WPMDH1100601 / 171010601
MagI3C Power Module
VDRM – Variable Step Down Regulator Module
Note that high values of the CSS capacitance will cause more output voltage droop when a load transient goes across the
DCM-CCM boundary. Use equation (22) in the “LIGHT LOAD OPERATION” section (page 33) to find the DCM-CCM load
current boundary for the specific operating conditions. If a fast load transient response is desired for steps between DCM
and CCM mode the soft-start capacitor value should be less than 0.018μF. Note that the following conditions will reset the
soft-start capacitor by discharging the SS input to ground with an internal 200μA current sink:
1. The enable input being “pulled low”
2. Thermal shutdown condition
3. Overcurrent fault
4. Internal UVLO at input
Step 7 Optional: select enable divider, RENT, RENB (external UVLO)
The enable input provides a precise 1.18V reference threshold to allow a direct logic drive or connection to a voltage divider
from a higher voltage such as VIN. The enable input also incorporates 90mV (typ.) of hysteresis resulting in a falling threshold
of 1.09V. The maximum recommended voltage into the EN pin is 6.5V. For applications where the midpoint of the enable
divider exceeds 6.5V, a small zener diode can be added to limit this voltage.
The function of the RENT and RENB divider shown in the application block diagram is to allow the designer to choose an input
voltage below which the circuit will be disabled. This implements the feature of programmable external under voltage
lockout. This is often used in battery powered systems to prevent deep discharge of the system battery. It is also useful in
system designs for sequencing of output rails or to prevent early turn-on of the supply as the main input voltage rail rises at
power-up. Most systems will benefit by using the precision Enable threshold to establish a system under voltage lockout.
Without an external enable divider the device would attempt to turn on around VIN = 3.5V. In case of output voltages higher
than this turn on threshold, the VOUT follows the VIN as long as VIN<VOUT and it might not have a monotonic rise. However
many systems need a smooth rise in the supply voltage. Therefore the recommended approach is to choose an input UVLO
level that is higher than the target regulated output voltage. In case of sequencing supplies, the divider is connected to a rail
that becomes active earlier in the power-up cycle than the MagI³C power module output rail. The two resistors should be
chosen based on the following ratio:
RENT VUVLO (external)
=
– 1
(18)
RENB
1.18V
VUVLO (external) = User programmable voltage threshold to turn the module ON/OFF.
The EN pin is internally pulled up to VIN and can be left floating for always-on operation. However, it is good practice to use
the enable divider and turn on the regulator when VIN is close to reaching its nominal value. This will guarantee smooth start
up behavior and will prevent overloading the input supply.
we-online.com
Würth Elektronik eiSos GmbH & Co. KG – Data Sheet Rev. 1.0
© September 2017
29/54
WURTH [ WURTH ELEKTRONIK GMBH & CO. KG, GERMANY. ]
