NXP Semiconductors AN10907, Примечание к применению

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Application note Rev. 1 — 28 December 2010 23 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
6.6 Value of the capacitors on SUPIC, SUPREG and SUPHS
Some practical examples are provided in Section 12 .
6.6.1 Value of the capacitor on SUPIC
6.6.1.1 General
It is generally advisable to use two types of capacitor on SUPIC. An SMD ceramic type,
with a smaller value located close to the IC, and an electrolytic type providing the major
part of the capacitance.
6.6.1.2 Start-up
When the supply is initially provided by an HV source before being handled by an auxiliary
winding, a larger capacitor is needed on SUPIC. The capacitor value should be large
enough to handle the start-up before the auxiliary winding takes over the supply of SUPIC.
Example:
This example provides an estimation and not an exact calculation.
I
SUPIC(start-up)
= 10 mA

V
SUPIC(start-up)
= 22 V

15 V = 7 V

t
Vaux>15V
= 70 ms
(1)
6.6.1.3 Normal operation
For normal operation, the main purpose of the capacitors on SUPIC is to keep the current
load variations (e.g. gate drive currents) local.
6.6.1.4 Burst mode operation
When burst mode operation is applied, the supply construction often uses an auxiliary
winding and start-up from the HV source. While in the burst mode there are long periods
during which the auxiliary winding is not able to charge the SUPIC because there is no
HBC switching (time between two bursts). Therefore, the capacitor value on SUPIC
should be large enough to keep the voltage above 15 V to prevent activating the SUPIC
under-voltage stop level.
Example:
This example provides an estimation and not an exact calculation.
I
SUPIC(between 2 bursts)
= 4 mA

V
SUPIC(burst)
= V
aux burst

15 V = 19 V

15 V = 4 V

t between 2 bursts = 25 ms
(2)
C
SUPIC
I
SUPIC start - up
 

t
Vaux

15 V

V
SUPIC start - up
 

------------------------------------------

10 mA
70 ms
7 V
---------------

100

F = =
C
SUPIC
I
SUPIC between 2 bursts
 

t
between 2 bursts

V
SUPIC burst
 

-----------------------------------------

4 mA
25 ms
4 V
---------------

25

F = =