SM8134A Datasheet, PDF (10/19 Pages) Nippon Precision Circuits Inc – White LED Driver IC

SM8134A
Thermal Shutdown Circuit (Overheating Protection)
The thermal shutdown circuit operates whenever the IC temperature exceeds approximately 170°C for what-
ever reason. VOUT output recommences when the IC temperature falls below approximately 150°C. In that
case, the setting register is saved.
Under Voltage Lockout Circuit (UVLO)
When a VIN voltage falls below the 1.9V (typ), the under voltage lockout circuit operates, initializing all the
registers to logic 0. In this mode, all previous data is reset, thus all dimming and LED control data must be
input again.
V_OUT Output Circuit Mode Switching
The SM8134A switches between 3 output states: standby mode (standby state), ×1.0 mode (VIN through
mode), and ×1.5 mode (×1.5 charge pump boost). This automatically adjusts the VOUT output to match the
drive LED characteristics and reduces the total power dissipation. Switching to and from ×1.0 and ×1.5 mode
occurs automatically in an internal circuit, and cannot be controlled using an external input.
Switching to standby mode
The internal circuit operating mode switches from ×1.0/×1.5 mode to standby mode when Reset resistor (mode
data “0H”, “EH”) was input, suppressing current consumption.
Switching from ×1.0 mode to ×1.5 mode
If the LED drive current set by serial interface can be driven without boosting the V_IN input voltage, the V_OUT
output operates in ×1.0 mode. In other words, if sufficient current flows even with the LED forward-direction
voltage drop “VF”, then V_OUT is less than 4.9V. 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
V_OUT mode switching time comparison due to drive LED “VF” variation
If the V_IN voltage falls or LED drive current set by serial interface increases such that the LED drive current is
too low in ×1.0 mode, then the LED drive circuit low-current detector operates, the V_OUT output is automati-
cally 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 5-channel LED drive circuits, thus it is recommended that LEDs
have small “VF” variation to optimize the total efficiency.
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