L6731BTR STMicroelectronics, L6731BTR Datasheet - Page 13

• Manufacturer Part Number: L6731BTR
• Description: IC CTRLR ADJ STEP DOWN 16-TSSOP
• Manufacturer: STMicroelectronics

Specifications of L6731BTR

• Applications: Controller, DDR
• Voltage - Input: 1.8 ~ 14 V
• Number Of Outputs: 1
• Voltage - Output: Adjustable down to 0.6V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP Exposed Pad, 16-eTSSOP, 16-HTSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-5099-2

L6731B
5.7
The output of the error amplifier is clamped with this voltage (Vss) until it reaches the
programmed value. No switching activity is observable if V
MOSFETs are off. When Vss is between 0.5V and 1.1V the low-side MOSFET is turned on
because the comp signal is lower than the valley of the triangular wave and so the duty-cycle is
0%. As V
MOSFET begins to switch and the output voltage starts to increase. The L6731B can always
sink or source current. If an over current is detected during the soft-start phase, the device
provides a constant-current-protection. In this way, in case of short soft-start time and/or small
inductor value and/or high output capacitors value and so, in case of high ripple current during
the soft-start, the converter can start in any case, limiting the current (see
protections) but not entering in HICCUP mode. During normal operation, if any under-voltage is
detected on one of the two supplies, the SS pin is internally shorted to GND and so the SS
capacitor is rapidly discharged.
Driver section
The high-side and low-side drivers allow using different types of power MOSFETs (also multiple
MOSFETs to reduce the R
supplied by V
time control avoids MOSFETs cross-conduction maintaining very short dead time duration in
the range of 20ns. The control monitors the phase node in order to sense the low-side body
diode recirculation. If the phase node voltage is less than a certain threshold (-350mV typ.)
during the dead time, it will be reduced in the next PWM cycle. The predictive dead time control
doesn’t work when the high-side body diode is conducting because the phase node doesn’t go
negative. This situation happens when the converter is sinking current for example and, in this
case, an adaptive dead time control operates.
SS
reaches 1.1V (i.e. the oscillator triangular wave inferior limit) even the high-side
CCDR
while the high-side driver is supplied by the BOOT pin. A predictive dead
DS(on)
), maintaining fast switching transitions. The low-side driver is
SS
is lower than 0.5V and both
5.8: Monitoring and
Device description
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