L5983 STMicroelectronics, L5983 Datasheet - Page 13

• Manufacturer Part Number: L5983
• Description: IC REG SW STEP DOWN 1.5A 8VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5983

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1.5A
• Frequency - Switching: 250kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• Output Voltage: 3 V
• Output Current: 1.5 A
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 220 KHz to 275 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• Low Dropout Operation: 100 % duty cycle
• For Use With: 497-6386 - BOARD EVAL FOR L5983
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L5983
4.4
Overcurrent protection
The L5983 implements the overcurrent protection sensing current flowing through the power
MOSFET. Due to the noise created by the switching activity of the power MOSFET, the
current sensing is disabled during the initial phase of the conduction time. This avoids an
erroneous detection of a fault condition. This interval is generally known as “masking time”
or “blanking time”. The masking time is about 200 ns.
When the overcurrent is detected, two different behaviors are possible depending on the
operating condition.
1.
2.
So the overcurrent protection can be summarized as a “hiccup” intervention when the output
is in regulation and a constant current during the soft-start phase.
If the output is shorted to ground when the output voltage is in regulation, the overcurrent is
triggered and the device starts cycling with a period of 2048 clock cycles between “hiccup”
(power MOSFET off and no current to the load) and “constant current” with very short ON
time and with reduced switching frequency (up to one eighth of normal switching frequency).
See
Figure 32
Output voltage in regulation. When the overcurrent is sensed, the power MOSFET is
switched off and the internal reference (V
error amplifier, is set to zero and kept in this condition for a soft-start time (T
clock cycles). After this time, a new soft-start phase takes place and the internal
reference begins ramping (see
Soft-start phase. If the overcurrent limit is reached, the power MOSFET is turned off
implementing the pulse by pulse overcurrent protection. During the soft-start phase,
under the overcurrent condition, the device can skip pulses in order to keep the output
current constant and equal to the current limit. If, at the end of the “masking time”, the
current is higher than the overcurrent threshold, the power MOSFET is turned off and it
skips one pulse. If, at the next switching on at the end of the “masking time”, the current
is still higher than the threshold, the device skips two pulses. This mechanism is
repeated and the device can skip up to seven pulses. While, if at the end of the
“masking time” the current is lower than the overcurrent threshold, the number of
skipped cycles is decreased by one unit. At the end of the soft-start phase the output
voltage is in regulation and if the overcurrent persists, the behavior explained above
takes place (see
for short-circuit behavior.
Figure
8.b).
Doc ID 13005 Rev 7
Figure
8.a).
REF
), that biases the non-inverting input of the
Functional description
SS
, 2048
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