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CA3277 Datasheet(PDF) 5 Page - Intersil Corporation

Part No. CA3277
Description  Dual 5V Regulator with Serial Data Buffer Interface for Microcontroller Applications
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
Logo INTERSIL - Intersil Corporation

CA3277 Datasheet(HTML) 5 Page - Intersil Corporation

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Data Comparator - The Data Comparator provides a means
of translating serial data from a high to low voltage. The
DATA IN terminal of the Data Comparator is biased to
receive signal input that is source referenced to the BATT
supply voltage level. In normal use the signal input would be
supplied from a remote Current Multiplier having a resistor
load tied to the BATT voltage supply. The DATA OUT output
from the Data Comparator is CMOS compatible 5V non-
inverting logic data referenced to GND. The switching
threshold at the DATA IN input is bias stabilized by the band-
gap voltage and is typically at (VBATT - 2.9V). The Data
Comparator is in a high state when DATA IN input is at the
BATT voltage level and is in a low state when DATA IN is at
(VBATT - 5V). The output stage of the Data Comparator is
internally supply biased from the Switched 5V Regulator
output to provide a high state of 5V and a low state of 0V
(GND). The DATA OUT terminal can typically sink 1.2mA in a
low state or source 50
µA in a high state.
In system applications the Data Comparator is used to
translate remote data at high voltage down to 5V logic levels.
The Current Multiplier is used to reverse the process by
translating 5V logic data back to the BATT voltage level
when sending data back to the remote system. The Data
Comparator and Current Multiplier are level matched for
remote communication between microcontroller systems
using the common BATT power supply voltage of the
CA3277. The current driven serial data from the Current
Multiplier is sent to a remote system by translating the signal
up to the BATT voltage level, or an external power supply
level that is compatible with the remote device. The Data
Comparator of the remote system receives the data,
interfaces to its microcontroller and responds with signal
drive from its Current Multiplier to translate the signal back to
the host. For best noise immunity the transmission in each
direction should be over a twisted pair or shielded line. As
such, two microcontrollers, each with the interface protection
of a CA3277, can provide intelligent master/slave system
communications under adverse environmental conditions.
TO OUT1 (+5V)
4, 5 AND
12, 13
Ignition Comparator - While the Ignition Comparator is pro-
vided as an essential part of the start-up control in automo-
tive systems, this circuit function may be used as an
independent switching comparator. It is important to note
that the thermal shutdown feature on the chip is dis-
abled when the IGN IN input is low. Disabling of the on-
chip thermal protection is done to satisfy the requirement of
low idle current when the system is in a standby condition.
The non-inverting IGN IN input has a switching threshold of
typically 6V with 200mV of hysteresis and is switched with
logic levels reference to GND as the low state and BATT as
the high state. The IGN OUT output is 5V CMOS compatible
logic, equivalent to the Data Comparator output stage, but is
internally supply biased from the Standby 5V Regulator. As
such, the high state is level referenced to OUT1. The IGN
OUT output terminal can typically sink 1.2mA in a low state
or source 70
µA in a high state.
Enable - A CMOS or TTL high at the ENABLE input
switches the regulated 5V/Switched Output ON at OUT2.
The ENABLE input has an internal pull-down of typically
µA to ensure that OUT2 is OFF when the ENABLE input
is not connected. The input threshold level for switching is
the bandgap voltage reference of 1.2V. When the ENABLE
input is low, all drive current to the output pass transistor is
cutoff and OUT2 voltage drops to ground level. The ENABLE
input is normally switched from the interfacing microcontrol-
ler but may be activated from a remote source.
Reset - The purpose of the Low Voltage Reset function is to
flag a low voltage condition at OUT1. When the RESET out-
put, pin 8 switches low, the voltage level at OUT1 has
dropped below the regulation level. The CRST and RESET
are high when OUT1 is at 5V. When OUT1 drops to less than
4.2V (typical), the CRST Capacitor at pin 7 is internally
discharged, causing the RESET pin to change from a high to
a low state, outputting a negative going pulse. The RESET
output is an NPN open collector driver requiring an external
load resistor, normally connected to OUT1. The RESET
output flag may be sent to a microcontroller to initiate a
power-down sequence. For any condition that causes OUT1
to drop below the reset threshold, such as undesired
transients, the RESET output is switched low for a delay
period, tRST determined by the value of the external
capacitor, CRST at CRST terminal. For a value of 0.47µF the
delay period is typically 141ms. This correlates to approxi-
10µA of charging current sourced from the CRST
terminal to charge CRST.
Regulation - The regulated output stages of the CA3277
have similar circuits, each having an error amplifier to
compare the output voltage to the bandgap reference
voltage. The circuit of the 5V/Switched regulator is shown in
Figure 3. By feedback, the output voltage is differentially
compared to the bandgap reference voltage. The error signal
is then amplified to drive a PNP pass transistor and maintain
a stable 5V output with both line and load regulation over the
full operating temperature range. Except for the ENABLE
control of OUT2, the OUT1 drive circuit is similar to the
OUT2 circuit.

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