ANP015 Datasheet, PDF (4/15 Pages) List of Unclassifed Manufacturers – Application Note AP2011 High Efficiency Synchronous PWM Controller

Application Note
AP2011 High Efficiency Synchronous PWM Controller
ANP015
Preliminary
2. Hardware
2.1 Introduction
AP2011 is a high efficiency and high performance synchronous PWM controller. With using one
P-channel MOSFET and one N-channel MOSFET to be the synchronous switch, AP2011 can make the
system operating in more than 92% efficiency situation. There are a lots of function built inside in AP2011 like
programmable current limit, UVLO, soft-start, shutdown, reference voltage, voltage clamping for high input
voltage, and the most important function is the Virtual Frequency Control^TM, which make the frequency
modulated automatically by the input and output voltage of the system. The functions’ description will show in
each section to let user know how to define the outside circuit.
2.2 Description of the built-in function
z Programmable Current Limit Control
The programmable current limit control circuit is designed for engineer who needs to control the limit
current to avoid too large system current. The current limit set pin (OCSET) just needs to add an outside
resistor between VCC and OCSET pin, which resistor can make a voltage drop to VCC with the internal
current source (70uA). This voltage drop will compare with the voltage drop of PWM waveform (Phase pin
waveform) because the voltage drop of PWM is made by output current and P-channel MOSFET RDSON, so
we can limit the output current by this formula:
I R I R ^{× = ×} LOAD
DS (on)−PMOS
OCSET
OCSET
If the comparator detected the PWM high voltage level is under the OCSET pin voltage level, it will sent turn
off signal to shutdown the PWM control and SS pin will discharge the outside capacitor with a 2uA current.
After SS pin voltage lower than 0.2V, AP2011 will reset to make PWM and start to charge SS pin. If SS pin
charges to 0.9V but PWM still lower than OCSET voltage, then the comparator will send the signal to
shutdown PWM again.
Anachip Corp.
www.anachip.com.tw
OCSET
PHASE
I_OCSET
+
PWM
-
Control
DRVP
DRVN
Figure 1. Programmable Current Limit Control Circuit
4/15
Rev. A.0 Oct, 29, 2004