LT3434 LINER [Linear Technology], LT3434 Datasheet - Page 19

• Manufacturer Part Number: LT3434
• Description: High Voltage 3A, 200kHz Step-Down Switching Regulator with 100uA Quiescent Current
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
100k TO V
500mV/DIV
500mV/DIV
2V/DIV
V
V
SHDN
OUT
V
PG
CT
IN
PG at 80% V
V
OUT
Figure 9. Power Good
LT3434
LT3434
U
PGFB
PGFB
Disconnect at 80% V
V
with 100ms Delay
V
PG
PG
TIME (10ms/DIV)
FB
C
FB
C
IN
IN
T
T
U
OUT
with 100ms Delay
0.27µF
0.27µF
200k
W
200k
153k
12k
100k
153k
12k
100k
OUT
3434 F09
C
C
Figure 10. Power Good Circuits
OUT
OUT
V
U
OUT
= 3.3V
V
OUT
= 3.3V
V
LAYOUT CONSIDERATIONS
As with all high frequency switchers, when considering
layout, care must be taken in order to achieve optimal
electrical, thermal and noise performance. For maximum
efficiency switch rise and fall times are typically in the
nanosecond range. To prevent noise both radiated and
conducted the high speed switching current path, shown
in Figure 11, must be kept as short as possible. This is
implemented in the suggested layout of Figure 12. Short-
ening this path will also reduce the parasitic trace induc-
tance of approximately 25nH/inch. At switch off, this
OUT
PG at V
LT3434
LT3434
Disconnect 3.3V Logic Signal
PGFB
PGFB
IN
with 100µs Delay
V
V
PG
PG
FB
C
FB
C
IN
IN
> 4V with 100ms Delay
T
T
511k
200k
0.27µF
270pF
200k
200k
165k
100k
866k
100k
3434 F10
C
OUT
C
V
OUT
OUT
= 3.3V
V
OUT
= 12V
LT3434
19
3434f