TLC5970
SBVS140 –MARCH 2010
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DEVICE PROTECTION
When the Short-Circuit Protection (SCP) and Overvoltage protection (OVP) are operating, the buck converter
stops. Afterwards, the buck converter is restarted with a soft-start when any data are written to the restart
operation address, 1001b. The TLC5970 has an LED Open Detection (LOD) and four device protections as
listed:
1. LED open detection (LOD): When SWOFF is connected to GND, the LOD can detect if one or two LEDs
are opened or if OUTn is shorted to GND. The LOD flag is set to '1' in the readout data register when LEDs
open or when OUTn is shorted to GND. If all LEDs are opened, the OVP flag comes up because the
OUT0-OUT2 voltage is not pulled up. When SWOFF is connected to the VREG level, the LOD flag is set to
'1' when the voltage of any OUTn is less than approximately 0.3 V at the 33rd GS clock from when OUTn is
turned on. Also, the LOD data are kept until the next 33rd GS clock. Therefore, GS data must be set at 33d
(decimal data) or more to ensure the correct LOD data.
2. Short-Circuit Protection (SCP): The SCP detects if the buck converter output is overloaded or if the FB line
is open. SCP operates in this manner:
(a) The SCP circuit observes the FB pin voltage.
(b) If the FB is under 4 V (typical), then the SCP timer starts to count the number of times the PH switches.
(c) When the SCP timer counts to 4, if FB voltage is still below 4 V, the SCP circuit stops the buck converter
and the LED driver from operating. Also, the buck converter target voltage is set to the FB voltage
programmed in the EEPROM at same time.
(d) The SCP flag is set in the readout register.
(e) The differential interface can be used even if buck converter is not operating.
It is required to write any data to the address 1001b to restart the device operation.
3. Overvoltage Protection (OVP): The OVP detects if the buck converter target voltage is set to the maximum
code. Also, the OVP detects when all LEDs are opened. The OVP does not work when the SWOFF signal
level is high. Therefore, the OVP flag in the SID is always '0'. The OVP circuit operates in this manner:
(a) The OVP circuit checks that the internal digital-to-analog converter (DAC) code is at the 33rd GS clock.
(b) If the DAC code is not the maximum code, the OVP period counter is reset. If the DAC code is the
maximum code, then the OVP period counter is counted up.
(c) When the OVP period counter becomes 4, the OVP circuit stops the LED driver from operating and sets
the DAC code to the FB voltage programmed in the EEPROM. Then the buck converter operation does
not stop.
(d) The OVP flag is set to '1' in the readout register.
(e) The differential interface can be used even if the buck converter is not operating.
(f) The LED driver cannot be controlled again until any data are written to the address 1001b to clear the
OVP flag.
4. Pre-Thermal Shutdown (PTD): The PTD stops the LED driver operation at TPTD (TPTD = +138°C, typical)
device temperature to avoid the device temperature from becoming higher. PTD operation follows this logic:
(a) The LED driver (OUT0to OUT2) is forced off.
(b) Set the PTD flag in the readout register.
(c) Start the LED driver control again when the device temperature drops below TPTD – THYSP (THYSP = +8°C,
typical).
5. Thermal Shutdown (TSD): The TSD stops the buck coverter/LED driver/differential interface operation at
TTSD (TTSD = +168°C, typical) device temperature to prevent the device temperature from becoming too high.
TSD operation follows this sequence:
(a) The buck converter switching/LED driver (OUT0 to OUT2)/differential interface are forced off.
(b) The TSD flag is set in the readout register.
(c) Buck converter target voltage is set to the FB voltage programmed in the EEPROM.
(d) Differential interface operation starts again when the device temperature drops below TTSD – THYST
(THYST = +10°C, typical). Then the buck converter starts to operate.
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