LM3207
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SNVS400A – AUGUST 2006 – REVISED APRIL 2007
LM3207 650mA Miniature, Adjustable, Step-Down DC-DC Converter for RF Power
Amplifiers with Integrated Vref LDO
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FEATURES
•
•
•
•
1
•
•
2
•
•
•
•
•
2MHz (typ.) PWM Switching Frequency
Operates from a single Li-Ion cell (2.7V to
5.5V)
Variable Output Voltage (0.8V to 3.6V)
650mA Maximum load capability
High Efficiency (95% Typ at 3.9VIN, 3.4VOUT at
400mA) from internal synchronous
rectification
Integrated Vref LDO
Regulated LDO Output up to 10mA max
Fast 3uS Vref LDO On/Off Time
9-pin micro SMD Package
Current Overload Protection
Thermal Overload Protection
APPLICATIONS
•
•
•
•
Cellular Phones
Hand-Held Radios
RF PC Cards
Battery Powered RF Devices
DESCRIPTION
The LM3207 is a DC-DC converter optimized for powering WCDMA / CDMA RF power amplifiers (PAs) from a
single Lithium-Ion cell; however they may be used in many other applications. It steps down an input voltage
from 2.7V to 5.5V to a variable output voltage from 0.8V(typ.) to 3.6V(typ.). Output voltage is set using a VCON
analog input for controlling power levels and efficiency of the RF PA.
The LM3207 also provides a regulated reference voltage(Vref) required by linear RF power amplifiers through an
integrated LDO that has a maximum Iref up to 10 mA. See Ordering Information table on page 2 for Voltage
Options.
The LM3207 is available in a 9-pin lead free micro SMD package. High switching frequency (2MHz) allows use of
surface-mount components. Only four small external surface-mount components are required, an inductor and
three ceramic capacitors.
Typical Application
Vin
2.7V to 5.5V
VOUT
3.3 PH
PVIN
EN
0.8V to 3.6V
SW
FB
10 PF
VCON
4.7 PF
LM3207
LDO OUT
ENLDO
SGND
LDO
PGND
100 nF
Figure 1. LM3207 Typical Application
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2006–2007, Texas Instruments Incorporated
LM3207
SNVS400A – AUGUST 2006 – REVISED APRIL 2007
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Connection Diagrams
SW
PVIN
A1
A2
A3
PGND
EN LDO
B1
EN
B2
B3
SGND
C1
C2
C3
LDO
FB
A
1
XVS/Device #
Vcon
Top View
Package Mark - Top View
9–Bump Thin Micro SMD Package, Large Bump NS Package Number TLA09TTA
(1)
Table 1. Pin Descriptions
Pin #
Name
A1
PVIN
B1
ENLDO
Description
Power Supply Voltage Input.
LDO Enable Input. Set this digital input high to turn on LDO (ENpin must also be set high). For shutdown, set
low.
C1
FB
C2
VCON
Feedback Analog Input. Connect to the output at the output filter capacitor.
Voltage Control Analog input. VCON controls VOUT in PWM mode.
C3
LDO
LDO Output Voltage.
B3
SGND
Analog and Control Ground.
A3
PGND
Power Ground.
A2
SW
Switch 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
LM3207.
B2
EN
PWM enable Input. Set this digital input high for normal operation. For shutdown, set low.
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.
2
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Absolute Maximum Ratings
(1) (2)
PVIN to SGND
−0.2V to +6.0V
PGND to SGND
−0.2V to +0.2V
EN, FB, VCON, ENLDO, LDO
(SGND −0.2V)
to (VDD +0.2V)
w/6.0V max
SW
(PGND −0.2V)
to (PVIN +0.2V)
w/6.0V max
PVIN
−0.2V to +0.2V
Continuous Power Dissipation
(3)
Internally Limited
Junction Temperature (TJ-MAX)
+150°C
Storage Temperature Range
−65°C to +150°C
Maximum Lead Temperature
(Soldering, 10 sec)
+260°C
(1)
(2)
(3)
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pins. The LM3207 is designed for mobile phone applications where turn-on after
power-up is controlled by the system controller and where requirements for a small package size overrule increased die size for internal
Under Voltage Lock-Out (UVLO) circuitry. Thus, it should be kept in shutdown by holding the EN pin low until the input voltage exceeds
2.7V.
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ = 150°C (typ.) and
disengages at TJ = 130°C (typ.).
Operating Ratings
(1) (2)
Input Voltage Range
2.7V to 5.5V
Recommended Load Current
0mA to 650mA
Junction Temperature (TJ) Range
−30°C to +125°C
Ambient Temperature (TA) Range
−30°C to +85°C
(3)
(1)
(2)
(3)
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under
which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed
performance limits and associated test conditions, see the Electrical Characteristics tables.
All voltages are with respect to the potential at the GND pins. The LM3207 is designed for mobile phone applications where turn-on after
power-up is controlled by the system controller and where requirements for a small package size overrule increased die size for internal
Under Voltage Lock-Out (UVLO) circuitry. Thus, it should be kept in shutdown by holding the EN pin low until the input voltage exceeds
2.7V.
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 (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP – (θJA × PD-MAX).
Thermal Properties
Junction-to-Ambient Thermal
100°C/W
Resistance (θJA), TLA09 Package
(1)
(1)
Junction-to-ambient thermal resistance (θJA) is taken from thermal measurements, performed under the conditions and guidelines set
forth in the JEDEC standard JESD51-7.
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Electrical Characteristics
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(1) (2) (3)
Limits in standard typeface are for TA = TJ = 25°C. Limits in boldface type apply over the full operating ambient temperature
range (−30°C ≤ TA = TJ ≤ +85°C). Unless otherwise noted, all specifications apply to all LM3207 LDO options with: PVIN = VIN
= ENLDO = EN = 3.6V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
+2.6
%
LDO
VLDO
LDO Output Voltage
Iout = 0 mA
VLDO,MIN
Minimum LDO Output Voltage
Iout = 10mA, PVIN = 3V
ISC
Short circuit current(DC)
VLDO = 0
IPUT
Pull-up current (transient)
VLDO = VLDO(nom)/2, PVIN = 3V
IPD
DC Pull-down current (DC)
VLDO = PVIN, ENLDO = 0
IPDT
Pull-down current (transient)
VLDO = 1.44V, PVIN = 3V
IQ_LDO + PWM
DC Bias current into PVIN
VCON = 2V, FB = 0V, No Switching,
ENLDO = EN = 3.6V (5)
IPIN,ENLDO
LDO Pin pull down current
(4)
-2.6
%
50
mA
150
mA
-50
mA
-200
mA
1.2
1.6
mA
5
10
uA
(4)
Switcher
VFB,
MIN
Feedback Voltage at minimum
setting
VCON = 0.32V
0.75
0.8
0.85
V
VFB,
MAX
Feedback Voltage at maximum
setting
VCON = 1.44V, PVIN = 4.2V
3.537
3.6
3.683
V
ISHDN
Shutdown supply current
EN = ENLDO= SW = VCON = 0V,
0.01
2
µA
IQ_PWM
DC bias current into PVIN
VCON = 2V, FB = 0V, ENLDO = 0V ,
EN = 3.6V, No Switching (5)
1.1
1.6
mA
RDSON(P)
Pin-pin resistance for PFET
ISW = 200mA
RDSON(N)
Pin-pin resistance for NFET
(6)
140
ISW = - 200mA
(7)
300
200
230
415
485
mΩ
mΩ
ILIM,PFET
Switch peak current limit
935
1100
1200
mA
FOSC
Internal oscillator frequency
1.7
2
2.3
MHz
VIH,EN
Logic high input threshold
(PWM, LDO)
1.2
VIL,EN
Logic low input threshold
(PWM, LDO)
IPIN,EN
PWM Pin pull down current
Gain
VCON to VOUT Gain
0.32V ≤ VCON ≤ 1.44V
ICON
VCON pin leakage current
VCON = 1.0V
(1)
(2)
(3)
(4)
(5)
(6)
(7)
4
V
0.5
5
10
2.5
V
µA
V/V
±1
µA
All voltages are with respect to the potential at the GND pins. The LM3207 is designed for mobile phone applications where turn-on after
power-up is controlled by the system controller and where requirements for a small package size overrule increased die size for internal
Under Voltage Lock-Out (UVLO) circuitry. Thus, it should be kept in shutdown by holding the EN pin low until the input voltage exceeds
2.7V.
Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the
most likely norm. Due to the pulsed nature of the testing TA = TJ for the electrical characteristics table.
The parameters in the electrical characteristics table are tested under open loop conditions at PVIN = 3.6V. For performance over the
input voltage range and closed loop results refer to the datasheet curves.
Transient Pull-up current (IPUT) and Transient Pull-down Current (IPDT) will be tested which are inversely proportional to charge and
discharge times tLDO, ON and tLDO, OFF respectively.
IQ specified here is when the part is operating at 100% duty cycle.
Shutdown current includes leakage current of PFET.
Current limit is built-in, fixed, and not adjustable. Refer to datasheet curves for closed loop data and its variation with regards to supply
voltage and temperature. Electrical Characteristic table reflects open loop data (FB = 0V and current drawn from SW pin ramped up until
cycle by cycle limit is activated). Closed loop current limit is the peak inductor current measured in the application circuit by increasing
output current until output voltage drops by 10%.
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System Characteristics
The following spec table entries are guaranteed by design providing the component values in the typical application circuit are
used (L = 3.0µH, (DCR = 0.12Ω, FDK MIPW3226D3R0M);
CIN = 10µF, (6.3V, 0805, TDK C2012X5R0J106K); COUT = 4.7µF, (6.3V, 0603, TDK C1608X5R0J475M); CLDO = 100nF, (10V,
0402, TDK C1005X5R1A104KT) (or 220nF, (6.3V, 0402, TDK C1005X5R0J224KT))) . These parameters are not
guaranteed by production testing. Min and Max values are specified over the VIN range = 2.7V to 5.5V and over the
ambient temp range TA = −30°C to 85°C unless otherwise specified. Typical values are specified at PVIN = EN = 3.6V and TA
= 25°C unless otherwise specified.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
PSRR
Power Supply Rejection
Ratio
Offset Freq = 1Khz, Cout = 100nF,
Iout = 1mA, PVin = Vout(nom) + 0.5V
50
dB
VLDO(NOISE)
Output Noise Voltage
BW = 10Hz to 100Khz, Iout = 1mA
30
uVrms
tLDO, ON
Time to reach 90% of
VLDO(nom) after ENLDO
signal goes high.
CLDO = 100nF, PWM mode assumed to be
fully functional before ENLDO goes high.
PVin = 3V, RLOAD = 562 Ω (1)
3
uS
CLDO = 220nF, PWM mode assumed to be
fully functional before ENLDO goes high.
PVin = 3V, RLOAD = 562 Ω (1)
5
uS
CLDO = 100nF, PVin = 3V, Iout = 0mA
3
CLDO = 220nF, PVin = 3V, Iout = 0mA
5
LDO
tLDO, OFF
Time to reach 10% of
VLDO(nom) after ENLDO
signal goes low.
(1)
uS
(1)
Switcher
TRESPONSE (Rise
time)
Time for VOUT to rise from
0.8V to 3.6V
PVIN = 4.2V, COUT = 4.7uF, L = 3.0uH,
RLOAD = 5.5Ω
20
30
µs
TRESPONSE (Fall
time)
Time for VOUT to fall from
3.6V to 0.8V
PVIN = 4.2V, COUT = 4.7uF, L = 3.0uH,
RLOAD = 10Ω
20
30
µs
CCON
VCON input capacitance
VCON = 1V,
Test frequency = 100 kHz
20
pF
VCON Linearity
Linearity in control
range 0.32V to 1.44V
PVIN = 3.9V, Monotonic in nature
+3
%
T_ON
Turn on time
(time for output to reach
3.6V from Enable low to
high transition)
EN = Low to High, PVIN = 4.2V,
VO = 3.6V, COUT = 4.7µF,
IOUT ≤ 1mA
70
100
µs
Efficiency
(L = 3.0µH, DCR ≤
100mΩ)
PVIN = 3.6V, VOUT = 0.8V, IOUT = 90mA
81
%
PVIN = 3.9V, VOUT = 3.4V, IOUT = 400mA
95
%
VO_ripple
Ripple voltage, PWM
mode
PVIN = 3V to 4.5V, VOUT = 0.8V,
IOUT = 10mA to 400mA, (2)
10
mVp-p
Line_tr
Line transient response
PVIN = 600mV perturbance,
TRISE = TFALL = 10µs, VOUT = 0.8V,
IOUT = 100mA
50
mV
PVIN = 3.1/3.6/4.5V, VOUT = 0.8V,
transients up to 100mA,
TRISE = TFALL = 10µs
50
mV
η
Load_tr
(1)
(2)
Load transient response
-3
Transient Pull-up current (IPUT) and Transient Pull-down Current (IPDT) will be tested which are inversely proportional to charge and
discharge times tLDO, ON and tLDO, OFF respectively.
Ripple voltage should measured at COUT electrode on good layout PC board and under condition using suggested inductors and
capacitors.
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Typical Performance Characteristics
(Circuit in Figure 3, See Operation Description Section),
PVIN = EN = 3.6V, L = 3.0µH, (DCR = 0.12Ω, FDK MIPW3226D3R0M); CIN = 10µF, (6.3V, 0805, TDK C2012X5R0J106K);
COUT = 4.7µF, (6.3V, 0603, TDK C1608X5R0J475M), CLDO = 100nF, 10V, (0402, TDK C1005X5R1A104KT) (or 220nF, (6.3V,
0402, TDK C1005X5R0J224KT)) can be used. TA = 25°C unless otherwise specified.
LDO Typical Performance Curves (2.875 Option)
LDO Voltage
vs
Load Current
(CLDO = 100nF)
LDO Dropout Voltage
vs
Load Current
(CLDO = 100nF), (1)
LDO Short Circuit Current
vs
Voltage
(VIN = 3.0V, CLDO = 100nF)
LDO Output Noise Density
(ILOAD = 1mA, CLDO = 100nF and 220nF)
LDO Power Supply Rejection Ratio
(VIN = Vout(nom) + 0.5V, CLDO = 100nF)
LDO Turn On Time
vs
VIN
(CLDO = 100nF)
50
RIPPLE REJECTION (dB)
40
ILOAD = 1mA
30
20
10
0
-10
-20
-30
-40
-50
100
1k
10k
100k
1M
FREQUENCY (Hz)
(1)
6
Dropout voltage is the voltage difference between the input and the output at which the output voltage drops to 100 mV below its
nominal value.
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LDO Typical Performance Curves (2.875 Option) (continued)
LDO Turn Off Time
vs
VIN
(CLDO = 100nF)
LDO Line Transient Response
(VIN = 3.0V to 3.6V, ILOAD = 10mA, CLDO = 100nF)
IL = 0 mA
1.4
TA = 25°C
TOFF (Ps)
1.2
TA = -30°C
1.0
TA = 85°C
0.8
0.6
3.0
3.5
4.0
4.5
5.0
5.5
PVIN (V)
LDO Load Transient Repsonse
(VIN= 3.2V, VOUT = 0.8V, CLDO = 100nF)
(VIN
LDO VLDO Out
vs
Temperature
= 3.6V,CLDO = 100nF)
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LDO Typical Performance Curves (2.53 Option)
LDO Voltage
vs
Load Current
(CLDO = 100nF)
LDO Dropout Voltage
vs
Load Current
(CLDO = 100nF), (1)
2.53
VLDO OUT (V)
VIN = 5.5V
DROPOUT VOLTAGE (mV)
VIN = 3.6V
VIN = 4.2V
2.52
VIN = 3.0V
VIN = 3.2V
2.51
0
5
10
15
20
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
-110
-120
-130
-140
-150
-160
-170
-180
-190
-200
TA = -30°C
TA = 85°C
TA = 25°C
0
2
4
6
8
10
LOAD CURRENT (mA)
LDO LOAD CURRENT (mA)
LDO Short Circuit Current
vs
Voltage
(VIN = 3.0V, CLDO = 100nF)
LDO Power Supply Rejection Ratio
(VIN = Vout(nom) + 0.5V, CLDO = 100nF)
10
60
0
RIPPLE REJECTION (dB)
TA = 25°C
50
ISC (mA)
40
TA = 85°C
30
TA = -30°C
20
10
0
0.0
8
-20
-30
-40
-50
-60
-70
0.5
1.0
1.5
2.0
2.5
3.0
1
10
100
1000
FREQUENCY (kHz)
VLDO (V)
(1)
ILOAD = 1 mA
-10
Dropout voltage is the voltage difference between the input and the output at which the output voltage drops to 100 mV below its
nominal value.
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LDO Typical Performance Curves (2.53 Option) (continued)
LDO Turn On Time
vs
VIN
(CLDO = 100nF)
LDO Turn Off Time
vs
VIN
(CLDO = 100nF)
1.6
1.2
ILOAD = 5 mA
ILOAD = 0 mA
1.1
1.4
TA = 85°C
TA = 25°C
1.0
1.2
0.9
TOFF (Ps)
TON (Ps)
TA = -30°C
0.8
0.7
TA = -30°C
1.0
0.8
TA = 85°C
0.6
0.6
TA = 25°C
0.5
0.4
0.4
3.0
3.5
4.0
4.5
5.0
5.5
3.0
3.5
4.0
4.5
5.0
5.5
PVIN (V)
PVIN (V)
(VIN
2.536
LDO VLDO Out
vs
Temperature
= 3.6V,CLDO = 100nF)
ILOAD = 0 mA
ILOAD = 5 mA
ILOAD = 1 mA
VLDO OUT (V)
2.534 ILOAD =
10 mA
2.532
2.530
2.528
VIN = 3.6V
2.526
-40
-20
0
20
40
60
80
100
TEMPERATURE (°C)
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SWITCHER Typical Performance Curves
Quiescent Current
vs
Supply Voltage
(VCON = 2V, FB = 0V, No Switching, LDO Disabled)
Quiescent Current
vs
Supply Voltage
(VCON = 2V, FB = 0V, No Switching, LDO Enabled)
Shutdown Current
vs
Temperature
(VCON = 0V, EN = 0V)
Switching Frequency
vs
Temperature
(VOUT = 1.3V, IOUT = 200mA)
SWITCHING FREQUENCY VARIATION (%)
4.0
3.0
VIN = 5.5V
2.0
VIN = 4.2V
1.0
0.0
-1.0
VIN = 3.6V
-2.0
VIN = 2.7V
-3.0
-4.0
-40
-20
0
20
40
60
80
100
AMBIENT TEMPERATURE (oC)
Output Voltage Regulation(%)
vs
Output Load
(VOUT = 1.5V)
(VIN
Output Voltage
vs
Temperature
= 3.6V, VOUT = 0.8V)
-0.30
-0.25
REGULATION (%)
-0.20
VIN = 3.6V
-0.15
-0.10
VIN = 2.7V
-0.05
-0.00
-0.05
-0.10
VIN = 5.5V
-0.15
VIN = 4.5V
-0.20
-0.25
-0.30
0
100
200
300
400
500
600
700
OUTPUT LOAD (mA)
10
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SWITCHER Typical Performance Curves (continued)
(VIN
Output Voltage
vs
Temperature
= 3.6V, VOUT = 3.4V)
Open/Closed Loop Current Limit
vs
Temperature
(PWM Mode)
VCON Voltage
vs
Output Voltage
(VIN = 4.2V, RLOAD = 8Ω)
Efficiency
vs
Output Voltage
(VIN = 3.9V)
Efficiency
vs
Output Current
(VOUT = 0.8V)
Efficiency
vs
Output Current
(VOUT = 3.4V)
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SWITCHER Typical Performance Curves (continued)
Load Transient Response
(VOUT = 0.8V)
Load Transient Response
(VIN = 4.2V, VOUT = 3.4V)
Startup
(VIN = 3.6V, VOUT = 1.3V, RLOAD = 1kΩ)
Startup
(VIN = 4.2V, VOUT = 3.4V, RLOAD = 5kΩ)
Shutdown Response
(VIN = 4.2V, VOUT = 3.4V, RLOAD = 10Ω)
Line Transient Reponse
(VIN = 3.0V to 3.6V, IOUT = 100mA)
VSW
5V/DIV
VIN = 4.2V
VOUT
VOUT = 3.4V
RL = 10:
2V/DIV
IL
500 mA/DIV
2V/DIV
EN
40 Ps/DIV
(VIN
VCON Voltage Response
= 4.2V, VCON = 0.32V/1.44V, RLOAD = 10Ω)
VSW
VCON and Load Transient
(VIN = 4.2V, VCON = 0.32V/1.44V, RLOAD = 15Ω/8Ω)
2V/DIV
2V/DIV
VSW
3.6V
VOUT
VIN = 4.2V
VCON = 0.32/1.44V
RL = 10:
3.6V
VOUT
0.8V
VIN = 4.2V
VCON = 0.32/1.44V
RL = 15:/8:
1.44V
VCON
0.32V
1.44V
VCON
40 Ps/DIV
12
0.8V
0.32V
40 Ps/DIV
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SWITCHER Typical Performance Curves (continued)
Timed Current Limit Response
(VIN = 3.6V)
Output Voltage Ripple
(VOUT = 1.3V)
Output Voltage Ripple
(VOUT = 3.4V)
Output Voltage Ripple in Pulse Skip
(VIN = 3.64V, VOUT = 3.4V, RLOAD = 5Ω)
VSW
2V/DIV
VSW
VIN = 3.64V
2V/DIV
VOUT = 3.4V
RL = 5:
VIN = 4.2V
VOUT = 3.4V
IOUT = 200 mA
VOUT
10 mV/DIV
AC Coupled
VOUT
10 mV/DIV
AC Coupled
IL
500 mA/DIV
IL
500 mA/DIV
400 ns/DIV
400 ns/DIV
RDSON
vs
Temperature (microSMD)
(P-ch, ISW = 200mA)
RDSON
vs
Temperature (microSMD)
(N-ch, ISW = -200mA)
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SWITCHER Typical Performance Curves (continued)
EN High Threshold
vs
VIN
14
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Block Diagram
PVIN
CURRENT
SENSE
OSCILLATOR
ERROR AMPLIFIER
FB
~
PWM
COMP
MOSFET
CONTROL
LOGIC
VCON
SW
MAIN CONTROL
EN
SHUTDOWN
CONTROL
PGND
PVIN
Active Charge Control
Vref
LDO
LDO Control
(Over Current and Thermal
Protection)
ENLDO
Active Discharge Control
PGND
Figure 2. Functional Block Diagram
Operation Description
The LM3207 is a simple, step-down DC-DC converter with a VREF LDO optimized for powering RF power
amplifiers (PAs) in mobile phones, portable communicators, and similar battery powered RF devices. The DC-DC
converter is designed to allow the RF PA to operate at maximum efficiency over a wide range of power levels
from a single Lithium-Ion battery cell. The DC-DC is based on current-mode buck architecture, with synchronous
rectification for high efficiency. It is designed for a maximum load capability of 650mA in PWM mode.
Maximum load range may vary from this depending on input voltage, output voltage and the inductor chosen.
The device has two pin-selectable operating modes required for powering RF PAs in mobile phones and other
sophisticated portable devices. Fixed-frequency PWM operation offers regulated output at high efficiency while
minimizing interference with sensitive IF and data acquisition circuits. Shutdown mode turns the device off and
reduces battery consumption to 0.01uA (typ).
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Efficiency is typically around 95% for a 400mA load with 3.9VIN, 3.4VOUT. The output voltage is dynamically
programmable from 0.8V (typ) to 3.6V (typ) by adjusting the voltage on the control pin without the need for
external feedback resistors. This ensures longer battery life by being able to change the PA supply voltage
dynamically depending on its transmitting power.
Additional features include current overload protection, and thermal overload shutdown.
The LM3207 is constructed using a chip-scale 9-pin micro SMD package. This package offers the smallest
possible size, for space-critical applications such as cell phones, where board area is an important design
consideration. Use of a high switching frequency (2MHz) reduces the size of external components. As shown in
Figure 1, only four external power components are required for implementation. Use of a micro SMD package
requires special design considerations for implementation. (See Micro SMD Package Assembly and use in the
Applications Information section.) The fine bump-pitch requires careful board design and precision assembly
equipment. Use of this package is best suited for opaque-case applications, where its edges are not subject to
high-intensity ambient red or infrared light. Also, the system controller should set EN low during power-up and
other low supply voltage conditions. (See Shutdown Mode in the Device Information section.)
VIN
10 PF
TX_ON/OFF
EN
R
F
I
C
DAC
VCON
RF_ON/OFF
ENLDO
3.3 PH
PVIN
SW
FB
LM3207
VCC
4.7 PF
RFin
PA
VREF
LDO
100 nF
Figure 3. Typical Application Circuit
Circuit Operation (DC-DC Converter)
Referring to Figure 1 and Figure 2, the LM3207 operates as follows. During the first part of each switching cycle,
the control block in the LM3207 turns on the internal PFET (P-channel MOSFET) switch. This allows current to
flow from the input through the inductor to the output filter capacitor and load. The inductor limits the current to a
ramp with a slope of around (PVIN - VOUT) / L, by storing energy in a magnetic field. During the second part of
each cycle, the controller turns the PFET switch off, blocking current flow from the input, and then turns the
NFET (N-channel MOSFET) synchronous rectifier on. In response, the inductor’s magnetic field collapses,
generating a voltage that forces current from ground through the synchronous rectifier to the output filter
capacitor and load. As the stored energy is transferred back into the circuit and depleted, the inductor current
ramps down with a slope around VOUT / L. The output filter capacitor stores charge when the inductor current is
high, and releases it when low, smoothing the voltage across the load.
The output voltage is regulated by modulating the PFET switch on time to control the average current sent to the
load. The effect is identical to sending a duty-cycle modulated rectangular wave formed by the switch and
synchronous rectifier at SW to a low-pass filter formed by the inductor and output filter capacitor. The output
voltage is equal to the average voltage at the SW pin.
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PWM Operation
While in PWM (Pulse Width Modulation) 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. Energy per cycle is set by
modulating the PFET switch on-time pulse width to control the peak inductor current. This is done by comparing
the signal from the current-sense amplifier with a slope compensated error signal from the voltage-feedback error
amplifier. At the beginning of each cycle, the clock turns on the PFET switch, causing the inductor current to
ramp up. When the current sense signal ramps past the error amplifier signal, the PWM comparator turns off the
PFET switch and turns on the NFET synchronous rectifier, ending the first part of the cycle. If an increase in load
pulls the output down, the error amplifier output increases, which allows the inductor current to ramp higher
before the comparator turns off the PFET. This increases the average current sent to the output and adjusts for
the increase in the load. Before appearing at the PWM comparator, a slope compensation ramp from the
oscillator is subtracted from the error signal for stability of the current feedback loop. The minimum on time of
PFET in PWM mode is 50ns (typ.)
Shutdown Mode
Setting the EN digital pin low (1.2V) enables normal operation.
EN should be set low to turn off the LM3207 during power-up and under voltage conditions when the power
supply is less than the 2.7V minimum operating voltage. The LM3207 is designed for compact portable
applications, such as mobile phones. In such applications, the system controller determines power supply
sequencing and requirements for small package size outweigh the additional size required for inclusion of UVLO
(Under Voltage Lock-Out) circuitry.
Internal Synchronous Rectification
While in PWM mode, the LM3207 uses an internal NFET as a synchronous rectifier to reduce rectifier forward
voltage drop and associated power loss. Synchronous rectification provides a significant improvement in
efficiency whenever the output voltage is relatively low compared to the voltage drop across and ordinary rectifier
diode.
The internal NFET synchronous rectifier is turned on during the inductor current down slope in the second part of
each cycle. The synchronous rectifier is turned off prior to the next cycle. The NFET is designed to conduct
through its intrinsic body diode during transient intervals before it turns on, eliminating the need for an external
diode.
Current Limiting
A current limit feature allows the LM3207 to protect itself and external components during overload conditions. In
PWM mode, a 1200mA (max.) cycle-by-cycle current limit is normally used. If an excessive load pulls the output
voltage down to approximately 0.375V, then the device switches to a timed current limit mode. In timed current
limit mode the internal PFET switch is turned off after the current comparator trips and the beginning of the next
cycle is inhibited for 3.5us to force the instantaneous inductor current to ramp down to a safe value. The
synchronous rectifier is off in timed current limit mode. Timed current limit prevents the loss of current control
evident in some products when the output voltage is pulled low in serious overload conditions.
Dynamically Adjustable Output Voltage
The LM3207 features dynamically adjustable output voltage to eliminate the need for external feedback resistors.
The output can be set from 0.8V(typ.) to 3.6V(typ.) by changing the voltage on the analog VCON pin. This feature
is useful in PA applications where peak power is needed only when the handset is far away from the base station
or when data is being transmitted. In other instances the transmitting power can be reduced. Hence the supply
voltage to the PA can be reduced, promoting longer battery life. See Setting the Output Voltage in the Application
Information section for further details.
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Thermal Overload Protection
The LM3207 has a thermal overload protection function that operates to protect itself from short-term misuse and
overload conditions. When the junction temperature exceeds 150°C, the device inhibits operation. The PFET and
NFET are turned off in PWM mode. The LDO is turned off as well. When the temperature drops below 130°C,
normal operation resumes. Prolonged operation in thermal overload conditions may damage the device and is
considered bad practice.
LDO Operation
An LDO is used to provide a regulated Vref supply to a RF PA with a fixed voltage. The LDO can be enabled
only after the PWM is running. The LDO will automatically be disabled whenever the EN or ENLDO is disabled.
Included in the LDO are active charge and discharge circuits to quickly move a 100nF capacitor to meet the 3us
timing requirements, or an 220nF capacitor to meet the 5us timing requirements. The charging and discharging
currents are controlled to minimize supply disturbances. The LM3207 was designed specifically to work with a
100nF or a 220nF ceramic capacitor and no bypass capacitor. See Ordering Information table on page 2 for
Voltage Options.
Application Information
SETTING THE DC-DC CONVERTER OUTPUT VOLTAGE
The LM3207 features a pin-controlled variable output voltage to eliminate the need for external feedback
resistors. It can be programmed for an output voltage from 0.8V (typ.) to 3.6V (typ.) by setting the voltage on the
VCON pin, as in the following formula:
VOUT = 2.5 x VCON
(2)
When VCON is between 0.32V and 1.44V, the output voltage will follow proportionally by 2.5 times of VCON.
If VCON is over 1.44V (VOUT = 3.6V), sub-harmonic oscillation may occur because of insufficient slope
compensation. If VCON voltage is less than 0.32V (VOUT = 0.8V), the output voltage may not be regulated due to
the required on-time being less than the minimum on-time (50ns). The output voltage can go lower than 0.8V
providing a limited VIN range is used. Refer to datasheet curve (VCON Voltage vs Output Voltage) for details. This
curve is for a typical part and there could have part-to-part variation for output voltages less than 0.8V over the
limited VIN range.
LDO CAPACITOR SELECTION
The output capacitor should be connected between the LDO output and a good ground connection. This
capacitor must be selected within specified capacitance range and have sufficiently low ESR. The ESR of the
capacitor is generally a major factor in LDO stability. Refer to manufacturer ESR curves for more detail. Table 2
suggests acceptable capacitors and their suppliers.
Table 2. Suggested capacitors and their suppliers
Model
Vendor
C1005X5R1A104KT, 100nF, 10V
TDK
C1005X5R0J224KT, 220nF, 6.3V
TDK
INDUCTOR SELECTION
A 3.3µH inductor with saturation current rating over 1200mA and low inductance drop at the full DC bias
condition is recommended for almost all applications. The inductor’s DC resistance should be less than 0.2Ω for
good efficiency. For low dropout voltage, lower DCR inductors are advantageous. The lower limit of acceptable
inductance is 1.7µH at 1200mA over the operating temperature range. Full attention should be paid to this limit,
because some small inductors show large inductance drops at high DC bias. These can not be used with the
LM3207. Table 3 suggests some inductors and suppliers.
Table 3. Suggested inductors and their suppliers
Model
NR3015T3R3M
18
Size (WxLxH) [mm]
3.0 x 3.0 x 1.5
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Table 3. Suggested inductors and their suppliers (continued)
Model
Size (WxLxH) [mm]
Vendor
DO3314-332MXC
3.3 x 3.3 x 1.4
Coilcraft
MIPW3226D3R0M
3.2 x 2.6 x 1.0
FDK
If a smaller inductance inductor is used in the application, the LM3207 may become unstable during line and load
transients and VCON transient response times may be affected. For low-cost applications, an unshielded bobbin
inductor is suggested. For noise critical applications, a toroidal or shielded-bobbin inductor is recommended. A
good practice is to layout the board with footprints accommodating both types for design flexibility. This allows
substitution of a low-noise toroidal inductor, in the event that noise from low-cost bobbin models is unacceptable.
Saturation occurs when the magnetic flux density from current through the windings of the inductor exceeds what
the inductor’s core material can support with a corresponding magnetic field. This can result in poor efficiency,
regulation errors or stress to DC-DC converter like the LM3207.
DC-DC CONVERTER CAPACITOR SELECTION
The LM3207 is designed with a ceramic capacitor for its input and output filters. Use a 10µF ceramic capacitor
for input and a 4.7µF ceramic capacitor for output. They should maintain at least 50% capacitance at DC bias
and temperature conditions. Ceramic capacitors types such as X5R, X7R 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 suggests acceptable part numbers and their 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-size capacitor for VIN, the operation of the LM3207should be carefully evaluated on
the system board. Output capacitors with smaller case sizes mitigate piezo electric vibrations when the output
voltage is stepped up and down at fast rates. However, they have a larger percentage drop in value with dc bias.
Use of multiple 2.2µF or 1µF capacitors in parallel may also be considered.
Table 4. Suggested capacitors and their suppliers
Model
Vendor
0805ZD475KA, 4.7µF, 10V
Taiyo-Yuden
C1608X5R0J475M, 4.7uF, 6.3V
TDK
C1608X5R0J106M, 10µF, 6.3V
TDK
C2012X5R0J106M, 10uF, 6.3V
TDK
C2012X5R1A475M, 4.7uF, 6.3V
TDK
The input filter capacitor supplies AC current drawn by the PFET switch of the LM3207 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 ESR
(Equivalent Series Resistance) to perform these functions. The ESR of the filter capacitors is generally a factor in
voltage ripple.
EN PIN CONTROL
Drive the EN and ENLDO pins using the system controller to turn the LM3207 ON and OFF. Use a comparator,
Schmidt trigger or logic gate to drive the EN and ENLDO pins. Set EN high (>1.2V) for normal operation and low
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