3772.pm65
1
LTC3772
3772f
No Current Sense Resistor Required
40A 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 8A Supply Current in Shutdown
Low Profile 8-Lead SOT-23 (1mm) and
(3mm 2mm) DFN (0.75mm) Packages
1- or 2-Cell Li-Ion Battery-Powered Applications
Wireless Devices
Portable Computers
Distributed Power Systems
550kHz Micropower Step-Down DC/DC Converter
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 40A 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.
I
TH
/RUN
LTC3772
20k
82.5k
174k
22pF
680pF
GND
V
FB
3772 TA01
SW
V
IN
PGATE
10F
3.3H
V
IN
2.75V TO 9.8V
V
OUT
2.5V
2A
47F
Efficiency and Power Loss vs Load Current
LOAD CURRENT (mA)
60
EFFICIENCY (%)
POWER LOSS (W)
80
100
50
70
90
1
100
1000
10000
3772 TA01b
40
0.01
1
10
0.1
0.001
10
V
IN
= 3.3V
V
IN
= 3.3V
FIGURE 5 CIRCUIT
V
IN
= 5V
V
IN
= 5V
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
Micropower No R
SENSE
Constant Frequency Step-Down
DC/DC Controller
, 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.
2
LTC3772
3772f
ORDER PART
NUMBER
(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 (<10s) ........................ 1A
LTC3772EDDB
T
JMAX
= 125C,
JA
= 76C/W
EXPOSED PAD (PIN 9) IS GND
MUST BE SOLDERED TO PCB
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
Consult LTC Marketing for parts specified with wider operating temperature ranges.
DDB8 PART MARKING
LBNR
Operating Temperature Range (Note 2) .. 40C to 85C
Junction Temperature (Note 3) ............................ 125C
Storage Temperature Range ................. 65C to 125C
Lead Temperature (Soldering, 10 sec)
TSOT-23 ........................................................... 300C
ORDER PART
NUMBER
LTC3772ETS8
T
JMAX
= 125C,
JA
= 230C/W
TS8 PART MARKING
LTBNQ
I
PRG
1
I
TH
/RUN 2
V
FB
3
GND 4
8 NC
7 SW
6 V
IN
5 PGATE
TOP VIEW
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
TOP VIEW
9
DDB PACKAGE
8-LEAD (3mm 2mm) PLASTIC DFN
5
6
7
8
4
3
2
1
GND
V
FB
I
TH
/RUN
I
PRG
PGATE
V
IN
SW
NC
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Voltage Range
2.75
9.8
V
Input DC Supply Current
(Note 4)
Normal Operation
V
ITH
/RUN = 1.3V
250
375
A
SLEEP Mode
40
60
A
Shutdown
V
ITH
/RUN = 0V
8
20
A
UVLO
V
IN
< UVLO Threshold 100mV
1
5
A
Undervoltage Lockout (UVLO) Threshold
V
IN
Rising
2.0
2.75
V
V
IN
Falling
1.85
2.60
V
Start-Up Current Source
V
ITH
/RUN = 0V
0.7
1.2
1.7
A
Shutdown Threshold (at I
TH
/RUN)
V
ITH
/RUN Rising
0.3
0.6
0.95
V
Regulated Feedback Voltage
0C T
A
85C (Note 5)
0.788
0.800
0.812
V
40C T
A
85C (Note 5)
0.780
0.800
0.812
V
Feedback Voltage Line Regulation
2.75V V
IN
9.8V (Note 5)
0.08
0.2
mV/V
Feedback Voltage Load Regulation
I
TH
/RUN = 1.6V (Note 5)
0.2
%
I
TH
/RUN = 1V (Note 5)
0.2
%
The
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 4.2V unless otherwise noted. (Note 2)
ELECTRICAL CHARACTERISTICS
3
LTC3772
3772f
V
FB
Input Current
(Note 5)
10
2
10
nA
Overvoltage Protect Threshold
Measured at V
FB
0.850
0.880
0.910
V
Overvoltage Protect Hysteresis
40
mV
Oscillator Frequency
Normal Operation
V
FB
= 0.8V
500
550
650
kHz
Output Short Circuit
V
FB
= 0V
200
kHz
Gate Drive Rise Time
C
LOAD
= 3000pF
40
ns
Gate Drive Fall Time
C
LOAD
= 3000pF
40
ns
Peak Current Sense Voltage
I
PRG
= GND (Note 6)
90
105
120
mV
I
PRG
= Floating
160
175
190
mV
I
PRG
= V
IN
228
245
262
mV
Default Soft-Start Time
0.6
ms
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
The
indicates specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. V
IN
= 4.2V unless otherwise noted. (Note 2)
ELECTRICAL CHARACTERISTICS
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 0C to 70C. Specifications over the 40C to 85C
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
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
U
W
Quiescent Current (No Load)
vs Input Voltage
INPUT VOLTAGE (V)
2
QUIESCENT CURRENT (
A)
40
50
10
3772 G01
30
20
4
6
8
3
5
7
9
60
35
45
25
55
TEMPERATURE (C)
60
QUIESCENT CURRENT (
A)
40
45
50
60
3772 G02
35
30
20
20
40
80
0
40
100
25
20
55
INPUT VOLTAGE (V)
2
QUIESCENT CURRENT (
A)
15
20
25
5
7
10
3772 G03
10
5
0
3
4
6
8
9
Quiescent Current (No Load)
vs Temperature
Quiescent Current (Shutdown)
vs Input Voltage
4
LTC3772
3772f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Quiescent Current (Shutdown)
vs Temperature
Shutdown Threshold
vs Temperature
Regulated Feedback Voltage
vs Temperature
TEMPERATURE (C)
60
QUIESCENT CURRENT (
A)
8
10
12
60
3772 G04
6
4
20
20
40
80
0
40
100
2
0
14
TEMPERATURE (C)
50
400
V
ITH
/RUN (mV)
500
600
700
800
30
10
10
30
3772 G05
50
70
90
V
IN
= 4.2V
TEMPERATURE (C)
50
V
FB
(mV)
804
808
812
10
50
3772 G06
800
796
30
10
30
80
90
792
788
V
IN
= 4.2V
Regulated Feedback Voltage
vs Input Voltage
Oscillator Frequency
vs Temperature
Oscillator Frequency
vs Input Voltage
INPUT VOLTAGE (V)
2
0.788
FEEDBACK VOLTAGE (V)
0.792
0.796
0.800
0.804
4
6
8
10
3772 G07
0.808
0.812
3
5
7
9
TEMPERATURE (C)
50
500
f
OSC
(kHz)
510
530
540
550
600
570
10
30
50
3772 G08
520
580
590
560
30
10
70
90
V
IN
= 4.2V
V
IN
(V)
2
540
f
OSC
(kHz)
545
550
555
560
3
4
5
6
3772 G09
7
8
9
10
T
A
= 25C
I
TH
/RUN Start-Up Current
vs Temperature
TEMPERATURE (C)
60
0.5
I
TH
/RUN PULL-UP CURRENT (
A)
0.6
0.8
0.9
1.0
1.5
1.2
20
20
40
3772 FG10
0.7
1.3
1.4
1.1
40
0
60
80
100
I
TH
/RUN = 0V
I
TH
/RUN Start-Up Current
vs Input Voltage
INPUT VOLTAGE (V)
0
I
TH
/RUN PULL-UP CURRENT (
A)
1.1
1.3
1.5
6
10
3772 G11
0.9
0.7
0.5
2
4
8
1.7
1.9
2.1
I
TH
/RUN = 0V
Undervoltage Lockout Thresholds
vs Temperature
TEMPERATURE (C)
60
1.5
INPUT VOLTAGE (V)
1.6
1.8
1.9
2.0
2.5
2.2
20
20
40
3772 G12
1.7
2.3
2.4
2.1
40
0
60
80
100
RISING
FALLING
5
LTC3772
3772f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Maximum Current Sense
Threshold vs Temperature
Soft-Start Time vs Temperature
Foldback Frequency
vs Temperature
TEMPERATURE (C)
60
0
MAXIMUM CURRENT SENSE THRESHOLD (mV)
50
100
150
200
20
20
60
100
3772 G13
250
300
40
0
40
80
I
PRG
= V
IN
I
PRG
= FLOAT
I
PRG
= GND
TEMPERATURE (C)
60
400
SOFT-START TIME (
s)
500
600
700
800
20
20
60
100
3772 G14
900
1000
40
0
40
80
TEMPERATURE (C)
60
FREQUENCY (Hz)
190
210
100
3772 G15
170
150
20
20
60
40
0
40
80
230
180
200
160
220
V
FB
= 0V
Efficiency vs Load Current
Efficiency vs Load Current
LOAD CURRENT (mA)
60
EFFICIENCY (%)
70
80
90
100
1
100
1000
10000
3772 G17
50
10
V
OUT
= 3.3V
FIGURE 5 CIRCUIT
V
OUT
= 2.5V
V
OUT
= 1.8V
Load Step
Start-Up
V
OUT
1V/DIV
I
TH
/RUN
1V/DIV
I
L
2A/DIV
V
IN
= 5V
V
OUT
= 2.5V
FIGURE 5 CIRCUIT
500s/DIV
3772 G18
V
OUT
100mV/DIV
AC COUPLED
I
LOAD
2A/DIV
I
L
2A/DIV
V
IN
= 5V
V
OUT
= 2.5V
I
LOAD
= 100mA TO 1.5A
FIGURE 5 CIRCUIT
20s/DIV
3772 G19
LOAD CURRENT (mA)
70
EFFICIENCY (%)
80
90
95
1
100
1000
10000
3772 G16
60
10
85
75
65
V
IN
= 3.3V
V
OUT
= 2.5V
FIGURE 5 CIRCUIT
V
IN
= 5V
V
IN
= 7V
V
IN
= 4.2V
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