SFFS584 july 2023 MC33063A-Q1

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a failure mode analysis (FMA) for the pins of the MC33063A-Q1. The failure modes covered in this document include the typical pin-by-pin failure scenarios:

Pin short-circuited to ground (see Table 4-2)
Pin open-circuited (see Table 4-3)
Pin short-circuited to an adjacent pin (see Table 4-4)
Pin short-circuited to supply (see Table 4-5)

Table 4-2 through Table 4-5 also indicate how these pin conditions can affect the device as per the failure effects classification in Table 4-1.

Table 4-1 TI Classification of Failure Effects

Class	Failure Effects
A	Potential device damage that affects functionality.
B	No device damage, but loss of functionality.
C	No device damage, but performance degradation.
D	No device damage, no impact to functionality or performance.

Figure 4-1 shows the MC33063A-Q1 pin diagram. For a detailed description of the device pins, see the Pin Configuration and Functions section in the MC33063A-Q1 data sheet.

Figure 4-1 Pin Diagram

Following are the assumptions of use and the device configuration assumed for the pin FMA in this section:

Device is used within the Recommended Operating Conditions and the Absolute Maximum Ratings found in the MC33063A-Q1 data sheet.
For the analysis, the step-up converter with V_IN = 12 V and V_OUT = 28V and the step-down converter with V_IN = 25 V and V_OUT = 5 V shown in the Typical Application section of the MC33063A-Q1 data sheet are considered.

Table 4-2 Pin FMA for Device Pins Short-Circuited to Ground

Pin Name	Pin No.	Description of Potential Failure Effects	Failure Effect Class
Switch Collector	1	Step-up converter: Short circuits V_IN through sense resistor and inductor. Converter does not operate.	B
Switch Collector	1	Step-down converter: Short circuits V_IN through the sense resistor. Converter does not operate.	B
Switch Emitter	2	Step-up converter: No effect.	D
Switch Emitter	2	Step-down converter: Short circuits synchronous rectifier. Power transistor might get damaged.	A
Timing Capacitor	3	Device is disabled.	B
GND	4	No effect.	D
Comparator Inverting Input	5	Step-up converter: Feedback loop open. Output may rail high and cause damage.	A
Comparator Inverting Input	5	Step-down converter: Feedback loop open. Converter output close to V_IN.	B
V_CC	6	Short circuits V_IN. Converter will not power up.	B
I_PK	7	Possible device damage.	A
Driver Collector	8	No effect on IC, but converter does not operate.	B

Table 4-3 Pin FMA for Device Pins Open-Circuited

Pin Name	Pin No.	Description of Potential Failure Effects	Failure Effect Class
Switch Collector	1	No effect on IC, but converter does not operate.	B
Switch Emitter	2	No effect on IC, but converter does not operate.	B
Timing Capacitor	3	Clock frequency will be much higher than intended.	C
GND	4	Possible device damage.	A
Comparator Inverting Input	5	Step-up converter: Feedback loop open. Output may rail high and cause damage.	A
Comparator Inverting Input	5	Step-down converter: Feedback loop open. Converter output close to V_IN.	B
V_CC	6	The device is not powered, so converter does not operate.	B
I_PK	7	No current limit function.	C
Driver Collector	8	No effect on IC, but converter does not operate.	B

Table 4-4 Pin FMA for Device Pins Short-Circuited to Adjacent Pin

Pin Name	Pin No.	Shorted to	Description of Potential Failure Effects	Failure Effect Class
Switch Collector	1	Switch Emitter	Step-up converter: Short circuits V_IN through sense resistor and inductor. Converter does not operate.	B
Switch Collector	1	Switch Emitter	Step-down converter: Short circuits V_IN through the sense resistor. Converter does not operate.	B
Switch Emitter	2	Timing Capacitor	Step-up converter: converter does not operate.	B
Switch Emitter	2	Timing Capacitor	Step-down converter: clock frequency unpredictable.	B
Timing Capacitor	3	GND	No effect on IC, but converter does not operate.	B
GND	4	Comparator Inverting Input	Step-up converter: Feedback loop open. Output may rail high and cause damage.	A
GND	4	Comparator Inverting Input	Step-down converter: Feedback loop open. Converter output close to V_IN.	B
Comparator Inverting Input	5	V_CC	No effect on IC, but converter not switching as too high output voltage is detected.	B
V_CC	6	I_PK	No current limit function.	C
I_PK	7	Driver Collector	Step-up converter: Possible drive transistor damage due to overcurrent.	A
I_PK	7	Driver Collector	Step-down converter: No effect.	D
Driver Collector	8	Switch Collector	Step-up converter: Possible power transistor damage due to overcurrent.	A
Driver Collector	8	Switch Collector	Step-down converter: No effect.	D

Table 4-5 Pin FMA for Device Pins Short-Circuited to supply

Pin Name	Pin No.	Description of Potential Failure Effects	Failure Effect Class
Switch Collector	1	Step-up converter: Possible power transistor damage due to overcurrent.	A
Switch Collector	1	Step-down converter: No current limit function.	C
Switch Emitter	2	Step-up converter: Short circuits V_IN. Converter will not power up.	B
Switch Emitter	2	Step-down converter: No effect on IC, but short circuits V_IN to V_OUT through the sense resistor.	B
Timing Capacitor	3	Possible power transistor damage due to overcurrent.	A
GND	4	Short circuits V_IN. Converter will not power up.	B
Comparator Inverting Input	5	No effect on IC, but converter not switching as too high output voltage is detected.	B
V_CC	6	No effect.	D
I_PK	7	No current limit function.	C
Driver Collector	8	Step-up converter: Possible drive transistor damage due to overcurrent.	A
Driver Collector	8	Step-down converter: No current limit function.	C