LM3402HVMR/NOPB National Semiconductor, LM3402HVMR/NOPB Datasheet - Page 23

• Manufacturer Part Number: LM3402HVMR/NOPB
• Description: IC LED DRVR HP CONST CURR 8-PSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r
• Type: High Power, Constant Currentr

Specifications of LM3402HVMR/NOPB

• Constant Current: Yes
• Topology: PWM, Step-Down (Buck)
• Number Of Outputs: 1
• Internal Driver: Yes
• Type - Primary: Automotive
• Type - Secondary: High Brightness LED (HBLED), White LED
• Frequency: 1MHz
• Voltage - Supply: 6 V ~ 75 V
• Mounting Type: Surface Mount
• Package / Case: 8-PSOP
• Operating Temperature: -40°C ~ 125°C
• Current - Output / Channel: 500mA
• Internal Switch(s): Yes
• Efficiency: 96%
• Primary Input Voltage: 75V
• No. Of Outputs: 1
• Output Voltage: 73V
• Output Current: 500mA
• Voltage Regulator Case Style: PSOP
• No. Of Pins: 8
• Operating Temperature Range: -40°C To +125°C
• Svhc: No SVHC (15-Dec-2010)
• Rohs Compliant: Yes
• For Use With: 551600000-001A/NOPB - BOARD WEBENCH SO8/SOP LM3404/2551600003-001A - BOARD WEBENCH MSOP LM3402LM3402HVEVAL - BOARD EVALUATION FOR LM3402HV
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Other names: LM3402HVMR

DCR loss, P
Recirculating diode loss, P
Current Sense Resistor Loss, P
Electrical efficiency, η = P
1.295 / (1.295 + 0.377) = 77%
DIE TEMPERATURE
Design Example 2: LM3402HV
The second example application is an RGB backlight for a flat
screen monitor. A separate boost regulator provides a 60V
±5% DC input rail that feeds three LM3402HV current regu-
lators to drive one series array each of red, green, and blue
1W LEDs. The target for average LED current is 350 mA ±5%
in each string. The monitor will adjust the color temperature
dynamically, requiring fast PWM dimming of each string with
external, parallel MOSFETs. 1W green and blue InGaN LEDs
have a typical forward voltage of 3.5V, however red LEDs use
AlInGaP technology with a typical forward voltage of 2.9V. In
order to match color properly the design requires 14 green
LEDs, twice as many as needed for the red and blue LEDs.
This example will follow the design for the green LED array,
providing the necessary information to repeat the exercise for
the blue and red LED arrays. The circuit schematic for Design
Example 2 is the same as the Typical Application on the front
page. The bill of materials (green array only) can be found in
Table 2 at the end of this datasheet.
OUTPUT VOLTAGE
R
A compromise in switching frequency is needed in this appli-
cation to balance the requirements of magnetics size and
efficiency. The high duty cycle translates into large conduc-
tion losses and high temperature rise in the IC. For best
response to a PWM dimming signal this circuit will not use an
output capacitor; hence a moderate switching frequency of
300 kHz will keep the inductance from becoming so large that
a custom-wound inductor is needed. This design will use only
surface mount components, and the selection of off-the-shelf
SMT inductors for switching regulators is poor at 1000 µH and
above. R
quency as follows:
ON
and t
R
T
Green Array: V
LM3402
ON
P
ON
Blue Array: V
Red Array: V
ON
L
= 49.2 / (1.34 x 10
= I
L
is selected from the equation for switching fre-
, in the inductor
F
T
= (0.028 + 0.05 + 0.078) x 200 = 31°C
2
LM3402
x DCR = 0.35
= (P
O(R)
O(B)
O(G)
O
D
C
= 7 x 2.9 + 0.2 = 20.5V
= 7 x 3.5 + 0.2 = 24.7V
= 14 x 3.5 + 0.2 = 49.2V
/ (P
= 119 mW
+ P
-10
2
SNS
O
x 0.096 = 11.8 mW
G
x 3 x 10
+ Sum of all loss terms) =
+ P
= 92 mW
S
) x θ
5
) = 1224 kΩ
JA
23
The closest 1% tolerance resistor is 1.21 MΩ. The switching
frequency and on-time of the circuit can then be found using
the equations relating R
USING AN OUTPUT CAPACITOR
This application is dominated by the need for fast PWM dim-
ming, requiring a circuit without any output capacitance.
OUTPUT INDUCTOR
In this example the ripple current through the LED array and
the inductor are equal. Inductance is selected to give the
smallest ripple current possible while still providing enough
Δv
signing to a desired Δv
average inductor current will equal the desired average LED
current of 350 mA yields the target current ripple in the in-
ductor and LEDs:
With the target ripple current determined the inductance can
be chosen:
The closest standard inductor value is 680 µH. As with the
previous example, the average current rating should be
greater than 350 mA. Separation between the LM3402HV
drivers and the LED arrays mean that heat from the inductor
will not threaten the lifetime of the LEDs, but an overheated
inductor could still cause the LM3402HV to enter thermal
shutdown.
The inductance itself of the standard part chosen is ±20%.
With this tolerance the typical, minimum, and maximum in-
ductor current ripples can be calculated:
The peak LED/inductor current is then estimated:
SNS
L
f
MIN
signal for the CS comparator to operate correctly. De-
SW
Δi
Δi
Δi
t
ON
F(MAX)
F(TYP)
Δi
F(MIN)
= [(60 – 49.2) x 2.7 x 10
= 49.2 / (1210000 x 1.34 x 10
F
= (1.34 x 10
= Δi
= [(60 - 49.2) x 2.7 x 10
= [(60 - 49.2) x 2.7 x 10
= [(60 - 49.2) x 2.7 x 10
Δi
L
I
F
L(PEAK)
= Δv
= 0.025 / 0.57 = 43.8 mA
SNS
SNS
ON
-10
= 43 mA
= 36 mA
= 54 mA
= I
and t
x 1210000) / 60 = 2.7 µs
/ R
of 25 mV and assuming that the
L
+ [Δi
SNS
ON
P-P
P-P
P-P
, R
L(MAX)
-6
to f
] / (0.044) = 663 µH
SNS
SW
-6
-6
-6
] / 2
-10
] / 680 x 10
] / 816 x 10
] / 544 x 10
= V
:
) = 303 kHz
SNS
/ I
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F
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