l6928 STMicroelectronics, l6928 Datasheet - Page 11

• Manufacturer Part Number: l6928
• Description: High Efficiency Monolithic Synchronous Step Down Regulator
• Manufacturer: STMicroelectronics

L6928
5
5.1
5.2
5.3
5.4
5.5
Additional features and protections
DROPOUT operation
The Li-Ion battery voltage ranges from approximately 3V and 4.1V-4.2V (depending on the
anode material). In case the regulated output voltage is from 2.5V and 3.3V, it can be that,
close to the end of the battery life, the battery voltage goes down to the regulated one. In
this case the device stops to switch, working at 100% of duty cycle, so minimizing the
dropout voltage and the device losses.
PGOOD (Power Good Output)
A power good output signal is available. The VFB pin is internally connected to a comparator
with a threshold set at 90% of the of reference voltage (0.6V). Since the output voltage is
connected to the VFB pin by a resistor divider, when the output voltage goes lower than the
regulated value, the VFB pin voltage goes lower than 90% of the internal reference value.
The internal comparator is triggered and the PGOOD pin is pulled down.
The pin is an open drain output and so, a pull up resistor should be connected to him.
If the feature is not required, the pin can be left floating.
Adjustable output voltage
The output voltage can be adjusted by an external resistor divider from a minimum value of
0.6V up to the input voltage. The output voltage value is given by:
Equation 4
OVP (Overvoltage Protection)
The device has an internal overvoltage protection circuit to protect the load.
If the voltage at the feedback pin goes higher than an internal threshold set 10% (typ) higher
than the reference voltage, the low side power MOSFET is turned on until the feedback
voltage goes lower than the reference one.
During the overvoltage circuit intervention, the zero crossing comparator is disabled so that
the device is also able to sink current.
Thermal shutdown
The device has also a thermal shutdown protection activated when the junction temperature
reaches 150°C. In this case both the high side MOSFET and the low side one are turned
off. Once the junction temperature goes back lower than 95°C, the device restarts the
normal operation.
V
OUT
=
0.6
⋅
⎛
⎝
1
+
R
------ -
R
Additional features and protections
2
1
⎞
⎠
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