LM3533 Datasheet, PDF (30/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
INTERRUPT OUTPUT MODE
When INT Mode is enabled (ALS Zone Information Register Bit [0] = 1), INT pin is configured as an interrupt output. INT is an open-
drain output with an active pulldown of typically 66Ω. In INT Mode the INT output pulls low if the ALS interface is enabled, and the
ALS input has changed zones. Reading back the ALS Zone Information while in this mode will clear the INT output and reset it to
its open-drain state.
Fault Flags/Protection Features
The LM3533 contains both an LED open and LED short fault detection. These fault detections are designed to be used in production
level testing and not normal operation. For the fault flags to operate, they must be enabled via the LED Fault Enable Register (see
Table 47). The following sections detail the proper procedure for reading back open and short faults in both the HVLED and LVLED
strings.
OPEN LED STRING (HVLED)
An open LED string is detected when the voltage at the input to any active high-voltage current sink has fallen below 200mV, and
the boost output voltage has hit the OVP threshold. This test assumes that the HVLED string that is being detected for an open is
connected to the LM3533's boost output (COUT+) (see Table 13). For an HVLED string not connected to the LM3533's boost output
voltage, but connected to another voltage source, the boost output will not trigger the OVP flag. In this case an open LED string
will not be detected.
The procedure for detecting an open fault in the HVLED current sinks (provided they are connected to the boost output voltage)
is:
• Apply power to the LM3533
• Enable Open Fault (Register 0xB2, bit [0] = 1)
• Configure HVLED1 and HVLED2 for LED string anode connected to COUT (Register 0x25, bits[1:0] = (1,1)
• Set Bank A full-scale current to 20.2mA (Register 0x1F = 0x13)
• Set Bank A brightness to max (Register 0x40 = 0xFF)
• Set the startup ramp times to the fastest setting (Register 0x12 = 0x00)
• Assign HVLED1 and HVLED2 to Bank A (Register 0x10, Bits [1:0] = (0, 0)
• Enable Bank A (Register 0x27 Bit[0] = 1
• Wait 4ms
• Read back bits[1:0] of register 0xB0. Bit [0] = 1 (HVLED1 open). Bit [1] = 1 (HVLED2 open)
• Disable all banks (Register 0x27 = 0x00)
SHORTED LED STRING (HVLED)
The LM3533 features an LED short fault flag indicating one or more of the HVLED strings have experienced a short. The method
for detecting a shorted HVLED strings is if the current sink is enabled and the string voltage (V_OUT - V_HVLED1/2) falls to below (V_IN -
1V) . This test must be performed on one HVLED string at a time. Performing the test with both current sinks enabled can result in
a faulty reading if one of the strings is shorted and the other is not.
The procedure for detecting a short in an HVLED string is:
• Apply power to the LM3533
• Enable Short Fault (Register 0xB2, bit [1] = 1)
• Enable Feedback on the HVLED Current Sinks (Register 0x25 = 0xFF)
• Set Bank A full-scale current to 20.2mA (Register 0x1F = 0x13)
• Set Bank A brightness to max (Register 0x40 = 0xFF)
• Set the startup ramp times to the fastest setting (Register 0x12 = 0x00)
• Assign HVLED1 to Bank A (Register 0x10, Bits [1:0] = (1, 0)
• Enable Bank A (Register 0x27 Bit[0] = 1
• Wait 4ms
• Read back bits[0] of register 0xB1. 1 = HVLED1 open
• Disable all banks (Register 0x27 = 0x00)
• Repeat the procedure for the HVLED2 string
OPEN LED (LVLED)
The LM3533 features an open LED fault flag indicating one or more of the active LVLED strings are open. An open in an LVLED
string is flagged if the voltage at the input to any active low-voltage current sink goes below 110mV.
Since the open LED detect is flagged when any active current sink input falls below 110mV, certain configurations can result in
falsely triggering an open. These include:
1. LED anode tied to CPOUT, charge pump in 1X gain, and VIN drops low enough to bring any active LVLED current sink below
110mV.
2. LED anode not tied to CPOUT and VLED_ANODE goes low enough to bring any active LVLED current sink below 110mV.
The following list describes a test procedure that can be used in detecting an open in the LVLED strings:
• Apply power to the LM3533
• Enable Open Fault (Register 0xB2, bit [0] = 1)
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