Cycle Skipping; The Cycle Skipping Circuitry - TCL SY33 Service Manual

Philips Semiconductors
GreenChip™II SMPS control IC
f
handbook, halfpage
(kHz)
175
25
VCO 2
Fig.7 VCO frequency as function of V
handbook, full pagewidth
1.5 V − V CTRL
CTRL
X2
V x
150 mV
The voltage levels dV and dV
1
2003 Sep 09
MGU509
175 kHz
VCO 1 V sense(max) (V)
level level
sense(max)
current
comparator
DRIVER
V
OSCILLATOR
I
are fixed in the IC to 50 mV (typical) and 18 mV (typical) respectively.
2
Fig.8 The cycle skipping circuitry.

Cycle skipping

At very low power levels, a cycle skipping mode will be
activated. A high control voltage will reduce the switching
frequency to a minimum of 25 kHz. If the voltage on the
control pin is raised even more, switch-on of the external
power MOSFET will be inhibited until the voltage on the
control pin has dropped to a lower value again (see Fig.8).
For system accuracy, it is not the absolute voltage on the
control pin that will trigger the cycle skipping mode, but a
signal derived from the internal VCO will be used.
Remark: If the no-load requirement of the system is such
that the output voltage can be regulated to its intended
.
level at a switching frequency of 25 kHz or above, the
cycle skipping mode will not be activated.
f osc
f max
DRIVER
f min
I sense
skipping
7
Product specification
TEA1506P; TEA1506AP;
TEA1506T; TEA1506AT
dV 2 dV 1
cycle
1
0
V x (mV)
150
V x (mV)
MGU510