LTC3805-5
1
38055fe
FEATURES DESCRIPTION
Adjustable Frequency
Current Mode Flyback/
Boost/SEPIC DC/DC Controller
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.
5V to 12V/1A Boost Converter
TYPICAL APPLICATION
n
V
IN
and V
OUT
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
Efficiency and Power Loss vs Load Current
LTC3805-5
GND
I
TH
RUN
GATE
OC
I
SENSE
SSFLT
FS FB
V
CC
118k
3k
8mΩ
22µF
×2
SYNC
1.33k
4.3µH
UPS840
V
IN
5V
V
OUT
12V
1A
13.7k
191k
100µF
38055 TA01a
0.1µF
20k
470pF
LOAD CURRENT (A)
0.01
EFFICIENCY (%)
POWER LOSS (W)
85
90
38055TA01b
80
75
0.1
1
10
100
95
1
1.5
0.5
0
2.5
2.0
5V EFFICIENCY
5V LOSS
8.5V LOSS
8.5V EFFICIENCY