LTC3772B
Micropower No R
SENSE
Constant Frequency Step-Down
DC/DC Controller
FEATURES
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DESCRIPTIO
No Current Sense Resistor Required
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 Pulse Skipping 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
®
3772B 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 LTC3772B automatically switches into pulse skipping
operation at light loads. It consumes only 200µA of quies-
cent current under a no-load condition.
The LTC3772B 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.
, LT, LTC and LTM are registered trademarks 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. Protected by
U.S. Patents including 5731694, 6127815.
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
GND
82.5k
V
FB
SW
V
IN
LTC3772B
PGATE
550kHz Micropower Step-Down DC/DC Converter
V
IN
2.75V TO 9.8V
10µF
Efficiency and Power Loss vs Load Current
(Figure 5 Circuit)
100
90
80
70
EFFICIENCY
1
10
EFFICIENCY (%)
3.3µH
47µF
V
OUT
2.5V
2A
60
50
40
30
POWER LOSS
0.01
V
IN
= 3.3V
V
IN
= 5V
1
10
100
1000
LOAD CURRENT (mA)
0.1
22pF
174k
3772B TA01
20
10
0
U
0.001
10000
U
U
POWER LOSS (W)
3772B TA01b
3772bfa
1
LTC3772B
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
Input Supply Voltage (V
IN
)........................ – 0.3V to 10V
IPRG Voltage ............................... – 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
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
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
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
ORDER PART NUMBER
LTC3772BEDDB
DDB PART MARKING
LBWP
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER
Input Voltage Range
Input DC Supply Current
No Load
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
FB
= 0.83V
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
≤
9V (Note 5)
I
TH
/RUN = 1.6V (Note 5)
I
TH
/RUN = 1V (Note 5)
●
●
●
●
2
U
U
W
W W
U
W
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 230°C/W
ORDER PART NUMBER
LTC3772BETS8
TS8 PART MARKING
LTBWN
MIN
2.75
TYP
MAX
9.8
UNITS
V
µA
µA
µA
V
V
µA
V
V
V
mV/V
%
%
200
8
1
2.0
1.85
0.7
0.3
0.788
0.780
1.2
0.6
0.800
0.800
0.08
0.5
–0.5
325
20
5
2.75
2.60
1.7
0.95
0.812
0.812
0.2
0.2
–0.2
3772bfa
LTC3772B
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
Time for V
FB
to Ramp from 0.05V to 0.75V
●
●
●
MAX
10
0.910
UNITS
nA
V
mV
500
550
200
40
40
650
kHz
kHz
ns
ns
55
120
190
70
138
208
0.8
85
155
225
mV
mV
mV
ms
Default Soft-Start Time
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 LTC3772BETS8/LTC3772BEDDB 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 LTC3772B is 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
225
220
QUIESCENT CURRENT (µA)
250
QUIESCENT CURRENT (µA)
215
210
205
200
195
2
3
4
5
QUIESCENT CURRENT (µA)
7
6
V
IN
(V)
8
U W
9
3772B G01
Quiescent Current (No Load)
vs Temperature
V
IN
= 5V
Quiescent Current (Shutdown)
vs Input Voltage
25
230
20
15
210
190
10
170
5
10
150
20
40 60
–60 –40 –20 0
TEMPERATURE (°C)
0
80 100
3772B G02
2
3
4
6
5
7
8
INPUT VOLTAGE (V)
9
10
3772B G03
3772bfa
3
LTC3772B
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
2
4
6
8
INPUT VOLTAGE (V)
10
3772B G11
INPUT VOLTAGE (V)
4
U W
80
3772B 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
3772B G05
3772B 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
3772B G07
3772B G08
3772B 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
3772B FG10
3772B G12
3772bfa
LTC3772B
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
300
250
I
PRG
= V
IN
200
150
100
I
PRG
= GND
50
0
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
I
PRG
= FLOAT
1100
1000
SOFT-START TIME (µs)
900
800
700
600
500
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
FREQUENCY (Hz)
Efficiency vs Load Current
100
V
IN
= 3.3V
90
V
IN
= 4.2V
90
100
EFFICIENCY (%)
EFFICIENCY (%)
80
70
60
50
40
1
10
100
1000
LOAD CURRENT (mA)
Start-Up
V
OUT
1V/DIV
V
OUT
100mV/DIV
(AC)
I
L
2A/DIV
I
LOAD
2A/DIV
I
TH
/RUN
1V/DIV
INDUCTOR
CURRENT
2A/DIV
500µs/DIV
V
IN
= 5V
V
OUT
= 2.5V
R
LOAD
= 1.5Ω
FIGURE 5 CIRCUIT
3772B G18
U W
80
3772B 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
3772B G14
3772B G15
Efficiency vs Load Current
V
OUT
= 3.3V
V
OUT
= 2.5V
V
IN
= 7V
V
IN
= 5V
80
V
OUT
= 1.8V
70
60
50
V
OUT
= 2.5V
FIGURE 5 CIRCUIT
10000
3772B G16
40
10
V
IN
= 5V
FIGURE 5 CIRCUIT
100
1000
LOAD CURRENT (mA)
10000
3772B G17
Load Step
V
IN
= 5V
20µs/DIV
V
OUT
= 2.5V
I
LOAD
= 100mA TO 1.5A
FIGURE 5 CIRCUIT
3772B G19
3772bfa
5
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