Acutechnology Semiconductor Inc.

BQ8211

www.acutechnology.com

7

Rev. 1.3 September 13, 2006

3. Output Voltage

The BQ8211 meets all specifications down to 1.175V output. It does not suffer from

performance degradation issues such as experienced with CMOS LDO’s.

The BQ8211 develops a 1.175V reference voltage between the adjust pin terminal and

ground. This voltage is applied across the resistor R2 to generate a constant current (I2). The

current from the adjust terminal could introduce error to the output, but since it is very small

(<0.5µA) compared with the current I2 and very constant with line and load changes, the

error can be ignored. The constant current I2 then flows through resistor R1 and sets the

output voltage to the desired level.

The BQ8211 regulates the voltage that appears between its output and ground pins or

between its adjust and ground pins. In some cases, line resistances can introduce errors to

the voltage across the load. To obtain the best load regulation a few precautions are needed.

For example, it is important to minimize the line resistances to the load. So, the load itself

should be tied directly to the output terminal on the positive side and directly to the ground

terminal on the negative side.

The best performance is obtained with the positive side of the resistor R1 tied near the load

and with the ground side of the resistor R2 tied near the ground of the regulator. This will

provide remote output sensing which will optimize regulation at the load.

4. Enable/Sequencing

The BQ8211 provides an enable function. The EN pin has to be at least 1V for the device to

be fully turned on. When the voltage of the EN pin is low the device is in shutdown mode and

it will not draw any current from the VIN terminal.

5. Protection Diodes

pin, no protection diode is needed to ensure device safety under short circuit conditions.

output capacitors are used (> 1000uF) and the input is instantaneously shorted to ground,

can damage occur.

6. Thermal Considerations

When an integrated circuit operates with an appreciable current, its junction temperature is

elevated. It is important to quantify its thermal limits in order to achieve acceptable

performance and reliability. This limit is determined by summing the individual parts

consisting of a series of temperature rises from the semiconductor junction to the operating

environment. The heat generated at the device junction flows through the die to the die

attach pad, through the lead frame to the surrounding case material, to the printed circuit

board, and eventually to the ambient environment.