLIMETERS MIN MAX 2.85 3.05 2.90 3.10 - 1.10 0.25 0.40 0.65 BSC 0.38 0.64 0.13 0.18 0.95 BSC 0.40 0.70 3 0.05 0.15 4.75 5.05
INCHES MIN MAX .112 .120 .114 .122 - 0.043 0.009 0.160 0.025 BSC 0.015 0.025 0.005 0.007 0.037 BSC 0.016 0.027 3 0.002 0.006 0.187 0.198
Note:
Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(0.006") on any side. Lead dimension shall not include solder coverage.
NOTES
MECHANICALS 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 (c) 2004 Rev. 1.1, 2005-02-25
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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