VDD regulated voltage L9777
16/25 DocID13496 Rev 4
4 VDD regulated voltage
L9777 provides a second regulated voltage in tracking with VCC main regulator capable to
source load with up to 100 mA output current capability.
VDD tracking regulator function is controlled by VDD_EN input pin. If pin is set high VDD
voltage becomes available. If pin is set low or left floating regulator is disabled.
Note that VDD regulator will be disable also in case of undervoltage condition on VCC main
regulator, so at power up regulator will start up only when VCC rises over undervoltage
threshold without TRD power up delay time, even if VDD_EN pin is set high.
DocID13496 Rev 4 17/25
L9777 VDD_LOW (option C)
24
5 VDD_LOW (option C)
VDD_LOW circuit monitors VDD regulated voltage. When VDD falls below VDDUN for a
filter time TFVDD VDD_LOW output voltage is set low.
VDDUN is a reference voltage 300 mV (Typ) lower than VCC regulated voltage.
Filter time TFVDD is spike dependent as TRR1 for VCC regulator so the same
consideration applies also in this case.
Figure 13. VDD_LOW filter time
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Device options L9777
18/25 DocID13496 Rev 4
6 Device options
6.1 Option A
This is the standard configuration with VDD output capable to source up to 100 mA to an
external load with low dropout (400 mV max.) and double reset function provided (NMI and
RESET output).
Note that as we can see in absolute section VDD and TIMING pin are capable to sustain
only short to VI pin.
With this option input digital pins VDD_EN and WD_EN are both pulled up by 5μA typ
current source (minimum quiescent current is 110μA typ.).
6.2 Option B
With this option VDD and TIMING pins are both capable to sustain short to 40V regardless
of VI battery voltage. To provide this feature a series diode is introduced between VI pin and
VDD power PMOS source. In this configuration current capability on VDD output is scaled
down to 50 mA while dropout voltage increases to 1.5V (Max). All other features are un-
changed and double reset capability is maintained.
In option B VDD_EN and WD_EN are both pulled down with 10μA typ internal current
source so minimum quiescent current is reduced to 100μA typ.
6.3 Option C
Using option C VDD is capable to sustain short to 40 V as in option B. VDD output current is
scaled down to 50 mA and dropout increase up to 1.5 V (Max).
Double reset feature is removed and RESET pin is used to monitor VDD output voltage
(VDD_LOW pin). A spike dependent filter time similar to VCC main regulator is provided and
same low voltage reset specifications applies to bipolar output driver (VDD_LOW driver).
For this reason TIMING pin is no more used and can be left floating or shorted to ground.
Note that NMI output pin behaves normally as in option A and becomes the main reset
signal for VCC and watchdog monitor.
As in option B VDD_EN and WD_EN are both pulled down with 10μA typ internal current
source so minimum quiescent current is reduced to 100μA typ.

L9777C

Mfr. #:
Manufacturer:
STMicroelectronics
Description:
LDO Voltage Regulators Low-Power Voltage Regulator
Lifecycle:
New from this manufacturer.
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