LTC3403
1.5MHz, 600mA
Synchronous Step-Down
Regulator with Bypass Transistor
FEATURES
s
s
DESCRIPTIO
s
s
s
s
s
s
s
s
s
s
s
s
Dynamically Adjustable Output from 0.3V to 3.5V
Very Low Quiescent Current: Only 20
µ
A
During Operation
600mA Output Current
Internal P-Channel MOSFET Bypass Transistor
High Efficiency: Up to 96%
1.5MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
2.5V to 5V Input Voltage Range
Drives Optional External P-Channel MOSFET
Shutdown Mode Draws < 1µA Supply Current
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Available in 8-Lead 3mm
×
3mm DFN Package
The LTC
®
3403 is a high efficiency monolithic synchro-
nous buck regulator optimized for WCDMA power ampli-
fier applications. The output voltage can be dynamically
programmed from 0.3V to 3.5V. At V
OUT
> 3.6V an internal
bypass P-channel MOSFET connects V
OUT
directly to V
IN
,
eliminating power loss through the inductor. Selectable
forced continuous mode enables fast V
OUT
response to the
controlling input.
Supply current is only 20µA in Burst Mode
®
operation and
drops to <1µA in shutdown. The 2.5V to 5V input voltage
range makes the LTC3403 ideally suited for single Li-Ion
battery-powered applications. 100% duty cycle provides
low dropout operation, extending battery life in portable
systems.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode.
The LTC3403 is available in a low profile 8-lead 3mm
×
3mm DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
APPLICATIO S
s
s
WCDMA Cell Phone Power Amplifiers
Wireless Modems
TYPICAL APPLICATIO
V
IN
2.7V
TO 5V
2.2µH*
C
IN†
10µF
CER
V
IN
MODE
RUN
REF
SW
GDR
V
OUT
LTC3403
C
OUT
**
4.7µF
CER
EFFICIENCY (%)
V
OUT
3× V
REF
600mA
OUTPUT
PROGRAMMING
DAC
GND
3
*MURATA LQH32CN2R2M11
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK212BJ106MN
WCDMA
RF PA
3403 F01a
Figure 1a. WCDMA Transmitter Power Supply
U
95
90
85
80
75
70
65
60
55
50
0.1
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
V
OUT
= 1.8V
1
10
100
OUTPUT CURRENT (mA)
1000
3403 F01b
U
U
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 4.2V
Figure 1b. Efficiency vs Output Current
3403f
1
LTC3403
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
GDR
V
IN
GND
SW
1
2
3
4
9
8
7
6
5
V
OUT
REF
MODE
RUN
Input Supply Voltage (< 300µs) .................. – 0.3V to 6V
Input Supply Voltage (DC) ....................... – 0.3V to 5.5V
RUN, REF, MODE, V
OUT
, GDR Voltages ..... – 0.3V to V
IN
SW Voltage .................................. – 0.3V to (V
IN
+ 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
Peak SW Sink and Source Current ........................ 1.3A
Bypass P-Channel FET Source Current ...................... 1A
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................ – 65°C to 150°C
(DD Package) .................................... –65°C to 125°C
ORDER PART
NUMBER
LTC3403EDD
DD PACKAGE
8-LEAD (3mm
×
3mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 9)
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 43°C/ W,
θ
JC
= 3°C/ W
DD PART MARKING
LAAX
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 3.6V unless otherwise specified.
SYMBOL
V
OUT
∆V
OUT
I
PK
V
LOADREG
V
IN
I
S
PARAMETER
Regulated Output Voltage
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Operating Current
Burst Mode Operation
Forced Continuous Mode Operation
Shutdown
Oscillator Frequency
Bypass PFET Turn-Off Threshold
Bypass PFET Turn-On Threshold
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
R
DS(ON)
of Bypass P-Channel FET
SW Leakage
Bypass PFET Leakage
RUN Threshold
RUN Input Current
MODE Threshold
MODE Input Current
REF Input Current
CONDITIONS
V
REF
= 1.1V, MODE = V
IN
V
REF
= 0.1V, MODE = V
IN
V
IN
= 2.5V to 5V
V
IN
= 3V, V
REF
= 0.9V
q
q
q
MIN
3.23
0.25
0.70
TYP
3.3
0.3
0.1
1
0.7
MAX
3.37
0.35
0.4
1.25
5
q
2.5
20
1.5
0.1
1.5
700
1.2
1.21
0.3
0.4
0.3
0.4
0.15
0.20
±0.01
±0.01
1
±0.01
1.5
±0.01
±0.01
UNITS
V
V
%/V
A
%
V
µA
mA
µA
MHz
kHz
V
V
Ω
Ω
Ω
Ω
Ω
Ω
µA
µA
V
µA
V
µA
µA
f
OSC
V
REF
R
PFET
R
NFET
R
BYPASS
I
LSW
I
LBYP
V
RUN
I
RUN
V
MODE
I
MODE
I
REF
MODE = 0V, SW = Open
MODE = V
IN
, SW = Open
V
RUN
= 0V, V
IN
= 4.2V
V
REF
≥
0.25V
V
REF
≤
0.1V
V
REF
=
V
REF
=
I
SW
= 160mA, Wafer Level
I
SW
= 160mA, DD Package
I
SW
= –160mA, Wafer Level
I
SW
= –160mA, DD Package
I
OUT
= 100mA, V
IN
= 3V, Wafer Level
I
OUT
= 100mA, V
IN
= 3V, DD Package (Note 4)
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
V
OUT
= 0V, V
IN
= 5V, V
REF
= 0V
V
RUN
= 2.5V or 0V
q
1.2
550
1.167
35
2.5
1
1.8
850
1.26
0.4
0.4
0.18
±1
±1
1.5
±1
2
±1
±1
q
q
q
q
q
0.3
0.3
2
U
3403f
W
U
U
W W
W
LTC3403
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3403E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
LTC3403: T
J
= T
A
+ (P
D
)(43°C/W)
Note 4:
When V
REF
> 1.2V and V
REF
x3 > V
IN
, the P-channel FET will be on
in parallel with the bypass PFET reducing the overall R
DS(ON)
.
Note 5:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs V
IN
100
95
90
85
I
L
= 100mA
I
L
= 300mA
I
L
= 600mA
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
80
75
70
65
60
55
50
2.5
I
L
= 10mA
3.0
3.5
V
IN
(V)
4.0
Efficiency vs Output Current
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
T
A
= 25°C
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
V
OUT
= 1.5V
1
10
100
OUTPUT CURRENT (mA)
1000
3403 G03
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 4.2V
EFFICIENCY (%)
V
IN
= 3.6V
FREQUENCY (MHz)
U W
3403 G01
(From Figure 1a)
Efficiency vs Output Current
100
90
80
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 4.2V
Efficiency vs V
OUT
100
90
80
70
60
50
40
T
A
= 25°C
V
IN
= 3.6V
0
1
2
V
OUT
(V)
3403 GO1a
100mA BURST
MODE 0PERATION
100mA FORCED
CONTINUOUS MODE
70
60
50
40
30
20
10
4
0
0.1
600mA FORCED
CONTINUOUS MODE
T
A
= 25°C
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
V
OUT
= 1.2V
1
10
100
OUTPUT CURRENT (mA)
1000
3403 G02
4.5
3
Efficiency vs Output Current
100
90
80
70
60
50
40
30
20
10
0
0.1
V
IN
= 3.6V
V
IN
= 4.2V
T
A
= 25°C
FORCED
CONTINUOUS
MODE
Burst Mode
OPERATION
V
OUT
= 2.5V
1
10
100
OUTPUT CURRENT (mA)
1000
3403 G04
Oscillator Frequency
vs Temperature
1.70
V
IN
= 3.6V
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
V
IN
= 3.6V
V
IN
= 4.2V
3403 G05
3403f
3
LTC3403
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Supply Voltage
1.8
T
A
= 25°C
1600
1400
FREQUENCY (kHz)
OSCILLATOR FREQUENCY (MHz)
1.7
1.6
1.5
1.4
1.3
1.2
2
3
4
5
SUPPLY VOLTAGE (V)
Output Voltage vs Load Current
1.844 T = 25°C
A
V
IN
= 3.6V
1.834
OUTPUT VOLTAGE (V)
1.824
R
DS(ON)
(Ω)
1.814
1.804
1.794
1.784
1.774
0 100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
3403 G07
R
DS(ON)
vs Temperature
0.7
V
IN
= 2.7V
0.6
V
IN
= 4.2V
0.5
R
DS(ON)
(Ω)
4500
V
IN
= 3.6V
DYNAMIC SUPPLY CURRENT (µA)
0.4
0.3
V
IN
= 3V
0.2
0.1
0
–50 –25
V
IN
= 4.2V
MAIN SWITCH
SYNCHRONOUS SWITCH
BYPASS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
V
IN
= 3.6V
4
U W
(From Figure 1a)
Frequency vs V
OUT
T
A
= 25°C
V
IN
= 3.6V
1200
1000
800
600
400
6
3403 G06
0
0.2
0.4
0.6
0.8
V
OUT
(V)
1.0
1.2
3403 F06a
R
DS(ON)
vs Input Voltage
0.7
0.6
0.5
0.4
0.3
0.2
BYPASS SWITCH
0.1
0
0
1
5
4
2
3
INPUT VOLTAGE (V)
6
7
3403 G08
T
A
= 25°C
MAIN
SWITCH
SYNCHRONOUS
SWITCH
Dynamic Supply Current
vs Supply Voltage
T
A
= 25°C
4000 V
OUT
= 1.8V
I
LOAD
= 0A
3500
3000
2500
2000
1500
1000
500
0
2
3
Burst Mode
OPERATION
4
SUPPLY VOLTAGE (V)
3403 G09
3403 G10
FORCED CONTINUOUS
MODE
5
6
3403f
LTC3403
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a)
Switch Leakage vs Temperature
300
V
IN
= 5.5V
RUN = 0V
250
SWITCH LEAKAGE (nA)
100
SWITCH LEAKAGE (pA)
80
60
40
20
0
SYNCHRONOUS
SWITCH
120
200
150
100
50
0
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
50
25
75
0
TEMPERATURE (°C)
100
125
Start-Up from Shutdown
RUN
2V/DIV
V
OUT
1V/DIV
I
L
500mA/DIV
3403 G13
V
IN
= 3.6V
40µs/DIV
V
REF
= 0.6V
R
LOAD
= 3Ω
MODE = 3.6V, FORCED CONTINUOUS MODE
Forced Continuous Mode
V
OUT
200mV/DIV
I
L
500mA/DIV
I
L
200mA/DIV
V
OUT
10mV/DIV
V
IN
= 3.6V
V
REF
= 0.6V
I
LOAD
= 0A
MODE = 3.6V
U W
Switch Leakage vs Input Voltage
T
A
= 25°C
RUN = 0V
MAIN
SWITCH
0
1
2
3
4
INPUT VOLTAGE (V)
5
6
3403 G12
3403 G11
Burst Mode Operation
V
OUT
0.1V/DIV
I
L
200mA/DIV
V
IN
= 3.6V
V
REF
= 0.6V
I
LOAD
= 60mA
MODE = 0V
2µs/DIV
3403 G14
Load Step Response
I
LOAD
500mA/DIV
V
IN
= 3.6V
20µs/DIV
V
REF
= 0.6V
I
LOAD
= 50mA TO 600mA
MODE = 0V, Burst Mode OPERATION
3403 G16
200ns/DIV
3403 G15
3403f
5
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