AN10907
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2010. All rights reserved.
Application note
Rev. 1 — 28 December 2010
47 of 82
NXP Semiconductors
AN10907
TEA1613T resonant power supply control IC
9. Burst
mode
operation
Burst mode operation can be used to improve the efficiency at low output loads.
By temporarily interrupting the switching, losses during the idle time are minimized.
Because the average power needed for the output is very low, it is easy for the converter
to deliver it during a short time of conversion which is a burst.
The burst mode operation of the TEA1613T is based on interrupting the switching while
maintaining regulation. Using an internal comparator, the regulation voltage can be
monitored to determine when to stop switching and when to continue. When restarting
after an interruption, no soft-start is applied as the system is still in regulation (close to the
regular working point). The timing of switching on and off is determined by the
regulation-loop of the system (normally by the output voltage). This deliberately creates a
small ripple on the output voltage during burst mode.
9.1 Burst mode implementation
Burst mode can be Implemented by a resistance divider from SNSFB to ground.
The comparator input monitors the regulation voltage SNSFB to a preset burst voltage
value by R
BURST1
and R
BURST2
. When the HBC output power is low, the regulation voltage
decreases. When the regulation voltage reaches V
BURST
= 3.5 V, the switching stops, no
energy is converted and the output voltage drops. Following this, the regulation voltage
increases again. As soon as the regulation voltage reaches V
BURST
+ 100 mV, the
switching resumes.
When the delivered power, during a burst, is larger than needed for the output, the
regulation voltage SNSFB quickly decreases again, stopping the switching at V
BURST
. The
time needed for the regulation voltage to reach V
BURST
, mainly depends on the output
voltage and its load.
When the HBC output load increases to high levels, normal operation is resumed again as
the regulation voltage does not reach the V
BURST
level.
Fig 32. Principle of burst mode operation with SNSFB and comparator levels
V
BURST
+ 100 mV
HB
V
BURST
SNSBURST
(= ratio of SNSFB)
P
o
normal operation
normal operation
burst
hold
hold burst
001aal456
