MIC24046-H Datasheet, PDF (13/24 Pages) Micrel Semiconductor – Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter

Micrel, Inc.
Application Information
Programming Start-Up Delay and External UVLO
The EN/DLY pin allows programming of an external start-
up delay. In this case, the driver for the EN/DLY pin
should be an open-drain/open-collector type as shown in
Figure 4:
MIC24046-H
The programmed V_IN UVLO threshold V_{IN_RISE} is given by:
V_{IN _ RISE}
=
EN _ R × 1+

R2 _{ − EN _ I × R2}
R1 _
Eq. 2
Figure 4. Programmable Start-Up Delay Function
The start-up delay is the delay time from the OFF falling
edge to the assertion of the enable power delivery signal
and can be calculated as shown in Equation 1:
t_{SU _ DLY}
=
EN _ R × C_DLY
EN _ I
Eq. 1
where:
EN_R = 1.21V
EN_I = 2µA
C_DLY = Delay programming external capacitor
The EN/DLY pin can also be used to program an UVLO
threshold for power delivery by means of an external
resistor divider, as described in the following Figure 5.
where:
EN_R = 1.21V
EN_I = 2µA
R1 and R2 = External resistors.
To desensitize the V_IN UVLO threshold against variations
of the pull-up current EN_I, it is recommended to run the
R1 − R2 voltage divider at a significantly higher current
level than the EN_I current.
The corresponding V_IN UVLO hysteresis VIN_HYS is
calculated as follows:
V_{IN _ HYS}
= 150mV
⋅
_{1 +}

R2 
R1 _
Eq. 3
Similar calculations also apply to the internal LDO
activation threshold.
Setting the Switching Frequency
The MIC24046-H switching frequency can be
programmed using FREQ as shown in Table 1:
Table 1. Switching Frequency Settings
FREQ
Frequency
Hi-Z (open)
400 kHz
0 (GND)
565 kHz
1 (VDDA)
790 kHz
Figure 5. Programmable External UVLO Function
July 7, 2015
13
Revision 1.1