MIC24045 Datasheet, PDF (19/46 Pages) Microchip Technology – I2C Programmable, 4.5V-19V Input, 5A Step-Down Converter

4.3 Enable (EN)
The EN pin starts/stops the power delivery to the out-
put. It does not turn off the internal LDO. The EN pin
does not act as a Reset signal for the I²C registers, only
the V_DDA UVLO circuit does.
Rising threshold is a precise 1.21V±70 mV. A 135 mV
typical hysteresis prevents chattering due to switching
noise and/or slow edges. A 2 µA typical pull-down cur-
rent with ±1 µA accuracy prevents unwanted start-ups
if the EN pin is momentarily floating. To achieve auto-
matic turn-on as soon as enough voltage is present,
connect EN to V_DDA.
4.4 Power Good (PG)
PG is an open-drain output. For asserting a logic HIGH
level, PG requires an external resistor connected to a
pull-up voltage (V_{PU_PG}), which should not exceed
5.5V.
PG is asserted with a typical delay of 0.45 ms when the
output voltage (OUTSNS) reaches 92.5% of its target
regulation voltage. PG is de-asserted with a typical
delay of 80 µs when the output voltage falls below 90%
of its target regulation voltage. The PG falling delay
acts as a de-glitch timer against very short spikes. The
PG output is always immediately de-asserted when the
EN pin is below the power delivery enable threshold
(EN_R/EN_F). The pull-up resistor should be large
enough to limit the PG pin current to below 2 mA. The
PG is in a defined state once the V_DDA voltage is
greater than about 1V, but with reduced current sinking
capability.
The PG is also immediately de-asserted (with no delay)
whenever an undervoltage condition on V_DDA is
detected, or in thermal shutdown.
4.5 Inductor (LX) and Bootstrap (BST)
The external inductor is connected to LX. The high-side
MOSFET driver circuit is powered between BST and
LX by means of an external capacitor (typically 100 nF)
that is replenished from rail V_DDP during the low-side
MOSFET ON-time. The bootstrap diode is internal.
4.6 Output Sensing (OUTSNS) and
Compensation (COMP)
OUTSNS should be connected exactly to the desired
point-of-load regulation, avoiding parasitic resistive
drops. The impedance seen into OUTSNS is high (tens
of k or more, depending on the selected output volt-
age value), therefore its loading effect is typically neg-
ligible. OUTSNS is also used by the slope
compensation generator.
COMP is the connection for the external compensation
network. COMP is driven by the output of the transcon-
ductance error amplifier. Care must be taken to return
the compensation network ground directly to A_GND.
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MIC24045
4.7 Soft-Start
The MIC24045 features four different I²C-selectable
soft-start slew-rate values (0.16V/ms, 0.38V/ms,
0.76V/ms and 1.5V/ms). See the section Section 5.0
“Registers Maps and I2C Programmability” for the
value vs. code mapping. The internal reference is
ramped up at the selected rate. Note that this is the
internal reference soft-start slew rate and that the
actual slew rate seen at the output should take into
account the internal divider attenuation, as detailed in
the Section 7.0 “Application Information”.
4.8 Start-Up Delay
The MIC24045 features eight different I²C-selectable
start-up delays (from 0 ms to 10 ms). These represent
the added delays from the EN rising edge to the begin-
ning of the power delivery (soft-start). See the section
Section 5.0, Registers Maps and I2C Programma-
bility for the value vs. code mapping.
4.9 Switching Frequency
The MIC24045 features eight different I²C-selectable
switching frequencies from 310 kHz to 1200 kHz. See
Section 5.0 “Registers Maps and I2C Programma-
bility” for the value vs. code mapping. Also pay atten-
tion to voltage conversion ratio limitations due to
minimum T_ON and T_OFF, as stated in Section 7.0
“Application Information”.
4.10 Pre-Biased Output Start-Up
The MIC24045 is designed to achieve safe start-up into
a pre-biased output without discharging the output
capacitors.
4.11 Thermal Warning and Thermal
Shutdown
The MIC24045 has a thermal shutdown protection that
prevents operation at excessive temperature. The ther-
mal shutdown threshold is typically set at +160°C with
a hysteresis of +25°C.
The MIC24045 features a Thermal Warning flag that is
readable through the I²C interface (register polling is
needed). The Thermal Warning flag signals the
approaching of thermal shutdown, so that appropriate
system-level countermeasures can be undertaken.
Note that a thermal shutdown event will not disable the
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still be read throughout the duration of the thermal shut-
down.
DS20005568A-page 19