LT4430IS6#PBF Linear Technology, LT4430IS6#PBF Datasheet - Page 19

• Manufacturer Part Number: LT4430IS6#PBF
• Manufacturer: Linear Technology

Specifications of LT4430IS6#PBF

• Operating Temperature (max): 125C
• Operating Temperature (min): -40C
• Pin Count: 6
• Mounting: Surface Mount
• Package Type: TSOT-23
• Case Length: 2.9mm
• Screening Level: Automotive
• Lead Free Status / RoHS Status: Compliant

APPLICATIONS INFORMATION
Next, increase C
tion box or solder each new value into the circuit. Monitor
the start-up and short-circuit recovery waveforms. Note
any changes. Figures 8b to 8e illustrate what happens as
C
increases.
C
ics, but start-up still exhibits about 1.5V of overshoot.
Short-circuit recovery is considerably more damped. C
= 0.022μF in Figure 8c damps start-up overshoot to 0.5V
and short-circuit recovery remains similar to that of Figure
8b. C
of overshoot and short-circuit recovery is slightly more
damped. C
shoot at the expense of additional damping and delay time
in short-circuit recovery. In this example, C
provides the best value for both start-up and short-circuit
recovery. Figure 8f provides an expanded scale of the
waveforms. After a C
and short-circuit recovery over the V
with higher output load conditions. Modify the value as
necessary.
Start-up and short-circuit recovery waveforms for various
designs will differ from the photos shown in this example.
Factors affecting these waveforms include the isolated
topology chosen, the primary-side and secondary-side
bias circuitry and input/output conditions. For instance,
in many isolated power supplies, a winding on the main
power transformer bootstraps the supply voltage for the
primary-side control circuitry. Under short-circuit condi-
tions, the primary-side control circuitry’s supply voltage
collapses, generating a restart cycle. Recovery from
OC
OC
= 0.0168μF in Figure 8b begins to affect loop dynam-
increases. In general, overshoot decreases as C
OC
= 0.033μF in Figure 8d provides under 100mV
OC
= 0.047μF in Figure 8e achieves zero over-
OC
’s value. Either use a capacitor substitu-
OC
value is selected, check start-up
IN
supply range and
OC
= 0.033μF
OC
OC
short-circuit is therefore identical to start-up. In the fl yback
example discussed, the primary-side control circuitry is
always active. Switching never stops in short-circuit. The
LT4430 error amplifi er COMP pin changes from its low
clamp level to its higher regulating value during start-up
and changes from its high clamp level to its lower regulat-
ing point during short-circuit recovery. This large-signal
behavior explains the observed difference in the start-up
versus short-circuit recovery waveforms.
A fi nal point of discussion involves the chosen C
LTC recommends that the designer use a value that con-
trols overshoot to the acceptable level, but is not made
overly large. The temptation arises to use the overshoot
control function as a power supply “soft-start” feature.
Larger values of C
overshoot, do result in smaller dV/dt rates and longer
start-up times. However, large values of C
feedback loop during start-up or short-circuit recovery,
resulting in an extended period of time that the output
voltage “fl atspots”. This voltage shelf may occur at an
intermediate value of output voltage, promoting anomalous
behavior with the powered load circuitry. If this situation
occurs with the desired C
circuit modifi cations. In particular, bias supply holdup
times are a prime point of concern as switching stops
during these output voltage fl atspots. As a reminder,
the purpose of this LT4430 circuitry is to control and
prevent excessive output voltage overshoot that would
otherwise induce damage or destruction, not to control
power supply timing, sequencing, etc. It is ultimately the
user’s responsibility to defi ne the acceptance criteria for
any waveforms generated by the power supply relative to
overall system requirements.
OC
, above what is required to control
OC
value, solutions may require
OC
LT4430
may stall the
OC
19
value.
4430fa