AP2002 Ver la hoja de datos (PDF) - Anachip Corporation
Número de pieza
componentes Descripción
Fabricante
AP2002 Datasheet PDF : 7 Pages
| |||
Synchronous PWM Controller
AP2002
Function Description (Continued)
Hiccup Mode
During power up, the SS/ SHDN pin is internally
pulled low until VCC reaches the under-voltage
lockout level of 4.2V. Once VCC has reached 4.2V,
the SS/ SHDN pin is released and begins to source
10uA of current to the external soft-start capacitor.
As the soft-start voltage rises, the output of the
internal error amplifier is clamped to this voltage.
When the error signal reaches the level of the
internal triangular oscillator, which swings from 1V
to 2V at a fixed frequency of 200KHz, switching
occurs. As the error signal crosses over the
oscillator signal, the duty cycle of the PWM signal
continues to increase until the output comes into
regulation. If an over-current condition has not
occurred the soft-start voltage will continue to rise
and level off at about 2.2V.
An over-current condition occurs when the
high-side drive is turned on, but the PHASE node
does not reach the voltage level set at the OCSET
pin. The PHASE node is sampled only once per
cycle during the vally of the triangular oscillator.
Once an over-current occurs, the high-side drive is
turned off and the low-side drive turns on and the
SS/ SHDN pin begins to sink 2uA. The soft-start
Marking Information
voltage will begin to decrease as the 2uA of current
discharge the external capacitor. When the
soft-start voltage reaches 0.8V, the SS/ SHDN pin
will begin to source 10uA and begin to charge the
external capacitor causing the soft-start voltage to
rise again. Again, when the soft-start voltage
reaches the level of the internal oscillator, switching
will occur.
If the over-current condition is no longer present,
normal operation will continue. If the over-current
condition is still present, the SS/ SHDN pin will
again begin to sink 2uA. This cycle will continue
indefinitely until the over-current condition is
removed.
In conclusion, above is shown a typical “12V
Application Circuit” which has a BSTH voltage
derived by bootstrapping input voltage to the
PHASE node through diode D1. This circuit is very
useful in cases where only input power of 5V(or
12V) is available.
In order to prevent substrate glitching, a
small-signal diode should be placed in close
proximity to the chip with cathode connected to
PHASE and anode connected to PGND.
Logo
Part No.
( Top View )
14
8
AC
AP2002
YY WW X X
1
7
SOP-14L
ID code: internal
Blank: normal
L: Lead Free Package
Xth week: 01~52
Year: "01" = 2001
"02" = 2002
Anachip Corp.
www.anachip.com.tw
Rev. 0.2 Apr 14, 2004
6/7
Share Link: 