NXP Semiconductors
TEA19362T
GreenChip SMPS primary side control IC with fixed frequency operation
TEA19362T All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product data sheet Rev. 1 — 9 August 2016
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• The optocoupler collector parasitics do not influence the loop. So, more freedom in
tuning the loop characteristics is ensured.
• Unlike the traditional situation where the optocoupler current becomes much higher at
lower output power, it retains the same low value in steady state at all powers.
Since the optocurrent is only 80 μA even at low powers, a load step to a very high
load can result in a maximum decrease of the optocurrent by this amount only. It limits
the possible power increase. To counter this possibility, the offset loop enters a fast
regulation mode when a significant optocurrent decrease is detected (to about 20 μA
under the regulation level). The fast regulation mode ensures a quick output power
increase.
8.8 Burst mode operation
When the output power drops to below the minimum level the system can supply
while operating at the minimum power setting (i.e. V
sense(peak)
is at its minimum), it can
no longer reduce the optocurrent level to the regulation level I
IO(reg)CTRL
(= 80 μA).
In this situation, the optocurrent increases to exceed the level of the burst threshold
(I
th(burst)CTRL
) and the burst mode is entered. Switching is paused and a burst-off period
commences. Consequently, the optocurrent decreases. When it drops to below the
I
th(burst)CTRL
, a new burst of switching cycles is started (see Figure 8 and Figure 9).
Figure 8 shows that the switching frequency within a burst remains the same as in the
DCM mode.The target burst repetition period is t
burst
.
The requested output power determines the number of pulses at each burst period. At
higher output power, the number of switching pulses increases. At low load, it decreases.
This burst mode regulation allows low-load operation without compromising on spectral
purity, while keeping the output ripple limited. In addition, the optocoupler current is
maintained at a very low level during low-load and standby operation. The result is a very
low standby power consumption.
To ensure good efficiency at very low load, the minimum number of switching cycles
is set to 1. When the minimum number of pulses is reached, the burst repetition period
cannot be reduced further. As the power decreases, the repetition rate of the single-pulse
bursts decreases as well to a very low value. To improve further, the no-load input power
and efficiency at low load, the current consumption of the IC is lowered to 250 μA during
the non-switching period in the burst mode.
