LM3402HVMR/NOPB National Semiconductor, LM3402HVMR/NOPB Datasheet - Page 19
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LM3402HVMR/NOPB
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
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Part Number:
LM3402HVMR/NOPB
Manufacturer:
NS/国半
Quantity:
20 000
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:
In the case of a short circuit across the LED array, the
LM3402HV will continue to deliver rated current through the
short but will reduce the output voltage to equal the CS pin
voltage of 200 mV. Worst-case peak current in this condition
would be equal to:
In the case of a short at the switch node, the output, or from
the CS pin to ground the short circuit current limit will engage
at a typical peak current of 735 mA. In order to prevent in-
ductor saturation during these fault conditions the inductor’s
peak current rating must be above 735 mA. A 680 µH off-the
Δi
L
MIN
F(LED-SHORT)
Δi
Δi
Δi
F(MAX)
F(TYP)
Δi
F(MIN)
= [(60 – 49.2) x 2.7 x 10
F
= Δi
I
I
L(PEAK)
F(PEAK)
= [(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
= [(63 – 0.2) x 2.7 x 10
= 0.025 / 0.57 = 43.8 mA
= 0.35 + 0.027 = 377 mA
= 0.35 + 0.156 = 506 mA
SNS
SNS
= 314 mA
= 43 mA
= 36 mA
= 54 mA
= I
/ R
of 25 mV and assuming that the
L
+ [Δi
SNS
P-P
P-P
P-P
, R
L(MAX)
P-P
-6
] / (0.044) = 663 µH
SNS
-6
-6
-6
] / 2
] / 680 x 10
] / 816 x 10
= V
] / 544 x 10
-6
] / 544 x 10
SNS
/ I
F
-6
-6
-6
-6
19
shelf inductor rated to 1.2A (peak) and 0.72A (average) with
a DCR of 1.1Ω will be used for the green LED array.
R
A preliminary value for R
Δi
tions for Δi
Sub-1Ω resistors are available in both 1% and 5% tolerance.
A 1%, 0.56Ω device is the closest value, and a 0.125W, 0805
size device will handle the power dissipation of 69 mW. With
the resistance selected, the average value of LED current is
re-calculated to ensure that current is within the ±5% toler-
ance requirement. From the expression for LED current ac-
curacy:
INPUT CAPACITOR
Following the calculations from the Input Capacitor section,
Δv
pacitance is:
In expectation that more capacitance will be needed to pre-
vent power supply interaction a 2.2 µF ceramic capacitor
rated to 100V with X7R dielectric in an 1812 case size will be
used. From the Design Considerations section, input rms cur-
rent is:
Ripple current ratings for 1812 size ceramic capacitors are
typically higher than 2A, more than enough for this design.
RECIRCULATING DIODE
The input voltage of 60V ±5% requires Schottky diodes with
a reverse voltage rating greater than 60V. Some manufactur-
ers provide Schottky diodes with ratings of 70, 80 or 90V;
however the next highest standard voltage rating is 100V.
Selecting a 100V rated diode provides a large safety margin
for the ringing of the switch node and also makes cross-ref-
erencing of diodes from different vendors easier.
The next parameters to be determined are the forward current
rating and case size. In this example the high duty cycle (D =
49.2 / 60 = 82%) places less thermals stress on D1 and more
on the internal power MOSFET of the LM3402. The estimated
average diode current is:
A Schottky with a forward current rating of 0.5A would be ad-
equate, however at 100V the majority of diodes have a mini-
mum forward current rating of 1A. To determine the proper
case size, the dissipation and temperature rise in D1 can be
calculated as shown in the Design Considerations section.
V
D
SNS
I
L
F
IN(MAX)
. This value should be re-evaluated based on the calcula-
for a small case size such as SOD-123F in a 100V, 1A
= 0.19 / 0.56 + 0.043 / 2 = 361 mA, 3% above 350 mA
I
C
IN-RMS
will be 1%
F
IN(MIN)
:
= 0.35 x Sqrt(0.82 x 0.18) = 134 mA
= (0.35 x 2.7 x 10
I
D
= 0.361 x 0.18 = 65 mA
P-P
= 600 mV. The minimum required ca-
SNS
was determined in selecting
-6
) / 0.6 = 1.6 µF
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