OKX
T/10 & T/16-D12 Series
Adjustable DOSA 10/16-Amp SIP DC/DC Converters
of the output can cause the overvoltage protection circuit to activate and shut
down the output.
Power derating of the converter is based on the combination of maximum
output current and the highest output voltage at the ouput pins. Therefore the
designer must insure:
(Vout at pins) x (Iout) ≤ (Max. rated output power)
Remote On/Off Control
On the input side, a remote On/Off Control can be ordered with either polarity.
Please refer to the Connection Diagram on page 1 for On/Off connections.
Positive: Standard models are enabled when the On/Off pin is left open or
is pulled high to +Vin with respect to –Vin. An internal bias current causes the
open pin to rise to +Vin. Therefore, the On/Off control can be disconnected if
the converter should always be on. Positive-polarity devices are disabled when
the On/Off is grounded or brought to within a low voltage (see Specifications)
with respect to –Vin.
Negative: Optional negative-polarity devices are on (enabled) when the On/
Off is grounded or brought to within a low voltage (see Specifications) with
respect to –Vin. The device is off (disabled) when the On/Off is left open or is
pulled high to +Vin with respect to –Vin.
Dynamic control of the On/Off function must sink appropriate signal current
when brought low and withstand appropriate voltage when brought high.
Be aware too that there is a finite time in milliseconds (see Specifications)
between the time of On/Off Control activation and stable, regulated output. This
time will vary slightly with output load type and current and input conditions.
Output Capacitive Load
These converters do not require external capacitance added to achieve rated
specifications. Users should only consider adding capacitance to reduce
switching noise and/or to handle spike current load steps. Install only enough
capacitance to achieve your noise and surge response objectives. Excess
external capacitance may cause regulation problems and possible oscillation
or instability. Proper wiring of the Sense inputs will improve these factors under
capacitive load.
The maximum rated output capacitance and ESR specification is given for a
capacitor installed immediately adjacent to the converter. Any extended output
wiring, smaller wire gauge or less ground plane may tolerate somewhat higher
capacitance. Also, capacitors with higher ESR may use a larger capacitance.
Sequence/Track Input (Optional)
After external input power is applied and the converter stabilizes, a high
impedance Sequence/Track input pin accepts an external analog voltage
referred to -Vin. The output power voltage will then track this Sequence/
Track input at a one-to-one ratio up to the nominal set point voltage for that
converter. This Sequencing input may be ramped, delayed, stepped or other-
wise phased as needed for the output power, all fully controlled by the user’s
external circuits. As a direct input to the converter’s feedback loop, response to
the Sequence/Track input is very fast (milliseconds).
Operation
To use the Sequence/Track pin after power start-up stabilizes, apply a rising
external voltage to the Sequence/Track input. As the voltage rises, the output
voltage will track the Sequence/Track input (gain = 1). The output voltage
will stop rising when it reaches the normal set point for the converter. The
Sequence/Track input may optionally continue to rise without any effect on
the output. Keep the Sequence/Track input voltage below the converter’s input
supply voltage.
Use a similar strategy on power down. The output voltage will stay constant
until the Sequence/Track input falls below the set point.
Guidelines for Sequence/Track Applications
[1] Leave the converter’s On/Off Enable control in the On setting. Normally,
you should just leave the On/Off pin open.
[2] Allow the converter to stabilize (typically less than 20 mS after +Vin
power on) before raising the Sequence/Track input. Also, if you wish to have
a ramped power down, leave +Vin powered all during the down ramp. Do not
simply shut off power.
[3] If you do not plan to use the Sequence/Track pin, leave it open.
[4] Observe the Output slew rate relative to the Sequence/Track input. A
rough guide is 2 Volts per millisecond maximum slew rate. If you exceed this
slew rate on the Sequence/Track pin, the converter will simply ramp up at it’s
maximum output slew rate (and will not necessarily track the faster Sequence/
Track input).
The reason to carefully consider the slew rate limitation is in case you want
two different POL’s to precisely track each other.
[5] Be aware of the input characteristics of the Sequence/Track pin. The high
input impedance affects the time constant of any small external ramp capaci-
tor. And the bias current will slowly charge up any external caps over time if
they are not grounded.
[6] Allow the converter to eventually achieve its full rated setpoint output
voltage. Do not remain in ramp up/down mode indefinitely. The converter is
characterized and meets all its specifications only at the setpoint voltage (plus
or minus any trim voltage).
[7] The Sequence/Track is a sensitive input into the feedback control loop
of the converter. Avoid noise and long leads on this input. Keep all wiring very
short. Use shielding if necessary.
Pre-Biased Startup
Some sections have external power already partially applied (possibly because
of earlier power sequencing) before POL power up. Or leakage power is pres-
ent so that the DC/DC converter must power up into an existing output voltage.
This power may either be stored in an external bypass capacitor or supplied by
an active source. These converters include a pre-bias startup mode to prevent
initialization problems.
This “pre-biased” condition can also occur with some types of program-
mable logic or because of blocking diode leakage or small currents passed
through forward biased ESD diodes. This feature is variously called “mono-
tonic” because the voltage does not decay or produce a negative transient
once the input power is applied and startup begins.
www.murata-ps.com
Technical enquiries
email: sales@murata-ps.com, tel:
+1 508 339 3000
MDC_MDC_OKX2_T10T16.A03
Page 8 of 15
MURATA-PS [ MURATA POWER SOLUTIONS INC. ]
