L4979D013TR ,LOW DROP VOLTAGE REGULATORElectrical Characteristics (continued)Pin Symbol Parameter Test Condition Min. Typ. Max. UnitVOLTAG ..
L4979MD ,LOW DROP VOLTAGE REGULATORAbsolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only an ..
L4979MD ,LOW DROP VOLTAGE REGULATORELECTRICAL CHARACTERISTICS (continued)Pin Symbol Parameter Test Condition Min. Typ. Max. Unit5V VOL ..
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L4979D013TR-L4979MD013TR
LOW DROP VOLTAGE REGULATOR
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L4979D
L4979MDOctober 2004
FEATURES OPERATING DC SUPPLY VOLTAGE RANGE
5.6V TO 31V LOW QUIESCENT CURRENT
(6µA Typ. @ 25°C with Enable Low) HIGH PRECISION OUTPUT VOLTAGE (2%) LOW DROPOUT VOLTAGE LESS THAN 0.5V RESET CIRCUIT SENSING THE OUTPUT
VOLTAGE DOWN TO 1V PROGRAMMABLE RESET PULSE DELAY
WITH EXTERNAL CAPACITOR WATCHDOG PROGRAMMABLE WATCHDOG TIMER WITH
EXTERNAL CAPACITOR THERMAL SHUTDOWN AND SHORT
CIRCUIT PROTECTION AUTOMOTIVE TEMPERATURE RANGE
(Tj = -40°C TO 150°C) ENABLE INPUT FOR ENABLING/DISABLING
THE VOLTAGE REGULATOR OUTPUT
LOW DROP VOLTAGE REGULATOR
Figure 2. Block DiagramRev. 5
L4979MD L4979D
Table 2. Pin Function
Figure 3. Pins Connection (Top view)
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L4979MD L4979D
Table 3. Absolute Maximum RatingsNote:1. Maximum ratings are absolute ratings; exceeding any one of these values may cause permanent damage to the integrated circuit.
Table 4. Thermal DatA
Table 5. Electrical Characteristcs(Vs = 5.6V to 31V, Tj = -40°C to +150°C unless otherwise specified)
L4979MD L4979D
Table 5: Electrical Characteristics (continued)
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L4979MD L4979DNote:1. see fig4 (behavior of output current versus regulated voltage Vo) guaranteed by design When Vo becomes lower than 4V, the reset reaction time decreases down to 2µs assuring a faster reset condition in this particular
case.
VOLTAGE REGULATORThe voltage regulator uses a p-channel MOS transistor as a regulating element. With this structure a low drop-
out voltage at current up to 150mA is achieved. The output voltage is regulated up to transient input supply volt-
age of 40V. No functional interruption due to over-voltage pulses is generated. The high precision of the output
voltage is obtained with a pre-trimmed reference voltage. A short circuit protection to GND is provided.
Figure 4. Behavior of output current versus regulated voltage Vo (see a.m. Note 1) RESETThe reset circuit monitors the output voltage Vo. If the output voltage drops below Vo_th then Res becomes low
with a delay time trr. Real trr value changes as a non-linear function of delta (Vo-th - Vo). The reset low signal is
guaranteed for an output voltage Vo greater than 1V.
When the output voltage becomes higher than Vo_th then Res goes high with a delay trd. This delay is obtained
by 512 periods of an oscillator (see fig. 5). The oscillator period is given by:
ELECTRICAL CHARACTERISTICS (continued)
L4979MD L4979Dand reset pulse delay trd is given by:
trd = 512 x Tosc
Figure 5. Reset Time Diagram. WATCHDOGThe watchdog input Wi monitors a connected microcontroller. If pulses are missing, the reset output Res is
set to low. The pulse sequence time can be set within a wide range thorough the external capacitor Ctw. The
watchdog circuit discharges the capacitor Ctw with the constant current Icwd. If the lower threshold Vwlth is
reached, a watchdog reset is generated. To prevent this reset, the microcontroller must generate a positive edge
during the discharge of the capacitor before the voltage has reached the threshold Vwlth. In order to calculate
the minimum time Tdis during which the microcontroller must generate the positive edge, the following equation
can be used:
(Vwhth - Vwlth) x Ctw = Icwd x Tdis
Each Wi positive edge switches the current source from discharging to charging; the same happens when the
lower Vwlth threshold is reached. When the voltage reaches the upper threshold Vwhth the current switches from
charging to discharging. The result is a saw tooth voltage at the watchdog timer capacitor Ctw.
Figure 6. Watchdog time diagramosc rhth Vrlth– () Ctr⋅ []cr---------------------------------------------------- V rhth Vrlth– () Ctr⋅ []dr ----------------------------------------------------+=
