SC403MLTRT Semtech, SC403MLTRT Datasheet - Page 20

• Manufacturer Part Number: SC403MLTRT
• Manufacturer: Semtech

Specifications of SC403MLTRT

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Applications Information (continued)
Output Over-Voltage Protection
Over-voltage protection becomes active as soon as the
device is enabled. The threshold is set at 750mV + 20%
(900mV). When V
high and the low-side MOSFET is turned on. DL remains
high and the controller remains off, until the EN/PSV input
is toggled or VDD is cycled. There is a 5μs delay built into
the OVP detector to prevent false transitions. PGOOD is
also low after an OVP event.
Output Under-Voltage Protection
When V
562.5mV) for eight consecutive switching cycles, the
switcher is shut off and the DH and DL drives are pulled
low to tri-state the MOSFETs. The controller stays off until
EN/PSV is toggled or VDD is cycled.
VDD UVLO, and POR
UVLO (Under-Voltage Lock-Out) circuitry inhibits switch-
ing and tri-states the DH/DL drivers until V
3.0V. An internal POR (Power-On Reset) occurs when V
exceeds 3.0V, which resets the fault latch and soft-start
counter to prepare for soft-start. The SC403 then begins a
soft-start cycle. The PWM will shut off if VDD falls below
2.4V.
LDO Regulator
SC403 has an option to bias the switcher by using an inter-
nal LDO from V
internally. The output of the LDO is programmable by using
external resistors from the VDD pin to AGND. The feedback
pin (FBL) for the LDO is regulated to 750mV (see Figure 9).
The LDO output voltage is set by the following equation.
VDD
VLDO
FB
falls 25% below its nominal voltage (falls to
Figure 9 — LDO Voltage Divider
750
IN
mV
. The LDO output is connected to VDD
FB
exceeds the OVP threshold, DL latches
1
R
LDO1
R
R
LDO
LDO
1
2
R
LDO2
To FBL pin
DD
rises above
DD
A minimum 0.1μF capacitor referenced to AGND is
required along with a minimum 1.0μF capacitor refer-
enced to PGND to filter the gate drive pulses. Refer to the
layout guidelines section for component placement
suggestions.
LDO ENL Functions
The ENL input is used to control the internal LDO. When
ENL is low (grounded), the LDO is off. When ENL is above
the V
switcher is also enabled if EN/PSV and VDD meet the
thresholds.
The ENL pin also acts as the switcher UVLO (under-voltage
lockout) for the V
grammable via a resistor divider at the VIN, ENL and AGND
pins.
If the ENL pin transitions from high to low within 2 switch-
ing cycles and is less than 1V, then the LDO will turn off
but the switcher remains on. If the ENL goes below the V
UVLO threshold and stays above 1V, then the switcher will
turn off but the LDO remains on. The V
has a typical threshold of 2.6V on the V
falling edge threshold is 2.4V.
Note that it is possible to operate the switcher with the
LDO disabled, but the ENL pin must be below the logic
low threshold (0.4V maximum). In this case, the UVLO
function for the input voltage cannot be used. The table
below summarizes the function of the ENL and EN pins,
with respect to the rising edge of ENL.
high
high
high
low
low
low
EN
IN
UVLO threshold, the LDO is enabled and the
high, < 2.6V
high, < 2.6V
high, > 2.6V
high, > 2.6V
low, < 0.4V
low, < 0.4V
ENL
IN
supply. The V
LDO status
off
off
on
on
on
on
IN
UVLO voltage is pro-
IN
Switcher status
IN
rising edge. The
UVLO function
SC403
off
on
off
off
off
on
20
IN