AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
52 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
The optimum level for burst mode can be determined experimentally as demonstrated in
the following example.
Example:
The required burst level frequency f
HB(burst)
= 90 kHz which corresponds to
SNSFB = 5.4 V.
For the basic presetting of the burst level, the internal compensation function can be
neglected.
(24)
This can be provided by the following values:
R
BURST1
= 36 k
,
R
BURST2
= 68 k
.
9.5.2 Advanced design of SNSBURST circuit
Tolerance on the value of the converters input voltage (boost voltage) can have a
considerable effect on the performance in burst mode. The SNSBURST function provides
a possibility to compensate the preset burst level for variations in the boost voltage.
The impedance of the resistor divider determines the amount of compensation. The
higher the impedance, the stronger the compensation is.
Remarks:
•
Note that a very high impedance is more susceptible to disturbance
•
The impedance should be higher than 20 k
to maintain normal regulation properties
on SNSFB and higher than 90 k
to prevent disabling the OLP function on SNSFB
•
The general advice is to use a total impedance (R
BURST1
+ R
BURST2
) of 100 k
or
higher
The compensation is obtained by an internal current source whose current value depends
on the SNSBOOST voltage. This current flows into the SNSBURST pin and gives a
voltage offset, depending on the resistance value of the (external) divider.
Because the SNSBOOST voltage determines the value of the compensation current, the
design of this function provides the nominal calculation value according to the relationship
shown in
3.5
V
5.4
V
R
BURST2
R
BURST1
R
BURST2
+
-------------------------------------------------
=
Fig 40. Compensation current on SNSBURST
001aal464
4
1
1.7
SNSBOOST [V]
I
cmp
[
μ
A]
2.5
