ca3277 Intersil Corporation, ca3277 Datasheet - Page 6

• Manufacturer Part Number: ca3277
• Description: Dual 5v Regulator With Serial Data Buffer Interface For Microcontroller Applications
• Manufacturer: Intersil Corporation

Protection - Both OUT1 and OUT2 PNP output pass tran-
sistors are protected with Over-Voltage Shutdown and Over-
Temperature Shutdown. Current Limiting for each output is
independent and is accomplished by limited drive current
from the pre-drivers (Q135 for OUT2) to the PNP output
pass transistor (Q136). Over-Voltage is sensed as a thresh-
old voltage level at the BATT input. Both output stages are
shutdown when the V
than 20.5V. When the Ignition voltage is high, the Over-Tem-
perature level is sensed as V
the bandgap reference voltage. When the chip temperature
exceeds 150 C, both output stages are shutdown. When
Over-Voltage or Over-Temperature thresholds are exceeded,
the sensed states are ORd to switch OFF drive to the output
stages. The ENABLE control for OUT2 is added to the OR
control of the OUT2 drive circuit. The Low Voltage Shutdown
control is added to the OR control of the OUT1 drive circuit.
Low Voltage Shutdown occurs at approximately 3.5V as the
BATT supply input is ramped down, forcing cutoff of the PNP
output pass transistor. The external capacitor on OUT1
holds charge, with a long RC time constant delay to sustain
shutdown control in the microcontroller. The internal shunt
resistance at the OUT1 terminal is typically 148K .
Under conditions of reverse battery or negative supply
voltages on the BATT input, current in the IC is primarily
reverse junction leakage. The design of the CA3277 is
configured to prevent high current if the power supply is
reversed. Exceptions to this are preventable. One example is
current through the DATA IN input line terminating resistor,
EN INPUT
50 A
FIGURE 3. OUTPUT2 DRIVER AND ERROR AMPLIFIER WITH THE ENABLE CONTROL
TO BATT
7
BATT
voltage level is typically greater
Q120
BE
V
REF
Q124
Q14
BG
OVER-VOLTAGE
I
B
changes and compared to
Q121
SHUTDOWN
ENABLE
SWITCH
Q122
Q16
Q125
Q119
Q123
V
REF
BG
Q129
CA3277
Q127
OVER-TEMPERATURE
Q126
7-44
ERROR
AMP
SHUTDOWN
normally connected directly to the BATT supply line. This
provides a path for current conduction into the IC through an
internal diode junction. The current is limited by the external
resistor and may be as high as 100mA at -26V. Where
negative supply voltages are potentially a problem, the
resistive load from DATA IN to BATT can be in series with a
reverse voltage blocking diode, such as a 1N914. This input
diode-resistor circuit is shown in Figure 2 as the remote
interface and load to the Current Multiplier output.
Dissipation - The CA3277 device dissipation is the com-
bined watts of input voltage times current less the external
watts of power supplied by the chip. For normal use, the
major contribution to on-chip dissipation is primarily the
BATT input dissipation. The Current Multiplier output has a
potential to add significant dissipation. The open collector
driver of the Current Multiplier Output, pin 9 may or may not
be in saturation when sinking current. Because it is a current
mirror output with a constant current drive, the voltage may
be increased on pin 9, with a significant increase in the
resulting dissipation. The chip dissipation is approximately
equal to:
where I
V
negligible dissipation for the Ignition Comparator, Data
Comparator and Reset outputs.
BATT
Q128
Q130
P
= V
D
IN
V
TRANSISTOR
Q132
IGN IN
OUT2 PASS
Q131
IN
[(V
is IGN IN and BATT input dissipation, assuming
IN
Q133
I
, and V
IN
Q75
) + (V
Q134
R29
0.87K
R30
2K
COUT
OUT1
LIMITED DRIVE
Q136
Q135
I
CURRENT
~
COUT
R31
23
V
OUT2
) - 5(I
R32
6.4K
R33
6.4K
~
15
OUT1
5V. This assumes
OUT2
+5V
+I
OUT2
)]