The LM3500 is a fixed-frequency step-up DC/DC converter that is ideal for driving white LEDs for display backlighting and other lighting functions. This device features fully integrated synchronous switching (no external Schottky diode required) and a low feedback voltage (500mV), making it highly efficient for lighting applications in wireless phones and other portable products (single cell Li-Ion or 3-cell NiMH battery supplies). The LM3500 operates with a fixed 1MHz switching frequency. When used with ceramic input and output capacitors, the LM3500 provides a small, low-noise, low-cost solution. Two LM3500 options are available with different output voltage capabilities. The LM3500-21 has a maximum output voltage of 21V and is typically suited for driving 4 or 5 white LEDs in series. The LM3500-16 has a maximum output voltage of 16V and is typically suited for driving 3 or 4 white LEDs in series (maximum number of series LEDs dependent on LED forward voltage). If the primary white LED network should be disconnected, the LM3500 uses internal protection circuitry on the output to prevent a destructive over-voltage event. A single external resistor is used to set the maximum LED current in LED-drive applications. The LED current can easily be adjusted using a pulse width modulated (PWM) signal on the shutdown pin. In shutdown, the LM3500 completely disconnects the LED power supply to prevent LED damage.
The LM3500 is a synchronous step‑up DC/DC converter designed for white LED backlighting and other lighting functions. It operates with a fixed 1 MHz switching frequency, uses only small surface‑mount components, and provides internal over‑voltage and shutdown protection.
Two versions are offered: the LM3500‑16 (max 16 V output) and the LM3500‑21 (max 21 V output). LED current is set with a single external resistor on the FB pin, and can be modulated via a PWM signal on the SHDN pin. The device is supplied in an 8‑bump micro‑SMD package.
| Input voltage range | 2.7 V to 7 V |
|---|---|
| Switching frequency | 1 MHz (fixed) |
The LM3500 operates from 2.7 V to 7 V input.
A single external resistor from the FB pin to GND sets the LED current, and it can be adjusted with a PWM signal on the SHDN pin.
The converter uses a fixed 1 MHz switching frequency.