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SM8134A Folha de dados(PDF) 10 Page - Nippon Precision Circuits Inc |
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SM8134A Folha de dados(HTML) 10 Page - Nippon Precision Circuits Inc |
10 / 19 page SM8134A SEIKO NPC CORPORATION —10 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. VOUT 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 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 4.9V. 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. If the VIN 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 VOUT 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. VOUT mode switching time comparison due to drive LED “VF” variation High High VF LED Low VF LED 1.0 mode (high efficiency) VIN input 1.5 mode (low efficiency) 1.5 mode (low efficiency) Low 1.0 mode (high efficiency) |
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Descrição semelhante - SM8134A |
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