FEATURE DESCRIPTIONS (CON.)
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. 34)
according to the following equation
This will result in the module sinking current if a pre-bias
voltage is present at the output of the module.
24950
R
1
½
Vin
0.05
The voltage at the sequencing pin will be 50mV when the
sequencing signal is at zero.
After the 10msec delay, an analog voltage is applied to the
SEQ pin and the output voltage of the module will track
this voltage on a one-to-one volt bases until the output
reaches the set-point voltage. To initiate simultaneous
shutdown of the modules, the SEQ pin voltage is lowered
in a controlled manner. The output voltage of the modules
tracks the voltages below their set-point voltages on a
one-to-one basis. A valid input voltage must be maintained
until the tracking and output voltages reach ground
potential.
When using the EZ-SEQUENCETM feature to control
start-up of the module, pre-bias immunity during startup is
disabled. The pre-bias immunity feature of the module
relies on the module being in the diode-mode during
start-up. When using the EZ-SEQUENCETM feature,
modules goes through an internal set-up time of 10msec,
and will be in synchronous rectification mode when the
voltage at the SEQ pin is applied.
Figure 34:
Circuit showing connection of the sequencing signal to
the SEQ pin.
Simultaneous
Simultaneous tracking (Figure 35) is implemented by
using the TRACK pin. The objective is to minimize the
voltage difference between the power supply outputs
during power up and down.
The simultaneous tracking can be accomplished by
connecting Vo
PS1
to the TRACK pin of PS2. Please note
the voltage apply to TRACK pin needs to always higher
than the Vo
PS2
set point voltage.
PS1
Vin
Vo
PS1
Vin
Vo
PS2
PS2
TRACK
On/Off
On/Off
Figure 35
Monotonic Start-up and Shutdown
The DCM 12A modules have monotonic start-up and
shutdown behavior for any combination of rated input
voltage, output current and operating temperature range.
DS_ DCM04S0A0S12PFA_10022013
E-mail: DCDC@delta.com.tw
http://www.deltaww.com/dcdc
P10
DELTA [ DELTA ELECTRONICS, INC. ]
