ANP015 Datasheet, PDF (5/15 Pages) List of Unclassifed Manufacturers – Application Note AP2011 High Efficiency Synchronous PWM Controller

Application Note
AP2011 High Efficiency Synchronous PWM Controller
ANP015
Preliminary
z Under Voltage Lock Out (UVLO)
The circuit shown in Figure 2 is a simple explanation of UVLO function. VCC voltage will make that two
resistors get a compared voltage with VREF. AP2011 is designed for UVLO voltage is 6.5V, and recovery
voltage is 6.8V (that 0.3V voltage is depend on the offset voltage of the comparator). If VCC voltage is lower
than 6.5V, the separate voltage of those two resistors is under 1.25V, than that comparator will send low level
signal to SS pin to shutdown AP2011. And if VCC is higher than 6.8V, that comparator will send high level
signal to SS and AP2011 will start to enter normal operation mode.
VCC
VREF
1.25V
+
VREF
-
SS/SHDN
Figure 2. Under Voltage Lock-Out circuit
z Soft-Start and Shutdown ( SS/ SHDN )
The circuit shown in Figure 3 is about soft-start and shutdown function. If outside system force SS pin
always under 0.2V, AP2011 will turn into shutdown mode and turn off the PWM. When SS pin higher than
0.2V, PWM will turn on to drive outside MOSFET, but now PWM duty is depend on the comparison of SS and
FB. According to SS pin raising curve, FB will follow this curve until SS reaches to VREF + 0.3V, and then
PWM duty will turn to depend on the comparison of VREF and FB.
VREF
FB
VCC
10uA
SS/SHDN
2uA
-
+
+
+- ^-
0.3V
+_-
0.2V
0.9V
-
+
PWM
Control
DRVP
DRVN
Anachip Corp.
www.anachip.com.tw
Figure 3. Soft-start and Shutdown circuit
5/15
Rev. A.0 Oct, 29, 2004