LTC3822
No R
SENSE
™, Low Input
Voltage, Synchronous Step-Down
DC/DC Controller
FEATURES
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DESCRIPTION
The LTC
®
3822 is a synchronous step-down switching
regulator controller that drives external N-channel power
MOSFETs using few external components. The constant
frequency current mode architecture with MOSFET V
DS
sensing eliminates the need for sense resistors and im-
proves efficiency.
A maximum duty cycle of 99% provides low dropout
operation. The switching frequency can be programmed
up to 750kHz, allowing the use of small surface mount
inductors and capacitors.
The LTC3822 is available in thermally enhanced DFN and
10-lead MSOP packages.
L,
LT, LTC and LTM 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.
No Current Sense Resistor Required
All N-Channel MOSFET Synchronous Drive
High Current Outputs Possible
Constant Frequency Current Mode Operation for
Excellent Line and Load Transient Response
V
IN
: 2.75V to 4.5V
±1% 0.6V Reference
Low Dropout Operation: 99% Duty Cycle
Selectable Frequency (300kHz/550kHz/750kHz)
Internal Soft-Start Circuitry
Selectable Maximum Peak Current Sense Threshold
Digital RUN Control Pin
Output Overvoltage Protection
Micropower Shutdown: I
Q
= 7.5μA
Tiny Thermally Enhanced Leadless (3mm
×
3mm)
DFN or 10-Lead MSOP Package
APPLICATIONS
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3.3V
IN
Systems
Li-Ion Battery Systems
TYPICAL APPLICATION
1.8V/8A High Efficiency, 550kHz Step-Down Converter
V
IN
2.75V TO 4.5V
47μF
RUN
FREQ
I
TH
5.1k
680pF
GND
V
FB
59k
118k
3822 TA01
Efficiency and Power Loss vs
Load Current
100
90
80
EFFICIENCY (%)
70
60
50
40
30
POWER LOSS
0.1
EFFICIENCY
POWER LOSS (W)
1
V
IN
= 3.3V
10
IPRG
V
IN
TG
LTC3822
SW
FDS6898A
0.47μH
100μF
0.22μF
BOOST
V
OUT
1.8V
8A
BG
20
10
0
100
1000
LOAD CURRENT (mA)
0.01
10000
3822 TA01b
3822fa
1
LTC3822
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (V
IN
) ....................... –0.3V to 4.5V
BOOST Voltage .......................................... –0.3V to 10V
FREQ, RUN, 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
TG, BG Peak Output Current (<10μs) ......................... 1A
Operating Temperature Range
(Note 2) ............................................... –40°C to 85°C
Storage Ambient Temperature Range..... –65°C to 125°C
Junction Temperature (Note 3) ............................ 125°C
Lead Temperature
(Soldering, 10 sec, MSE only) .......................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
BG
TG
BOOST
V
IN
SW
1
2
3
4
5
11
10 RUN
9 I
TH
8 V
FB
7 IPRG
6 FREQ
BG
TG
BOOST
V
IN
SW
1
2
3
4
5
10
9
8
7
6
RUN
I
TH
V
FB
IPRG
FREQ
11
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD IS GND
(MUST BE SOLDERED TO PCB)
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W
EXPOSED PAD IS GND
(MUST BE SOLDERED TO PCB)
ORDER INFORMATION
LEAD FREE FINISH
LTC3822EDD#PBF
LTC3822EMSE#PBF
TAPE AND REEL
LTC3822EDD#TRPBF
LTC3822EMSE#TRPBF
PART MARKING
LCBF
LTCBG
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3822fa
2
LTC3822
ELECTRICAL CHARACTERISTICS
PARAMETER
Main Control Loops
Input DC Supply Current
Normal Operation
Shutdown
UVLO
Undervoltage Lockout Threshold
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
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 Duty Cycle
Maximum Current Sense Voltage (V
IN
– SW)
(ΔV
SENSE(MAX)
)
Soft-Start Time
Oscillator
Oscillator Frequency
FREQ = Floating
FREQ = 0V
FREQ = V
IN
480
240
640
550
300
750
600
340
850
kHz
kHz
kHz
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
C
L
= 3000pF
In Dropout
IPRG = Floating
IPRG = 0V
IPRG = V
IN
Time for V
FB
to Ramp from 0.05V to 0.55V
l
l
l
The
l
indicates specifications that apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.3V unless otherwise noted.
CONDITIONS
(Note 4)
RUN = 0
V
IN
= UVLO Threshold – 200mV
V
IN
Falling
V
IN
Rising
(Note 5)
2.75V < V
IN
< 4.5V (Note 5)
I
TH
= 1.3V to 0.9V (Note 5)
I
TH
= 1.3V to 1.7V
(Note 5)
Measured at V
FB
0.66
l
l
l
MIN
TYP
MAX
UNITS
340
7.5
10
1.95
2.15
0.7
0.594
2.25
2.45
1.1
0.6
0.025
0.1
–0.1
10
0.68
20
40
40
50
40
99
110
70
185
120
82
200
650
500
20
20
2.55
2.75
1.4
0.606
0.1
0.5
–0.5
50
0.70
μA
μA
μA
V
V
V
V
%/V
%
%
nA
V
mV
ns
ns
ns
ns
%
140
100
220
mV
mV
mV
μs
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 LTC3822E 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
)
Note 4:
Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5:
The LTC3822 is tested in a feedback loop that servos I
TH
to a
specified voltage and measures the resultant V
FB
voltage.
3822fa
3
LTC3822
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Efficiency vs Load Current
100
95
90 V
OUT
= 2.5V
EFFICIENCY (%)
EFFICIENCY (%)
85
80
75
70
65
60
55
50
100
V
IN
= 3.3V
1000
LOAD CURRENT (mA)
10000
3822 G01
Efficiency and Power Loss vs
Load Current
100
90
80
V
IN
= 3.3V
V
IN
= 4.2V
EFFICIENCY
CURRENT LIMIT (%)
POWER LOSS (W)
1
10
100
80
60
40
20
0
V
OUT
= 1.8V
1000
LOAD CURRENT (mA)
0.01
10000
–20
Maximum Current Sense Voltage
vs I
TH
Pin Voltage
V
OUT
= 1.0V
70
60
50
40
30
20
10
0
100
V
OUT
= 1.8V
V
IN
= 4.2V
POWER LOSS
V
IN
= 3.3V
0.1
0.5
1
1.5
I
TH
VOLTAGE (V)
2.0
3822 G03
3822 G02
Load Step
V
OUT
100mV/DIV
I
L
2A/DIV
Start-Up with Internal Soft-Start
V
OUT
1.8V
500mV/DIV
I
LOAD
2A/DIV
40μs/DIV
V
IN
= 3.3V
V
OUT
= 1.8V
I
LOAD
= 1A TO 3A
3822 G04
200μs/DIV
V
IN
= 4.2V
R
LOAD
= 1Ω
3822 G05
3822fa
4
LTC3822
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Regulated Feedback Voltage
vs Temperature
0.604
0.603
FEEDBACK VOLTAGE (V)
0.602
INPUT VOLTAGE (V)
0.601
0.600
0.599
0.598
0.597
0.596
–50
0
50
TEMPERATURE (°C)
100
3822 G06
Undervoltage Lockout Threshold
vs Temperature
2.55
2.50
2.45
2.40
2.35
2.30
V
IN
FALLING
2.25
2.20
2.15
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
RUN VOLTAGE (V)
V
IN
RISING
1.15
1.20
Shutdown (RUN) Threshold
vs Temperature
1.10
1.05
1.00
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
3822 G07
3822 G08
Maximum Current Sense
Threshold vs Temperature
MAXIMUM CURRENT SENSE THRESHOLD (mV)
130
IPRG = FLOAT
NORMALIZED FREQUENCY SHIFT (%)
10
8
6
4
2
0
–2
–4
–6
–8
Oscillator Frequency
vs Temperature
5
NORMALIZED FREQUENCY SHIFT (%)
4
3
2
1
0
–1
–2
–3
–4
Oscillator Frequency
vs Input Voltage
125
120
115
110
20 40 60
–60 –40 –20 0
TEMPERATURE (°C)
80
100
–10
–60 –40 –20 0
20 40 60
TEMPERATURE (°C)
80
100
–5
2.5
3.0
4.0
3.5
INPUT VOLTAGE (V)
4.5
3822 G11
3822 G09
3822 G10
Shutdown Quiescent Current
vs Input Voltage
18
16
360
SHUTDOWN CURRENT (μA)
12
10
8
6
4
2
0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
3822 G12
Quiescent Current in Normal
Operation vs Input Voltage
370
QUIESCENT CURRENT (μA)
14
350
340
330
320
310
2.6
3.6
INPUT VOLTAGE (V)
4.6
3822 G13
3822fa
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