A Power Management Interface Circuit For Telecom Hot Swap With Local Dc/dc Conve

Description: New cellular phones have incorporated high-resolution cameras that require bright illumination of the surrounding area to achieve high-quality pictures. Traditional xenon-filled photo flashes cannot be used due to the limited space available in cellular phone cameras. Instead, design engineers utilize a white LED with high pulse current. Although it occupies less PCB space compared to a traditional photo flash, it also provides significantly lower light output. Furthermore, this high current can overload the phone battery during flash operation. A potential solution to this issue is to use two or three LEDs instead of one to enhance light output and employ a supercapacitor to prevent battery overload. An example of this solution involves three SP7618 LED driver ICs, each connected to one photo flash LED, along with a 0.5F supercapacitor that serves as an energy storage element during the flash pulse.

The SP7618 is a linear low-side constant current driver designed to drive high-power LEDs from an input voltage rail. This driver functions as a high current source, ensuring a constant LED current across a broad range of input voltages. The SP7618 facilitates the implementation of a cost-effective LED driver suitable for various applications. Its internal circuitry maintains a preset constant current output over a wide voltage range at the LED input. The LED current can be adjusted up to 1033mA using an external clock applied to the CTRL pin. Dimming can be achieved by either sequencing the CTRL pin or supplying a PWM signal to the EN pin. The device includes built-in thermal protection that automatically halts LED current to prevent overheating. Additionally, a timeout function acts as a fail-safe, shutting down the output for currents exceeding 266mA after 4 seconds of continuous operation. The device can be disabled by using the EN pin or by holding the CTRL pin low for more than 100 microseconds.

The schematic for this application would typically include three SP7618 ICs, each connected to a separate high-power white LED. The anodes of the LEDs are connected to the output of each driver, while the cathodes are connected to ground. The input voltage rail for the SP7618s should be appropriately chosen to match the requirements of the LEDs being used. The CTRL pins of the SP7618s can be interconnected to allow for synchronized operation or individually controlled for independent dimming effects. The EN pins can be connected to a microcontroller or a dedicated control circuit to manage the operational state of the drivers.

The supercapacitor, rated at 0.5F, should be connected in parallel with the power supply to the SP7618s to provide the necessary energy during the flash pulse. The supercapacitor's voltage rating must exceed the maximum input voltage to ensure reliable operation. Proper bypass capacitors should also be placed near the power pins of the SP7618s to stabilize the supply voltage during high current demands. This arrangement allows for enhanced brightness in the flash operation while mitigating the risk of battery overload, thereby improving the overall performance of the cellular phone camera system.New cellular phones have incorporated high resolution cameras, which require high brightness illumination of the ambient area in order to achieve high quality pictures. Traditional xenon-filled photo Flash cannot be used in the very tight space available to photo cameras in cellular phones.

Instead, design engineers use a white LED with high pulse d current. It occupies small PCB space when compared with a traditional photo Flash however, it also provides significantly lower light. Additionally, this high current CAN overload the phone battery during Flash A possible solution to this problem is to use two or three LEDs instead of one in order to improve the light output and use a super capacitor to avoid battery overload.

An example of this solution is shown below in Figures 1 and 2. The circuit uses three SP7618 LED Driver ICs with one photo Flash LED connected to each driver and 0. 5F super capacitor that acts as an energy storage element during the Flash pulse. DESCRIPTION AND BOARD SCHEMATIC The SP7618 is a linear low-side constant-current driver designed to drive high power LEDs from an input voltage rail.

The driver acts as a high current source, ensuring constant LED current for the full range of input voltage. The SP7618 allows implementing the lowest cost LED Driver for a variety of applications. Internal circuitry maintains the preset constant current output for a wide voltage range at the LED input.

The LED current CAN be adjusted up to 1033mA with an external Clock applied to the CTRL pin. Dimming CAN be achieved by using the sequencing CTRL pin or feeding a PWM signal to the EN pin. The built-in thermal protection automatically stops LED current to prevent overheating. A timeout function serves as a fail safe, shutting down the output for currents greater than 266mA after 4 seconds of continuous operation. The part CAN be shut down by using the EN pin or holding the CTRL pin low for more than 100 µS.