Rainbow Electronics BA4900 - Manual (Page 9)

259
Regulator ICs BA4900
F
Operation notes
(1) Although the quality of this IC is rigorously con-
trolled, the IC may be destroyed when supply voltage or
operating temperature exceeds its absolute maximum
rating. Because short mode or open mode cannot be
specified when the IC is destroyed, be sure to take physi-
cal safety measures such as fusing if special mode is ex-
pected.
(2)
Example of application
The application circuit of Fig. 2 is recommended for use.
Make sure to confirm the adequacy of parts characteris-
tics. When using the circuit with changes to external cir-
cuit constants, make sure to leave sufficient margins in
consideration of fluctuations in the IC and external com-
ponents including static and transitional characteristics.
Note that ROHM has not carried out extensive survey re-
garding the patent right of this application.
(3)
Operating power supply voltage
When operating within proper ranges of power supply
voltage and ambient temperature, most circuit functions
are guaranteed. Although the rated values of electrical
characteristics cannot be absolutely guaranteed, char-
acteristic values do not change drastically within the
proper ranges.
(4)
Power dissipation (Pd)
Refer to the heat reduction characteristics and the rough
estimation of IC power dissipation given on separate
pages. Make sure your design allows the maximum re-
quired power within the operating temperature range.
(5)
Overvoltage protection circuit
The overvoltage protection circuit turns OFF each output
when the potential difference between V
CC
(pin 7) and
GND (pin 12) is more than about 26V at normal tempera-
ture. Make sure to use the IC within this voltage limit.
(6)
Preventing oscillation at each output
To stop oscillation of output, make sure to connect a ca-
pacitor having a capacitance of 10
µ
F or greater between
GND and each of the V
DD
(pin 5), COM (pin 9), RADIO
(pin 10), FM (pin 11), and VAR (pin 1) output pins. We rec-
ommend using a tantalum electrolytic capacitor whose
capacitance is unsusceptible to temperature.
(7) Overcurrent protection circuit
An overcurrent protection circuit is installed on the V
DD
(pin 5), AMP (pin 6), ANT (pin 8), COM (pin 9), RADIO
(pin 10), FM (pin 11), and VAR (pin 1) outputs, based on
the respective output current. This prevents IC destruc-
tion by overcurrent, by limiting the current with a curve
shape of “7” in the voltage-current graph. The IC is de-
signed with margins so that current flow will be restricted
and latching will be prevented even if a large current sud-
denly flows through a large capacitor. The circuit should
be carefully set because output current is further re-
stricted when output voltage is less than 1V
F
(considered
as short mode).
(8)
Thermal shutdown circuit
The thermal shutdown circuit prevents thermal damage
to the IC. All outputs except V
DD
are switched OFF when
the circuit operates, and revert to the original state when
the chip temperature drops to a certain level.
(9)
Output circuit configurations
Each of the V
DD
(pin 5), COM (pin 9), RADIO (pin 10), FM
(pin 11), and VAR (pin 1) output circuits has a PNP power
transistor. A measure is taken to protect the IC in case the
voltage of V
CC
(pin 7) drops and the output-side voltage
becomes greater than the V
CC
-side voltage due to the
output-side external transistor.
(10) Grounding
Each ground line in the application circuit of Fig. 2 must
be adequately short from GND (pin 12). Make sure to ar-
range the ground traces in a pattern that prevents mutual
interference.