FEATURES
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LTC3809
No R
SENSE
™, Low EMI,
Synchronous DC/DC Controller
DESCRIPTION
The LTC
®
3809 is a synchronous step-down switching regu-
lator controller that drives external complementary power
MOSFETs using few external components. The constant
frequency current mode architecture with MOSFET V
DS
sensing eliminates the need for a current sense resistor
and improves efficiency.
For noise sensitive applications, the LTC3809 can be exter-
nally synchronized from 250kHz to 750kHz. Burst Mode is
inhibited during synchronization or when the SYNC/MODE
pin is pulled low to reduce noise and RF interference. To
further reduce EMI, the LTC3809 incorporates a novel
spread spectrum frequency modulation technique.
Burst Mode operation provides high efficiency operation
at light loads. 100% duty cycle provides low dropout
operation, extending operating time in battery-powered
systems.
The switching frequency can be programmed up to 750kHz,
allowing the use of small surface mount inductors and
capacitors.
The LTC3809 is available in tiny footprint thermally
enhanced DFN and 10-lead MSOP packages.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
No R
SENSE
is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5481178, 5929620, 6580258, 6304066, 5847554,
6611131, 6498466. Other Patents pending.
No Current Sense Resistor Required
Selectable Spread Spectrum Frequency Modulation
for Low Noise Operation
Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
True PLL for Frequency Locking or Adjustment
(Frequency Range: 250kHz to 750kHz)
Wide V
IN
Range: 2.75V to 9.8V
Wide V
OUT
Range: 0.6V to V
IN
0.6V ±1.5% Reference
Low Dropout Operation: 100% Duty Cycle
Selectable Burst Mode
®
/Pulse-Skipping/Forced
Continuous Operation
Auxiliary Winding Regulation
Internal Soft-Start Circuitry
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9μA
Tiny Thermally Enhanced Leadless (3mm
×
3mm)
DFN and 10-lead MSOP Packages
APPLICATIONS
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1- or 2-Cell Lithium-Ion Powered Devices
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATION
High Efficiency, 550kHz Step-Down Converter
10μF
V
IN
TG
2.2μH
15k
187k
470pF
V
FB
I
TH
RUN
GND
SW
BG
IPRG
47μF
V
OUT
2.5V
2A
V
IN
2.75V TO 9.8V
Efficiency and Power Loss vs Load Current
100
EFFICIENCY
90
EFFICIENCY (%)
V
IN
= 3.3V
V
IN
= 5V
80
POWER LOSS
V
IN
= 4.2V
V
IN
= 4.2V
100
1k
POWER LOSS (mW)
10k
LTC3809
PLLLPF
SYNC/MODE
59k
70
10
60
FIGURE 10 CIRCUIT
V
OUT
= 2.5V
1
10
100
1000
LOAD CURRENT (mA)
1
50
0.1
10000
3809 TA01
3809 TA01b
3809fc
1
LTC3809
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ........................ –0.3V to 10V
PLLLPF, RUN, SYNC/MODE,
IPRG Voltages ............................... –0.3V to (V
IN
+ 0.3V)
V
FB
, I
TH
Voltages ...................................... –0.3V to 2.4V
SW Voltage ......................... –2V to V
IN
+ 1V (10V Max)
TG, BG Peak Output Current (<10μs) ......................... 1A
Operating Temperature Range (Note 2)....–40°C to 85°C
Storage Temperature Range...................–65°C to 125°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature (Soldering, 10 sec)
MSOP Package ................................................. 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
PLLLPF
SYNC/MODE
V
FB
I
TH
RUN
1
2
3
4
5
11
10 SW
9 V
IN
8 TG
7 BG
6 IPRG
PLLLPF
SYNC/MODE
V
FB
I
TH
RUN
1
2
3
4
5
10
9
8
7
6
SW
V
IN
TG
BG
IPRG
11
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 11) IS GND
(MUST BE SOLDERED TO PCB)
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED PAD (PIN 11) IS GND
(MUST BE SOLDERED TO PCB)
ORDER INFORMATION
LEAD FREE FINISH
LTC3809EDD#PBF
LTC3809EMSE#PBF
LEAD BASED FINISH
LTC3809EDD
LTC3809EMSE
TAPE AND REEL
LTC3809EDD#TRPBF
LTC3809EMSE#TRPBF
TAPE AND REEL
LTC3809EDD#TR
LTC3809EMSE#TR
PART MARKING
LBQY
LTBQT
PART MARKING
LBQY
LTBQT
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
3809fc
2
LTC3809
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Operation
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold (UVLO)
Shutdown Threshold of RUN Pin
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB
Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Auxiliary Feedback Threshold
Top Gate (TG) Drive Rise Time
Top Gate (TG) Drive Fall Time
Bottom Gate (BG) Drive Rise Time
Bottom Gate (BG) Drive Fall Time
Maximum Current Sense Voltage (ΔV
SENSE(MAX)
)
(V
IN
– SW)
Soft-Start Time (Internal)
Oscillator and Phase-Locked Loop
Oscillator Frequency
Unsynchronized (SYNC/MODE Not Clocked)
PLLLPF = Floating
PLLLPF = 0V
PLLLPF = V
IN
SYNC/MODE Clocked
Minimum Synchronizable Frequency
Maximum Synchronizible Frequency
f
OSC
> f
SYNC/MODE
f
OSC
< f
SYNC/MODE
Minimum Switching Frequency
Maximum Switching Frequency
SYNC/MODE = 2.2V
480
260
650
550
300
750
200
1000
–3
3
460
635
2.6
600
340
825
250
kHz
kHz
kHz
kHz
kHz
μA
μA
kHz
kHz
μA
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
IPRG = Floating (Note 6)
IPRG = 0V (Note 6)
IPRG = V
IN
(Note 6)
Time for V
FB
to Ramp from 0.05V to 0.55V
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise noted.
CONDITIONS
(Note 4)
RUN = 0V
V
IN
= UVLO Threshold – 200mV
V
IN
Falling
V
IN
Rising
(Note 5)
2.75V < V
IN
< 9.8V (Note 5)
I
TH
= 0.9V (Note 5)
I
TH
= 1.7V
(Note 5)
Measured at V
FB
0.66
0.325
l
l
l
MIN
TYP
MAX
UNITS
350
105
9
3
1.95
2.15
0.8
0.591
2.25
2.45
1.1
0.6
0.01
0.1
–0.1
9
0.68
20
0.4
40
40
50
40
110
70
185
0.5
125
85
204
0.74
500
150
20
10
2.55
2.75
1.4
0.609
0.04
0.5
–0.5
50
0.7
0.475
μA
μA
μA
μA
V
V
V
V
%/V
%
%
nA
V
mV
V
ns
ns
ns
ns
140
100
223
0.9
mV
mV
mV
ms
Phase-Locked Loop Lock Range
750
Phase Detector Output Current
Sinking
Sourcing
Spread Spectrum Frequency Range
SYNC/MODE Pull-Down Current
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3809E is guaranteed to meet specified performance from
0°C to 85°C. Specifications over the –40°C to 85°C operating 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:
T
J
= T
A
+ (P
D
•
θ
JA
°C/W)
Note 4:
Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5:
The LTC3809 is tested in a feedback loop that servos I
TH
to a
specified voltage and measures the resultant V
FB
voltage.
Note 6:
Peak current sense voltage is reduced dependent on duty cycle to
a percentage of value as shown in Figure 1.
3809fc
3
LTC3809
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
1
SYNC/MODE =
V
IN
V
IN
= 5V
10
100
1k
LOAD CURRENT (mA)
10k
3809 G01
Efficiency vs Load Current
100
FIGURE 10 CIRCUIT
95 V
IN
= 5V, V
OUT
= 2.5V
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
1
10
100
1k
LOAD CURRENT (mA)
10k
3809 G02
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
100
80
CURRENT LIMIT (%)
60
40
20
0
–20
Burst Mode OPERATION
(I
TH
RISING)
Burst Mode OPERATION
(I
TH
FALLING)
FORCED CONTINUOUS
MODE
PULSE SKIPPING
MODE
FIGURE 10 CIRCUIT
V
OUT
= 3.3V
V
OUT
= 2.5V
V
OUT
= 1.2V
V
OUT
= 1.8V
BURST MODE
(SYNC/MODE =
V
IN
)
FORCED
CONTINUOUS
(SYNC/MODE = 0V)
PULSE SKIPPING
(SYNC/MODE = 0.6V)
0.5
1
1.5
I
TH
VOLTAGE (V)
2
3809 G03
Load Step
(Burst Mode Operation)
V
OUT
200mV/DIV
AC COUPLED
V
OUT
200mV/DIV
AC COUPLED
Load Step
(Forced Continuous Mode)
I
L
2A/DIV
I
L
2A/DIV
100μs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/MODE = V
IN
FIGURE 10 CIRCUIT
3809 G04
100μs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/MODE = 0V
FIGURE 10 CIRCUIT
3809 G05
Load Step (Pulse-Skipping Mode)
V
OUT
200mV/DIV
AC COUPLED
Start-Up with Internal Soft-Start
V
OUT
1.8V
500mV/DIV
I
L
2A/DIV
100μs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
SYNC/MODE = V
FB
FIGURE 10 CIRCUIT
3809 G06
200μs/DIV
V
IN
= 4.2V
R
LOAD
= 1Ω
FIGURE 10 CIRCUIT
3809 G07
3809fc
4
LTC3809
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
0.606
0.604
FEEDBACK VOLTAGE (V)
INPUT VOLTAGE (V)
0.602
0.600
0.598
0.596
0.594
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
2.55
2.50
2.45
2.40
2.35
2.30
V
IN
FALLING
2.25
2.20
80
100
2.15
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
1.00
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
RUN VOLTAGE (V)
V
IN
RISING
1.15
Undervoltage Lockout Threshold
vs Temperature
1.20
Shutdown (RUN) Threshold
vs Temperature
1.10
1.05
3809 G08
3809 G09
3809 G10
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
135
SYNC/MODE PULL-DOWN CURRENT (μA)
IPRG = FLOAT
2.80
2.75
SYNC/MODE Pull-Down Current
vs Temperature
10
8
NORMALIZED FREQUENCY (%)
100
6
4
2
0
–2
–4
–6
–8
80
Oscillator Frequency
vs Temperature
130
2.70
2.65
2.60
2.55
2.50
2.45
2.40
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
125
120
115
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
–10
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
3809 G11
3809 G12
3809 G13
Oscillator Frequency
vs Input Voltage
5
NORMALIZED FREQUENCY SHIFT (%)
4
SHUTDOWN CURRENT (μA)
3
2
1
0
–1
–2
–3
–4
–5
2
3
4
7
8
5
6
INPUT VOLTAGE (V)
9
10
18
16
Shutdown Quiescent Current
vs Input Voltage
130
120
14
12
10
8
6
4
80
2
0
2
3
4
8
7
6
5
INPUT VOLTAGE (V)
70
9
10
SLEEP CURRENT (μA)
110
100
90
Sleep Current vs Input Voltage
2
3
4
7
8
5
6
INPUT VOLTAGE (V)
9
10
3809 G14
3809 G15
3809 G16
3809fc
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