SFFS609 February 2025 TPS35

4 Pin Failure Mode Analysis (Pin FMA)

This section provides a Failure Mode Analysis (FMA) for the pins of the TPS35 and TPS36. 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 show the TPS35 and TPS36 pin diagram. For a detailed description of the device pins please refer to TPS35, or TPS36 in the Pin Configuration and Functions section of the data sheet.

Figure 4-1 Pin Configuration Option D
DDF Package,8-Pin SOT-23,
TPS35 and TPS36 Top View

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

Output reset Pullup Resistor (R_PULLUP) = 10kΩ, Output reset pullup voltage (V_PULLUP)= 5.5V, output reset load (C_LOAD) = 10pF, WDO Pullup Resistor (R_{PULLUP_WDO}) = 10kΩ, WDO pullup voltage (V_{PULLUP_WDO} = 5.5V)
Tables valid over the operating free-air temperature range of – 40°C to 125°C, unless otherwise noted.
Typical values are at T_A = 25°C, VDD = 6.0V unless stated otherwise.

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

PIN NAME	PIN NO.	DESCRIPTION OF POTENTIAL FAILURE EFFECT(S)	FAILURE EFFECT CLASS
SET0	1	Unexpected behavior if application needs SET0 = 1.	B
WD-EN	2	Watchdog functionality disabled.	B
WDI	3	Constant WD timeout faults.	B
GND	4	Expected operating condition.	D
SET1	5	Unexpected behavior if application needs SET1 = 1.	B
WDO (Open Drain)	6	WDO constantly asserted; some additional current can flow through pullup resistor.	B
WDO (Push Pull)	6	Functionality lost and can cause permanent damage.	A
RESET(Open Drain)	7	RESET constantly asserted; some additional current can flow through pullup resistor.	B
RESET(Push Pull)	7	Functionality lost and can cause permanent damage.	A
VDD	8	Device non-operational.	B

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

PIN NAME	PIN NO.	DESCRIPTION OF POTENTIAL FAILURE EFFECT(S)	FAILURE EFFECT CLASS
SET0	1	Leads to large indeterminate voltage levels. This causes large currents that can damage the device. The output behavior is not deterministic.	A
WD-EN	2	Nothing happens until error condition or power cycle, then WD is disabled.	B
WDI	3	Leads to large indeterminate voltage levels. This causes large currents that can damage the device. The output behavior is not deterministic.	C
GND	4	Device is non-operational.	B
SET1	5	Leads to large indeterminate voltage levels. This causes large currents that can damage the device. The output behavior is not deterministic.	A
WDO (Open Drain)	6	Constant high, no WDO functionality.	B
WDO (Push Pull)	6	High impedance output, no WDO functionality.	B
RESET(Open Drain)	7	Constant high, no RESET functionality.	B
RESET(Push Pull)	7	High impedance output, no RESET functionality.	B
VDD	8	Device is non-operational.	B

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

PIN NAME	PIN NO.	SHORTED TO	DESCRIPTION OF POTENTIAL FAILURE EFFECT(S)	FAILURE EFFECT CLASS
SET0	1	WD-EN	SET0 toggles with WD-EN.	B
WD-EN	2	WDI	High current at a system level can flow to the device driving WD-EN or WDI.	B
WDI	3	GND	Constant WD timeout faults.	B
GND	4	SET1	Unexpected behavior if application needs SET1 = 1.	B
SET1	5	WDO (Open Drain)	High current can flow from SET1 or WDO based on the pullup resistor value.	B
SET1	5	WDO (Push Pull)	Can cause permanent damage.	A
WDO (Open Drain)	6	RESET(Open Drain)	Proper operation ORing WDO and RESET outputs.	B
RESET (Open Drain)	7	VDD	Large current can flow into RESET when in error condition. This can cause permanant damage.	A
RESET (Push Pull)	7	VDD	Can cause permanent damage.	A
VDD	8	SET0	Unexpected behavior if application needs SET0 = 0.	B

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

PIN NAME	PIN NO.	DESCRIPTION OF POTENTIAL FAILURE EFFECT(S)	FAILURE EFFECT CLASS
SET0	1	Unexpected behavior if application needs SET0 = 0.	B
WD-EN	2	Watchdog is always enabled, loss of WD-disable functionality.	B
WDI	3	Constant WD timeout faults.	B
GND	4	Device is non-operational.	B
SET1	5	Unexpected behavior if application needs SET1 = 0.	B
WDO (Open Drain)	6	Large current can flow into WDO when in error condition. This can cause permanent damage.	A
WDO (Push Pull)	6	Can cause permanent damage.	A
RESET(Open Drain)	7	Large current can flow into RESET when in error condition. This can cause permanent damage.	A
RESET(Push Pull)	7	Can cause permanent damage.	A
VDD	8	Normal operation.	D