LED2000DR datasheet(28/40 Pages) STMICROELECTRONICS

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Application information

LED2000

28/40

DocID023432 Rev 4

Example 3(see Example 1):

VIN = 12 V, VFW_LED = 3.5 V, nLED = 2, ILED = 700 mA

The typical output voltage is:

Equation 36

RDSON_HS has a typical value of 95 m and RDSON_LS is 69 m at 25 °C.

For the calculation we can estimate RDSON_HS = 140 m and RDSON_LS = 100 mas

a consequence of TJ increase during the operation.

TSW_EQ is approximately 12 ns.

IQ has a typical value of 1.5 mA at VIN = 12 V.

The overall losses are:

Equation 37

Equation 38

The junction temperature of the device is:

Equation 39

where TA is the ambient temperature and RthJ-A is the thermal resistance junction-to-

ambient. The junction-to-ambient (RthJ-A) thermal resistance of the device assembled in the

HSO8 package and mounted on the board is about 40 °C/W.

Assuming the ambient temperature is around 40 °C, the estimated junction temperature is:

7.4

Short-circuit protection

In overcurrent protection mode, when the peak current reaches the current limit threshold,

the device disables the power element and it is able to reduce the conduction time down to

the minimum value (approximately 100 nsec typical) to keep the inductor current limited.

This is the pulse-by-pulse current limitation to implement the constant current protection

feature.

VOUT

nLED VFW_LED VFB



7,1V

PTOT

RDSON_HS IOUT





2 DR

DSON_LS

IOUT





–





VIN IOUT fSW TSW





VIN IQ



PTOT

0,14 0,7

2 0,6 0,1 0,72 0,4



0,7 12 10

–

850 10

12 1,5 10

–







205mW



TA RthJA

–

PTOT



60 0,205 40 68

C





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