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Part: CA3262AM96
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Company: Intersil Corporation
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No. AN9201.1
April 1994
Application Note
PROTECTION CIRCUITS FOR QUAD AND OCTAL LOW SIDE POWER DRIVERS
by Wayne Austin
Overview
Normally, the defined requirements for a Quad or Octal Driver are very much affected by the type of protection circuits used on the chip. Fault protection for an open or shorted load is an interactive function, making it important in the decision process of specifying the proper IC for an application. The various types of on-chip features may include protection for over-current, overvoltage and over-temperature. The response action to a fault condition may be either limiting or shutdown. Shutdown methods may include hysteresis and may require a logic reset. On-chip clamp diodes provide current steering to an external zener diode clamp as over-voltage protection from inductive switching pulses. Internal Zener diodes are also used to limit the output voltage on the output driver of the IC. In addition, fault detection is available with diagnostic feedback, including serial bus (SPI) control. All of the protection features noted are represented in the Table 1 listing of Quad and Octal Low Side Drivers:
TABLE 1. QUAD & OCTAL LOW SIDE POWER DRIVERS TYPE CA3242 DESCRIPTION Quad Gated Inverting Power Dr. Quad Gated Inverting Power Dr. KEY FEATURES Over-Current Latch-Off, Fast Fault Shut-Down, Output Protection Diodes Over-Current Limiting, OverTemperature Limiting, Output Protection Diodes Same as CA3262 plus +125oC Max. TA Range.
While the CA3282 Octal Driver is quite different from the quad drivers, it is included here because it is used in similar applications. The CA3282, HIP0080 and HIP0081 feature Power BiMOS with MOSFET Output Drivers for higher current and voltage capability. Because of the additional dissipation associated with these drivers, the CA3282 and HIP0081 are provided in a 15 pin SIP power package. The other Quad Drivers are available in the 16 pin DIP and/or 28 lead PLCC packages which have special construction for improved heat dissipation. All of these Low Side Switches generally share a common characteristic of 5V input CMOS or TTL logic level control. The Quad and Octal Power Drivers include a wide variation of choice in selecting a device type. The available types are listed in TABLE 1 which also highlights the key parameters for most applications. By-type, the protection features of the Quad and Octal Drivers are listed in the table and are explained in the following detail of this IC Application Note to assist the user in making an intelligent device selection for the application of interest.
CA3262
CA3242 Quad Power Driver
In normal use, the supply voltage is applied through a load to an NPN open collector output of the CA3242 quad driver. The functional block diagram is shown in Figure 1. The maximum current rating of 1A does not distinguish between average and peak. Each output is independently protected and latches "OFF" when the load current exceeds the latchoff threshold in the "ON" state. The CA3242E feature of short circuit protection is a responsive high-speed shutdown of the output drive to a shorted load. Under worse-case shorted load conditions, the supply voltage is applied direct to the output device. The latch-off threshold is typically 1.3V (ISCRON), where RON is the saturated "ON" resistance of the output. The CA3242 latches "OFF" at a typical short circuit current of 1.2A with 25µs nominal delay. The ENABLE or the IN pin of the latch-tripped channel must be toggled to reset the latch. To better understand the mechanism of protection when the CA3242 is subjected to a shorting condition, Figure 2 illustrates that part of the Figure 1 noted as the "PROT" functional block. When an over-load current is applied to an output driver, the VSAT increases to a threshold level set in a
CA3262A Quad Gated Inverting Power Dr. CA3272 Quad Gated Inverting Over-Current and Temp. Limand Power Dr. with Fault iting, Fault Flag Output, CA3272A Mode Diag. Flag Output +125oC Max. TA Range. CA3272A has improved Fault Flag Output Drive Capability. CA3282 Octal Driver with SPI Over-Current and Over-VoltLogic Control age Fault Mode Protection with Fault Mode Feedback/ Control with -40oC to +125oC Max. TA Range. CA3292A Quad Gated Inverting Similar to CA3272A with addPower Dr. with Fault ed Internal Over-Voltage OutMode Diag. Flag Output put Clamp. HIP0080 1A and 2A Quad Gated Over-Current (Latch-Off), and Inverting Power Drs. Over-Temperature (GatesHIP0081 with Multi-mode Diag. Off), Open Load and Output Feedback Ground Short Detection, OverVoltage Internal Output Clamp Diodes, Fault Mode Feedback/Control and -40oC to +125oC Max. TA Range.
Copyright
© Intersil Corporation 1992 11-170
Application Note 9201
TABLE 2. QUAD AND OCTAL DRIVER FEATURES CA3272 CA3272A 60V 0.6A CA3282 (OCTAL DR.) 32V Typ. (Clamp) 1A
CA3242 Max. Output Voltage, No Load Max. Output Load Current 50V 0.6A
CA3262 60V 0.7A
CA3262A 60V 0.7A
CA3292A 32V Typ. (Clamp) 0.6A
HIP0080 36V Typ. (Clamp) 1A
HIP0081 80V Typ. (Clamp) 2A
Max. VSAT Output Voltage 0.8V at 0.6A 0.6V at 0.6A 0.5V at 0.6A 0.4V at 0.5A 0.4V at 0.5A Max. RON Output Resis1.0 at 0.5A tance Max. Load Switching Voltage, VCE(SUS) or VCLAMP Limited Typical Output Current Limiting and/or Shutdown Protection Output Thermal Limiting and/or Shutdown Protection (Temp. TJ) Over-Voltage Protection Fault Diagnostics Temp. Range, -40oC to __oC Packages: 16 DIP Pwr WEB (PC Bd, JA) 28 PLCC Pwr WEB (PC Bd, JA) 15 SIP (Tab H.S., JC) 105oC 35V 40V 40V 40V 28V 27V
0.5 at 1A 73V
1 at 0.5A 30V
1.4A (Latches Off) None
1.6A
1.3A
1.2A
1.2A
1.8A (Latches Off) 150oC (15oC hys.)
3.5A (Latches Off) 150oC (15oC hys.)
1.5A (Latches Off) None
155oC (Limits)
155oC (Limits)
165oC (15oC hys.) None
165oC (15oC hys.)
Current Steering Clamp Diode No 85oC
Zener Diode Feedback Clamp Fault Mode Flag and Feedback 125oC
Fault Flag
40oC/W
40oC/W
40oC/W 30oC/W 30oC/W 30oC/W 30oC/W 3oC/W 3oC/W
comparator circuit. The comparator outputs a switching signal to the protection latch and the input drive is "latched-off". The input may be reset with an INPUT or ENABLE toggle, or by and ON-OFF toggle of the power supply to the control circuits.
11 V+ 9 PROT QD 8 7 CLAMP 6 OUT C QC 14 ENABLE IN B 15 PROT QB 3 OUT B 2 1 16 IN A PROT QA OUT A CLAMP OUT D
VCC IN D
Proper application will protect the CA3242E during turn-off under shorted load conditions. Observations of wide ranging conditions have been done to test the shutdown behavior and has revealed several pitfalls that should be addressed to assure safe shutdown. One should be aware that a forced short circuit test condition may be considerably more severe than a normal application shorted load. In either case, two problems arise that affect the severity of the overload during shutdown. These are: 1. A shorted load is inductive and causes the generation of voltage spikes, exposing the output device to at least 2 times the value of the V+ supply voltage. 2. Lack of bypassing can provoke severe oscillations during the delay period before shutdown is complete. This is typically less than 25µs. The result of this oscillation with an inductive load is to alternately stress the output device in both a forward and reverse direction at rates as high as 1mHz, lasting until shutdown occurs. This problem is compounded in some applications when 2 or more devices are used in parallel to increase drive output. In this case, a short may now draw twice the current of one driver which, in turn, results in almost twice the unclamped voltage spike developed across each output transistor. To suppress oscillations during shutdown requires some attention to the use of adequate bypassing of both the +5V VCC supply and the battery or output supply voltage. Bypassing the output supply will minimize both the transient oscillations and the voltage spike effects of lead inductance.
IN C
10
PROT
PINS 4, 5, 12 AND 13 GROUND
FIGURE 1. CA3242 FUNCTIONAL BLOCK DIAGRAM
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Application Note 9201
Then, the shorted output is stressed in the forward bias mode with the shorted current determined by voltage source, duration of short, line resistance and the resistance of the saturated output. In a practical application, the load and any potential short may occur in a remote location. As such, bypassing the output supply may not be practical. Bypassing the +5V supply with a 0.1µF capacitor closely wired to pins 11 and 12 of the CA3242E constitutes adequate bypassing of the +5V supply. Because voltage spikes are normal to the application, a 30V zener "clamp" diode is needed to limit the device output voltage spikes to less than the maximum rating of 35V. The zener clamp diode protection should be closely wired to pins of the output divide in order to avoid any delay in the voltage clamping action. Alternatively, the on-chip diodes may be used in a free wheeling mode by connecting the CLAMP pins to the supply voltage if it does not exceed 30V during transients. Zener diode clamp protection is preferred over the power supply clamp option, primarily because the power supply may be subject to large transient changes. In order to clamp high voltage pulses which may be generated by switching inductive energy in the load circuit, zener diodes with a value not greater than 30V should be connected to the CLAMP pins. On-chip diodes are connected from each output to one of the two CLAMP pins and are intended for use as steering diodes to provide a path for the clamped pulse current to a CLAMP pin; allowing the use of one zener diode to clamp all outputs. Alternatively, the onchip diodes may be used in a free-wheeling mode by connecting the CLAMP pins to the supply voltage if it does not exceed 30V during transients. Zener diode clamp protection is preferred over the power supply clamp option, primarily because the power supply voltage may be subject to large transient changes. Note that the rate of change of the output current during switching is very fast. Therefore, even small values of inductance (such as the inductance of several meters of wire) in the load circuit can generate voltage spikes of considerable amplitude on the output terminals and may require clamping to prevent damage. The CA3262A is a lower VSAT version of the CA3262 and is rated for +125oC ambient temperature applications. The CA3262 is limited to about +100oC (data sheet rating at +85oC) ambient temperatures. Otherwise, the protection features described here apply to both versions. Figure 3 shows a functional block diagram for the CA3262 and CA3262A. Each type has independent current limiting and thermal limiting protection for each output driver. The maximum current rating of each output is typically greater than 1.2A. However, this is not a users choice rating, the current limiting may range from 0.7A to as high as 2A. Typical applications of the CA3242 and CA3262 quad drivers with the recommended method for use of the current steering diodes is shown in the circuit of Figure 4. Where inductive loads are not used, the protective diodes need not be externally connected. However, the user should be alert to the potential for stored energy in long wire connections to the load circuits.
VCC IN D (16) ILIM 10 IN C EN IN B (17) 14 (26) 15 (27) ILIM 16 IN A (28) ILIM PINS 4, 5, 12 AND 13 GROUND (PACKAGE E) PINS 5-11 AND 19-25 GROUND (PACKAGE Q) PIN #'S IN PARENTHESIS APPLY TO PACKAGE Q TLIM TLIM ILIM 3 TLIM (4) 2 OUT B 11 V+ (18) 9 TLIM 8 OUT D (14) 7 CLAMP (13) 6 OUT C (12)
CLAMP INPUT_ +VCC OUT_ ENABLE VREF SCR LATCH +
-
FIGURE 2. CA3242 FUNCTIONAL DIAGRAM FOR EACH OUTPUT CHANNEL SHOWN WITH PROTECTION CIRCUIT
CA3262 and CA3262A Quad Power Drivers
The CA3262 is a quad-gated inverting low-side driver capable of switching 700mA load currents (at +25oC) in each output without interaction between the outputs. Shown in Figure 3, each output is independently protected with overcurrent limiting and over temperature limiting features. If an output load is shorted, the remaining three outputs function normally unless the junction temperature of their output device exceeds the over temperature limiting threshold of +155oC (typical). Current limiting prevents the output current from exceeding a value determined by the design (1.2A typical), independent of the load condition. The power dissipation of the shorted output driver is equal to the product of the limiting value of current and the applied output collector voltage. If this value causes the junction temperature to exceed +155oC (typical), the base drive to the output transistor, and thereby it's collector current, is reduced until the resulting power dissipation is equal to that value which maintains the junction temperature at the thermal limit value. The current which flows in the output transistor in a short circuit mode is therefore a function of the ambient temperature, the thermal resistance of the package in the application, the total power dissipated in the package. If the short is removed, normal operation resumes automatically.
CLAMP (3) 1 OUT A (2)
FIGURE 3. CA3262 AND CA3262A FUNCTIONAL BLOCK DIAGRAM
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Application Note 9201
11 +5V P.S. (18) 9 (16) ILIM TLIM V+ TLIM
8 (14) 7 (13) 6
RELAY
VBATT
10 TTL OR CMOS LOGIC LEVEL INPUTS (17) 14 (26) 15 (27)
(12)
SOLENOID VBATT
ILIM 3 TLIM (4) 2 ILIM TLIM (3) 1 HIGH CURRENT HIGH SIDE DR MOTOR
16 (28)
(2)
LAMP
VBATT
ILIM
FIGURE 4. TYPICAL APPLICATION CIRCUIT FOR THE CA3262 AND CA3262A QUAD POWER DRIVERS WITH PROTECTION DIODES EXTERNALLY CONNECTED TO A ZENER CLAMP DIODE FOR INDUCTIVE LOAD PROTECTION.
The CA3262 and CA3262A will typically survive when shorted if the output supply voltage is less than 18V. This potential for failure is flagged in the data sheet as a note under the Electrical Characteristics table. It takes a few milliseconds to shutdown when the output is short circuited. During shutdown the dissipation may be excessive and is primarily determined by ISC which is the limiting current. The short-circuit current will be limited but the voltage that the shorted output sees may approach VSUPPLY. Not considering transient effects, the worst case dissipation would be PD = (VSUPPLY)x(ISC). Normally, a shorted solenoid or relay will have a few ohms of impedance which should prevent catastrophic IC failure in 12V automotive applications. A typical value for ISC is 1.3A. RON is the saturated collector resistance of the output transistor with a typical value of 1. VSUPPLY is normally 9V to 16V in automotive applications. The thermal shutdown could be made faster but the circuit would not be able to effectively drive lamps which have a very low resistance in a cold start-up. Lamp drive capability is a common application use for the CA3262 and CA3262A.
down characteristics differ from the CA3262 by having hysteresis, the same precaution applies for potential damage from high transient dissipation during thermal shutdown. The CA3272Q, CA3272AQ and CA3292AQ Quad Driver are provided in the 28 pin web-leadframe PLCC package. This package has slightly lower thermal resistance than the 16 lead DIP package with a web leadframe. The FAULT DETECTOR circuit of the CA3272, CA3272A and CA3292A is shown in Figure 6 as an equivalent logic block diagram. Channel A is one of 4 power switching functions displayed in the diagram. Transistor QA is the protected power transistor switch that drives the "OUT A" terminal. The FAULT DETECTOR block illustrates the logic functions associated with FAULT DETECTION. The ENABLE input is common to each of the 4 power switches and also disables the FAULT output when it is low. From the "IN A" input to the "OUT A" output, the switch condition is inverting (NAND). When IN is high, OUT is low. The FAULT DETECTOR senses the IN and OUT states and switches QF "ON" if a fault is detected. Transistor QF activates a sink current source to pull-down the FAULT pin to a 0 (low) state when the fault is detected. Both shorted and open load conditions are detected. The CA3292A is equivalent to the CA3272A except that it has internal clamp diodes on the outputs to handle inductive switching pulses from the output load. The CA3272A and CA3292A have significantly higher IOL FAULT output drive than the CA3272. Expanded functional block diagram detail of the fault logic is similar to that of the CA3272 as shown in Figure 6. The structure of each CA3292A output, shown in Figure 6B, includes a zener diode from collector-to-base of the output transistor. This is a different form of protection than the CA3242 or CA3262 which have current steering clamp diodes on each output, paired to one of two "CLAMP"
CA3272 and CA3292 Quad Power Drivers with Fault Mode Flag
The CA3272 and CA3292 are quad-gated inverting low-side power drivers with a fault diagnostic flag output. They are rated for +125oC ambient temperature applications and have current limiting and thermal shutdown. As shown in Figure 5, they differ from the CA3262A by not having output clamp diodes but do have the diagnostic short-circuit flag outputs. Each output driver is capable of switching 400mA load currents at +125oC ambient without interaction between the outputs. Current limiting functions in the same manner as the CA3262 with a typical limit value of 1.2A. The current limiting range is set for 0.6A to 1.6A. While the thermal shut-
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Application Note 9201
output pins. The CA3292A output transistor will turn-on at the clamp voltage threshold which is typically 32V and the output transistor will dump the pulse energy through the output driver to ground.
ENABLE 26 F TLIM IN D 16 ILIM F TLIM IN C 17 ILIM F TLIM IN B 27 ILIM F TLIM IN A 28 ILIM FAULT 1 GROUND PINS 5-11, 19-25 QA 0.02 QB 0.02 QC 0 .0 2 QD 0 .0 2 VCC 18 OUT D 14
OUT C 12
OUT B 4
Each of the outputs are independently protected with overcurrent limiting and over-temperature shutdown with thermal hysteresis. If an output is shorted, the remaining outputs function normally unless the temperature rise of the other output devices can be made to exceed their shutdown temperature of +165oC (typical). When the junction temperature of a driver exceeds the +165oC thermal shutdown value, that output is turned off. When and output is shutdown, the resulting decrease in power dissipation allows the junction temperature to decrease. When the junction temperature decreases by approximately 15oC, the output is turned on. The output will continue to turn on and off for as long as the shorted condition exists or until shutdown by the input logic. The resulting frequency and duty cycle of the output current flow is determined by the ambient temperature, the thermal resistance of the package in the application, the total power dissipation in the package. Since each output is independently protected, the frequency and duty cycle of the current flow into multiple shorted outputs will not be related in time. Long lead lengths in the load circuit may lead to oscillatory behavior if more than two output loads are shorted. A diagnostic flag indicates when an output is shorted. This information can be used as input to a microprocessor or dedicated logic circuit to provide a fast switch-off when a short occurs and also to determine by sequence action, which output is shorted. A fault condition in any output load will cause the FAULT output to switch to a logic "low". Added detail of the fault logic is shown in Figure 6A. Since a fault condition will be indicated during switching, use of an appropriate size capacitor to filter the FAULT output is recommended (see data sheet). This will prevent the FAULT output voltage from reaching a logic level "0" within the maximum switching time. The FAULT detection circuitry compares the state of the input and the state of the output. The output is considered to be in a high state if the voltage exceeds the typical FAULT threshold reference voltage, VTHD of 4V. If the output voltage is less
1
OUT A 2
FIGURE 5. CA3272 AND CA3272A FUNCTIONAL BLOCK DIAGRAM
TO CHANNELS B, C AND D
FAULT
QF ENABLE TO B,C,D AND FAULT ENABLE 4V EN FAULT DETECTOR TLIM 2 TLIM IN A QA OUT A
OVER-VOLTAGE ZENER CLAMP DIODE
2 OUT A
QA
ILIM
0.02
ILIM
0.02
FIGURE 6A. FAULT DETECTOR SHOWN WITH THE CA3272 AND CA3272A OUTPUT STAGE
FIGURE 6B. CA3292A OUTPUT STAGE WITH CLAMP DIODE
FIGURE 6. FAULT DETECTION FUNCTIONAL BLOCK DIAGRAM OF THE CA3272, CA3272A AND CA3292A
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