LM3552SDEV National Semiconductor, LM3552SDEV Datasheet - Page 9

• Manufacturer Part Number: LM3552SDEV
• Description: BOARD EVALUATION LM3552SD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM3552SDEV

• Current - Output / Channel: 700mA
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 4 V
• Features: Flash Timeout Protection
• Voltage - Input: 2.7 ~ 5.5V
• Utilized Ic / Part: LM3552
• Core Chip: LM3552
• Topology: Boost
• No. Of Outputs: 1
• Output Current: 1A
• Input Voltage: 2.7V To 5.5V
• Development Tool Type: Hardware - Eval/Demo Board
• Mcu Supported Families: LM3552
• Lead Free Status / RoHS Status: Not applicable / Not applicable

the output will droop at a rate determined by the value of the
output capacitor and current leakage through the OVP pin and
any other leakage path. When the output voltage drops to
10.6V(typ), switching will resume. The LM3551 and LM3552
will go back into OVP if the failure is still present resulting in
a pulsed output condition.
Note: To disable OVP, ground to OVP pin. CAUTION: The LM3551 and
Under-Voltage Protection (UVP)
Both the LM3551 and LM3552 have under-voltage protection
circuitry (UVP). This protects the NMOS power device during
startup and shutdown by preventing operation at voltages
less than the minimum input voltage. The UVP protection is
enabled at 2.48V(typ.) and will not disable until the input volt-
age rises above 2.58V(typ.) .
Torch/Flash Pin (T/F)
The TORCH/FLASH pin (T/F) controls whether the LM3551/2
is in continuous torch mode, or in flash mode. A logic '0' places
the part into torch mode and a logic '1' places the part into
flash mode. There are no pull-ups or pull-downs internally
connected to T/F. When placed into torch mode, FET-T is
enabled allowing the current set by R
FET-F is not enabled. Flash mode enables both FET-T and
FET-F allowing the sum total of the current set by the two
external resistors, R
LM3552 may be damaged if an OVP condition occurs and OVP
is disabled.
T
and R
F
, to flow.
T
to flow. In torch mode,
Flash Timeout Protection Diagram
9
Flash Timeout Protection (FTP)
When SD is low(LM3551) or EN is high(LM3552), and T/F is
high, a current is output to an external capacitor, C
causes the voltage on the capacitor to rise. If the voltage
reaches Vtrip (1.16V(typ)), the timeout circuit forces the
INTERNAL_EN signal to go low, which in turn shuts-off the
low-side torch and flash FETs in addition to disabling the main
power SW FET. At such time, the LED will be turned off. The
part will remain disabled until SD is pulled high (LM3551) or
EN is pulled low (LM3552) and/or T/F is pulled low. At that
point, the part will return to normal operating mode. The dia-
gram below shows a first pulse which exceeds the timeout
period and internal_EN being driven low. The second FLASH
pulse is shorter than the timeout period and therefore the
voltage on C
ponent selection, please see the FLASH TIMEOUT EQUA-
TIONS below.
To disable the timeout function, ground the FTO pin.
FTO
C
T
FTO
ΔV
FTO
T
never reaches Vtrip. For information on com-
FTO
FTO
(µF) = T
= Desired Timeout Duration
= C
= 1.16V and I
FTO
FTO
× (ΔV
(sec.) × 1.21(µA/V)
FTO
FTO
÷ I
= 1.4µA
FTO
20151204
)
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FTO
. This