TLD5045EJ_15 Datasheet, PDF (19/30 Pages) Infineon Technologies AG – 700mA High Integration - DC/DC Step-Down Converter

Infineon® LITIX™ Power
TLD5045EJ
Open Load Diagnosis
7.3
Open Load Diagnosis in different Application Conditions
7.3.1 Light module application without µC
Most of the time, the open load diagnosis of the whole light module is done via the current sense of the driver IC
(e.g. PROFET) located in the light control module (or BCM module). See Figure 8-6 for a simplified application
schematic. The light module needs to sink a specified minimum current (e.g. 100mA) to indicate normal operation.
To guarantee this minimum current also under light load conditions (e.g. high efficiency LED bin at high supply
voltages = min. load current required) system designers often have to place resistors in parallel to the application
circuit (see Resistors connected to supply lines in Figure 8-6). When using such resistors connected between V_S
and GND, an open LED diagnosis is not possible anymore. To overcome this issue an internal transistor (open
collector) is connected to the ST pin of the TLD5045EJ. During normal operation the ST pin is LOW and a minimum
module current can be guaranteed.
As soon as an open load occurs the internal ST transistor switches off. Due to this, the current on the V_REC pin
decreases below the open load detection threshold of the driver IC located in the light control module.
Note: Open Load is only detected during the ON cycle of the switching transistor. During the OFF state the ST
signal displays what was detected in the previous ON state.
V_PWMI
V_PWMI,OFF
VPWMI,ON
Open Load
Event
V_SW
ST
t
Open Load
t
High - z
t_OL
t
ST pull -down transistor ON
Figure 7-1 Open Load Diagnosis using Internal PWM Mode
t
ST pull-down transistor OFF
Data Sheet
19
Revision 1.0
2015-05-28