IR1155S
www.irf.com
14
?2011 International Rectifier
IR1155 Modes of operation (refer to States & Transitions Diagram)
UVLO/Sleep Mode: The IC is in the UVLO/Sleep
mode when either the VCC pin voltage is below
V
CC,UVLO
and/or the OVP/EN pin voltage is below
V
SLEEP
. The UVLO/Sleep mode is accessible from
any other state of operation. This mode can be
actively invoked by pulling the OVP/EN pin below
the Sleep threshold V
SLEEP
even if VCC pin
voltage is above V
CC,ON
. In the UVLO/Sleep state,
the gate drive circuit is inactive, most of the
internal circuitry is unbiased and the IC draws a
quiescent current of I
SLEEP
which is typically 200uA
or less. Also, the internal logic of the IC ensures
that whenever the UVLO/Sleep mode is actively
invoked, the COMP pin is actively discharged
below V
COMP,START
prior to entering the sleep
mode,   in   order   to   facilitate   soft-start   upon
resumption of operation.
Stand-by Mode: The IC is placed in Stand-by
mode   whenever   an   Open-loop   situation   is
detected.   An   open-loop   situation   is   sensed
anytime VFB pin voltage is less than V
OLP
. All
internal circuitry is biased in the Stand-by Mode,
but the gate is inactive and the IC draws a few mA
of current. This state is accessible from any other
state of operation of the IC. COMP pin is actively
discharged to below V
COMP,START
whenever this
state is entered from normal operation in order to
facilitate soft-start upon resumption of operation.
Soft Start Mode: During system start-up, the soft-
start mode is activated once the VCC voltage has
exceeded   V
CC,ON
,   the   VFB   pin   voltage   has
exceeded   V
OLP
  and   OVP   pin   voltage   has
exceeded V
SLEEP(ON)
. The soft start time is the time
required   for   the   VCOMP   voltage   to   charge
through its entire dynamic range i.e. through
V
COMP,EFF
. As a result, the soft-start time is
dependent upon the component values selected
for compensation of the voltage loop on the
COMP pin. As VCOMP voltage raises gradually,
the IC allows a higher and higher RMS current
into the PFC converter. This controlled increase
of the input current amplitude contributes to
reducing system component stress during start-
up. It is clarified that, during soft-start, the IC is
capable of full duty cycle modulation (from 0% to
MAX DUTY), based on the instantaneous ISNS
signal from system current sensing. .
For all practical purposes, the Soft-start mode of
the IC is the same as the Normal mode (only
difference being that the DC bus voltage is
approaching the regulation point). All protection
functions of the IC are active during soft-start
mode.
Normal Mode: The IC enters the normal operating
mode seamlessly following conclusion of soft-start.
At this point the DC bus is well regulated and all
protection functions of the IC are active. If, from
the normal mode, the IC is pushed into either a
Stand-by mode or Sleep mode then COMP pin is
actively discharged below V
COMP,START
and system
will go through soft-start upon resumption of
operation.
OVP Mode: The IC enters OVP fault mode
whenever an overvoltage condition is detected. A
system overvoltage condition is recognized when
OVP/EN pin voltage exceeds V
OVP
threshold. When
this happens the IC immediately disables the gate
drive. The gate drive is re-enabled only when
OVP/EN   pin   voltage   is   less   than   V
OVP(RST)
threshold. This state is accessible from both the
soft start and normal modes of operation.
IPK LIMIT Mode: The IC enters IPK LIMIT fault
mode whenever the magnitude of ISNS pin voltage
exceeds the V
ISNS(PK)
threshold triggering cycle-by-
cycle peak over current protection. When this
happens, the IC immediately disables the gate
drive. Gate drive is re-enabled when magnitude of
ISNS pin voltage drops below V
ISNS(PK)
threshold.
This state is accessible from both the soft start and
normal modes of operation.