Sample &
Buy
Product
Folder
Support &
Community
Tools &
Software
Technical
Documents
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
LM3242 6-MHz, 750-mA Miniature Adjustable Step-Down DC-DC Converter With Auto
Bypass for RF Power Amplifiers
1 Features
3 Description
•
The LM3242 is a DC-DC converter optimized for
powering RF power amplifiers (PAs) from a single
lithium-ion cell; however, it may be used in many
other applications. It steps down an input voltage
from 2.7 V to 5.5 V to an adjustable output voltage
from 0.4 V to 3.6 V. Output voltage is set using a
VCON analog input for controlling power levels and
efficiency of the RF PA.
1
•
•
•
•
•
•
•
•
•
2.7-V to 5.5-V Input Voltage Operating From
Single Li-Ion Cell
6-MHz (typical) PWM Switching Frequency
0.4-V to 3.6-V Adjustable Output Voltage
750-mA Maximum Load Capability
(up to 1 A in Bypass)
High Efficiency (95% typical at 3.9 VIN,
3.3 VOUT at 500 mA)
Automatic ECO/PWM/BP Mode Change
Current Overload Protection
Thermal Overload Protection
Soft-Start Function
Small Chip Inductor in 0805 (2012) case size
The LM3242 offers five modes of operation. In PWM
mode the device operates at a fixed frequency of
6 MHz (typical) which minimizes RF interference
when driving medium-to-heavy loads. At light load,
the device enters into ECO mode automatically and
operates with reduced switching frequency. In ECO
mode, the quiescent current is reduced and extends
the battery life. Shutdown mode turns the device off
and reduces battery consumption to 0.1 µA (typical).
In low-battery condition Bypass mode reduces the
voltage dropout to less than 50 mV (typical). The part
also features a Sleep mode.
2 Applications
•
•
•
•
Battery-Powered 3G/4G RF PAs
Battery-Powered RF Devices
Hand-Held Radios
RF PC Cards
The LM3242 is available in a 9-bump lead-free
DSBGA package. A high switching frequency (6 MHz)
allows use of only three tiny surface-mount
components: one inductor and two ceramic
capacitors.
Device Information(1)
PART NUMBER
LM3242
PACKAGE
DSBGA (9)
BODY SIZE (MAX)
1.51 mm × 1.385 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Typical Application
VIN
2.7V to 5.5V
VIN
BPEN
10 PF
0.5 PH
VOUT = 2.5 x VCON
0.4V to 3.6V
SW
EN
LM3242
FB
GPO1
VCON
4.7 PF
SGND
PGND
DAC
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
Table of Contents
1
2
3
4
5
6
7
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
4
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
4
4
4
4
5
6
6
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
System Characteristics ............................................
Timing Requirements ................................................
Typical Characteristics ..............................................
Detailed Description ............................................ 11
7.1 Overview ................................................................. 11
7.2 Functional Block Diagram ....................................... 12
7.3 Feature Description................................................. 12
7.4 Device Functional Modes........................................ 13
8
Application and Implementation ........................ 16
8.1 Application Information............................................ 16
8.2 Typical Application ................................................. 16
9 Power Supply Recommendations...................... 20
10 Layout................................................................... 21
10.1 Layout Guidelines ................................................. 21
10.2 Layout Examples................................................... 23
10.3 DSBGA Package Assembly and Use ................... 25
11 Device and Documentation Support ................. 26
11.1
11.2
11.3
11.4
11.5
11.6
Device Support......................................................
Documentation Support ........................................
Community Resources..........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
26
26
26
26
26
26
12 Mechanical, Packaging, and Orderable
Information ........................................................... 26
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision D (March 2013) to Revision E
•
Added Device Information and Pin Configuration and Functions sections, ESD Ratings table, Feature Description,
Device Functional Modes, Application and Implementation, Power Supply Recommendations, Layout, Device and
Documentation Support, and Mechanical, Packaging, and Orderable Information sections ................................................. 1
Changes from Revision C (March 2013) to Revision D
•
2
Page
Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 25
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
5 Pin Configuration and Functions
YFQ Package
9-Pin DSBGA
Top View (left); Bottom View (right)
VCON
SGND
PGND
PGND
SGND
VCON
EN
NC
SW
SW
NC
EN
BPEN
FB
VIN
VIN
FB
BPEN
Pin Functions
PIN
TYPE
DESCRIPTION
NUMBER
NAME
A1
VCON
A/I
Voltage control analog input. VCON controls VOUT in PWM and ECO modes. VCON may also
be used to force bypass condition by setting VCON > VIN/2.5.
A2
SGND
G
Signal ground for analog and control circuitry.
A3
PGND
G
Power ground for the power MOSFETs and gate drive circuitry
B1
EN
D/I
Enable Input. Set this digital input high for normal operation. For shutdown, set low. Do not
leave EN pin floating.
B2
NC
—
Do not connect to PGND directly — Internally connected to SGND.
B3
SW
P/O
Switching node connection to the internal PFET switch and NFET synchronous rectifier.
Connect to an inductor with a saturation current rating that exceeds the maximum Switch Peak
Current Limit specification of the LM3242.
C1
BPEN
D/I
Bypass Enable input. Set this digital input high to force bypass operation. For normal operation
with automatic bypass, set low or connect to ground. Do not leave this pin floating.
C2
FB
A
Feedback analog input and bypass FET output. Connect to the output at the output filter
capacitor.
C3
VIN
P/I
Voltage supply input for SMPS converter.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
3
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
VIN to SGND
MIN
MAX
UNIT
−0.2
6
V
−0.2
0.2
V
EN, VCON, BPEN
(SGND − 0.2)
(VIN + 0.2) w/ 6 V
V
SW, FB
(PGND – 0.2)
(VIN + 0.2)
V
PGND to SGND
Continuous power dissipation
(2)
Internally limited
Maximum lead temperature (soldering, 10 sec)
260
°C
Junction temperature, TJ-MAX
150
°C
150
°C
−65
Storage temperature, Tstg
(1)
(2)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typical) and
disengages at TJ = 125°C (typical).
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22C101 (2)
±1250
Machine model
±200
UNIT
V
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted) (1)
MIN
Input voltage
Recommended load current
MAX
UNIT
5.5
V
0
750
mA
PWM mode
0
750
mA
Bypass mode
0
1000
mA
−30
125
°C
−30
90
°C
Junction temperature, TJ
Ambient temperature, TA
(1)
(2)
NOM
2.7
(2)
All voltages are with respect to the potential at the GND pins.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may
have to be de-rated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP =
125°C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to ambient thermal resistance of the
part/package in the application (RθJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (RθJA × PD-MAX).
6.4 Thermal Information
LM3242
THERMAL METRIC (1)
YFQ (DSBGA)
UNIT
9 PINS
RθJA
(1)
4
Junction-to-ambient thermal resistance
85
°C/W
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
6.5 Electrical Characteristics
All typical limits in are for TA = TJ = 25°C; all minimum and maximum limits apply over the full operating ambient temperature
range (−30°C ≤ TA = TJ ≤ +90°C). Unless otherwise noted, all specifications apply to the Typical Application with VIN = EN =
3.6 V, and BPEN = NC = 0 V.
MIN
TYP
MAX
UNIT
VFB,MIN
PARAMETER
Feedback voltage at
minimum setting
PWM mode, VCON = 0.16 V (1)
TEST CONDITIONS
0.38
0.4
0.42
V
VFB,MAX
Feedback voltage at
maximum setting
PWM mode, VCON = 1.44 V, VIN = 4 V
3.55
3.6
3.65
V
ISHDN
Shutdown supply current
EN = SW = VCON = FB = BPEN = NC = 0 V (2)
0.1
1
µA
IQ_PWM
PWM mode quiescent
current
PWM mode, No switching
VCON = 0.13 V, FB = 1 V (3)
650
795
µA
IQ_SLEEP
Low-power SLEEP mode
EN = VIN, BPEN = NC = 0 V, SW = TriState
VCON < 0.08 V (3)
60
80
IQ_ECO
ECO mode Quiescent
current
ECO mode, No switching
VCON = 0.8 V, FB = 2.05 V (3)
60
80
µA
RDSON (P)
Pin-pin resistance for PFET VIN = VGS = 3.6 V, ISW = 200 mA
170
260
mΩ
RDSON (N)
Pin-pin resistance for NFET VIN = VGS = 3.6 V, ISW = −200 mA
110
200
mΩ
RDSON (BP)
Pin-Pin resistance for
BPFET
80
110
mΩ
1300
1450
1600
mA
310
400
6
VIN = VGS = 3.1 V, ISW = −200 mA
(4)
ILIM
P
PFET switch peak current
limit
See
ILIM
BP
BPFET switch peak current
limit
VFB = VIN − 1 V (4)
FOSC
Internal oscillator frequency
5.7
VIH
EN, BPEN logic high input
threshold
1.2
VIL
EN, BPEN logic low input
threshold
Gain
VCON to VOUT gain
0.16 V ≤ VCON ≤ 1.44 V (5)
IVCON
VCON pin leakage current
VCON = 1 V
VBP,NEG
Auto bypass detection
negative threshold
VCON = 1.2 V (VOUT-SET = 3 V)
VIN = 3.2 V, RL = 6 Ω, IOUT = 500 mA (6)
165
VBP,POS
Auto bypass detection
positive threshold
VCON = 1.2 V (VOUT-SET = 3 V)
VIN = 3.25 V, RL = 6 Ω, IOUT = 500 mA (7)
215
IBP,SLEW
Auto bypass IOUT slew
current
BPEN = High, Forced bypass
(1)
(2)
(3)
(4)
(5)
(6)
(7)
µA
mA
6.3
MHz
V
0.4
2.5
V
V/V
±1
µA
200
235
mV
250
285
mV
1600
mA
All 0.4-V VOUT specifications are at steady-state only.
Shutdown current includes leakage current of PFET.
IQ specified here is when the part is not switching under test mode conditions. For operating quiescent current at no load, refer to
Typical Characteristics.
Current limit is built-in, fixed, and not adjustable.
Care must be taken to keep the VCON pin voltage less than the VIN pin voltage as this can place the part into a manufacturing test
mode.
Entering Bypass mode VIN is compared to the programmed output voltage (2.5 × VCON). When VIN − (2.5 × VCON) falls below VBP,NEG
longer than TBP,NEG, the Bypass FET turns on, and the switching FET turns on.
Bypass mode is exited when VIN − (2.5 × VCON) exceeds VBP,POS longer than TBP,POS, and PWM mode resumes. The hysteresis for
the bypass detection threshold VBP,POS – VBP,NEG is always positive and will be approximately 50 mV.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
5
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
6.6 System Characteristics
The following spec table entries are ensured by design providing the component values in the Typical Application are used.
These parameters are not ensured by production testing. Minimum and Maximum values apply over the full operating
ambient temperature range (−30°C ≤ TA ≤ +90°C) and over the VIN range = 2.7 V to 5.5 V unless otherwise specified. L = 0.5
µH, DCR = 50 mΩ, CIN = 10 µF, 6.3 V, 0603 (1608), COUT = 4.7 µF, 6.3 V, 0402.
PARAMETER
D
TEST CONDITIONS
MIN
Maximum duty cycle
RBP
Bypass mode resistance
CVCON
VCON input capacitance
VOUT
Linearity
η
MAX
UNIT
100%
(1)
Maximum output current
capability
IOUT
TYP
VCON range 0.16 V to 1.44 V
Efficiency
VIN = VGS = 3.1 V, IOUT = –500 mA
VCON > 1.16 V
75
2.7 V ≤ VIN ≤ 5.5 V
2.5 × VCON ≤ VIN − 285 mV
mΩ
750
mA
2.7 V ≤ VIN ≤ 5.5 V
2.5 × VCON ≥ VIN – 165 mV, Bypass
mode
1000
VCON = 1 V, Test frequency = 100 KHz
(VIN − 0.2 V)/2.5
X
1
1
X
X
> 130 mV, < (VIN − 0.2 V)/2.5
> 100 mA
< 50 mA
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
13
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
7.4.1 PWM Mode Operation
While in PWM mode operation, the converter operates as a voltage-mode controller with input voltage
feedforward. This allows the converter to achieve excellent load and line regulation. The DC gain of the power
stage is proportional to the input voltage. To eliminate this dependence, feed forward inversely proportional to the
input voltage is introduced. While in PWM mode, the output voltage is regulated by switching at a constant
frequency and then modulating the energy per cycle to control power to the load. At the beginning of each clock
cycle the PFET switch is turned on and the inductor current ramps up until the comparator trips and the control
logic turns off the switch. The current limit comparator can also turn off the switch in case the current limit of the
PFET is exceeded. Then the NFET switch is turned on and the inductor current ramps down. The next cycle is
initiated by the clock turning off the NFET and turning on the PFET.
7.4.2 Bypass Mode Operation
The LM3242 contains an internal BPFET switch for bypassing the PWM DC-DC converter during Bypass mode.
In Bypass mode, this BPFET is turned on to power the PA directly from the battery for maximum RF output
power. When the part operates in the Bypass mode, the output voltage is the input voltage less the voltage drop
across the resistance of the BPFET in parallel with the PFET + Switch Inductor. Bypass mode is more efficient
than operating in PWM mode at 100% duty cycle because the combined resistance is significantly less than the
series resistance of the PWM PFET and inductor. This translates into higher voltage available on the output in
Bypass mode, for a given battery voltage. The part can be set to bypass mode by sending BPEN pin high. This
is called Forced Bypass Mode and it remains in bypass mode until BPEN pin goes low. Alternatively the part can
go into Bypass mode automatically. This is called Auto-Bypass mode or Automatic Bypass mode. The bypass
switch turns on when the difference between the input voltage and programmed output voltage is less than 200
mV (typical) for longer than 10 µs (typical). The bypass switch turns off when the input voltage is higher than the
programmed output voltage by 250 mV (typical) for longer than 0.1 µs (typical). This method is very system
resource friendly in that the Bypass PFET is turned on automatically when the input voltage gets close to the
output voltage, a typical scenario of a discharging battery. It is also turned off automatically when the input
voltage rises, a typical scenario when connecting a charger. When VOUT < 300 mV, BPEN is ignored.
7.4.3 ECO Mode Operation
At very light loads (50 mA to 100 mA), the LM3242 enters ECO mode operation with reduced switching
frequency and supply current to maintain high efficiency. During ECO mode operation, the LM3242 positions the
output voltage slightly higher (7 mV typical) than the normal output voltage during PWM mode operation, allowing
additional headroom for voltage drop during a load transient from light to heavy load.
ECO Mode at Light Load
High ECO Threshold
Load current increases
Target Output Voltage
Low ECO Threshold
PWM Mode at Heavy Load
Figure 22. Operation In ECO Mode and Transfer to PWM Mode
7.4.4 Sleep Mode Operation
When VCON is less than 80 mV in 10 µs, the LM3242 goes into SLEEP mode — the SW pin is in Tri-state
(floating), which operates like ECO mode with no switching. The LM3242 device returns to normal operation
immediately when VCON ≥ 130 mV in PWM mode or ECO mode, depending on load detection.
14
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
7.4.5 Shutdown Mode
Setting the EN digital pin low (< 0.4 V) places the LM3242 in Shutdown mode (0.1 µA typical). During shutdown,
the PFET switch, the NFET synchronous rectifier, reference voltage source, control and bias circuitry of the
LM3242 are turned off. Setting EN high (> 1.2 V) enables normal operation. EN must be set low to turn off the
LM3242 during power-up and undervoltage conditions when the power supply is less than the 2.7V minimum
operating voltage. The LM3242 has an undervoltage lock-out (UVLO) comparator to turn the power device off in
the case the input voltage or battery voltage is too low. The typical UVLO threshold is around 2 V for lock and 2.1
V for release.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
15
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
8 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Setting The Output Voltage
The LM3242 features a pin-controlled adjustable output voltage to eliminate the need for external feedback
resistors. It can be programmed for an output voltage from 0.4 V to 3.6 V by setting the voltage on the VCON
pin, as in Equation 1:
VOUT = 2.5 × VCON
(1)
When VCON is between 0.16 V and 1.44 V, the output voltage will follow proportionally by 2.5 times of VCON.
If VCON is less than 0.16 V (VOUT = 0.4 V), the output voltage may not be well regulated. Refer to Figure 21 for
more detail. This curve exhibits the characteristics of a typical part, and the performance cannot be ensured as
there could be a part-to-part variation for output voltages less than 0.4 V. For VOUT lower than 0.4 V, the
converter might suffer from larger output ripple voltage and higher current limit operation.
8.1.2 FB
Typically the FB pin is connected to VOUT for regulating the output voltage maximum of 3.6 V.
8.2 Typical Application
VIN
2.7V to 5.5V
VIN
BPEN
10 PF
VOUT = 2.5 x VCON
0.4V to 3.6V
0.5 PH
SW
EN
LM3242
FB
GPO1
VCON
4.7 PF
SGND
PGND
DAC
Figure 23. LM3242 Typical Application
16
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
Typical Application (continued)
8.2.1 Design Requirements
For typical step-down DC-DC applications, use the parameters listed in Table 2.
Table 2. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Minimum input voltage
2.7 V
Minimum output voltage
0.4 V
Output current
0 to 750 mA
Switching frequency
6 MHz (typical)
8.2.2 Detailed Design Procedure
8.2.2.1 Inductor Selection
There are two main considerations when choosing an inductor; the inductor must not saturate, and the inductor
current ripple is small enough to achieve the desired output voltage ripple. Different manufacturers follow
different saturation current rating specifications, so attention must be given to details. Saturation current ratings
are typically specified at 25°C so ratings over the ambient temperature of application should be requested from
manufacturer.
Minimum value of inductance to ensure good performance is 0.3 µH at bias current (ILIM (typical)) over the
ambient temperature range. Shielded inductors radiate less noise and are preferred. There are two methods to
choose the inductor saturation current rating:
8.2.2.1.1 Method 1
The saturation current must be greater than the sum of the maximum load current and the worst-case averageto-peak inductor current. This can be written as:
ISAT > IOUT_MAX + IRIPPLE
§VIN - VOUT
© 2xL
x
§
©
§
©
IRIPPLE =
§ VOUT
© VIN
x
§1
©f
§
©
where
where
•
•
•
•
•
•
IRIPPLE: average-to-peak inductor current
IOUT_MAX: maximum load current (750 mA)
VIN: maximum input voltage in application
L minimum inductor value including worst-case tolerances (30% drop can be considered for Method 1)
F: minimum switching frequency (5.7 MHz)
VOUT: output voltage
(2)
8.2.2.1.2 Method 2
A more conservative and recommended approach is to choose an inductor that can handle the maximum current
limit of 1600 mA.
The resistance of the inductor must be less than approximately 0.1 Ω for good efficiency. Table 3 lists suggested
inductors and suppliers.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
17
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
Table 3. Suggested Inductors
MODEL
SIZE (W × L × H) (mm)
VENDOR
2 × 1.2 × 1
FDK
LQM21PNR54MG0
2 × 1.25 × 0.9
Murata
LQM2MPNR47NG0
2 × 1.6 × 0.9
Murata
CIG21LR47M
2 × 1.25 × 1
Samsung
CKP2012NR47M
2 × 1.25 × 1
Taiyo Yuden
MIPSZ2012D0R5
8.2.2.2 Capacitor Selection
The LM3242 is designed for use with ceramic capacitors for its input and output filters. Use a 10-µF ceramic
capacitor for input and a sum total of 4.7-µF ceramic capacitors for the output. They must maintain at least 50%
capacitance at DC bias and temperature conditions. Ceramic capacitors types such as X5R, X7R, and B are
recommended for both filters. These provide an optimal balance between small size, cost, reliability and
performance for cell phones and similar applications. Table 4 lists some suggested part numbers and suppliers.
DC bias characteristics of the capacitors must be considered when selecting the voltage rating and case size of
the capacitor. If it is necessary to choose a 0603 (1608) size capacitor for VIN and 0402 (1005) size capacitor for
VOUT, the operation of the LM3242 must be carefully evaluated on the system board. Use of a 2.2-µF capacitor in
conjunction with multiple 0.47 µF or 1 µF capacitors in parallel may also be considered when connecting to
power amplifier devices that require local decoupling.
Table 4. Suggested Capacitors and Their Suppliers
CAPACITANCE
MODEL
SIZE (W × L) (mm)
VENDOR
2.2 µF
GRM155R60J225M
1 × 0.5
Murata
2.2 µF
C1005X5R0J225M
1 × 0.5
TDK
2.2 µF
CL05A225MQ5NSNC
1 × 0.5
Samsung
4.7 µF
C1608JB0J475M
1.6 × 0.8
TDK
4.7 µF
C1005X5R0J475M
1 × 0.5
TDK
4.7 µF
CL05A475MQ5NRNC
1 × 0.5
Samsung
10 µF
C1608X5R0J106M
1.6 × 0.8
TDK
10 µF
GRM155R60J106M
1 × 0.5
Murata
10 µF
CL05A106MQ5NUNC
1 × 0.5
Samsung
The input filter capacitor supplies AC current drawn by the PFET switch of the LM3242 in the first part of each
cycle and reduces the voltage ripple imposed on the input power source. The output filter capacitor absorbs the
AC inductor current, helps maintain a steady output voltage during transient load changes and reduces output
voltage ripple. These capacitors must be selected with sufficient capacitance and sufficiently low Equivalent
Series Resistance (ESR) to perform these functions. The ESR of the filter capacitors is generally a major factor
in voltage ripple.
18
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
8.2.3 Application Curves
VOUT = 2 V
VOUT = 2 V
Figure 24. Output Voltage Ripple In PWM Mode
VIN = 3.9 V
VOUT = 0.4 V to 3.6 V
RLOAD=10 Ω
Figure 25. Output Voltage Ripple In ECO Mode
VIN = 3.6 V to 4.2 V
IOUT = 10 mA/250 mA
VOUT = 0.8 V
RLOAD= 8 Ω
Figure 27. Line Transient Response
Figure 26. VCON Transient Response
VOUT = 2.5 V
IOUT = 50 mA
IOUT = 200 mA
VOUT = 0.6 V
Figure 28. Load Transient Response
IOUT = 10 mA/60 mA
Figure 29. Load Transient Response
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
19
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
VIN = 4.2 V
VOUT = 2.4 V
RLOAD= 3.6 Ω
Figure 30. Start-Up
9 Power Supply Recommendations
The LM3242 device is designed to operate from an input voltage supply range between 2.7 V and 5.5 V. This
input supply must be well regulated.
20
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
10 Layout
10.1 Layout Guidelines
PC board layout is critical to successfully designing a DC-DC converter into a product. As much as a 20-dB
improvement in RX noise floor can be achieved by carefully following recommended layout practices. A properly
planned board layout optimizes the performance of a DC-DC converter and minimizes effects on surrounding
circuitry while also addressing manufacturing issues that can have adverse impacts on board quality and final
product yield.
10.1.1 PCB Considerations
Poor board layout can disrupt the performance of a DC-DC converter and surrounding circuitry by contributing to
EMI, ground bounce, and resistive voltage loss in the traces. Erroneous signals could be sent to the DC-DC
converter device, resulting in poor regulation or instability. Poor layout can also result in re-flow problems leading
to poor solder joints between the DSBGA package and board pads. Poor solder joints can result in erratic or
degraded performance of the converter.
10.1.1.1 Energy Efficiency
Minimize resistive losses by using wide traces between the power components and doubling up traces on
multiple layers when possible.
10.1.1.2 EMI
By its very nature, any switching converter generates electrical noise, and the circuit board designer’s challenge
is to minimize, contain, or attenuate such switcher-generated noise. A high-frequency switching converter, such
as the LM3242, switches Ampere level currents within nanoseconds, and the traces interconnecting the
associated components can act as radiating antennas. The following guidelines are offered to help to ensure that
EMI is maintained within tolerable levels.
To minimize radiated noise:
• Place the LM3242 switcher, its input capacitor, and output filter inductor and capacitor close together, and
make the interconnecting traces as short as possible.
• Arrange the components so that the switching current loops curl in the same direction. During the first half of
each cycle, current flows from the input filter capacitor, through the internal PFET of the LM3242 and the
inductor, to the output filter capacitor, then back through ground, forming a current loop. In the second half of
each cycle, current is pulled up from ground, through the internal synchronous NFET of the LM3242 by the
inductor, to the output filter capacitor and then back through ground, forming a second current loop. Routing
these loops so the current curls in the same direction prevents magnetic field reversal between the two halfcycles and reduces radiated noise.
• Make the current loop area(s) as small as possible.
To minimize ground-plane noise:
• Reduce the amount of switching current that circulates through the ground plane: Connect the ground bumps
of the LM3242 and its input filter capacitor together using generous component-side copper fill as a pseudoground plane. Then connect this copper fill to the system ground-plane (if one is used) with multiple vias.
These multiple vias help to minimize ground bounce at the LM3242 by giving it a low-impedance ground
connection.
To minimize coupling to the DC-DC converter’s own voltage feedback trace:
• Route noise sensitive traces, such as the voltage feedback path, as directly as possible from the switcher FB
pad to the VOUT pad of the output capacitor, but keep it away from noisy traces between the power
components.
To decouple common power supply lines, series impedances may be used to strategically isolate circuits:
• Take advantage of the inherent inductance of circuit traces to reduce coupling among function blocks, by way
of the power supply traces.
• Use star connection for separately routing VBATT to PVIN and VBATT_PA.
• Inserting a single ferrite bead in-line with a power supply trace may offer a favorable tradeoff in terms of
board area, by allowing the use of fewer bypass capacitors.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
21
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
Layout Guidelines (continued)
10.1.2 Manufacturing Considerations
The LM3242 package employs a 9-pin (3 mm × 3 mm) array of 250 micron solder balls, with a 0.4-mm pad pitch.
A few simple design rules go a long way to ensuring a good layout.
• Pad size must be 0.225 ± 0.02 mm. Solder mask opening must be 0.325 ± 0.02 mm.
• As a thermal relief, connect to each pad with 7 mil wide, 7 mil long traces, and incrementally increase each
trace to its optimal width. Symmetry is important to ensure the solder bumps re-flow evenly (refer to TI
Application Note AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009).
10.1.3 LM3242 Evaluation Board
The following figures are drawn from a 4-layer board design, with notes added to highlight specific details of the
DC-DC switching converter section.
Figure 31. Simplified LM3242 RF Evaluation Board Schematic
1.
2.
3.
4.
5.
6.
7.
8.
Bulk Input Capacitor C2 must be placed closer to LM3242 than C1.
Add a 1nF (C1) on input of LM3242 for high frequency filtering.
Bulk Output Capacitor C3 must be placed closer to LM3242 than C4.
Add a 1nF (C4) on output of LM3242 for high frequency filtering.
Connect both GND terminals of C1 and C4 directly to System GND layer of phone board.
Connect bumps SGND (A2), NC (B2), BPEN (C1) directly to System GND.
Use 0402 caps for both C2 and C3 due to better high frequency filtering characteristics over 0603 capacitors.
TI has seen some improvement in high frequency filtering for small bypass caps (C1 and C4) when they are
connected to System GND instead of same ground as PGND. These capacitors must be 01005 case size for
minimum footprint and best high frequency characteristics.
Figure 32. LM3242 Recommended Parts Placement (Top View)
22
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
Layout Guidelines (continued)
10.1.3.1 Component Placement
• PVIN
1. Use a star connection from PVIN to LM3242 and PVIN to PA VBATT connection (VCC1). Do not daisychain PVIN connection to LM3242 circuit and then to PA device PVIN connection.
• TOP LAYER
1. Place a via in LM3242 SGND(A2), BPEN(C1) pads to drop and connect directly to System GND Layer 4.
2. Place two vias at LM3242 SW solder bump to drop VSW trace to Layer 3.
3. Connect C2 and C3 capacitor GND pads to PGND bump on LM3242 using a star connection. Place vias
in C2 and C3 GND pads that connect directly to System GND Layer 4.
4. Add 01005/0201 capacitor footprints (C1, C4) to input/output of LM3242 for improved high frequency
filtering. C1 and C4 GND pads connect directly to System GND Layer 4.
5. Place three vias at L1 inductor pad to bring up VSW trace from Layer 3 to top Layer.
• LAYER 2
1. Make FB trace at least 10 mils (0.254 mm) wide.
2. Isolate FB trace away from noisy nodes and connect directly to C3 output capacitor. Place a via in
LM3242 SGND(A2), BPEN(C1) pads to drop and connect directly to System GND Layer 4.
• LAYER 3
1. Make VSW trace at least 15 mils (0.381 mm) wide.
• LAYER 4 (System GND
1. Connect C2 and C3 PGND vias to this layer.
2. Connect C1 and C4 GND vias to this layer.
3. Connect LM3242 SGND(A2), BPEN(C1), NC(B2) pad vias to this layer.
10.2 Layout Examples
Figure 33. Board Layer 1 – PVIN and PGND Routing
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
23
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
Layout Examples (continued)
Figure 34. Board Layer 2 – FB and PVIN Routing
Figure 35. Board Layer 3 – SW, VCON and EN Routing
24
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
LM3242
www.ti.com
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
Layout Examples (continued)
Figure 36. Board Layer 4 – System GND Plane
10.3 DSBGA Package Assembly and Use
Use of the DSBGA package requires specialized board layout, precision mounting and careful re-flow
techniques, as detailed in Texas Instruments Application Note 1112. Refer to the section Surface Mount
Assembly Considerations. For best results in assembly, alignment ordinals on the PC board must be used to
facilitate placement of the device. The pad style used with DSBGA package must be the NSMD (non-solder
mask defined) type. This means that the solder-mask opening is larger than the pad size. This prevents a lip that
otherwise forms if the solder-mask and pad overlap, from holding the device off the surface of the board and
interfering with mounting. See SNVA009 for specific instructions how to do this.
The 9-bump package used for LM3242 has 250-micron solder balls and requires 0.225-mm pads for mounting on
the circuit board. The trace to each pad must enter the pad with a 90°angle to prevent debris from being caught
in deep corners. Initially, the trace to each pad must be 7 mil wide, for a section approximately 7 mil long, as a
thermal relief. Then each trace must neck up or down to its optimal width. The important criterion is symmetry.
This ensures the solder bumps on the LM3242 re-flow evenly and that the device solders level to the board. In
particular, special attention must be paid to the pads for bumps A3 and C3. Because VIN and GND are typically
connected to large copper planes, inadequate thermal reliefs can result in late or inadequate re-flow of these
bumps.
The DSBGA package is optimized for the smallest possible size in applications with red or infrared opaque
cases. Because the DSBGA package lacks the plastic encapsulation characteristic of larger devices, it is
vulnerable to light. Backside metallization and/or epoxy coating, along with front-side shading by the printed
circuit board, reduce this sensitivity. However, the package has exposed die edges. In particular, DSBGA
devices are sensitive to light, in the red and infrared range, shining on the package’s exposed die edges.
Adding a 10-nF capacitor between VCON and ground is recommended for non-standard ESD events or
environments and manufacturing processes. It prevents unexpected output voltage drift.
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
25
LM3242
SNOSB48E – OCTOBER 2011 – REVISED AUGUST 2015
www.ti.com
11 Device and Documentation Support
11.1 Device Support
11.1.1 Third-Party Products Disclaimer
TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT
CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES
OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER
ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.
11.2 Documentation Support
11.2.1 Related Documentation
For additional information, see the following:
TI Application Note AN-1112 DSBGA Wafer Level Chip Scale Package (SNVA009).
11.3 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
11.4 Trademarks
E2E is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
11.6 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
26
Submit Documentation Feedback
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: LM3242
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM3242TME/NOPB
ACTIVE
DSBGA
YFQ
9
250
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 90
SN
LM3242TMX/NOPB
ACTIVE
DSBGA
YFQ
9
3000
RoHS & Green
SNAGCU
Level-1-260C-UNLIM
-30 to 90
SN
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
