SSL4120T All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Objective data sheet Rev. 1 — 21 June 2012 14 of 47
NXP Semiconductors
SSL4120T
Resonant power supply control IC with PFC
In applications where the SSL4120T is supplied from a separate DC source (e.g. a
standby supply), the SSL4120T will not automatically stop switching if an error condition
causes the output voltage to fall. For this reason, the SSL4120T outputs are provided with
undervoltage protection (UVP output; see Section 7.9
). A UVP output event will restart the
IC if V
SNSOUT
drops below V
uvp(SNSOUT)
(typ. 2.3 V).
During start-up, the output voltage will be below V
uvp(SNSOUT)
for a time. This should not
be considered an error condition provided it doesn’t last longer than expected. For this
reason, the protection timer is started as soon as V
SNSOUT
drops below V
uvp(SNSOUT)
. The
Restart state is activated if the UVP output event is still active once the protection time has
expired.
7.5.6 OverTemperature Protection (OTP)
Accurate internal overtemperature protection is provided in the SSL4120T. When the
junction temperature exceeds the overtemperature protection activation temperature, T
otp
(typ. 150 °C), the IC will go to the Thermal hold state. The SSL4120T will exit the Thermal
hold state when the temperature falls again, to around 10 °C below T
otp
.
7.6 Burst mode operation (pin SNSOUT)
The HBC and PFC controllers can be operated in Burst mode. In Burst mode the
controllers will be on for a period, then off for a period. Burst mode operation increases
efficiency under low-load conditions.
A low-load condition can be detected using a simple external circuit that makes use of the
information from the feedback loop or from the average primary current. The detection
circuit can pull down pin SNSOUT to pause operation of the SSL4120T for a burst-off
time. Both controllers, or only the HBC controller, can be paused during the burst-off time:
• Burst-off level for HBC, V
burst(HBC)
(typ. 1 V).
When V
SNSOUT
drops below V
burst(HBC)
, operation of the HBC controller will be
suspended. Both the high-side and the low-side power switches will be off. The PFC
continues to operate normally. When V
SNSOUT
rises above V
burst(HBC)
again, the HBC
controller will resume normal operation, without executing a soft start sequence.
• Burst-off level for PFC, V
burst(PFC)
(typ. 0.4 V).
When V
SNSOUT
drops below V
burst(PFC)
, operation of the PFC controller will also be
suspended (the HBC will have been paused already). When V
SNSOUT
rises above
V
burst(PFC)
again, the PFC controller will resume normal operation via a PFC soft start
(see Section 7.7.6
).
To ensure Burst mode is not activated before the output voltage becomes valid, a current
from the SNSOUT pin (typ. 100 μA) will hold V
SNSOUT
at V
pu(SNSOUT)
, which is above both
burst levels. The resistance between the SNSOUT pin and ground should therefore be
greater than 20 kΩ.
