L4979MD Datasheet L4979DTR-E, L4979MD, L4979D013TR | P10-P12

Application information L4979D, L4979MD

10/22 Doc ID 10262 Rev 9

3 Application information

3.1 Voltage regulator

The voltage regulator uses a p-channel MOS transistor as a regulating element. With this

structure a low dropout voltage at current up to 150 mA is achieved. The output voltage is

regulated up to transient input supply voltage of 40 V. 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 3. Behavior of output current versus regulated voltage V

3.2 Reset

The reset circuit monitors the output voltage V

. If the output voltage drops below V

o_th

then

becomes low with a delay time t

. Real t

value changes as a non-linear function of

delta (V

o-th

- V

). The reset low signal is guaranteed for an output voltage V

greater than

1V.

When the output voltage becomes higher than V

o_th

then R

goes high with a delay t

. This

delay is obtained by 512 periods of an oscillator (see fig. 5). The oscillator period is given by:

and reset pulse delay t

is given by:

6O? REF

)OUT)SHORT )LIM

6O? REF

)OUT)SHORT )LIM

("1($'5

OSC

rhth

rlth

–C



------------------------------------------------------

rhth

rlth

–C



------------------------------------------------------+=

512 T

OSC

=

L4979D, L4979MD Application information

Doc ID 10262 Rev 9 11/22

Table 10. Reset time diagram

3.3 Watchdog

The watchdog input W

monitors a connected microcontroller. If pulses are missing, the

reset output R

is set to low. The pulse sequence time can be set within a wide range

through the external capacitor C

. The watchdog circuit discharges the capacitor C

with

the constant current I

cwd

. If the lower threshold V

wlth

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 V

wlth

. In order to

calculate the minimum time T

dis

during which the microcontroller must generate the positive

edge, the following equation can be used:

Each W

positive edge switches the current source from discharging to charging; the same

happens when the lower V

wlth

threshold is reached. When the voltage reaches the upper

threshold V

whth

the current switches from charging to discharging. The result is a saw tooth

voltage at the watchdog timer capacitor C

Figure 4. Watchdog time diagram

TRR

TRR

TRD4OSC

4OSC

6RHTH

6RLTH

2ES

6CR

6OUT?TH

'!0'#&4

whth

wlth

–C

 I

cwd

dis

=



2ES

6CW

7I

LTH

6WHTH

TWOL

4WO P

4DIS

'!0'#&4

Package and PCB thermal data L4979D, L4979MD

12/22 Doc ID 10262 Rev 9

4 Package and PCB thermal data

4.1 SO-8 thermal data

Figure 5. SO-8 PC board

1. Layout condition of R

and Z

measurements (PCB: FR4 area = 58 mm x 58 mm, PCB thickness = 2 mm,

Cu thickness = 35 mm, Copper areas: from minimum pad lay-out to 2cm

Figure 6. R

thj-amb

vs PCB copper area in open box free air condition

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P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P22

L4979MD

Mfr. #:

Buy L4979MD

Manufacturer:

STMicroelectronics

Description:

LDO Voltage Regulators 5.0 Volt 0.5 Amp

Lifecycle:

New from this manufacturer.

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L4979MD

L4979MD

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