LTC3805-5_15 Datasheet, PDF (1/20 Pages) Linear Technology – Adjustable Frequency Current Mode Flyback/ Boost/SEPIC DC/DC Controller

LTC3805-5
FEATURES
Adjustable Frequency
Current Mode Flyback/
Boost/SEPIC DC/DC Controller
DESCRIPTION
n _{VIN and VOUT Limited Only by External Components}
n _{4.5V Undervoltage Lockout Threshold}
n _{Adjustable Slope Compensation}
n _{Adjustable Overcurrent Protection with Automatic}
Restart
n _{Adjustable Operating Frequency (70kHz to 700kHz)}
With One External Resistor
n _{Synchronizable to an External Clock}
n _{±1.5% Reference Accuracy}
n _{Only 100mV Current Sense Voltage Drop}
n _{RUN Pin with Precision Threshold and Adjustable}
Hysteresis
n _{Programmable Soft-Start with One External Capacitor}
n _{Low Quiescent Current: 360µA}
n _{Small 10-Lead MSOP and 3mm × 3mm DFN}
APPLICATIONS
n _{Automotive Power Supplies}
n _{Telecom Power Supplies}
n _{Isolated Electronic Equipment}
n _{Auxiliary/Housekeeping Power Supplies}
n _{Power over Ethernet}
The LTC^®3805-5 is a current mode DC/DC controller de-
signed to drive an N-channel MOSFET in flyback, boost
and SEPIC converter applications. Operating frequency
and slope compensation can be programmed by external
resistors. Programmable overcurrent sensing protects
the converter from overload and short-circuit conditions.
Soft-start can be programmed using an external capacitor
and the soft-start capacitor also programs an automatic
restart feature.
The LTC3805-5 provides ±1.5% output voltage accuracy
and consumes only 360µA of quiescent current during
normal operation and only 40µA during micropower start-
up. Using a 9.5V internal shunt regulator, the LTC3805-5
can be powered from a high V_IN through a resistor or it
can be powered directly from a low impedance DC voltage
from 4.7V to 8.8V.
The LTC3805-5 is available in the 10-lead MSOP package
and the 3mm × 3mm DFN package.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered
trademarks, No R_SENSE and ThinSOT are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V to 12V/1A Boost Converter
V_IN
5V
20k
470pF
4.3µH
22µF
×2
0.1µF
V_CC
RUN
GATE
LTC3805-5
I_TH
OC
SSFLT
I_SENSE
FS
FB
118k ^{SYNC GND}
1.33k
3k
UPS840
V_OUT
12V
100µF ^1A
191k
8mΩ
13.7k
38055 TA01a
Efficiency and Power Loss vs Load Current
100
2.5
95
5V EFFICIENCY
2.0
8.5V EFFICIENCY
90
1.5
8.5V LOSS
5V LOSS
85
1
80
0.5
75
0.01
0.1
1
LOAD CURRENT (A)
0
10
38055TA01b
38055fe
1