SM8131B00B Ver la hoja de datos (PDF) - Nippon Precision Circuits

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Fabricante

SM8131B00B

White LED Driver IC

Nippon Precision Circuits  

SM8131B

Switching from ×1.0 mode to ×1.5 mode

If the LEDs can be driven solely by the current determined by RSET and EN pulse input without boosting the

VIN input voltage, the VOUT output operates in ×1.0 mode. In other words, if sufficient current flows even with

the LED forward-direction voltage drop “VF”, then VOUT is less than 4.2V. Operation in the more efficient

×1.0 mode reduces the total power dissipation and extends the battery drive time. And if low “VF” LEDs are

used or the LED drive current setting is LOW, the operating time in ×1.0 mode is also extended.

1.0 mode

(high efficiency)

High VF LED

1.5 mode

(low efficiency)

1.0 mode

(high efficiency)

Low VF LED

1.5 mode

(low efficiency)

High

VIN input

Low

VOUT mode switching time comparison due to drive LED “VF” variation

If the VIN voltage falls or RSET increases such that the LED drive current is too low in ×1.0 mode, then the

LED drive circuit low-current detector operates, the VOUT output is automatically switched to ×1.5 mode, and

the charge pump boosts the output voltage. This occurs even if only one LED low-current condition is detected

among the 6-channel LED drive circuits, thus it is recommended that LEDs have small “VF” variation to opti-

mize the total efficiency.

VIN

input voltage

Low ILED

detector

Low ILED

detected

1.0 1.5 threshold

(1)

VOUT mode

1.0 mode

VOUT

output voltage

1.5 mode

(2)

4.2V

(3)

VIN voltage drop and VOUT output voltage

(1) When VIN falls, VOUT cannot overcome the LED “VF” rating, causing insufficient current flows and the

ILED low-current signal becomes active.

(2) When the ILED low-current condition is detected, the VOUT output circuit switches to ×1.5 mode (charge

pump mode).

(3) Prior to switching to ×1.5 mode, the VOUT voltage may be lower than 4.2V but sufficient current is sup-

plied to the LED.

If after startup, the LED connected to a DIN pin is switched, the LED connection detector circuit flags an error,

and correct mode switching may not occur. If the DIN pin does not control the LED drive current, the low-cur-

rent detector does not operate and the device cannot switch to ×1.5 mode.

NIPPON PRECISION CIRCUITS INC.—11

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