LM3532 datasheet(12/52 Pages) TI2

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LM3532

SNVS653E – JULY 2011 – REVISED AUGUST 2015

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Feature Description (continued)

7.3.7 Interrupt Output

INT is an open drain output that pulls low when the ALS is enabled and when one of the ALS inputs transitions

into a new zone. At the same time, the ALS Zone Information register is updated with the current ALS zone, and

the software flag (bit 3 of the ALS Zone Information register) is written high. A readback of the Zone Information

at INT is typically 125

Ω.

7.3.8 Protection Features

7.3.8.1 Overvoltage Protection

The LM3532 devices’s boost converter provides open-load protection, by monitoring the OVP pin. The OVP pin

is designed to connect as close as possible to the positive terminal of the output capacitor. In the event of a

disconnected load (LED current string with feedback enabled), the output voltage rises in order to try and

maintain the correct headroom across the feedback enabled current sinks (see Table 13). Once VOUT climbs to

the OVP threshold (VOVP) the boost converter is turned off, and switching stops until VOUT falls below the OVP

hysteresis (VOVP – 1 V). Once the OVP hysteresis is crossed the LM3532 device’s boost converter begins

switching again. In open load conditions this would result in a pulsed on/off operation.

7.3.8.2 Current Limit

The LM3532 device’s peak current limit in the NFET is set at typically 1 A (880 mA, minimum). During the

positive portion of the switching cycle, if the NFET's current rises up to the current limit threshold, the NFET turns

off for the rest of the switching cycle. At the start of the next switching cycle the NFET turns on again. For loads

that cause the LM3532 to hit current limit each switching cycle, the output power can become clamped because

the headroom across the feedback enabled current sinks is no longer being regulated when the device is in

current limit. See Maximum Output Power below for guidelines on how peak current affects the LM3532 device's

maximum output power.

7.4 Device Functional Modes

7.4.1 LED Current Ramping

The LM3532 provides 4 methods to control the rate of rise or fall of the LED current during these events:

1. Start-up from 0 to the initial target

2. Shutdown

3. Ramp up from one brightness level to the next

4. Ramp down from one brightness level to the next

See Table 4 and Table 5.

7.4.2 Start-up and Shutdown Current Ramping

The start-up and shutdown ramp rates are independently programmable in the Start-up/Shutdown Ramp Rate

rates are independently programmable from the shutdown ramp rates, but not independently programmable for

each Control Bank. For example, programming a start-up or shutdown ramp rate, programs the same ramp rate

for each Control Bank.

7.4.3 Run-Time Ramp Rates

Current ramping from one brightness level to the next is programmed via the Run-Time Ramp Rate Register (see

Table 5). There are 8 different ramp-up and 8 different ramp-down rates. The ramp-up rate is independently

programmable from the ramp-down rate, but not independently programmable for each Control Bank. For

example, programming a ramp-up or a ramp-down rate programs the same rate for each Control Bank.

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