MIC24046-H Datasheet, PDF (10/24 Pages) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

Micrel, Inc.
Figure 1. EN/DLY Pin Functionality
The threshold for power delivery (EN_R) is a precise
1.21V ±70mV. A 150mV typical hysteresis prevents
chattering due to switching noise and/or slow edges.
A 2µA typical pull-up current with ±1µA accuracy permits
the implementation of a start-up delay by means of an
external capacitor. In this case, it is necessary to use an
open-drain driver to disable the MIC24046-H while
maintaining the start-up delay function.
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 100nF) that
is replenished from rail VDDP during the low-side
MOSFET ON-time. The bootstrap diode is internal.
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 kΩ),
therefore its loading effect is typically negligible.
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
transconductance error amplifier. Care must be taken to
return the compensation network ground directly to
AGND.
Soft-Start
The MIC24046-H internal reference is ramped up at a
0.45V/ms 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 Application Information
section.
MIC24046-H
Switching Frequency (FREQ)
The MIC24046-H features three different selectable
switching frequencies: 400kHz, 565kHz, and 790kHz.
Pre-Biased Output Start-Up
The MIC24046-H is designed to achieve safe start-up
into a pre-biased output without discharging the output
capacitors.
Thermal Shutdown
The MIC24046-H has thermal-shutdown protection that
prevents operation at excessive temperature. The
thermal-shutdown threshold is typically set at 160°C with
a hysteresis of 25°C.
Overcurrent Protection (ILIM) and Hiccup Mode
Short-Circuit Protection
The MIC24046-H features instantaneous cycle-by-cycle
current limit with current sensing both on the low-side and
high-side switches, and hiccup mode for prolonged
overloads or short-circuit conditions.
Low-side cycle-by-cycle protection detects the current
level of the inductor current during the low-side MOSFET
ON time. The high-side MOSFET turn-on is inhibited as
long as the low-side MOSFET current limit is above the
current-limit threshold level. The inductor current will
continue decaying until the current falls below the
threshold, then the high-side MOSFET will be enabled
again according to the duty cycle requirement from the
PWM modulator. The mechanism is illustrated in Figure
2.
Figure 2. Low-Side Cycle-by-Cycle Current-Limit Action
July 7, 2015
10
Revision 1.1