TLD5541-1QV Datasheet, PDF (48/82 Pages) Infineon Technologies AG – H-Bridge DC/DC Controller with SPI Interface

H-Bridge DC/DC Controller with SPI Interface
TLD5541-1QV
Protection and Diagnostic Functions
Table 10 Adjustable Short Circuit threshold overview
nled
LEDCHAIN
14
V_OUT
46.2
V_{OUT_OVLO}
59.3
k = R_VFBL /
V_{open_led}
(R_VFBH + R_VFBL)
0.025
54.4
V_{short_led} (V)
(V_{FB1,2_S2G} / k)
41.1
15
49.5 59.3
0.025
54.4
44.2
16
52.8 59.3
0.025
54.4
47.2
V_{VFB1,2_S2G}(V) Default
Condition
1.013
1.088
1.163
During Limp Home state the short circuit threshold V_{VFB_S2G} is fixed at the default value (V_{VFB_S2G} / V_{VFB_OVTH}),
approx. 1/3 of the fixed overvoltage protection circuit in the application. There is no relationship between the
analog dimming feature at VSET pin and the V_{VFB_S2G} threshold. The customer must take care by adjusting the
default voltage at SET pin to program the V_OUT be higher than the default short circuit threshold.
During start-up the TLD5541-1QV ignores the detection of a short circuit or an open load until the soft-start
capacitor reaches 1.75V. To prevent false tripping after startup, a large enough soft-start capacitor must be used
to allow the output to get up to approximately 50% of the final value.
Note: If the short circuit condition disappears, the device will re-start with the soft start routine as described in
Chapter 6.2.
10.2.2 Overvoltage Protection
A voltage divider between V_OUT, VFB pin and AGND is used to adjust the Overvoltage protection threshold (refer
to Figure 28).
To fix the overvoltage protection threshold the following Equation (12) is used:
V = V ⋅ ^R _R ^{+ R} _{OUT _ OV _ protected}
VFB _ OVTH
VFBH
VFBL
VFBL
(12)
If V_VFB gets higher than its overvoltage threshold V_{VFB_OVTH} , the SPI flag (OUTOV) in the STD diagnosis set to
HIGH and the gate drivers stop switching for output regulation (Break-Low condition both LS MOSFETs ON).
When V_{VFB_OVTH}- V_{VFB_OVTH,HYS} threshold is reached the device will auto restart. The dedicated diagnosis flag
(OUTOV) will be cleared after the next reading cycle of the STD diagnosis.
If the SWTMOD.OUTOVLAT bit is set to HIGH the overvoltage protection is changed into latched behavior and the
µC has to set the DVCCTRL.CLRLAT bit to reset the OUTOV flag and restart the switching activities.
10.2.3 Open Load Protection
To reliably detect an open load event, two conditions will be observed:
1) Voltage threshold: V_VFB>V_{VFB_OL,rise}
2) output information: V_(FBH-FBL)<V_{FBH_FBL_OL}
After an open load error, the SPI flag (OL) in the STD diagnosis is set to HIGH and the gate drivers stop switching
(Break-Low condition). The Device will auto restart with a soft start routine. The dedicated diagnosis flag (OL) will
be cleared after the next reading cycle of the STD diagnosis.
After an Open Load error the TLD5541-1QV is autorestarting the output control accordingly to the implemented
Softstart routine. An Open Load error causes an increase of the output voltage as well. An Overvoltage condition
could be reported in combination with an Open Load error (in general, multiple error detection may happen if more
error detection thresholds are reached during the autorestart funcion, as possible consequence of reactive
behavior at the output node during open load).
The COMP capacitor is discharged during an Open Load condition to prevent spikes if load reconnects. This
measure could artificially generate Short Circuit detections after open loads events.
Data Sheet
48
Rev. 1.0, 2016-05-20