12

NXP Semiconductors

34845

5.2.5

WAKE operation

The WAKE pin provides the means to set the device for low power consumption (shutdown mode) without the need of an extra logic signal

for enable. This is achieved by connecting the WAKE and PWM pins together, and tying the EN pin to ground. In this configuration, the

PWM signal is used to control the LED channels, while allowing low power consumption by setting the device into its shutdown mode

every time the PWM signal is kept low for longer time than the WAKE time out of 27 ms.

5.2.6

Overtemperature shutdown and temperature control circuits

The 34845 includes over-temperature protection. If the internal temperature exceeds the over-temp threshold OTTSHUTDOWN, then the

device shuts down all functions. Once the temperature falls below the low level threshold, the device is re-enabled.

5.2.7

FAIL pin

The FAIL pin is at its low-impedance state when no error is detected. However, if an error such as an LED channel open or boost

overcurrent is detected, the FAIL pin goes into high-impedance. Once a failure is detected, the FAIL pin can be cleared by recycling the

EN pin or applying a complete power-on-reset (POR). If the detected failure is an Over-current time-out, the EN pin or a POR must be

cycled/executed to restart the part.

5.3

Typical performance curves

Figure 6. Typical system efficiency vs duty cycle (FPWM = 25 kHz)

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100.0

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30

4050

607080

90

100

Duty Cycle (%)

Vin=9V

Fs = 600kHz

L=10uH, 68mOhm (IHLP2525CZER100M01)

Schottky 5A, 100V (PDS5100HDICT-ND)

COUT = 2x2.2µF

FPWM=25kHz

Load = 9 LEDs, 20mA/channel

VLED = 27.8V, ±0.5V /channel