NXP Semiconductors AN10881, Примечание к применению

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AN10881 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Application note Rev. 2 — 26 September 2011 51 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
(27)
Example:
Requirement: f
HB(min)
= 57 kHz
(28)
8.4.3.2 Maximum frequency setting for RFMAX
(29)
(30)
(31)
Analog to the situation with I
oscillator(min)
:
(32)
(33)
(34)
(35)
Example:
Requirement: f
HB(max)
= 180 kHz and CFMIN = 330 pF
(36)
(37)
Remark: The average multiplication factor is 4.7. There is a small deviation in value
depending on other parameters and presetting conditions. Practical verification of the
result is advised.
8.4.4 RFMAX and High Frequency Protection (HFP)
Normally, the converter does not operate continuously at the preset maximum frequency.
This maximum frequency is only used for a short time during soft-start or temporary
fault/overload conditions.
CFMIN
I
oscillator min
 
2 2

f
HB min
 

V
oscillator
 
------------------------------------------------------------------------
150

A
8 f
HB min
 

----------------------------
= =
CFMIN
150

A
2 2

57 kHz

2

----------------------------------------------
0.00015
456000
-------------------
329 pF = = =
I
oscillator max
 
4.7 I
RFMAX max
 

I
oscillator min
 
+ =
I
RFMAX max
 
V
f max
 
RFMAX
---------------------
=
RFMAX
V
f max
 
I
RFMAX max
 
------------------------------
2.5 V
I
RFMAX max
 
------------------------------
= =
f
HB max
 
I
oscillator max
 
4 CFMIN

V
oscillator
 
---------------------------------------------------------------
4.7 I
RFMAX max
 
I
oscillator min
 
+

4 CFMIN

2

------------------------------------------------------------------------------------
= =
I
RFMAX max
 
8 CFMIN

f
HB max
 
I
oscillator min
 
–

4.7
------------------------------------------------------------------------------------------------
=
I
RFMAX max
 
8 CFMIN

f
HB max
 
150

A –

4.7
--------------------------------------------------------------------------------
=
RFMAX
2.5 V
I
RFMAX max
 
------------------------------
11.75
8 CFMIN

f
HB max
 
150

A –

--------------------------------------------------------------------------------
= =
I
RFMAX max
 
8 330 pF

180 kHz 150

A –

4.7
-------------------------------------------------------------------------------
475

A 150

A –
 
4.7
------------------------------------------------
69.15

A = = =
RFMAX
2.5 V
69.15

A
-----------------------
36 k

= =