UQQ-12 Datasheet, PDF (14/18 Pages) Murata Manufacturing Co., Ltd. – Wide Input Range Single Output DC-DC Converters

UQQ Series
Wide Input Range Single Output DC-DC Converters
Start-Up Threshold and Undervoltage Shutdown
Under normal start-up conditions, the UQQ Series will not begin to regulate
properly until the ramping input voltage exceeds the Start-Up Threshold. Once
operating, devices will turn off when the applied voltage drops below the
Undervoltage Shutdown point. Devices will remain off as long as the undervolt-
age condition continues. Units will automatically re-start when the applied
voltage is brought back above the Start-Up Threshold. The hysteresis built into
this function avoids an indeterminate on/off condition at a single input voltage.
See Performance/Functional Specifications table for actual limits.
should not be allowed to exceed 0.5V. Consider using heavier wire if this drop
is excessive.
Sense is connected at the load and corrects for resistive errors only. Be careful
where it is connected. Any long, distributed wiring and/or significant inductance
introduced into the Sense control loop can adversely affect overall system stabil-
ity. If in doubt, test the application, and observe the DC-DC’s output transient
response during step loads. There should be no appreciable ringing or oscilla-
tion. You may also adjust the output trim slightly to compensate for voltage loss
in any external filter elements. Do not exceed maximum power ratings.
Start-Up Time
The VIN to VOUT Start-Up Time is the interval between the point at which a ramp-
ing input voltage crosses the Start-Up Threshold voltage and the point at which
the fully loaded output voltage enters and remains within its specified accuracy
band. Actual measured times will vary with input source impedance, external
input capacitance, and the slew rate and final value of the input voltage as it
appears to the converter. The On/Off to VOUT start-up time assumes that the
converter is turned off via the Remote On/Off Control with the nominal input
voltage already applied.
On/Off Control
The primary-side, Remote On/Off Control function (pin 2) can be specified to
operate with either positive or negative polarity. Positive-polarity devices ("P"
suffix) are enabled when pin 2 is left open or is pulled high. Positive-polarity
devices are disabled when pin 2 is pulled low or left open (with respect to
–Input). Negative-polarity devices are off when pin 2 is high and on when pin 2
is pulled low or grounded. See Figure 4.
Dynamic control of the remote on/off function is best accomplished with a
mechanical relay or an open-collector/open-drain drive circuit (optically iso-
lated if appropriate). The drive circuit should be able to sink appropriate current
(see Performance Specifications) when activated and withstand appropriate
voltage when deactivated.
1 +VIN
+5V
2
ON/OFF
CONTROL
EQUIVALENT CIRCUIT FOR
POSITIVE AND NEGATIVE
LOGIC MODELS
CONTROL
3 _–VIN
REF
COMMON
Current Limiting (Power limit with current mode control)
As power demand increases on the output and enters the specified “limit
inception range” (current in voltage mode and power in current mode) limiting
circuitry activates in the DC-DC converter to limit/restrict the maximum current
or total power available. In voltage mode, current limit can have a “constant or
foldback” characteristic. In current mode, once the current reaches a certain
range the output voltage will start to decrease while the output current con-
tinues to increase, thereby maintaining constant power, until a maximum peak
current is reached and the converter enters a “hiccup” (on off cycling) mode of
operation until the load is reduced below the threshold level, whereupon it will
return to a normal mode of operation. Current limit inception is defined as the
point where the output voltage has decreased by a pre-specified percentage
(usually a 2% decrease from nominal).
Short Circuit Condition (Current mode control)
The short circuit condition is an extension of the “Current Limiting” condition.
When the monitored peak current signal reaches a certain range, the PWM
controller’s outputs are shut off thereby turning the converter “off.” This is
followed by an extended time out period. This period can vary depending on
other conditions such as the input voltage level. Following this time out period,
the PWM controller will attempt to re-start the converter by initiating a “normal
start cycle” which includes softstart. If the “fault condition” persists, another
“hiccup” cycle is initiated. This “cycle” can and will continue indefinitely until
such time as the “fault condition” is removed, at which time the converter will
resume “normal operation.” Operating in the “hiccup” mode during a fault
condition is advantageous in that average input and output power levels are
held low preventing excessive internal increases in temperature.
Thermal Shutdown
UQQ converters are equipped with thermal-shutdown circuitry. If the internal
temperature of the DC-DC converter rises above the designed operating
temperature (See Performance Specifications), a precision temperature sensor
will power down the unit. When the internal temperature decreases below the
threshold of the temperature sensor, the unit will self start.
Figure 4. Driving the Remote On/Off Control Pin
Sense Input
Note: The sense and VOUT lines are internally connected through low-value
resistors. Nevertheless, if sense is not used for remote regulation, the user
must connect + sense to + VOUT and -sense to -VOUT at the converter pins.
Sense is intended to correct small output accuracy errors caused by the
resistive ohmic drop in output wiring as output current increases. This output
drop (the difference between Sense and VOUT when measured at the converter)
Output Overvoltage Protection
The output voltage is monitored for an overvoltage condition via magnetic cou-
pling to the primary side. If the output voltage rises to a fault condition, which
could be damaging to the load circuitry (see Performance Specifications), the
sensing circuitry will power down the PWM controller causing the output volt-
age to decrease. Following a time-out period the PWM will restart, causing the
output voltage to ramp to its appropriate value. If the fault condition persists,
and the output voltages again climb to excessive levels, the overvoltage
circuitry will initiate another shutdown cycle. This on/off cycling is referred to
as “hiccup” mode.
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MDC_UQQ.D03 Page 14 of 18