DS1227 Datasheet, PDF (5/20 Pages) Dallas Semiconductor – KickStarter Chip

DS1227
Initially, when V_CCO1 is off, the INT/ACK pin is collapsed
to ground. At the time that voltage is switched to the
V_CCO1 output pin during kickstarting, the INT/ACK pin
will be latched such that it will remain in a low state. This
signals the microcontroller that a power on reset has oc-
curred. The OFF1, ON2/OFF2, and ON3/OFF3 inputs
are all ignored until the microcontroller acknowledges
this power on reset condition. This acknowledgement is
performed via the same INT/ACK pin, which also per-
forms the function of an interrupt acknowledge input.
This is made possible due to the fact that the pin has a
weak NMOS pulldown which forms a latch. When INT/
ACK is externally driven with a sufficiently strong high
signal (as described in the “Electrical Characteristics”
section) the state of the latch will be switched and as a
result the interrupt condition will be reset.
After the power on reset interrupt has been acknowl-
edged and the DS1227 is in a power on condition, the
INT/ACK pin will be again taken low to signal the detec-
tion of active signalling on the ON1 or SENSE inputs.
Further activity on the RXIN input will not cause a sub-
sequent interrupt condition. The INT/ACK can be re-
turned to its high (reset) state again by externally driving
it with a sufficiently strong high signal.
The OFF1 input is used to turn off the V_CCO1 output un-
der software control. It is typically interfaced to the sys-
tem microcontroller via a port pin configured as an out-
put. As noted above, it is active only when V_CCO1 is on
and INT/ACK has been set high.
STIMULUS INPUTS
ON1 is a simple TTL-level compatible input which is de-
signed to detect a negative-going edge. V_CCO1 is kick-
started whenever an active edge is detected on this pin.
The RXIN input can be used to initiate the kickstarting
action in response to the detection of incoming serial
data. In this configuration, the RXIN pin is interfaced to
an incoming serial data line, typically from an RS232
transceiver. RXOUT is the corresponding output and is
used to route the serial data to the microcontroller. RXIN
remains internally disconnected from RXOUT until
V_CCO1 is powered on. At that time, the two lines are con-
nected and serial data is passed straight through the de-
vice to the microcontroller.
The SENSE pin is intended to be connected to an exter-
nal sensor circuit which is powered from V_CCO4. This
circuit is then momentarily powered from the Kickstart-
er’s V_CCO4 output in response to a negative going edge
applied to the ON4 input. V_CCO4 will stay powered for an
amount of time determined by the circuitry on the
MODE4 pin. During the time that V_CCO4 is on, the
SENSE pin has an internal pulldown device which is ac-
tivated. SENSE is sampled just prior to the V_CCO4 out-
put being disconnected. If SENSE is externally driven
high (V_IH) at this time, it kickstarts V_CCO1 power. Any
time that V_CCO4 power is off, the SENSE pin appears as
a high impedance to external circuitry.
The amount of time that V_CCO4 is on is determined by
the configuration of the MODE4 pin. MODE4 is intended
to either be tied high (typically to V_DCO) or tied to an ex-
ternal capacitor. The V_CCO4 on time is thereby deter-
mined either by the amount of time between falling
edges on ON4 or by the value of the capacitor.
If the MODE4 pin is tied high at the time that ON4 is acti-
vated, then V_CCO4 will remain on until the next falling
edge is detected on ON4. Figure 5 illustrates the timing
associated with this mode of operation. If the Kickstarter
is also configured for boost regulation and V_CCO1,
V_CCO2, and V_CCO3 are turned off, the DC-DC converter
will be briefly enabled so that +5V will be supplied on
V_CCO4 for the duration of the time that it is on.
The alternative MODE4 configuration is illustrated in
Figure 6A. As shown in the figure, it is recommended for
most applications that a large resistor also be con-
nected between MODE4 and ground in addition to the
capacitor. For the configuration shown, the MODE4 pin
will be sensed low by the Kickstarter just following the
negative-going edge at ON4. Following this condition, a
constant current specified as I_M4ON is supplied out of
the MODE4 pin. This will cause the voltage on MODE4
to rise linearly. V_CCO4 will remain on until the voltage on
MODE4 reaches a threshold specified as VM4OFF (ap-
proximately 0.5 V_DCO). At this time, V_CCO4 will be shut
off. At the same time, the constant current source on the
MODE4 pin will be disconnected and an internal resis-
tive element (specified as R_M4DIS) will be connected be-
tween the MODE4 pin and ground. This internal resis-
tive element along with any external resistance will
cause the voltage on the capacitor to decay exponen-
tially until it reaches a threshold specified as V_M4DIS (ap-
proximately 0.1 V_DCO). When this condition is reached,
the internal resistive element will be disconnected, and
the MODE4 pin will appear as a high impedance until the
next active transition occurs on ON4. The external re-
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