L6566BH View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6566BH' PDF : 51 Pages View PDF
L6566BH
Application information
Figure 11. Load-dependent operating modes: timing diagrams
COMP
(pin 9)
VCOMPBM
20 mV
hys ter.
fosc
t
MODE/SC=Open
fsw
MODE/SC=VREF
t
GD
(pin 4)
MODE/SC=Open
MODE/SC=VREF
FF Mode
QR Mode
Burs t-m ode
Burs t-m ode
Valley-skipping Mode
FF Mode
t
QR Mode
AM11487v1
Figure 12. Addition of an offset to the current sense lowers the burst-mode
operation threshold
Vcso
=
Vref
R
R
+ Rc
Vref
10
4
L6566BH
37
Rc
R
Rs
AM11488v1
5.4
Adaptive UVLO
A major problem when optimizing a converter for minimum no-load consumption is that the
voltage generated by the auxiliary winding under these conditions falls considerably as
compared even to a few mA load. This very often causes the supply voltage Vcc of the
control IC to drop and go below the UVLO threshold so that the operation becomes
intermittent, which is undesired. Furthermore, this must be traded off against the need to
generate a voltage not exceeding the maximum allowed by the control IC at full load.
To help the user overcome this problem, the device, besides reducing its own consumption
during burst-mode operation, also features a proprietary adaptive UVLO function. It consists
of shifting the UVLO threshold downwards at light load, namely when the voltage at the
COMP pin falls below a threshold VCOMPO internally fixed, so as to have more headroom. To
Doc ID 16610 Rev 2
23/51
Share Link: 
