TB9000AFG
TOSHIBA BiCMOS Integrated Circuit Silicon Monolithic
TB9000AFG
5 V Voltage Regulator with Watchdog Timer
The TB9000AFG is an IC specially designed for microcomputer
systems in automobiles. It features low standby current and
various system reset functions.
With an external pass Tr., the TB9000AFG can supply a high
output current. A current limiter function is incorporated as a
protective function.
System reset includes low-voltage reset, power-on reset, and
watchdog timer functionality.
Weight: 0.14 g (typ.)
Features
•
•
•
•
•
•
Accurate output: 5.0 V
±
0.15 V
Low current consumption: 120
µA
(V
IN
=
12 V, Ta
=
25°C) at 5 V output
+
reset timer
Reset functions: Low-voltage reset/power-on reset/watchdog timer
Current limiter: Adjustable with external resistor
Operating temperature:
−40
to 125°C
Small SMD package: SSOP-16-pin
About solderability, the following conditions were confirmed.
Solderability
(1) Use of Sn-37Pb solder Bath
solder bath temperature = 230°C
dipping time = 5 seconds
the number of times = once
use of R-type flux
(2) Use of Sn-3.0Ag-0.5Cu solder Bath
solder bath temperature = 245°C
dipping time = 5 seconds
the number of times = once
use of R-type flux
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TB9000AFG
Pin Description
Pin No.
1
Symbol
V
IN
Description
Power supply input pin. It contains a current limiter and startup circuit.
Detection pin for the V
CC
current limiter.
Any voltage drop occurring in the external resistor R
S
between pins V
IN
and V
S
is monitored.
The current limiter is actuated when the voltage drop exceeds 0.3 V.
Ex.) When the current limiter need to be actuated at a load current of 600 mA:
R
S
=
0.3 V/600 mA
=
0.5
Ω.
This pin is used to connect the base of an external PNP transistor.
The output voltage is controlled by an internal op-amp to maintain it stably at 5 V.
Since the recommended I
OUT
current is 8 mA, an output current of 600 mA can be run if H
FE
of the external transistor is 80 or more.
Phase-compensating pin for V
CC
.
Connect a phase-compensating capacitor between pin V
CC
and this pin.
Voltage detection pin for the 5 V constant-voltage power supply, V
CC
.
It also supplies power to the reset timer circuit.
Grounded
Reset output pin for power-on reset and watchdog timer.
Generates a reset signal that is determined by CT at the TC pin.
If no clock is fed to the CK input, this pin generates a reset pulse intermittently.
This is an N-MOS drain output with a 100 k
Ω
pull-up resistor to V
CC
.
Time setup pin for the reset and watchdog timers. Connect capacitor CT to GND.
The time is set up by internal constant current.
Clock input pin for the watchdog timer.
This pin detects the rising edge of the input signal and does not require external coupling
capacitor.
Watchdog timer function ON/OFF control pin.
Set to LOW for active mode and HIGH for inactive mode.
Not connected. (Electrically, this pin is completely open.)
3
V
S
4
OUT
5
6
8
COMP
V
CC
GND
9
RESET
11
TC
13
CK
14
2, 7, 10,
12, 15, 16
WS
NC
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TB9000AFG
Functional Description
The TB9000AFG incorporates a constant-voltage 5 V power supply function to feed stable power to the CPU,
while the system reset and CPU monitor functions ensure stable operation of the CPU, etc. These functions are
explained below.
(1) Constant-Voltage 5 V Power Supply Function
This constant-voltage function has a reference voltage V
ref
in the IC that is insusceptible to temperature
changes and input voltage fluctuations. The power supply circuit is designed in such a way that this
voltage is stepped up to 5 V by using an OP amp and a voltage-dividing resistor. The OP amp, dividing
resistor and an output transistor connected to the OP amp output together configure a closed loop.
An overcurrent protection function is incorporated as a protective measure in case a fault such as
shorting to GND occurs in the 5 V output. A current detecting resistor is inserted between the V
IN
and the
V
S
pins, and a voltage drop across this resistor is detected by a comparator, thereby suppressing the
operation of the OP amp to ensure that the voltage drop will not exceed 0.3 V. In this way, a current
limiter function is actuated to prevent any more current from flowing.
(2) System Reset Function
(see Timing Charts)
●
Voltage monitoring function
When powered on, the power-on reset timer starts counting the moment the voltage V
CC
applied to
the CPU exceeds VTH. When powered off, this voltage monitoring function outputs a reset signal
immediately when V
CC
drops below VTH. A reset signal is also output immediately when V
CC
drops for
some reason during normal operation. Then, when V
CC
is restored to the normal voltage and exceeds
VTH, the power-on reset timer starts counting.
The reset signal is output from the
RESET pin.
●
Power-on reset timer function
To allow the 5 V constant voltage to stabilize at power-on, as well as provide sufficient time for the
clock oscillation in the CPU to stabilize, the device remains reset for a predetermined time before being
released from the reset state. The duration of this time can be set as desired by choosing appropriate
values for the external capacitor connected to the TC pin.
The system starts charging the capacitor when the V
CC
voltage exceeds VTH. When this charge
voltage exceeds 4 V, the capacitor is discharged by the IC’s internal transistor. When the capacitor is
discharged down to 2 V, the reset signal is inverted to deactivate the reset.
●
Watchdog timer function
Program your system to output a clock each time one program routine is finished in the CPU system
software, and input this clock to the CK pin of the IC. The IC’s TC pin is repeatedly charged and
discharged between 2 V and 4 V. However, when a clock is input, it switches over and starts
discharging in the middle of charging and then starts charging from 2 V again. Since the clock is
generated at predetermined intervals when the CPU system is operating normally, the TC pin switches
over and starts discharging before the charge voltage reaches 4 V. However, if no clock is input while
being charged from 2 V to 4 V, the clock is assumed to have stopped, i.e., the CPU system has gone wild,
so that a reset signal is output to reset the CPU system.
●
Watchdog timer stop function
The watchdog timer can be switched ON or OFF by use of the WS pin. If the WS pin is fixed to LOW,
the watchdog timer will be active. (See Timing Chart 1.) If the WS pin is fixed to HIGH, the watchdog
timer will be inactive. (See Timing Chart 2.) When the WS pin is fixed to HIGH, no reset signal is
output, in which case only the power-on reset timer is useful.
Note: The overcurrent protection feature is intended only to protect the IC from a temporary short circuit. A short
circuit over an extended period of time may place excessive stress on the IC, possibly causing it to be
damaged. The system must be configured so that any overcurrent condition will be eliminated as soon as
possible.
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