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參數(shù)資料
| 型號(hào)： | LT4430 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | Secondary-Side Optocoupler Driver |
| 中文描述： | 二次側(cè)驅(qū)動(dòng)光電耦合器 |
| 文件頁數(shù)： | 15/20頁 |
| 文件大?。?/td> | 2118K |
| 代理商： | LT4430 |
LT4430
15
4430f
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APPLICATIO
The LT4430’s overshoot control circuitry plus one external
capacitor (C
OC
) provide independent control of startup
and short-circuit recovery response without compro-
mising small-signal frequency compensation. Choosing
the optimum C
OC
value is a straightforward laboratory
procedure. The following description and set of pictures
explain this procedure.
Before choosing a value for the OC pin capacitor, complete
the remainder of the power supply design. This process
includes evaluating the chosen V
IN
bias generator topology
(
please consult prior applications information section
)
and optimizing frequency compensation under all normal
operating conditions. During this design phase, set C
OC
to its minimum value of 100pF. This ensures negligible
interaction from the overshoot control circuitry. Once these
steps are complete, construct a test setup that monitors
startup and short-circuit recovery waveforms. Perform this
testing with the output lightly loaded. Light load, following
full slew operation, is the worst-case as the feedback loop
transitions from full to minimal power delivery.
As an example, refer to the schematic on the last page
illustrating the 5V, 2A isolated flyback converter. All of
the following photos are taken with V
IN
= 48V and I
LD
=
20mA. Figure 8a demonstrates the power supply startup
and short-circuit recovery behavior with no overshoot
control compensation (C
OC
= 100pF minimum). The 5V
output overshoots by several volts on both startup and
short-circuit recovery due to the conservative nature of
the small-signal frequency compensation values.
Next, increase C
OC
’s value. Either use a capacitor substitu-
tion box or solder each new value into the circuit. Monitor
the startup and short-circuit recovery waveforms. Note
any changes. Figures 8b to 8e illustrate what happens as
C
OC
increases. In general, overshoot decreases as C
OC
increases.
C
OC
= 0.0168μF in Figure 8b begins to affect loop dynam-
ics, but startup still exhibits about 1.5V of overshoot.
Short-circuit recovery is considerably more damped. C
OC
= 0.022μF in Figure 8c damps startup overshoot to 0.5V
and short-circuit recovery remains similar to that of Figure
8b. C
OC
= 0.033μF in Figure 8d provides under 100mV
of overshoot and short-circuit recovery is slightly more
damped. C
OC
= 0.047μF in Figure 8e achieves zero over-
W
U
U
shoot at the expense of additional damping and delay time
in short-circuit recovery. In this example, C
OC
= 0.033μF
provides the best value for both startup and short-circuit
recovery. Figure 8f provides an expanded scale of the
waveforms. After a C
OC
value is selected, check startup
and short-circuit recovery over the V
IN
supply range and
with higher output load conditions. Modify the value as
necessary.
Startup 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
short-circuit is therefore identical to startup. In the flyback
example discussed, the primary-side control circuitry is
always active. Switching never stops in short-circuit. The
LT4430 error amplifier COMP pin changes from its low
clamp level to its higher regulating value during startup
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 startup
versus short-circuit recovery waveforms.
A final point of discussion involves the chosen C
OC
value.
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
OC
, above what is required to control
overshoot, do result in smaller dV/dt rates and longer
startup times. However, large values of C
OC
may stall the
feedback loop during startup or short-circuit recovery,
resulting in an extended period of time that the output
voltage “flatspots”. 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
OC
value, solutions may require
circuit modifications. In particular, bias supply holdup
times are a prime point of concern as switching stops
during these output voltage flatspots. As a reminder,
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LT4430_1 | 制造商:LINER 制造商全稱:Linear Technology 功能描述:Secondary-Side Opto-Coupler Driver Ground-Referenced Opto-Coupler Drive |
| LT4430ES6 | 制造商:Linear Technology 功能描述: |
| LT4430ES6#PBF | 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 制造商:Linear Technology 功能描述:OPTO-COUPLER DRIVER 20V TSOT 制造商:Linear Technology 功能描述:OPTO-COUPLER DRIVER, 20V, TSOT-23-6; IC Function:Optocoupler Driver; Supply Voltage Min:3V; Supply Voltage Max:20V; Operating Temperature Min:-40C; Operating Temperature Max:125C; Digital IC Case Style:TSOT-23; No. of Pins:6 ;RoHS Compliant: Yes |
| LT4430ES6#TR | 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 T/R |
| LT4430ES6#TRM | 制造商:Linear Technology 功能描述:Secondary Side Optocoupler Driver 6-Pin TSOT-23 T/R |
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