IS32BL3552
Integrated Silicon Solution, Inc. – www.issi.com 9
Rev. A, 07/20/2015
(1) Any string is open
(2) LED short circuit protection
(3) Shut down under abnormal condition
(4) Over voltage protection
(5) Over temperature protection
(6) Schottky Diode short protection
(7) VOUT Short/Open Schottky Diode protection
PROTECTION FEATURES
The IS32BL3552 is designed with integrated safety
features for a reliable and stable operation in the
normal operating range. In the event of more than one
fault condition occurring, the higher priority condition
will take precedence.
SOFT START
The internal soft start circuit prevents a high inrush
current during startup.
OVER VOLTAGE PROTECTION
The IS32BL3552 integrates an OVP circuit to prevent
system damage should the output voltage become
excessive. To maintain a safe output level, the
integrated OVP circuit continuously monitors the
voltage output level. The OVP pin is connected to the
center tap of voltage-divider (R
OV1
and R
OV2
)
connected between high voltage output and GND. If
the voltage on OVP pin exceeds 2.0V the IS32BL3552
stops switching, which causes the output voltage to
drop. When the OVP pin voltage drops below the
threshold the device begins oscillating once again,
which causes the output voltage to rise. This OVP
hysteresis is 250mV (V
OVP_HYS
). The formula to
calculate V
OVP
can be expressed as below Equation
(4):
2
21
0.2
OV
OVOV
OVP
R
VRR
V
(4)
V
OVP
= OVP voltage
V
OVP_HYS
= OVP hysteresis voltage
OVER CURRENT PROTECTION
The IS32BL3552 integrates an OCP circuit. The CS
pin is connected to the external voltage-sense resistor
(R
CS
) that is placed between the Drain of MOS and
GND. If the voltage on CS pin exceeds 0.56V (V
LIMIT
), it
is turned OFF immediately and will not turn ON until
the next cycle begins.
SCHOTTKY DIODE/INDUCTOR SHORT CIRCUIT
PROTECTION
The IS32BL3552 features a Schottky diode/inductor
short-circuit protection circuit. When CS pin voltage
exceeds 0.8V (V
LIMIT2
) for more than 16 switching
clocks, the IC will latch. The voltage of CS is monitored
after a short delay of Leading Edge Blanking signal.
LED OPEN CIRCUIT PROTECTION
The IS32BL3552 integrates an LED open-circuit
protection circuit. When any LED string is open, V
OUT
will boost up until the voltage at OVP pin reaches an
approximate 2.0V threshold. The IC will automatically
ignore the open string whose corresponding pin
voltage is less than 100mV and the remaining string
will continue operation. If all the strings are open and
the voltage at OVP reaches a threshold of 2.0V, the
MOSFET drive GATE will turn off and IC will shut down
and latch.
LED SHORT CIRCUIT PROTECTION
The IS32BL3552 integrates an LED short-circuit
protection circuit. If the voltage at any of the two
channel pins exceeds a threshold of approximately
7.3V (V
LED_S
) during normal operation, the
corresponding string is turned off and is latched off. To
reset the latch and start operation, the V
IN
and/or EN
must be toggled OFF/ON. The priority of the LED short
detecting logic is lower than the open LED and OVP
logic. The LED short circuit detection logic is triggered
when V
LED_MIN
is <0.1V under dimming on mode. It is
disabled when an LED open occurs or when the output
voltage resumes to the regulated output level.
V
OUT
SHORT / OPEN SCHOTTKY DIODE
PROTECTION
The IS32BL3552 monitors the OVP pin, if the OVP pin
voltage is less than 0.1V, MOSFET drive output will
turn off. This protects the converter if the output
schottky diode is open or V
OUT
is shorted to ground.
UNDER VOLTAGE LOCKOUT
The IS32BL3552 provides an under voltage lockout
circuit with built in hysteresis to prevent an undefined
status during startup. The UVLO circuit shuts down the
device when V
CC
drops below 3.6V (Typ.) and will turn
when V
CC
rises above 3.8V. The UVLO circuit has a
200mV (V
UVLO_HYS
) hysteresis, which means the device
will start up when V
CC
rises above 3.8V.
OVER TEMPERATURE PROTECTION
The thermal overload protection prevents excessive
power dissipation from overheating and damaging the
IS32BL3552. If the junction temperature exceeds
approximately 160ºC (T
OTSD
), the IC will shut down to
allow it to cool down. The device will begin a soft-start
process when the junction temperature (T
J
) of the die
falls below approximately 140ºC (T
HYS
).
SHUT DOWN UNDER ABNORMAL CONDITION
The IS32BL3552 integrates a shutdown under
abnormal condition protection circuit. When the OVP
pin voltage exceeds 3.2V (V
OVP_SH
), the IC will latch.
The EN pin must then be toggled to restart the IC. This
feature can be used for any other protection to shut
down the IC.
