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.