LTC3620 Datasheet, PDF (1/16 Pages) Linear Technology – Ultralow Power 15mA Synchronous Step-Down Switching Regulator

FEATURES
n _{High Efficiency: Up to 95%}
n _{Maximum Current Output: 15mA}
n _{Externally Programmable Frequency Clamp with}
Internal 50kHz Default Minimizes Audio Noise
n _{18μA IQ Current}
n _{2.9V to 5.5V Input Voltage Range}
n _{Low-Battery Detection}
n _{0.6V Reference Allows Low Output Voltages}
n _{Shutdown Mode Draws <1μA Supply Current}
n _{2.8V Undervoltage Lockout}
n _{Unique Low Noise Control Architecture}
n _{Internal Power MOSFETs}
n _{No Schottky Diodes Required}
n _{Internal Soft-Start}
n _{Tiny 2mm × 2mm 8-Lead DFN Package}
APPLICATIONS
n _{Hearing Aids}
n _{Wireless Headsets}
n _{Li-Ion Cell Applications}
n _{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.
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.
TYPICAL APPLICATION
High Efficiency Low Power
Step-Down Converter
V_IN
2.9V TO 5.5V
V_IN
RUN LOBATB
SW
1μF
LTC3620
CER
FMIN/MODE V_FB
GND
22μH
22pF
V_OUT
1.1V
432k
523k
1μF
CER
3620 TA01a
Output Voltage Ripple
vs Load Current
25
V_OUT = 1.1V
FMIN/MODE = 0V
L = 22μH
20
V_IN = 5.5V
15
V_IN = 3.6V
10
5
0
0
5
10
15
OUTPUT CURRENT (mA) 3620 TA01b
Efficiency vs Load Current
100
3.0
90 EFFICIENCY
80
2.5
70
2.0
60
50
40 ^{VIN = 3V}
FMIN/MODE = 0V
30
V_OUT = 1.1V
20
V_OUT = 1.8V
V_OUT = 2.5V
10
1.5
1.0
LOSS
0.5
0
0
0.1
1
10
LOAD CURRENT (mA)
3620 TA01c
3620f
1