Datasheet

DS_DCT12S0A0S03NFA_11142013
13
When an analog voltage is applied to the SEQ pin, the
output voltage tracks this voltage until the output reaches
the set-point voltage. The final value of the SEQ voltage
must be set higher than the set-point voltage of the
module. The output voltage follows the voltage on the
SEQ pin on a one-to-one basis. By connecting multiple
modules together, multiple modules can track their output
voltages to the voltage applied on the SEQ pin.
For proper voltage sequencing, first, input voltage is
applied to the module. The On/Off pin of the module is
left unconnected (or tied to GND for negative logic
modules or tied to VIN for positive logic modules) so that
the module is ON by default. After applying input voltage
to the module, a minimum 10msec delay is required
before applying voltage on the SEQ pin. This delay gives
the module enough time to complete its internal power-up
soft-start cycle. During the delay time, the SEQ pin
should be held close to ground (nominally 50mV ± 20
mV). This is required to keep the internal op-amp out of
saturation thus preventing output overshoot during the
start of the sequencing ramp. By selecting resistor R1
(see Figure. 39) according to the following equation









05.0
24950
1
Vin
R
Figure 38: Sequential Start-up
The voltage at the sequencing pin will be 50mV when
the sequencing signal is at zero.
FEATURE DESCRIPTIONS (CON.)
Voltage Margining
Output voltage margining can be implemented in the DCT
modules by connecting a resistor, R margin-up, from the Trim
pin to the ground pin for margining-up the output voltage
and by connecting a resistor, Rmargin-down, from the Trim pin
to the output pin for margining-down. Figure 37 shows the
circuit configuration for output voltage margining. If
unused, leave the trim pin unconnected. A calculation tool
is available from the evaluation procedure which
computes the values of Rmargin-up and Rmargin-down for a
specific output voltage and margin percentage.
Vo
On/Off
Vin
GND
Trim
Q2
Q1
Rmargin-up
Rmargin-down
Rtrim
Figure 37: Circuit configuration for output voltage margining
Output Voltage Sequencing
The DCT 12V 3A modules include a sequencing feature,
EZ-SEQUENCE that enables users to implement various
types of output voltage sequencing in their applications.
This is accomplished via an additional sequencing pin.
When not using the sequencing feature, either tie the SEQ
pin to VIN or leave it unconnected.