TEA1750_2 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 02 — 15 December 2008 6 of 29
NXP Semiconductors
TEA1750
GreenChip III SMPS control IC
When the PFC is started, there is initially no supply take-over from the auxiliary winding.
To make a small V
CC
capacitor possible, the V
CC
voltage is regulated to the V
startup
level,
as long as the flyback converter has not yet started. Regulation is done by hysteretic
control with a limited (high level) charge current. The hysteresis is typically 300 mV.
If during start-up the LATCH pin does not reach the V
en(LATCH)
level before V
CC
reaches
V
th(UVLO)
, the LATCH pin output is de-activated and the charge current is switched on
again.
As soon as the flyback converter is started, the voltage on the FBCTRL pin is monitored. If
the output voltage of the flyback converter does not reach its intended regulation level in a
predefined time, the voltage on the FBCTRL pin reaches the V
to(FBCTRL)
level and an error
is assumed. The TEA1750 then initiates a safe restart.
When one of the protection functions is activated, both converters stop switching and the
V
CC
voltage drops to V
th(UVLO)
. A latched protection recharges the V
CC
capacitor via the
HV pin, but does not restart the converters. For a safe-restart protection, the capacitor is
recharged via the HV pin and the device restarts (see Figure 1)
In the event of an overvoltage protection of the PFC circuit
(V
I
on pin VOSENSE > V
ovp(VOSENSE)
), only the PFC controller stops switching until the
VOSENSE pin voltage drops below V
ovp(VOSENSE)
again. Also, if a mains undervoltage is
detected (V
I
on pin VINSENSE < V
stop(VINSENSE)
), only the PFC controller stops switching
until V
I
on pin VINSENSE > V
start(VINSENSE)
again.
When the voltage on pin V
CC
drops below the undervoltage lock-out level, both controllers
stop switching and re-enter the safe restart mode. In the safe restart mode the driver
outputs are disabled and the V
CC
pin voltage is recharged via the HV pin.
