l6730cqtr STMicroelectronics, l6730cqtr Datasheet - Page 29

• Manufacturer Part Number: l6730cqtr
• Description: Adjustable Step-down Controller With Synchronous Rectification
• Manufacturer: STMicroelectronics

L6730C - L6730D
5.14.2 No-sink at zero current operation
Figure 24. 12V -> 3.3V@0A in no-sink
The L6730C can work in no-sink mode. If output current is zero the converter skip some pulses
and works with a lower switching frequency. Between two pulses can pass a relatively long time
(say 200-300µs) during which there’s no switching activity and the current into the inductor is
zero. In this condition the phase node is at the output voltage and in some cases this is not
enough to keep the bootstrap cap charged. For example, if Vout is 3.3V the voltage across the
bootstrap cap is only 1.7V. The high-side MOSFET cannot be effectively turned-on and the
regulation can be lost. Thanks to the “bootstrap anti-discharging system” the bootstrap cap is
always kept charged. The following picture shows the behaviour of the device in the following
conditions: 12V 3.3V@0A.
It can be observed that between two pulses trains the low-side is turned-on in order to keep the
bootstrap cap charged.
Minimum Bootstrap Voltage
Pulse train
I
L
V
Device description
PHASE
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