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MM74C908 Dual CMOS 30-Volt Relay Driver
October 1987 Revised January 1999
MM74C908 Dual CMOS 30-Volt Relay Driver
General Description
The MM74C908 is a general purpose dual high voltage driver capable of sourcing a minimum of 250 mA at VOUT = VCC - 3V, and TJ = 65C. The MM74C908 consists of two CMOS NAND gates driving an emitter follower Darlington output to achieve high current drive and high voltage capabilities. In the "OFF" state the outputs can withstand a maximum of -30V across the device. These CMOS drivers are useful in interfacing normal CMOS voltage levels to driving relays, regulators, lamps, etc.
Features
s Wide supply voltage range: s High noise immunity: s High voltage: -30V s High current: 250 mA 3V to 18V 0.45 VCC (typ.) s Low output "ON" resistance: 8 (typ.)
Ordering Code:
Order Number MM74C908N Package Number N08E Package Description 8-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" Wide
Connection Diagram
Pin Assignments for DIP
Top View
(c) 1999 Fairchild Semiconductor Corporation
DS005912.prf
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MM74C908
Absolute Maximum Ratings(Note 1)
Voltage at any Input Pin Voltage at any Output Pin Operating Temperature Range Operating VCC Range Absolute Maximum VCC ISOURCE Storage Temperature Range (TS) -0.3V to VCC +0.3V 32V -40C to +85C 4V to 18V 19V 500 mA +150C -65C to +150C
Lead Temperature (TL) (Soldering, 10 seconds) Power Dissipation (PD) 260C Refer to Maximum Power Dissipation vs Ambient Temperature Graph
Note 1: "Absolute Maximum Ratings" are those values beyond which the safety of the device cannot be guaranteed. Except for "Operating Temperature Range" they are not meant to imply that the devices should be operated at these limits. The Electrical Characteristics table provides conditions for actual device operation.
DC Electrical Characteristics
Min/Max limits apply across temperature range, unless otherwise noted Symbol CMOS TO CMOS VIN(1) VIN(0) IIN(1) IIN(0) ICC Logical "1" Input Voltage Logical "0" Input Voltage Logical "1" Input Current Logical "0" Input Current Supply Current Output "OFF" Voltage CMOS/LPTTL INTERFACE VIN(1) VIN(0) VOUT Logical "1" Input Voltage Logical "0" Input Voltage Output Voltage VCC = 4.75V VCC = 4.75V IOUT = -300 mA, VCC 5V, TJ = 25C IOUT = -250 mA, VCC 5V, TJ = 65C IOUT = -175 mA, VCC 5V, TJ = 150C RON Output Resistance IOUT = -300 mA, VCC 5V, TJ = 25C IOUT = -250 mA, VCC 5V, TJ = 65C IOUT = -175 mA, VCC 5V, TJ = 150C Output Resistance Coefficient JA Thermal Resistance MM74C908 (Note 2) (Note 2) 100 45 110 55 C/W C/W VCC-2.7 VCC-3.0 VCC-3.15 VCC-1.8 VCC-1.9 VCC-2.0 6.0 7.5 10 0.55 9.0 12 18 0.80 VCC - 1.5 0.8 V V V V V %/C VCC = 5V VCC = 10V VCC = 5V VCC = 10V VCC = 15V, VIN = 15V VCC = 15V, VIN = 0V VCC = 15V, Outputs Open Circuit VIN = VCC, IOUT = -200 A -1.0 0.005 -0.005 0.05 -30 15 3.5 8.0 1.5 2.0 1.0 V V V V A A A V Parameter Conditions Min Typ Max Units
OUTPUT DRIVE
Note 2: JA measured in free air with device soldered into printed circuit board.
AC Electrical Characteristics
Symbol tpd1 Parameter Propagation Delay to a Logical "1"
(Note 3)
Conditions Min Typ 150 65 2.0 4.0 5.0 Max 300 120 10 20 Units ns ns s s pF
VCC = 5V, RL = 50, CL = 50 pF, TA = 25C VCC = 10V, RL = 50, CL = 50 pF, TA = 25C
tpd0
Propagation Delay to a Logic "0"
VCC = 5V, RL = 50, CL = 50 pF, TA = 25C VCC = 10V, RL = 50, CL = 50 pF, TA = 25C
CIN
Input Capacitance
(Note 4)
Note 3: AC Parameters are guaranteed by DC correlated testing. Note 4: Capacitance is guaranteed by periodic testing.
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MM74C908
Typical Performance Characteristics
Maximum Power Dissipation vs Ambient Temperature Typical IOUT vs Typical VOUT
Maximum VCC - VOUT vs IOUT
Typical IOUT vs Typical VOUT
Typical IOUT vs Typical VOUT
AC Test Circuit
Switching Time Waveforms
tr = tf = 20 ns
3
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MM74C908
Power Considerations
Calculating Output "ON" Resistance (RL > 18) The output "ON" resistance, RON, is a function of the junction temperature, TJ, and is given by: RON = 9 (TJ - 25) (0.008) + 9: and TJ is given by: TJ = TA + PDAV JA,: (2) where TA = ambient temperature, JA = thermal resistance, and PDAV is the average power dissipated within the device. PDAV consists of normal CMOS power terms (due to leakage currents, internal capacitance, switching, etc.) which are insignificant when compared to the power dissipated in the outputs. Thus, the output power term defines the allowable limits of operation and includes both outputs, A and B. PD is given by: PD = IOA2RON + IOB2 RON, (3) (1) Equations (1), (4), and (6b) can be used in an iterative method to determine the output current, output resistance and junction temperature.
where IO is the output current, given by: For example, let VCC = 15V, RLA = 100, RLB = 100, VL = 0V, TA = 25C, JA = 110C/W, Duty CycleA = 50%, Duty CycleB = 75%. Assuming RON = 11, then:
(4) VL is the load voltage. The average power dissipation, PDAV, is a function of the duty cycle: PDAV = IOA2RON (Duty CycleA) + IOB2 RON(Duty CycleB) where the duty cycle is the % time in the current source state. Substituting equations (1) and (5) into (2) yields: TJ = TA + JA [9 (TJ - 25) (0.008) + 9]: (6a) [IOA2 (Duty CycleA) + IOB2 (Duty CycleB)] simplifying: (5)
and
and RON = 9 (TJ - 25) (0.008) + 9 = 9(52.6 - 25) (0.008) + 9 = 11
Applications
(See AN-177 for applications)
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MM74C908 Dual CMOS 30-Volt Relay Driver
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" Wide Package Number N08E
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Fairchild does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and Fairchild reserves the right at any time without notice to change said circuitry and specifications.

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