L6730TR STMicroelectronics, L6730TR Datasheet - Page 25

• Manufacturer Part Number: L6730TR
• Description: IC CTRLR ADJ STEP DOWN 20-TSSOP
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L6730TR

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: Adj to 0.6V
• Frequency - Switching: 100kHz ~ 1MHz
• Voltage - Input: 1.8 ~ 14 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP Exposed Pad, 20-eTSSOP, 20-HTSSOP
• Output Voltage: 0.6 V
• Input Voltage: 1.8 V to 14 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• For Use With: 497-5868 - EVAL BOARD 30A 400KHZ L6730497-5501 - EVAL BOARD FOR L6730XX
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 497-5098-2

L6730 - L6730B
Device description
enters in HICCUP mode (L6730): the high-side and low-side MOSFET(s) are turned off, the
soft-start capacitor is discharged with a constant current of 10 µA and when the voltage at
the SS pin reaches 0.5 V 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
ON
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 Ton can’t be less than masking time plus propagation delay (see
Chapter 5.9: Adjustable
masking time on page
27) because during the masking time the peak-current-protection is
disabled. In case of very hard short circuit, even with this short T
, the current could
ON
escalate. The valley-current-protection 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:
−
Vin
Vout
=
+
⋅
(4)
I
I
T
MAX
VALLEY
ON
,
MIN
L
In constant current protection a current control loop limits the value of the error amplifier’s
output (comp), in order to avoid its saturation and thus recover faster when the output
returns in regulation.
Figure 19
shows the behaviour of the device during an over current
condition that persists also in the soft-start phase.
Figure 19. Constant current and hiccup mode during an OCP (L6730)
VSS
VCOMP
I
L
Using the L6730B there is the possibility to set the constant-current-protection also after the
soft-start. The following figures show the behaviour of the L6730B during an overcurrent
event.
Figure 20
shows the intervention of the peak OCP: the high-side MOSFET(s) is turned-off
when the current exceeds the OCP threshold. In this way the duty-cycle is reduced, the
V
is reduced and so the maximum current can be fixed even if the output current is
OUT
escalating.
Figure 21
shows the limit of this protection: the on-time can be reduced only to
the masking time and, if the output current continues to increase, the maximum current can
increase too. Notice how the Vout remains constant even if the output current increases
because the on-time cannot be reduced anymore.
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