L6738A STMicroelectronics, L6738A Datasheet - Page 16

• Manufacturer Part Number: L6738A
• Description: Current Mode PWM Controllers Single-phase PWM Light Load EFF
• Manufacturer: STMicroelectronics

Specifications of L6738A

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Output voltage setting and protections
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Output voltage setting and protections
The L6738A is capable of precisely regulating an output voltage as low as 0.8 V. In fact, the
device comes with a fixed 0.8 V internal reference that guarantees the output regulated
voltage to be within ±0.5 % tolerance over line and temperature variations (excluding output
resistor divider tolerance, when present).
Output voltage higher than 0.8 V can be easily achieved by adding a resistor R
the FB pin and ground. Referring to
where V
The L6738A monitors the voltage at the VSEN pin and compares it to the internal reference
voltage in order to provide undervoltage and overvoltage protections, as well as PGOOD
signal. According to the level of VSEN, different actions are performed from the controller:
●
●
●
●
●
Protections are active also during soft-start (See
PGOOD
If the voltage monitored through VSEN exits from the PGOOD window limits, the device
de-asserts the PGOOD signal.
PGOOD is asserted at the end of the soft-start phase with 3x clock cycles delay.
Undervoltage protection (UV)
If the voltage at the VSEN pin drops below the UV threshold, the device turns off both
HS and LS MOSFETs, latching the condition. Cycle VCC or EN to recover.
UV is also active during SS acting as VIN detection protection. See description below.
Overvoltage protection (OV)
If the voltage at the VSEN pin rises over the OV threshold, overvoltage protection turns
off the HS MOSFET and turns on the LS MOSFET. The LS MOSFET is turned off as
soon as VSEN goes below Vref/2. The condition is latched, cycle VCC/EN to recover.
Note that, even if the device is latched, the device still controls the LS MOSFET and
can switch it on whenever VSEN rises above the OV threshold.
PreOVP protection
Monitors VSEN when IC is disabled. If VSEN surpasses the OV threshold, IC turns on
the low-side MOSFET to protect the load. On the EN rising edge, the protection is
disabled and the IC implements the SS procedure.
PreOVP is disabled when EN is high but the OV protection becomes operative.
VIN detection
UV Protection active during SS allows the IC to detect whether input voltage VIN is
present. If UV is triggered during the soft-start, it resets the SS procedure: the
controller re-implements the initial delay and re-ramps-up the reference with the same
SS timings described in
The UV protection is then avoiding that IC starts-up if VIN is not present.
REF
is 0.8 V.
Section
Doc ID 18134 Rev 1
V
OUT
Figure
5.
=
V
REF
1, the steady-state DC output voltage is:
⋅
⎛
⎝
Section
1
+
---------- -
R
R
OS
FB
⎞
⎠
5).
OS
between
L6738A