CS8151
Definition of Terms
Dropout Voltage:
The input-output voltage differential at which the cir-
cuit ceases to regulate against further reduction in
input voltage. Measured when the output voltage has
dropped 100mV from the nominal value obtained at
14V input, dropout voltage is dependent upon load
current and junction temperature.
Input Voltage:
The DC voltage applied to the input terminals with
respect to ground.
Line Regulation:
The change in output voltage for a change in the
input voltage. The measurement is made under con-
ditions of low dissipation or by using pulse tech-
niques such that the average chip temperature is not
significantly affected.
Load Regulation:
The change in output voltage for a change in load
current at constant chip temperature.
Quiescent Current:
The part of the positive input current that does not
contribute to the positive load current. The regulator
ground lead current.
Ripple Rejection:
The ratio of the peak-to-peak input ripple voltage to
the peak-to-peak output ripple voltage.
Current Limit:
Peak current that can be delivered to the output.
Circuit Description
Functional Description
To reduce the drain on the battery a system can go into a
low current consumption mode when ever its not per-
forming a main routine. The WAKE UP signal is generated
continuously and is used to interrupt a microcontroller
that is in sleep mode. The nominal output is a 5 volt
square wave with a duty cycle of 50% at a frequency that
is determined by a timing capacitor, C
Delay
.
When the microprocessor receives a rising edge from the
WAKE UP output, it must issue a watchdog pulse and
check its inputs to decide if it should resume normal oper-
ations or remain in the sleep mode.
The first falling edge of the watchdog signal causes the
WAKE UP to go low within 2µs (typ) and remain low until
the next WAKE UP cycle (see Figure 2). Other watchdog
pulses received within the same cycle are ignored (Figure
1).
During power up, RESET is held low until the output volt-
age is in regulation. During operation, if the output volt-
age shifts below the regulation limits, the RESET toggles
low and remains low until proper output voltage regula-
tion is restored. After the RESET delay, RESET returns
high.
The WATCHDOG circuitry continuously monitors the
input watchdog signal (WDI) from the microprocessor.
The absence of a falling edge on the WATCHDOG input
during one WAKE UP cycle will cause a RESET pulse to
occur at the end of the WAKE UP cycle. (see Figure 1b).
The WAKE UP output is pulled low during a RESET
regardless of the cause of the RESET . After the RESET
returns high, the WAKE UP cycle begins again (see
Figures 1b).
The RESET pulse width, WAKE UP signal frequency and
RESET high to WAKE UP delay time are all set by one
external capacitor C
Delay
.
WAKE UP period=(4x10
5
)C
Delay
RESET Delay
Time=(5x10
4
)C
Delay
RESET HIGH to WAKE UP Delay Time =(2x10
5
)C
Delay
5
WAKE UP
Response to
______
RESET
Capacitor temperature coefficient and tolerance as well as the
tolerance of the CS8151 must be taken into account in order
to get the correct system tolerance for each parameter.
WAKE UP
WDI
WAKE UP
Response to
WDI
Figure 2. WAKE UP response to WDI
______
RESET
WAKE UP
Figure 3. WAKE UP response to RESET (Low Voltage)
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
