UM1693 datasheet(78/196 Pages) STMICROELECTRONICS

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Load compatibility

UM1693

78/196

DocID025505 Rev 1

Figure 55. LED cluster example 2–tail & brake light (VW Passat B6)

The first example shows a simple LED cluster with serial-parallel combination of LEDs and

resistors. On second example there is a schematic and V/A characteristic measured on real

LED lamp (VW Passat B6). As seen on schematic, on top of the serial-parallel LED/resistor

strings there is a reverse battery protection diode, ESD capacitor on input terminal and

“dummy load” circuitry with bipolar transistors. This circuitry is used to adapt the LED string

behavior (V/A characteristic) according to diagnostic requirements (open load in on-state,

open load in off-state).

Example 1: Switching losses–measurement

Following example shows switching losses measurement on VND7140AJ-E with LED

cluster example 1 (LED test board - 6 x 3 LEDs OSRAM LA E67-4) using an oscilloscope

with mathematical functions. The first function F1 shows the actual power dissipation on the

HSD (VBAT - VOUT) * IOUT, the second function F4 shows the HSD energy (integral of F1).

Conditions:

•

VBAT:

16 V

•

Temperature:

23 °C

•

PWM:

200 Hz, 70 %

•

Load:

test board with 6 x 3 LED OSRAM LA E67-4 (see Figure 54)

•

Device:

VND7140AJ-E

UM1693 Datasheet(PDF) 78 Page - STMicroelectronics