Texas Instruments UCC3946PWTR, UCC3946PW, UCC3946N, UCC3946DTR, UCC3946D Datasheet

UCC1946

UCC2946

UCC3946

Microprocessor Supervisor with Watchdog Timer

FEATURES

•Fully Programmable Reset Threshold

•Fully Programmable Reset Period

•Fully Programmable Watchdog Period

•2% Accurate Reset Threshold

•VDD Can Go as Low as 2V

•18 A Maximum IDD

•Reset Valid Down to 1V

DESCRIPTION

The UCC3946 is designed to provide accurate microprocessor supervision, including reset and watchdog functions. During power up, the IC asserts a reset signal RES with VDD as low as 1V. The reset signal remains asserted until the VDD voltage rises and remains above the reset threshold for the reset period. Both reset threshold and reset period are programmable by the user. The IC is also resistant to glitches on the VDD line. Once RES has been deasserted, any drops below the threshold voltage need to be of certain time duration and voltage magnitude to generate a reset signal. These values are shown in Figure 1. An I/O line of the microprocessor may be tied to the watchdog input (WDI) for watchdog functions. If the I/O line is not toggled within a set watchdog period, programmable by the user, WDO will be asserted. The watchdog function will be disabled during reset conditions.

The UCC3946 is available in 8-pin SOIC(D), 8-pin DIP (N or J) and 8-pin TSSOP(PW) packages to optimize board space.

BLOCK DIAGRAM

					VDD
					8
		400nA			POWER TO
					CIRCUITRY
RP	4
		1.235V .			3	RES
RTH	2
		POWER ON RESET
		400nA
			8-BIT COUNTER
WP	6			A3
				A2
		100mV	CLR	A1	5	WDO
				A0
			CLK
		1.235V
		WATCHDOG TIMING
WDI	7	EDGE DETECT
			1
			GND			UDG-98001

Note: Pinout represents the 8-pin TSSOP package.

SLUS247B - FEBRUARY 2000

UCC1946

UCC2946

UCC3946

ABSOLUTE MAXIMUM RATINGS

CONNECTION DIAGRAM

VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10V Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C Junction Temperature. . . . . . . . . . . . . . . . . . . –55°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C

Currents are positive into, negative out of the specified terminal. Consult Packaging Section of the Databook for thermal limitations and considerations of packages.

SOIC-8, TSSOP-8, DIL-8 (Top View) D, PW, N or J Package

GND			1					8	VDD
RTH			2					7	WDI
RES			3					6	WP
	RP		4					5	WDO

ELECTRICAL CHARACTERISTICS: Unless otherwise specified, VDD = 2.1V to 5.5V for UCC1946 and UCC2946;

VDD = 2V to 5.5V for UCC3946; TA = 0°C to 70°C for UCC3946, –40°C to 95°C for UCC2946, and –55°C to 125°C for UCC1946; TA = TJ

PARAMETERS	TEST CONDITIONS			MIN		TYP		MAX	MIN	TYP	MAX	UNITS
					UCC3946				UCC1946 & UCC2946
Operating Voltage				2.0				5.5	2.1		5.5	V
Supply Current						10		18		12	18	A
Minimum VDD	(Note 1)							1			1.1	V
Reset Section
Reset Threshold	VDD Rising			1.210		1.235		1.260	1.170	1.235	1.260	V
Threshold Hysteresis						15				15		mV
Input Leakage								5			5	nA
Output High Voltage	ISOURCE = 2mA			VDD –					VDD –			V
				0.3					0.3
Output Low Voltage	ISINK = 2mA							0.1			0.1	V
	VDD = 1V, ISINK = 20uA							0.2			0.4	V
VDD to Output Delay	VDD = -1mV/ s (Note 2)					120				120		s
Reset Period	CRP = 64nF			160		200		260	140	200	320	ms
Watchdog Section
WDI Input High				0.7·					0.7·			V
				VDD					VDD
WDI Input Low								0.3·			0.3·	V
								VDD			VDD
Watchdog Period	CWP = 64nF			1.12		1.60		2.08	0.96	1.60	2.56	s
Watchdog Pulse Width				50					50			ns
Output High Voltage	ISOURCE = 2mA			VDD –					VDD –			V
				0.3					0.3
Output Low Voltage	ISINK = 2mA							0.1			0.1	V

Note 1: This is the minimum supply voltage where RES is considered valid.

Note 2: Guaranteed by design. Not 100% tested in production.

2