Acutechnology Semiconductor Inc.
BQ8211
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
Unlike older regulators, the BQ8211 requires no protection diodes between the
ADJ
pin and
V
OUT
or from the V
OUT
to the V
IN
to prevent over-stressing the die. Internal resistors are
limiting the internal current paths on the
ADJ
pin. Therefore, even with capacitors on the
ADJ
pin, no protection diode is needed to ensure device safety under short circuit conditions.
External diodes between the V
IN
and V
OUT
are not usually needed. Only if high value
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.
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Rev. 1.3 September 13, 2006
ACUTECH [ ACUTECHNOLOGY SEMICONDUCTOR ]
