LTC3772
Micropower No R
SENSE
Constant Frequency Step-Down
DC/DC Controller
FEATURES
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DESCRIPTIO
No Current Sense Resistor Required
40µA No-Load Quiescent Current
High Output Currents Easily Achieved
Internal Soft-Start Ramps V
OUT
Wide V
IN
Range: 2.75V to 9.8V
Low Dropout: 100% Duty Cycle
Constant Frequency 550kHz Operation
Low Ripple Burst Mode
®
Operation at Light Load
Output Voltage as Low as 0.8V
±1.5%
Voltage Reference Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Only 8µA Supply Current in Shutdown
Low Profile 8-Lead SOT-23 (1mm) and
(3mm
×
2mm) DFN (0.75mm) Packages
The LTC
®
3772 is a constant frequency current mode
step-down DC/DC controller in a low profile 8-lead SOT-23
(ThinSOT
TM
) and a 3mm
×
2mm DFN package. The No
R
SENSE
TM
architecture eliminates the need for a current
sense resistor, improving efficiency and saving board
space.
The LTC3772 automatically switches into Burst Mode
operation at light loads to increase efficiency at low output
current. It consumes only 40µA of quiescent current
under a no-load condition.
The LTC3772 incorporates an undervoltage lockout fea-
ture that shuts down the device when the input voltage
falls below 2V. To maximize the runtime from a battery
source, the external P-channel MOSFET is turned on
continuously in dropout (100% duty cycle). High switch-
ing frequency of 550kHz allows the use of a small inductor
and capacitors. An internal soft-start smoothly ramps the
output voltage from zero to its regulation point.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT and No R
SENSE
are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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1- or 2-Cell Li-Ion Battery-Powered Applications
Wireless Devices
Portable Computers
Distributed Power Systems
TYPICAL APPLICATIO
680pF
20k
I
TH
/RUN
LTC3772
GND
82.5k
V
FB
SW
PGATE
V
IN
550kHz Micropower Step-Down DC/DC Converter
V
IN
2.75V TO 9.8V
10µF
Efficiency and Power Loss vs Load Current
100
V
IN
= 3.3V
90
V
IN
= 5V
EFFICIENCY (%)
80
70
60
0.01
50
40
1
FIGURE 5 CIRCUIT
100
1000
10
LOAD CURRENT (mA)
0.1
V
IN
= 5V
V
IN
= 3.3V
3.3µH
47µF
V
OUT
2.5V
2A
22pF
174k
3772 TA01
U
10
1
POWER LOSS (W)
U
U
0.001
10000
3772 TA01b
3772f
1
LTC3772
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Input Supply Voltage (V
IN
)........................ – 0.3V to 10V
IPRG, PGATE Voltages ................ – 0.3V to (V
IN
+ 0.3V)
V
FB
, I
TH
/RUN Voltages ............................. – 0.3V to 2.4V
SW Voltage ........... – 2V to (V
IN
+ 1V) or 10V Maximum
PGATE Peak Output Current (<10µs) ........................ 1A
PACKAGE/ORDER INFORMATION
TOP VIEW
GND 1
V
FB
2
I
TH
/RUN 3
I
PRG
4
9
8
7
6
5
PGATE
V
IN
SW
NC
ORDER PART
NUMBER
LTC3772EDDB
I
PRG
1
I
TH
/RUN 2
V
FB
3
GND 4
TOP VIEW
8 NC
7 SW
6 V
IN
5 PGATE
DDB PACKAGE
8-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 9) IS GND
MUST BE SOLDERED TO PCB
DDB8 PART MARKING
LBNR
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Voltage Range
Input DC Supply Current
Normal Operation
SLEEP Mode
Shutdown
UVLO
Undervoltage Lockout (UVLO) Threshold
Start-Up Current Source
Shutdown Threshold (at I
TH
/RUN)
Regulated Feedback Voltage
Feedback Voltage Line Regulation
Feedback Voltage Load Regulation
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. (Note 2)
CONDITIONS
●
(Note 4)
V
ITH
/RUN = 1.3V
V
ITH
/RUN = 0V
V
IN
< UVLO Threshold – 100mV
V
IN
Rising
V
IN
Falling
V
ITH
/RUN = 0V
V
ITH
/RUN Rising
0°C
≤
T
A
≤
85°C (Note 5)
–40°C
≤
T
A
≤
85°C (Note 5)
2.75V
≤
V
IN
≤
9.8V (Note 5)
I
TH
/RUN = 1.6V (Note 5)
I
TH
/RUN = 1V (Note 5)
●
●
●
●
2
U
U
W
W W
U
W
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec)
TSOT-23 ........................................................... 300°C
ORDER PART
NUMBER
LTC3772ETS8
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 230°C/W
TS8 PART MARKING
LTBNQ
MIN
2.75
TYP
MAX
9.8
UNITS
V
µA
µA
µA
µA
V
V
µA
V
V
V
mV/V
%
%
250
40
8
1
2.0
1.85
0.7
0.3
0.788
0.780
1.2
0.6
0.800
0.800
0.08
0.2
–0.2
375
60
20
5
2.75
2.60
1.7
0.95
0.812
0.812
0.2
3772f
LTC3772
ELECTRICAL CHARACTERISTICS
PARAMETER
V
FB
Input Current
Overvoltage Protect Threshold
Overvoltage Protect Hysteresis
Oscillator Frequency
Normal Operation
Output Short Circuit
Gate Drive Rise Time
Gate Drive Fall Time
Peak Current Sense Voltage
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. (Note 2)
CONDITIONS
(Note 5)
Measured at V
FB
MIN
–10
0.850
TYP
2
0.880
40
V
FB
= 0.8V
V
FB
= 0V
C
LOAD
= 3000pF
C
LOAD
= 3000pF
I
PRG
= GND (Note 6)
I
PRG
= Floating
I
PRG
= V
IN
●
●
●
MAX
10
0.910
UNITS
nA
V
mV
500
550
200
40
40
650
kHz
kHz
ns
ns
90
160
228
105
175
245
0.6
120
190
262
mV
mV
mV
ms
Default Soft-Start Time
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3772ETS8/LTC3772EDDB are guaranteed to meet
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:
T
J
= T
A
+ (P
D
•
θ
JA
°C/W)
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
The LTC3772 are tested in a feedback loop that servos V
FB
to the
output of the error amplifier while maintaining I
TH
/RUN at the midpoint of
the current limit range.
Note 6:
Peak current sense voltage is reduced dependent on duty cycle as
given in Figure 1.
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current (No Load)
vs Input Voltage
60
55
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
50
45
40
35
30
25
20
2
3
4
6
7
5
8
INPUT VOLTAGE (V)
9
10
45
40
35
30
25
20
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
QUIESCENT CURRENT (µA)
80
100
U W
3772 G01
Quiescent Current (No Load)
vs Temperature
55
50
Quiescent Current (Shutdown)
vs Input Voltage
25
20
15
10
5
0
2
3
4
6
5
7
8
INPUT VOLTAGE (V)
9
10
3772 G02
3772 G03
3772f
3
LTC3772
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current (Shutdown)
vs Temperature
14
12
800
QUIESCENT CURRENT (µA)
10
8
6
4
2
0
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
V
ITH
/RUN (mV)
600
V
FB
(mV)
Regulated Feedback Voltage
vs Input Voltage
0.812
0.808
FEEDBACK VOLTAGE (V)
0.804
0.800
0.796
0.792
0.788
2
3
4
f
OSC
(kHz)
f
OSC
(kHz)
8
7
6
5
INPUT VOLTAGE (V)
I
TH
/RUN Start-Up Current
vs Temperature
1.5
1.4
I
TH
/RUN = 0V
I
TH
/RUN PULL-UP CURRENT (µA)
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
I
TH
/RUN PULL-UP CURRENT (µA)
1.5
1.3
1.1
0.9
0.7
0.5
0
2
6
INPUT VOLTAGE (V)
4
8
10
3772 G11
INPUT VOLTAGE (V)
4
U W
80
3772 G04
Shutdown Threshold
vs Temperature
V
IN
= 4.2V
812
808
Regulated Feedback Voltage
vs Temperature
V
IN
= 4.2V
700
804
800
796
500
792
100
400
–50
–30
50
–10 10
30
TEMPERATURE (°C)
70
90
788
–50 –30
30
50
–10 10
TEMPERATURE (°C)
80
90
3772 G05
3772 G06
Oscillator Frequency
vs Temperature
600
590
580
570
560
550
540
530
520
510
9
10
Oscillator Frequency
vs Input Voltage
560
T
A
= 25°C
V
IN
= 4.2V
555
550
545
500
–50
540
–30
30
–10 10
50
TEMPERATURE (°C)
70
90
2
3
4
5
7
6
V
IN
(V)
8
9
10
3772 G07
3772 G08
3772 G09
I
TH
/RUN Start-Up Current
vs Input Voltage
2.1
1.9
1.7
I
TH
/RUN = 0V
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
Undervoltage Lockout Thresholds
vs Temperature
RISING
FALLING
1.5
–60 –40 –20 0 20 40 60
TEMPERATURE (°C)
80
100
3772 FG10
3772 G12
3772f
LTC3772
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
300
250
200
150
I
PRG
= GND
100
50
0
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
I
PRG
= V
IN
SOFT-START TIME (µs)
1000
900
800
700
600
500
400
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
FREQUENCY (Hz)
I
PRG
= FLOAT
Efficiency vs Load Current
95
V
IN
= 3.3V
90
V
IN
= 4.2V
85
EFFICIENCY (%)
90
100
EFFICIENCY (%)
80
75
70
65
60
1
10
100
1000
LOAD CURRENT (mA)
Start-Up
V
OUT
1V/DIV
I
TH
/RUN
1V/DIV
I
L
2A/DIV
3772 G18
V
IN
= 5V
500µs/DIV
V
OUT
= 2.5V
FIGURE 5 CIRCUIT
U W
80
3772 G13
Soft-Start Time vs Temperature
230
220
210
200
190
180
170
160
80
100
Foldback Frequency
vs Temperature
V
FB
= 0V
100
150
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
3772 G14
3772 G15
Efficiency vs Load Current
FIGURE 5 CIRCUIT
V
OUT
= 3.3V
V
IN
= 5V
V
IN
= 7V
80
V
OUT
= 2.5V
V
OUT
= 1.8V
70
60
V
OUT
= 2.5V
FIGURE 5 CIRCUIT
10000
3772 G16
50
1
10
100
1000
LOAD CURRENT (mA)
10000
3772 G17
Load Step
V
OUT
100mV/DIV
AC COUPLED
I
L
2A/DIV
I
LOAD
2A/DIV
3772 G19
20µs/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 100mA TO 1.5A
FIGURE 5 CIRCUIT
3772f
5
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