Output Current Limiting

Current limiting inception is defined as the point at which full power falls

below the rated tolerance. See the Performance/Functional Specifica-

tions. Note particularly that the output current may briefly rise above its

rated value in normal operation as long as the average output power is

not exceeded. This enhances reliability and continued operation of your

application. If the output current is too high, the converter will enter the

short circuit condition.

Output Short Circuit Condition

When a converter is in current-limit mode, the output voltage will drop

as the output current demand increases. If the output voltage drops too

low (approximately 98% of nominal output voltage for most models), the

magnetically coupled voltage used to develop primary side voltages will

also drop, thereby shutting down the PWM controller. Following a time-out

period, the PWM will restart, causing the output voltage to begin ramping

up to its appropriate value. If the short-circuit condition persists, another

shutdown cycle will initiate. This rapid on/off cycling is called “hiccup

mode”. The hiccup cycling reduces the average output current, thereby

preventing excessive internal temperatures and/or component damage. A

short circuit can be tolerated indefinitely.

The “hiccup” system differs from older latching short circuit systems

because you do not have to power down the converter to make it restart.

The system will automatically restore operation as soon as the short circuit

condition is removed.

Remote On/Off Control

The remote On/Off Control can be ordered with either polarity. Please refer

to the Connection Diagram on page 1 for On/Off connections.

Positive polarity 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. 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 polarity devices are on (enabled) when the On/Off is open or

brought to within a low voltage (see Specifications) with respect to –Vin.

The device is off (disabled) when the On/Off is pulled high with respect to

–Vin (see specifications).

Dynamic control of the On/Off function should be able to 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 cur-

rent 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 noise objectives. Excess external

capacitance may cause regulation problems, degraded transient response

and possible oscillation or instability.

Soldering Guidelines

Murata Power Solutions recommends the specifications below when installing these

converters. These specifications vary depending on the solder type. Exceeding these

specifications may cause damage to the product. Your production environment

may differ therefore please thoroughly review these guidelines with your process

engineers.

Recommended Lead-free Solder Reflow Profile

High trace = normal upper limit

Low trace - normal lower limit

0

50

100

150

200

250

0

30

60

90

120

150

180

210

240

270

300

Time (sec)

Preheating Zone

240 sec max

Soaking Zone

120 sec max

Reflow Zone

time above 217° C

45-75 sec

Peak Temp.

235-260° C

<1.5° C/sec

Reflow Solder Operations for surface-mount products (SMT)

For Sn/Ag/Cu based solders:

Preheat Temperature

Less than 1 ºC. per second

Time over Liquidus

45 to 75 seconds

Maximum Peak Temperature

260 ºC.

Cooling Rate

Less than 3 ºC. per second

For Sn/Pb based solders:

Preheat Temperature

Less than 1 ºC. per second

Time over Liquidus

60 to 75 seconds

Maximum Peak Temperature

235 ºC.

Cooling Rate

Less than 3 ºC. per second

OKL-T/1-W12 Series

Programmable Output 1-Amp iLGA SMT PoLs

www.murata-ps.com

email: sales@murata-ps.com

09 Feb 2011

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