NCP1611
http://onsemi.com
28
Reference Section
The circuit features an accurate internal 2.5 V reference
voltage (V
REF
) optimized to be ?.4% accurate over the
temperature range.
OFF Mode
As previously mentioned, the circuit turns off when one
of the following faults is detected:
" Incorrect feeding of the circuit (UVLO high when
V
CC
< V
CC(off)
, V
CC(off)
equating 9 V typically).
" Excessive die temperature detected by the thermal
shutdown.
" UnderV oltage Protection.
" BrownOut Fault and
static OVP (see block diagram)
Generally speaking, the circuit turns off when the
conditions are not proper for desired operation. In this mode,
the controller stops operating. The major part of the circuit
sleeps and its consumption is minimized.
More specifically, when the circuit is in OFF state:
" The drive output is kept low
" All the blocks are off except:
The UVLO circuitry that keeps monitoring the V
CC
voltage and controlling the startup current source
accordingly.
The TSD (thermal shutdown)
The UnderVoltage Protection (UVP).
The brownout circuitry
" V
CONTROL
is grounded so that when the fault is
removed, the device startsup under the soft start mode
(B Version).
" The internal pfcOK signal is grounded.
" The output of the V
TON
processing block is grounded
Failure detection
When manufacturing a power supply, elements can be
accidentally shorted or improperly soldered. Such failures
can also happen to occur later on because of the components
fatigue or excessive stress, soldering defaults or external
interactions. In particular, adjacent pins of controllers can be
shorted, a pin can be grounded or badly connected. Such
open/short situations are generally required not to cause fire,
smoke nor big noise. The NCP1611 integrates functions that
ease meet this requirement. Among them, we can list:
" Floating feedback pin
A 250 nA sink current source pulls down the voltage on
the feedback pin if it is floating so that the UVP
protection trips and prevents the circuit from operating.
This current source is small (450 nA maximum) so that
its impact on the bulk voltage regulation level remains
negligible with typical feedback resistor dividers.
" Fault of the GND connection
If the GND pin is properly connected, the supply
current drawn from the positive terminal of the V
CC
capacitor, flows out of the GND pin to return to the
negative terminal of the V
CC
capacitor. If the GND pin
is not connected, the circuit ESD diodes offer another
return path. The accidental non connection of the GND
pin can hence be detected by detecting that one of this
ESD diode is conducting. Practically, the CS/ZCD ESD
diode is monitored. If such a fault is detected for 200
ms, the circuit stops operating.
" Detection the CS/ZCD pin improper connection
The CS/ZCD pin sources a 1 mA current to pull up the
pin voltage and hence disable the part when the pin is
floating. If the CS/ZCD pin is grounded, the circuit
cannot monitor the ZCD signal and the 200 ms
watchdog timer is activated. When the watchdog time
has elapsed, the circuit sources a 250 mA current source
to pullup the CS/ZCD pin voltage. No drive pulse is
initiated until the CS/ZCD pin voltage exceeds the ZCD
0.75 V threshold. Hence, if the pin is grounded, the
circuit stops operating. Circuit proper operation requires
the pin impedance to be 3.9 kW or more, the tolerance
of the NCP1611 impedance testing function being
considered over the 40癈 to 125癈 temperature range.
" Boost or bypass diode short
The NCP1611 addresses the short situations of the
boost and bypass diodes (a bypass diode is generally
placed between the input and output highvoltage rails
to divert this inrush current). Practically, the overstress
protection is implemented to detect such conditions and
forces a low dutycycle operation until the fault is gone.
Refer   to   application   note   AND9064   available   at
http://www.onsemi.com/pub_link/Collateral/AND9064-D.PDF
for
more details.
ORDERING INFORMATION
Device
Circuit Version
Package
Shipping
NCP1611ADR2G
NCP1611A
SOIC8
(PbFree)
3000 / Tape & Reel
NCP1611BDR2G
NCP1611B
For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging
Specifications Brochure, BRD8011/D.