CA3277E View Datasheet(PDF) - Intersil
Part Name
Description
Manufacturer
CA3277E Datasheet PDF : 8 Pages
| |||
CA3277
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 VBATT voltage level is typically greater
than 20.5V. When the Ignition voltage is high, the Over-Tem-
perature level is sensed as VBE changes and compared to
the bandgap reference voltage. When the chip temperature
exceeds 150οC, 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 148KΩ.
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,
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:
PD ≈ [(VINIIN) + (VCOUTICOUT) - 5(IOUT1+IOUT2)]
where IINVIN is IGN IN and BATT input dissipation, assuming
VBATT = VIGN IN, and VOUT1 ~ VOUT2 ~ 5V. This assumes
negligible dissipation for the Ignition Comparator, Data
Comparator and Reset outputs.
TO BATT
Q14
IB
VBG
REF
Q119
Q16
7
EN INPUT
Q121 Q122
Q120
Q123
50µA
Q124
Q125
ENABLE
SWITCH
Q126
OUT2 PASS
TRANSISTOR
Q131 Q75
Q136
Q134
Q133
Q127 Q128
VBG
REF
ERROR
AMP
Q129
Q130
Q132
R29
0.87K
Q135
R30
2K
R31
23
15 OUT2
+5V
R32
6.4K
R33
6.4K
OVER-VOLTAGE
SHUTDOWN
OVER-TEMPERATURE
SHUTDOWN
CURRENT
LIMITED DRIVE
FIGURE 3. OUTPUT2 DRIVER AND ERROR AMPLIFIER WITH THE ENABLE CONTROL
7-44
Share Link: 