LTC3809-1
LTC3809-1
No R
SENSE
TM
, Low Input
Voltage, Synchronous DC/DC
Controller with Output Tracking
FEATURES
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DESCRIPTIO
Programmable Output Voltage Tracking
No Current Sense Resistor Required
Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
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
Selectable Maximum Peak Current Sense Threshold
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 9µA
Tiny Thermally Enhanced Leadless (3mm
×
3mm)
DFN or 10-lead MSOP Package
The LTC
®
3809-1 is a synchronous step-down switching
regulator 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.
Optional Burst Mode operation provides high efficiency
operation at light loads. 100% duty cycle provides low
dropout operation, extending operating time in battery-
powered systems. Burst Mode is inhibited when the
MODE pin is pulled low to reduce noise and RF interfer-
ence.
The LTC3809-1 allows either coincident or ratiometric
output voltage tracking. Switching frequency is fixed at
550kHz. Fault protection is provided by an overvoltage
comparator and a short-circuit current limit comparator.
The LTC3809-1 is available in the tiny footprint thermally
enhanced DFN package or 10-lead MSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark 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.
APPLICATIO S
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One- or Two-Cell Lithium-Ion Powered Devices
Notebook and Palmtop Computers, PDAs
Portable Instruments
Distributed DC Power Systems
TYPICAL APPLICATIO
High Efficiency, 550kHz Step-Down Converter
10µF
IPRG
MODE
59k
15k
187k
470pF
V
FB
I
TH
RUN
GND
38091 TA01
Efficiency and Power Loss vs Load Current
V
IN
2.75V TO 9.8V
100
EFFICIENCY
90
EFFICIENCY (%)
V
IN
= 3.3V
V
IN
= 5V
80
TYPICAL POWER
LOSS (V
IN
= 4.2V)
V
IN
= 4.2V
100
1k
POWER LOSS (mW)
10k
V
IN
TG
2.2µH
SW
BG
47µF
V
OUT
2.5V
2A
LTC3809-1
70
60
FIGURE 8 CIRCUIT
V
OUT
= 2.5V
1
10
100
1k
LOAD CURRENT (mA)
50
U
10
1
0.1
10k
38091f
38091 TA02
U
U
1
LTC3809-1
ABSOLUTE
AXI U RATI GS
Input Supply Voltage (V
IN
)........................ – 0.3V to 10V
RUN, TRACK/SS, 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
PACKAGE/ORDER I FOR ATIO
TOP VIEW
MODE
TRACK/SS
V
FB
I
TH
RUN
1
2
3
4
5
11
10 SW
9 V
IN
8 TG
7 BG
6 IPRG
ORDER PART
NUMBER
LTC3809EDD-1
MODE
TRACK/SS
V
FB
I
TH
RUN
1
2
3
4
5
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
DD PART
MARKING
LBQZ
T
JMAX
= 125°C,
θ
JA
= 37°C/W
EXPOSED PAD (PIN 11) IS GND
(MUST BE SOLDERED TO PCB)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise noted.
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Operation
Sleep Mode
Shutdown
UVLO
Undervoltage Lockout Threshold (UVLO)
Shutdown Threshold of RUN Pin
Start-Up Current Source
Regulated Feedback Voltage
Output Voltage Line Regulation
Output Voltage Load Regulation
V
FB
Input Current
Overvoltage Protect Threshold
TRACK/SS = 0V
(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
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
(Note 4)
RUN = 0V
V
IN
= UVLO Threshold –200mV
V
IN
Falling
V
IN
Rising
●
●
2
U
U
W
W W
U
W
(Note 1)
Storage Ambient Temperature Range
DFN .................................................. – 65°C to 125°C
MSOP ............................................... – 65°C to 150°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature (Soldering, 10 sec)
MSOP Package ................................................. 300°C
TOP VIEW
10
9
8
7
6
SW
V
IN
TG
BG
IPRG
ORDER PART
NUMBER
LTC3809EMS-1
MS PART
MARKING
LTBQV
11
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 130°C/W
EXPOSED PAD (PIN 11) IS GND
(MUST BE SOLDERED TO PCB)
MIN
TYP
MAX
UNITS
350
105
9
9
1.95
2.15
0.8
0.65
0.591
2.25
2.45
1.1
1
0.6
0.01
0.1
–0.1
9
0.68
500
150
20
20
2.55
2.75
1.4
1.35
0.609
0.04
0.5
–0.5
50
0.7
µA
µA
µA
µA
V
V
V
µA
V
%/V
%
%
nA
V
38091f
LTC3809-1
The
●
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 4.2V unless otherwise noted.
PARAMETER
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 (∆V
SENSE(MAX)
)
(SENSE
+
– SW)
Soft-Start Time (Internal)
Oscillator Frequency
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3809E-1 is guaranteed to meet specified performance
from 0°C to 70°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)
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
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
0.325
TYP
20
0.4
40
40
50
40
MAX
0.475
UNITS
mV
V
ns
ns
ns
ns
110
70
185
0.5
480
125
85
204
0.74
550
140
100
223
0.9
600
mV
mV
mV
ms
kHz
Note 4:
Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5:
The LTC3809-1 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.
38091f
3
LTC3809-1
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency vs Load Current
100
95
90
V
OUT
= 3.3V
FIGURE 8 CIRCUIT
100
V
OUT
= 2.5V
EFFICIENCY (%)
85
80
75
70
65
60
1
V
OUT
= 1.8V
EFFICIENCY (%)
85
80
75
70
65
60
CURRENT LIMIT (%)
V
OUT
= 1.2V
MODE =
V
IN
V
IN
= 5V
10
100
1k
LOAD CURRENT (mA)
10k
38091 G01
Load Step (Burst Mode
Operation)
V
OUT
200mV/DIV
AC COUPLED
V
OUT
200mV/DIV
AC COUPLED
I
L
2A/DIV
100µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
MODE = V
IN
FIGURE 8 CIRCUIT
Start-Up with Internal Soft-Start
(TRACK/SS = V
IN
)
V
IN
= 4.2V
R
LOAD
= 1
FIGURE 8 CIRCUIT
4
U W
T
A
= 25°C unless otherwise noted.
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
100
80
Burst Mode OPERATION
(I
TH
RISING)
Burst Mode OPERATION
(I
TH
FALLING)
FORCED CONTINUOUS
MODE
PULSE SKIPPING
MODE
Efficiency vs Load Current
FIGURE 8 CIRCUIT
95 V
IN
= 5V, V
OUT
= 2.5V
90
BURST MODE
(MODE = V
IN
)
FORCED
CONTINUOUS
(MODE = 0V)
60
40
20
0
–20
55
50
1
PULSE SKIPPING
(MODE = 0.6V)
10
100
1k
LOAD CURRENT (mA)
10k
38091 G02
0.5
1
1.5
I
TH
VOLTAGE (V)
2
38091 G03
Load Step (Forced Continuous
Mode)
V
OUT
200mV/DIV
AC COUPLED
Load Step (Pulse Skipping Mode)
I
L
2A/DIV
I
L
2A/DIV
38091 G04
100µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
MODE = 0V
FIGURE 8 CIRCUIT
38091 G05
100µs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 300mA TO 3A
MODE = V
FB
FIGURE 8 CIRCUIT
38091 G06
Start-Up with External Soft-Start
(C
SS
= 10nF)
V
OUT
1.8V
500mV/DIV
V
OUT
1.8V
500mV/DIV
200µs/DIV
38091 G07
1ms/DIV
V
IN
= 4.2V
R
LOAD
= 1
FIGURE 8 CIRCUIT
38091 G08
38091f
LTC3809-1
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up with Coincident Tracking
(V
OUT
= 0V at 0s)
V
x
2.5V
V
OUT
1.8V
500mV/DIV
10ms/DIV
V
IN
= 4.2V
R
TA
= 590
R
TB
= 1.18k
FIGURE 8 CIRCUIT
38091 G09
Regulated Feedback Voltage vs
Temperature
0.606
0.604
FEEDBACK VOLTAGE (V)
INPUT VOLTAGE (V)
2.55
2.50
2.45
0.602
0.600
0.598
0.596
0.594
–60 –40 –20
2.40
2.35
2.30
V
IN
FALLING
2.25
2.20
2.15
–60 –40 –20
0
20 40 60
TEMPERATURE (°C)
80
100
RUN VOLTAGE (V)
20 40 60
0
TEMPERATURE (°C)
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
135
IPRG = FLOAT
TRACK/SS START-UP CURRENT (µA)
130
125
120
115
–60 –40 –20
U W
80
T
A
= 25°C unless otherwise noted.
Start-Up with Ratiometric
Tracking (V
OUT
= 0V at 0s)
Start-Up with Coincident Tracking
(V
OUT
= 0.8V at 0s)
V
x
2.5V
V
OUT
1.8V
500mV/DIV
V
x
2.5V
V
OUT
1.8V
500mV/DIV
10ms/DIV
V
IN
= 4.2V
R
TA
= 590
R
TB
= 1.18k
FIGURE 8 CIRCUIT
38091 G10
10ms/DIV
V
IN
= 4.2V
R
TA
= 590
R
TB
= 1.69k
FIGURE 8 CIRCUIT
38091 G11
Undervoltage Lockout Threshold
vs Temperature
1.20
V
IN
RISING
Shutdown (RUN) Threshold vs
Temperature
1.15
1.10
1.05
100
1.00
–60 –40 –20
0
20 40 60
TEMPERATURE (°C)
80
100
38091 G012
38091 G13
38091 G14
TRACK/SS Start-Up Current vs
Temperature
1.04
TRACK/SS = 0V
1.02
1.00
0.98
0.96
0
20 40 60
TEMPER
ATURE
(°C)
80
100
0.94
–60 –40 –20
0
20 40 60
TEMPERATURE (°C)
80
100
38091 G15
38091 G16
38091f
5
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