NXP公司的 SSL3250A是照相闪光灯LED驱动器,设计用于以电池为能源的移动设备如手机和PDA等.它的升压转换器能为高亮度LED提供高达500mA的电流,效率超过85%.输入电压2.7V到5.5V,输出电压高达9.5V,开关频率1.2MHz, I2C总线可编程到400 kHz.本文介绍SSL3250A主要特性,方框图以及典型应用定路,包括仅采用I2C接口的应用电路图, 采用I2C接口和TX-Masking的应用电路图以及采用直接控制的应用电路图,建议采用的元件和SSL3250A HVQFN20的典型PCB设计图.
SSL3250A: Photo flash dual LED driver
The SSL3250A is a photo flash LED driver designed for battery operated mobile devices such as mobile phones and PDAs. The boost converter delivers high performance and drives a single or dual, high brightness LED at up to 500 mA with over 85 % efficiency. The driver can be programmed to operate in Flash, Torch or Indicator / Video-on mode.
The small silicon size and the high internal switching frequency of 1.2 MHz minimize the SSL3250A footprint making it very suitable for mobile phones where space is limited, and only requiring four external components. Driving a high power flash LED within its safe operating limits was a concern when the SSL3250A was designed, so a time-out function can be programmed via the I2C interface, which will prevent overstressing the LED. Due to the specific requirements of a mobile phone, the flash current can be rapidly lowered during RF transmit by using optional external setting resistors.
High power single, or dual, LED output driving up to 500 mA flash current
Separate indicator LED output of 2.5 mA to 20 mA
Output voltage of up to 9.5 V
Wide input voltage range of 2.7 V to 5.5 V
High efficiency, over 85 % at optimum output current
Switching frequency of 1.2 MHz
Flash, Torch, and Indicator mode supported
Internally timed flash operation up to 820 ms
I2C-bus, programmable up to 400 kHz
Strobe signal to avoid I2C latency for flash
Discrete enable signals for stand-alone operation
Optional resistor configurable output currents
Fast response to accommodate external TxMasking functionality
Soft start in Torch and Flash modes to avoid battery overloading
Integrated protection circuits for enhanced system reliability
Internal time-out function
OverTemperature Protection (OTP)
UnderVoltage LockOut (UVLO)
OverVoltage Protection (OVP)
Output current protection
Interrupt signaling to system controller
Low device shut-down current, less than 1 uA
SOT758-3, thermally enhanced 16 terminal HVQFN package
White LED driver for battery powered portable devices
Photo flash LED driver for mobile phones and digital cameras
The SSL3250A has two general control modes: Direct control and I2C control. In Direct control mode the IC is designed to be directly controlled by the application. The I2C control is designed to change the timing and current settings of the SSL3250A, although it can also be used to switch the driver to Flash mode, Torch mode or Indicator mode. In Direct control mode, EN1 and EN2 are used. In I2C control mode, SCL, SDA and STRB are used. In a typical application only one control mode can be used.
图5. SSL3250A HVQFN20的典型PCB设计图