MIC24045 Datasheet, PDF (33/46 Pages) Microchip Technology – I2C Programmable, 4.5V-19V Input, 5A Step-Down Converter

For polarized output capacitor, compensator pole
placement at the ESR zero frequency is achieved, as
shown in Equation 7-20 below:
EQUATION 7-20:
C_C2 = -C---------_O-------_U-------RT-------_C-------₁----E----1----S--------R-------_–-----C-------1--_C------₁--
For ceramic output capacitor, compensator pole place-
ment at N × f_XO (N  5, N × f_{XO <} f_S) is achieved, as
detailed in Equation 7-21:
EQUATION 7-21:
C_C2
=
-------------------------------1--------------------------------
2

R_C1

N

f_XO
–
----1-----
C_C1
7.8 Output Voltage Soft-Start Rate
The MIC24045 features internal, I²C programmable
soft-start, such that the output voltage can be smoothly
increased to the target regulation voltage. The soft-start
rate given in the Electrical Characteristics refers to the
error amplifier reference, and therefore the effective
soft-start rate value seen at the output of the module
has to be scaled according to the internal feedback
divider attenuation values listed in Table 7-2. To calcu-
late the effective output voltage soft-start slew rate
SS_SR_OUT, based on the particular output voltage set-
ting and the reference soft-start slew rate SS_SRx
(x = 0, 1, 2, 3 depending on selection), use the follow-
ing formula:
EQUATION 7-22:
where:
SS_SR_OUT = A  SS_SRx
A = amplification (see Table 7-2 for A values.)
MIC24045
7.9 Minimum T_ON and Minimum T_OFF
Limitations
The valley current-mode control method utilized in the
MIC24045 allows very small minimum controllable ON
time (around 26 ns), so that it is possible to convert
from 19V down to very low voltages at high frequency.
Note that the high-side current limit circuit may not be
able to detect an overcurrent event if the ON time is
below the high side switch current limit leading edge
blanking time (LEB, see Electrical Characteristics).
Conversely, some minimum OFF time is needed for
valley current-mode modulator operation. This
T_OFF(MIN) specification (see Electrical Characteristics)
may dictate a limit on the maximum attainable output
voltage for a given V_IN voltage. The maximum
attainable output voltage (at no load) is calculated as
follows:
EQUATION 7-23:
V_OUT,max = V_IN  1 – f_S  T_OFF(MIN)
It is advisable to use a safe headroom margin against
the calculated value of V_OUT,max for DC load and good
dynamic performance.
 2016 Microchip Technology Inc.
DS20005568A-page 33