L6727 STMicroelectronics, L6727 Datasheet - Page 13

• Manufacturer Part Number: L6727
• Description: IC PWM CTLR SGL PHASE SO-8
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6727

• Internal Switch(s): No
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: Adj to 0.8V
• Frequency - Switching: 300kHz
• Voltage - Input: 1.5 ~ 12 V
• Operating Temperature: -20°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Output Current: 1.5 A
• Input Voltage: - 0.3 V to + 15 V
• Switching Frequency: 300 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 80 %
• For Use With: 497-8266 - BOARD EVAL BASED ON L6727497-6258 - BOARD EVAL 1PH STPDWN CONV L6727
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

L6727
7
7.1
Overcurrent protection
The overcurrent feature protects the converter from a shorted output or overload, by sensing
the output current information across the low side MOSFET drain-source on-resistance,
R
expensive and space-consuming sense resistors.
The low side R
node when LS MOSFET is turned on with the programmed OCP threshold voltage,
internally held. If the monitored voltage drop (GND to PHASE) exceeds this threshold, an
overcurrent event is detected. If two overcurrent events are detected in two consecutive
switching cycles, the protection will be triggered and the device will turn off both LS and HS
MOSFETs for 2048 clock cycles (plus internal SS remaining time, if triggered during a SS
phase); then it will begin a new soft-start.
If the overcurrent condition is not removed, the continuous fault will cause L6727 to go into a
hiccup mode with a typical period of 13.6 ms
and very low power dissipation.
Overcurrent threshold setting
When supplied with VCC = 5 V, L6727 allows to easily program an overcurrent threshold
ranging from 50 mV to 500 mV, simply by adding a resistor (R
VCC.
During a short period of time (5.5 ms - 6.5 ms) following the first enable (given VCC over
UVLO threshold), an internal 60µA current (I
voltage drop across R
COMP, divided by a factor 3, will be sampled and internally held by the device as Over
Current Threshold until next VCC cycling. Differential sensing versus VCC allows OCSET
procedure to be fully independent from VIN rail. The OC setting procedure overall time
length ranges from 5.5 ms to 6.5 ms, proportionally to the threshold being set.
Connecting an R
be:
R
If the voltage drop across R
inrush current and noise. This can result in a continuous OCP triggering and hiccup mode.
In this case, consider to increase R
In case R
threshold.
If the device is supplied with a VCC higher than 7 V, R
case, as soon as VCC rises over V
(internally fixed value).
See
dsON
OCSET
Figure 5
. This method reduces cost and enhances converter efficiency by avoiding the use of
values range from 2.5 kΩ to 25 kΩ.
OCSET
for OC threshold setting and soft start oscilloscope sample waveforms.
dsON
is not connected (and VCC = 5 V), the device will set the maximum
OCSET
current sense is implemented by comparing the voltage at the PHASE
OCSET
resistor between COMP and VCC, the programmed threshold will
OCSET
. This voltage drop, differentially sensed between VCC and
I
Doc ID 12933 Rev 4
OCth
is too low, the system will be very sensitive to start-up
CC_OC
OCSET
=
1
-- -
3
(8 V typ.), L6727 switches OC threshold to 400mV
value.
⋅
I
------------------------------------------- -
OCSET
OCSET
(Figure
R
) is sunk from COMP pin, determining a
dsON
5), guaranteeing safe load protection
⋅
OCSET
R
OCSET
must be not connected. In this
OCSET
Overcurrent protection
) between COMP and
13/34