LTC1735
TYPICAL PERFOR A CE CHARACTERISTICS
V
OUT(RIPPLE)
(Burst Mode Operation)
I
LOAD
= 1.5A
V
OUT
20mV/DIV
FIGURE 1
V
OUT
50mV/DIV
I
L
5A/DIV
I
L
5A/DIV
FCB = 5V
V
IN
= 15V
V
OUT
= 1.6V
5µs/DIV
Start-Up
V
OUT
1V/DIV
V
RUN/SS
5V/DIV
V
OUT
10mV/DIV
I
L
5A/DIV
V
IN
= 15V
V
OUT
= 1.6V
R
LOAD
= 0.16Ω
5ms/DIV
PI FU CTIO S
C
OSC
:
External capacitor C
OSC
from this pin to ground sets
the operating frequency.
RUN/SS:
Combination of Soft-Start and Run Control In-
puts. A capacitor to ground at this pin sets the ramp time
to full output current. The time is approximately 1.25s/µF.
Forcing this pin below 1.5V causes the device to shut
down. (See Applications Information section for quiescent
current note.) In shutdown all functions, including INTV
CC
,
are disabled. Latchoff overcurrent protection is also in-
voked via this pin as described in the Applications Infor-
mation section.
I
TH
:
Error Amplifier Compensation Point. The current
comparator threshold increases with this control voltage.
Nominal voltage range for this pin is 0V to 2.4V.
FCB:
Forced Continuous/Synchronization Input. Tie this
pin to ground for continuous synchronous operation, to a
resistive divider from the secondary output when using a
secondary winding or to INTV
CC
to enable Burst Mode
operation at low load currents. Clocking this pin with a
signal above 1.5V
P–P
disables Burst Mode operation but
allows cycle-skipping at low load currents and synchro-
nizes the internal oscillator with the external clock.
The
FCB pin must not be driven when the device is shut down
(RUN/SS pin low).
SGND:
Small-Signal Ground. All small-signal components
such as C
OSC
, C
SS
, the feedback divider plus the loop com-
pensation resistor and capacitor(s) should single-point tie
to this pin. This pin should, in turn, connect to PGND.
1735fc
U W
Load Step (Burst Mode Operation)
FIGURE 1
V
OUT
50mV/DIV
Load Step (Continuous Mode)
FIGURE 1
I
L
5A/DIV
1735 G27
10mA TO
9A LOAD STEP
FCB = 5V
V
IN
= 15V
V
OUT
= 1.6V
10µs/DIV
1735 G26
0A TO
9A LOAD STEP
FCB = 0V
V
IN
= 15V
V
OUT
= 1.6V
10µs/DIV
1735 G25
V
OUT(RIPPLE)
(Synchronized)
I
LOAD
= 10mA
FIGURE 1
V
OUT
20mV/DIV
V
OUT(RIPPLE)
(Burst Mode Operation)
I
LOAD
= 50mA
FIGURE 1
I
L
5A/DIV
1735 G22
I
L
5A/DIV
EXT SYNC f = f
O
V
IN
= 15V
V
OUT
= 1.6V
10µs/DIV
1735 G23
FCB = 5V
V
IN
= 15V
V
OUT
= 1.6V
50µs/DIV
1735 G24
U
U
U
7
LINER [ LINEAR TECHNOLOGY ]
