AN10907
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© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
54 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
An alternative to the basic circuit construction given in
is a construction with
an additional series resistance in the connection of SNSBURST (R
SBURST
).
This construction allows lower impedance values to be used for the resistor divider while
obtaining the same behavior for boost voltage compensation. The lower impedance has a
positive effect on disturbance pickup, benefiting PCB-layout design. The series resistor
can be placed directly near the SNSBURST pin, thereby minimizing the high-impedance
track.
Example:
Nominal SNSBOOST voltage is 2.5 V with I
cmp
= 1
A.
The required burst frequency f
HB(burst)
= 90 kHz which corresponds to SNSFB = 5.4 V.
Impedance target for R
BURST1
= 22 k
and the result should be the same as the example
in
V
SNSFB
=
(27)
(28)
Choose the value of R
SBURST
to obtain the same compensation as in example
(indicator gave 72 Hz/V). Because the relationships are complex, the
calculation tool can be used to vary the R
SBURST
value to reach this indicator value.
R
SBURST
= 46 k
R
BURST2
= 43 k
Note that for the same compensation (as in the example in
) the impedance
of the network is much lower.
To obtain a better overview of the relationship between SNSBOOST and SNSBURST and
the effect on impedance of the resistors, regarding the compensation design, the
calculation sheet can used.
9.5.4 Other aspects regarding SNSBURST
Aspects that influence choices regarding the design of the SNSBURST circuit with respect
to burst mode are:
•
Voltage on SNSBOOST at nominal input voltage V
BOOST
•
SNSFB voltage regulation levels in combination with the preset frequency range by
RFMAX and CFMIN
•
Dynamic behavior of the regulation during burst mode and during normal operation
(large load variations)
3.5
V
R
SBURST
I
cmp
R
BURST1
I
cmp
R
BURST1
+
3.5
V
R
SBURST
I
cmp
+
R
BURST2
----------------------------------------------------------
+
+
5.4
V
=
3.5
V
R
SBURST
1
A
22
k
1
A
22
k
R
BURST2
---------------------
+
3.5
V
R
SBURST
1
A
+
+
+
5.4
V
=
