FEATURES
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LTC3620
Ultralow Power 15mA
Synchronous Step-Down
Switching Regulator
DESCRIPTION
The LTC
®
3620 is a high efficiency, synchronous buck
regulator, suitable for very low power, very small footprint
applications powered by a single Li-Ion battery.
The internal synchronous switches increase efficiency
and eliminate the need for external Schottky diodes. Low
output voltages are easily supported by the 0.6V feedback
reference voltage. The LTC3620-1 option is internally
programmed to provide a 1.1V output.
The LTC3620 uses a unique variable frequency architecture
to minimize power loss and achieve high efficiency. The
switching frequency is proportional to the load current, and
an internal frequency clamp forces a minimum switching
frequency at light loads to minimize noise in the audio
range. The user can program the frequency of this clamp
by applying an external clock to the FMIN/MODE pin.
The battery status output, LOBATB, indicates when the
input voltage drops below 3V. To help prevent damage to
the battery, an undervoltage lockout (UVLO) circuit shuts
down the part if the input voltage falls below 2.8V.
The LTC3620 is available in a low profile, 2mm
×
2mm
8-lead DFN package.
High Efficiency: Up to 95%
Maximum Current Output: 15mA
Externally Programmable Frequency Clamp with
Internal 50kHz Default Minimizes Audio Noise
18μA I
Q
Current
2.9V to 5.5V Input Voltage Range
Low-Battery Detection
0.6V Reference Allows Low Output Voltages
Shutdown Mode Draws <1μA Supply Current
2.8V Undervoltage Lockout
Unique Low Noise Control Architecture
Internal Power MOSFETs
No Schottky Diodes Required
Internal Soft-Start
Tiny 2mm
×
2mm 8-Lead DFN Package
APPLICATIONS
n
n
n
n
Hearing Aids
Wireless Headsets
Li-Ion Cell Applications
Button Cell Replacement
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 7528587.
TYPICAL APPLICATION
High Efficiency Low Power
Step-Down Converter
V
IN
2.9V TO 5.5V
V
IN
V
OUT
1.1V
V
OUT
(mV
P-P
)
RUN
1μF
CER
LOBATB
SW
22μH
22pF
15
V
IN
= 3.6V
10
25
Output Voltage Ripple
vs Load Current
V
OUT
= 1.1V
FMIN/MODE = 0V
L = 22μH
EFFICIENCY (%)
V
IN
= 5.5V
100
90
80
70
60
50
40
30
1μF
CER
5
20
10
3620 TA01a
Efficiency vs Load Current
3.0
EFFICIENCY
2.5
POWER LOSS (mW)
2.0
1.5
V
IN
= 3V
FMIN/MODE = 0V
V
OUT
= 1.1V
V
OUT
= 1.8V
V
OUT
= 2.5V
1.0
0.5
0
1
LOAD CURRENT (mA)
10
3620 TA01c
20
LTC3620
FMIN/MODE V
FB
GND
432k
523k
LOSS
0
0
10
5
OUTPUT CURRENT (mA)
15
3620 TA01b
0
0.1
3620fa
1
LTC3620
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SW 1
GND 2
FMIN/MODE 3
LOBATB 4
9
GND
8 V
IN
7 RUN
6 V
FB
5 NC
Input Supply Voltage .................................... –0.3V to 6V
RUN Voltage ................................. –0.3V to (V
IN
+ 0.3V)
V
FB
Voltage ................................... –0.3V to (V
IN
+ 0.3V)
LOBATB Voltage ........................................... –0.3V to 6V
FMIN/MODE Voltage ..................... –0.3V to (V
IN
+ 0.3V)
SW Voltage .................................. –0.3V to (V
IN
+ 0.3V)
P-channel Switch Source Current (DC) ..................50mA
N-channel Switch Sink Current (DC) ......................50mA
Operating Junction Temperature Range
(Note 2)..................................................–40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
DC PACKAGE
8-LEAD (2mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 88.5°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3620EDC#PBF
LTC3620EDC-1#PBF
TAPE AND REEL
LTC3620EDC#TRPBF
LTC3620EDC-1#TRPBF
PART MARKING
LFJJ
LFJK
PACKAGE DESCRIPTION
8-Lead (2mm
×
2mm) Plastic DFN
8-Lead (2mm
×
2mm) Plastic DFN
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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
FB
PARAMETER
Input Voltage Range
Regulated Feedback Voltage (Note 3)
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for T
A
= 25°C (Note 2). V
IN
= 3.6V unless otherwise noted.
CONDITIONS
l
MIN
2.9
0.594
0.588
1.089
1.078
TYP
0.6
0.6
1.1
1.1
0.05
18
0.01
0.5
35
MAX
5.5
0.606
0.612
1.111
1.122
0.15
0.5
25
1
UNITS
V
V
V
V
V
%/V
%
μA
μA
μA
mA
kHz
V
LTC3620
LTC3620
LTC3620-1
LTC3620-1
V
IN
= 3V to 5.5V (Note 3)
(Note 3)
V
FB
= 0.65V, FMIN/MODE = V
IN
RUN = 0V
RUN = V
IN
, V
IN
= 2.5V
l
l
ΔV
FB
V
LOADREG
I
Q
I
QSD
I
QU
I
PK
f
SW
V
RUN
I
RUN
Reference Voltage Line Regulation
Output Voltage Load Regulation
Quiescent Current, No Switching
Quiescent Current in Shutdown
Quiescent Current in UVLO Condition
Peak Inductor Current
Minimum Switching Frequency (Internal) V
FB
= 0.65V, FIN/MODE = 0
RUN Input Voltage High
RUN Input Voltage Low
RUN Leakage Current
l
40
0.8
50
0.3
±0.01
±1
V
μA
3620fa
2
LTC3620
ELECTRICAL CHARACTERISTICS
SYMBOL
V
FMIN
f
EXT
I
FMIN/MODE
I
SW
I
FB
V
UVLO
V
LOBATB
R
LOBATB
V
HLOBATB
R
PFET
R
NFET
PARAMETER
FMIN/MODE Input Voltage High
FMIN/MODE Input Voltage Low
FMIN/MODE Input Frequency
FMIN/MODE Pin Leakage Current
Switch Leakage Current
V
FB
Pin Current
Undervoltage Lockout (UVLO)
LOBATB Threshold Voltage
LOBATB Pull-Down On-Resistance
LOBATB Hysteresis Voltage
R
DS(ON)
of P-channel FET (Note 4)
R
DS(ON)
of N-channel FET (Note 4)
I
SW
= 50mA, V
IN
= 3.6V
I
SW
= –50mA, V
IN
= 3.6V
V
RUN
= 0V, V
SW
= 0V or 5.5V, V
IN
= 5.5V
LTC3620, V
FB
= 0.6V
LTC3620-1, V
FB
= 1.1V
V
IN
Decreasing
V
IN
Decreasing
2.7
2.93
20
±0.01
±0.01
0
1.2
2.8
3.0
15
100
2.0
1.0
The
l
denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for T
A
= 25°C (Note 2). V
IN
= 3.6V unless otherwise noted.
CONDITIONS
MIN
0.9
0.7
300
±1
±1
±30
2.0
2.9
3.08
TYP
MAX
UNITS
V
V
kHz
μA
μA
nA
μA
V
V
Ω
mV
Ω
Ω
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 LTC3620 is tested under pulsed load conditions such that T
J
≈ T
A
.
LTC3620E is guaranteed to meet specifications from 0°C to 85°C
junction temperature. Specifications over the –40°C to 85°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls. Note that the maximum
ambient temperature consistent with these specifications is determined by
specific operating conditions in conjunction with board layout, the rated
package thermal impedance and other environmental factors. The junction
temperature (T
J
, in °C) is calculated from the ambient temperature (T
A
, in °C)
and power dissipation (P
D
, in Watts) according to the formula:
T
J
= T
A
+ (P
D
•
θ
JA
), where
θ
JA
(in °C/W) is the package thermal
impedance.
Note 3:
The LTC3620 is tested in a proprietary test mode that connects V
FB
to the output of the error amplifier.
Note 4:
The DFN switch-on resistance is guaranteed by correlation to
wafer level measurements.
3620fa
3
LTC3620
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
vs Load Current, FMIN/MODE
1000
200kHz, EXTERNAL
FMIN/MODE = 0V
FMIN/MODE = V
IN
0.5
Load Regulation
V
IN
= 3.6V
V
OUT
= 1.1V
FMIN/MODE = 0V
T
A
= 25°C
V
FB
(mV)
620
615
610
605
600
595
590
–0.3
585
–0.5
0
10
5
LOAD CURRENT (mA)
15
3620 G02
LTC3620 Feedback Voltage
vs Temperature
V
IN
= 3.6V
V
OUT
= 1.1V
FMIN/MODE = 0V
SWITCHING FREQUENCY (kHz)
V
OUT
VOLTAGE CHANGE (%)
T
A
= 25°C
V
IN
= 3.6V
V
OUT
= 1.1V
0.3
0.1
100
–0.1
10
0.01
1
0.1
LOAD CURRENT (mA)
10 20
3620 G01
580
–50
50
0
TEMPERATURE (°C)
100
130
3620 G03
LTC3620-1 Feedback Voltage
vs Temperature
1.125
1.120
1.115
1.110
V
FB
(V)
1.105
1.100
1.095
1.090
1.085
1.080
–50
50
0
TEMPERATURE (°C)
100
130
3620 G04
Quiescent Current vs Temperature
30
2.85
V
OUT
= 1.1V
FMIN/MODE = V
IN
UVLO THRESHOLD (V)
2.84
2.83
2.82
2.81
2.80
2.79
2.78
2.77
2.76
50
0
TEMPERATURE (°C)
100
130
3620 G05
UVLO Threshold vs Temperature
V
OUT
= 1.1V
FMIN/MODE = 0V
V
IN
= 3.6V
FMIN/MODE = 0V
QUIESCENT CURRENT (μA)
28
26
24
22
20
18
16
14
12
V
IN
= 5V
V
IN
= 3.6V
10
–50
2.75
–50
50
0
TEMPERATURE (°C)
100
130
3620 G06
LOBATB Threshold
vs Temperature
3.05
3.04
3.03
LOBATB THRESHOLD (V)
3.02
I
PEAK
(mA)
3.01
3.00
2.99
2.98
2.97
2.96
2.95
–50
50
0
TEMPERATURE (°C)
100
130
3620 G07
Peak Inductor Current
vs Temperature
40
V
OUT
= 1.1V
L = 22μH
V
IN
= 5.5V
38
37
36
35
34
–50
V
IN
= 3.6V
V
SW
2V/DIV
39
V
OUT
(AC)
20mV/DIV
Switching Waveforms at 250μA
Load, FMIN/MODE = 0V
V
OUT
= 1.1V
FMIN/MODE = 0V
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
4μs/DIV
3620 G09
0
50
TEMPERATURE (°C)
100
130
3620 G08
3620fa
4
LTC3620
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Waveforms at 1mA
Load, FMIN/MODE = 0V
V
OUT
(AC)
20mV/DIV
V
OUT
(AC)
20mV/DIV
V
SW
2V/DIV
Switching Waveforms at 12mA
Load, FMIN/MODE = 0V
V
FMIN/MODE
1V/DIV
V
OUT
(AC)
20mV/DIV
V
SW
2V/DIV
Switching Waveforms at 250μA
Load, FMIN/MODE = 200kHz Clock
V
SW
2V/DIV
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
4μs/DIV
3620 G10
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
400ns/DIV
3620 G11
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
2μs/DIV
3620 G12
Switching Waveforms at 1mA
Load, FMIN/MODE = 200kHz Clock
V
FMIN/MODE
1V/DIV
V
OUT
(AC)
20mV/DIV
V
SW
2V/DIV
V
FMIN/MODE
1V/DIV
V
OUT
(AC)
20mV/DIV
V
SW
2V/DIV
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
2μs/DIV
3620 G13
Switching Waveforms at 12mA
Load, FMIN/MODE = 200kHz
Start-Up Waveforms
V
OUT
200mV/DIV
I
L
25mA/DIV
I
L
25mA/DIV
V
OUT
= 1.1V
V
IN
= 3.6V
T
A
= 25°C
400ns/DIV
3620 G14
V
OUT
= 1.1V
200μs/DIV
V
IN
= 3.6V
I
OUT
= 0mA
FMIN/MODE = 0V
T
A
= 25°C
3620 G15
Transient Response, 250μA to 3mA
Step, FMIN/MODE = 0V
Transient Response, 1mA to 10mA
Step, FMIN/MODE = 0V
2.3
2.1
PFET R
DS(ON)
vs Temperature
I
SW
= 35mA
V
OUT
(AC)
10mV/DIV
V
OUT
(AC)
20mV/DIV
R
DS(ON)
(Ω)
1.9
1.7
1.5
1.3
1.1
0.9
V
IN
= 3.6V
V
OUT
= 1.1V
T
A
= 25°C
4ms/DIV
3620 G17
V
IN
= 3.6V
V
IN
= 5V
I
LOAD
5mA/DIV
V
IN
= 3.6V
V
OUT
= 1.1V
T
A
= 25°C
4ms/DIV
3620 G16
I
LOAD
5mA/DIV
0.7
0.5
–50
50
0
TEMPERATURE (°C)
100
130
3620 G18
3620fa
5
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