LM2754SQX/NOPB National Semiconductor, LM2754SQX/NOPB Datasheet - Page 10

• Manufacturer Part Number: LM2754SQX/NOPB
• Description: IC LED DRIVER PHOTO FLASH 24-LLP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: Photo Flash LEDr

Specifications of LM2754SQX/NOPB

• Constant Current: Yes
• Topology: Switched Capacitor (Charge Pump)
• Number Of Outputs: 4
• Internal Driver: Yes
• Type - Primary: Flash/Torch
• Type - Secondary: White LED
• Frequency: 700kHz ~ 1.3MHz
• Voltage - Supply: 2.8 V ~ 5.5 V
• Voltage - Output: 4.7 V ~ 5.1 V
• Mounting Type: Surface Mount
• Package / Case: 24-LLP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 800mA
• Internal Switch(s): Yes
• Efficiency: 90%
• For Use With: LM2754SQEV - BOARD EVALUATION LM2754SQ
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM2754SQX

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Application Information
THERMAL PROTECTION
Internal thermal protection circuitry disables the LM2754
when the junction temperature exceeds 150˚C (typ.). This
feature protects the device from being damaged by high die
temperatures that might otherwise result from excessive
power dissipation. The device will recover and operate nor-
mally when the junction temperature falls below 120˚C (typ.).
It is important that the board layout provide good thermal
conduction to keep the junction temperature within the speci-
fied operating ratings.
POWER DISSIPATION
The power dissipation (P
ture (T
is the power generated by the 1x/1.5x/2x charge pump, P
is the power consumed by the LEDs, T
temperature, and θ
sistance for the LLP-24 package. V
the LM2754, V
I
LED
is the programmed LED current.
J
= [Gain x V
) can be approximated with the equations below. P
LED
P
DISSIPATION
IN
is the nominal LED forward voltage, and
JA
x (4 x I
is the junction-to-ambient thermal re-
DISSIPATION
LED
= P
)] − (V
IN
IN
) and junction tempera-
- P
is the input voltage to
LED
LED
(Continued)
x 4 x I
A
is the ambient
LED
)
LED
IN
10
The junction temperature rating takes precedence over the
ambient temperature rating. The LM2754 may be operated
outside the ambient temperature rating, so long as the junc-
tion temperature of the device does not exceed the maxi-
mum operating rating of 125˚C. The maximum ambient tem-
perature rating must be derated in applications where high
power dissipation and/or poor thermal resistance causes the
junction temperature to exceed 125˚C.
PCB Layout Considerations
The LLP is a leadframe based Chip Scale Package (CSP)
with very good thermal properties. This package has an
exposed DAP (die attach pad) at the center of the package
measuring 2.6mm x 2.6mm. The main advantage of this
exposed DAP is to offer lower thermal resistance when it is
soldered to the thermal land on the PCB. For PCB layout,
National highly recommends a 1:1 ratio between the pack-
age and the PCB thermal land. To further enhance thermal
conductivity, the PCB thermal land may include vias to a
ground plane. For more detailed instructions on mounting
LLP packages, please refer to National Semiconductor Ap-
plication Note AN-1187.
T
J
= T
A
+ (P
DISSIPATION
x θ
JA
)