LTC3805 Linear Technology, LTC3805 Datasheet - Page 17

• Manufacturer Part Number: LTC3805
• Description: Adjustable Frequency Current Mode Flyback DC/DC Controller
• Manufacturer: Linear Technology

www.datasheet4u.com
internal soft-start time t
environments a small C
in the oscillator.
If there is an overcurrent fault detected on the OC pin, the
LTC3805 enters a shutdown mode while a 2μA current
discharges the voltage on the SSFLT pin from 4.75V to
about 0.7V. The fault timeout t
At this point, the LTC3805 attempts a restart.
APPLICATIONS INFORMATION
TYPICAL APPLICATION
36V TO
8.66k
221k
V
72V
R5
R8
IN
t
+
V
FTO(EXT)
IN
NOTE: CAN ALSO USE TRICKLE CHARGER AS SHOWN IN FIGURE 10
Figure 9. Low Power Isolated Telecom Supply with NPN Preregulator
V
IN
C
2.2μF
100V
IN1
–
R20
118k
C23, 0.1μF
= C
1
2
3
4
5
SSFLT
I
FB
RUN
FS
TH
LTC3805EMSE
SS
C
2.2μF
100V
IN2
GND
U1
11
4.75V − 0.7V
I
GATE
SENSE
SYNC
R3
221k
V
SS(IN)
OC
SS
CC
D2
PDZ6.8B
6.8V
2µA
10
9
8
7
6
can be valuable to limit jitter
V
CC
= 1.8ms. However, in noisy
FTO(EXT)
Q2
MMBTA42
R16, 1.33k
C17
4.7μF
3.01k
R19
BAS516
is therefore
R23
221k
FDC2512
D4
Q1
0.068Ω
R
CS
150pF
200V
C16
NECPS2801-1
220Ω
BAT760
R6
D4
51Ω
R30
250VAC
2200pF
ISO2
C15
V
CC
4
1
5
2
R11
6.8k
PA1861NL
In the event of a persistent fault, such as a short-circuit
on the converter output, the converter enters a “hiccup”
mode where it continues to try and restart at repetition
rate determined by C
the converter successfully restarts.
T1
10
7
8
9
BAS516
D2
C21
1μF
C22
0.47μF
UPS840
D1
2Ω
R2
1
2
3
LT4430ES6 OPT
V
GND
OC
IN
274Ω
R9
C01
100μF
6.3V
U2
0.6V FB
COMP
OPTO
SS
100
80
70
60
40
90
50
30
20
10
vs Load Current and V
0
. If the fault is eventually removed
0.01
6
5
4
V
IN
BAT54CWTIG
Effi ciency and Power Loss
C02
100μF
6.3V
47nF
C20
D6
36V
48V
60V
72V
47pF
C19
LOAD CURRENT (A)
0.1
R15
2.0k
3805 TA02a
+V
C03
100μF
6.3V
OUT
LTC3805
R12
100k
IN
1
R14
22.1k
; V
V
3.3V
3A
V
OUT
OUT
O
C18
330pF
= 3.3V
3805 TA02b
+
–
17
10
10
1
0
3805fb