LM3532 datasheet(10/52 Pages) TI2

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ILED1

ILED2

ILED3

GND

OVP

Feedback

Enable

VHR Min

400 mV

Boost

Controller

COUT

250 m:

Error Amplifier

VIN

CIN

LM3532

SNVS653E – JULY 2011 – REVISED AUGUST 2015

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Feature Description (continued)

7.3.2 Hardware Enable Input

HWEN is the LM3532 device's global hardware enable input. This pin must be driven high to enable the device.

HWEN is a high-impedance input so cannot be left floating. Typically HWEN would be connected through a

pullup resistor to the logic supply voltage or driven high from a microcontroller. Driving HWEN low places the

LM3532 into a low-current shutdown state and force all the internal registers to their power-on reset (POR)

states.

7.3.3 Feedback Enable

Each current sink can be set for feedback enable or feedback disable. When feedback is enabled, the boost

converter maintains at least 400 mV across each active current sink. This causes the boost output voltage (VOUT)

to raise up or down depending on how many LEDs are placed in series in the highest voltage string. This

ensures there is a minimum headroom voltage across each current sink. The potential drawback is that for large

differentials in LED counts between strings, the LED voltage can be drastically different causing the excess

voltage in the lower LED string to be dropped across its current sink. In situations where there are other voltage

sources available, or where the LED count is low enough to use VIN as the power source, the feedback can be

disabled on the specific current sink. This allows for the current sink to be active, but eliminates its control over

the boost output voltage (see Figure 10). In this situation care must be taken to ensure there is always at least

400 mV of headroom voltage across each active current sink to avoid the current from going out of regulation.

Control over the feedback enable/disable is programmable via the Feedback Enable Register (see Table 13).

Figure 10. LM3532 Feedback Enable/Disable

7.3.4 LM3532 Current Sink Configuration

Control of the LM3532 device’s three current sinks is done by configuring the three internal control banks

(Control A, Control B, and Control C) (see Figure 11). Any of the current sinks (ILED1, ILED2, or ILED3) can be

mapped to any of the three control banks. Configuration of the control banks is done via the Output Configuration

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