L6731BTR STMicroelectronics, L6731BTR Datasheet - Page 15

• 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
Figure 8.
The device realizes the over-current-protection (OCP) sensing the current both on the high-
side MOSFET(s) and the low-side MOSFET(s) and so 2 current limit thresholds can be set (see
OCH pin and OCL pin in
●
●
The Peak Current Protection is active when the high-side MOSFET(s) is turned on, after a
masking time of about 100ns. The valley-current-protection is enabled when the low-side
MOSFET(s) is turned on after a masking time of about 400ns. If, when the soft-start phase is
completed, an over current event occurs during the on time (peak-current-protection) or during
the off time (valley-current-protection) the device enters in HICCUP mode: the high-side and
low-side MOSFET(s) are turned off, the soft-start capacitor is discharged with a constant
current of 10µA and when the voltage at the SS pin reaches 0.5V the soft-start phase restarts.
During the soft-start phase the OCP provides a constant-current-protection. If during the T
the OCH comparator triggers an over current the high-side MOSFET(s) is immediately turned
off (after the masking time and the internal delay) and returned on at the next pwm cycle. The
limit of this protection is that the T
because during the masking time the peak-current-protection is disabled. In case of very hard
short circuit, even with this short T
is very helpful in this case to limit the current. If during the off-time the OCL comparator triggers
an over current, the high-side MOSFET(s) is not turned on until the current is over the valley-
current-limit. This implies that, if it is necessary, some pulses of the high-side MOSFET(s) will
be skipped, guaranteeing a maximum current due to the following formula:
In constant current protection a current control loop limits the value of the error amplifier output
(comp), in order to avoid its saturation and thus recover faster when the output returns in
regulation.
persists also in the soft-start phase.
OVP: the low-side MOSFET is turned-on in advance.
Peak Current Limit
Valley Current Limit
Figure 9.
shows the behaviour of the device during an over current condition that
I
Table 3.
MAX
I
VALLEY
Pins function):
ON
ON
can't be less than masking time plus propagation delay
, the current could escalate. The valley-current-protection
Vin
L
Vout
109%
T
ON
,
MIN
V
V
LGate
OUT
FB
Device description
15/24
ON