7 5 W , D U A L O U T P U T , M I X E D - V O L T A G E D C / D C C O N V E R T E R S
BCP Models
If the Sync pin detects the appropriate input signal, it will configure itself as a
Short Circuit Condition
slave; if no signal is detected, it will generate master Sync pulses.
As described under "Current Limiting," when the BCP Series DC/DC con-
verter output is subjected to a short circuit condition, the output current will
remain at the Short Circuit Current limit. In this state there is negligible power
dissipated in the load. Therefore, most of the input power is dissipated within
the converter, causing the internal temperature to increase. If this condition
persists, Thermal Shutdown will activate and shutdown the DC/DC converter.
When the internal temperature is sufficiently decreased, the converter will
self-start.
Synchronization of converters requires that the master switching frequency
exceed the slave frequency by a minimum of 60kHz.
At the start of each DC/DC converter switching cycle, an internally generated
ꢀ00-450ns pulse will be present at the Sync pin. If, however, the unit
receives an external Sync pulse, the DC/DC converter’s switching cycle will
be terminated and a new cycle initiated. Since the master frequency is higher
than the slave switching frequency, the slave cycles are always terminated
prematurely, thereby never allowing internal Synch pulses to be generated.
The external signal’s rising edge initiates the slave Sync process. External
signals must adhere to min./ max. limits stated in Performance/Functional
Specifications.
Thermal Shutdown
The BCP Series is equipped with Thermal Shutdown circuitry. If the internal
temperature of the DC/DC converter rises above the designed operating
temperature, 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.
Operating the BCP series DC/DC converters at higher switching frequencies
via the external Sync function will result in a slight degradation of efficiency.
Contact DATEL for further information.
Input Reverse-Polarity Protection
Output Overvoltage Protection
Upon applying a reverse-polarity voltage to the DC/DC converter, an internal
diode will be forward biased and draw excessive current from the power
source. Therefore, it is required that the input current be limited be either an
appropriately rated input fuse or a current limited power source.
Each voltage output of the BCP Series converter is independently monitored
via an auxiliary winding in the output inductor. If the output voltage
should rise to a level which could be damaging to the load circuitry (see
Performance/Functional Specifications for limits), the overvoltage circuitry will
power down the PWM controller and latch off the DC/DC converter. The
device must now be restarted by powering cycling VIN.
Heat Sinks for BCP Series
DATEL offers two standard heat sinks that can be mounted to the half-brick
package to extend the converter's operating temperature range. Along with
the standard ꢀ.3" x ꢀ.4" x 0.5" (HS-CP) heat sink, DATEL has designed
a low-profile heat sink for height-restricted applications. This new heat sink
(HS-CPLPꢀ) is designed with radiant fins that extend 0.51" beyond either
side of the ꢀ.4" dimension of the BCP package. The convenience of this
design is that the finned extensions protrude only 0.31" below the top surface
of the DC/DC converter, allowing components with a profile height less than
0.ꢀ15" to be mounted on the pc board below the heat sink. Therefore, while
the surface area of the low-profile heat sink measures ꢀ.3" x 3.5", pcb real
estate is unaffected.
Current Limiting
When output current demands exceed the maximum output current rating by
1072 to 1332, the DC/DC converter will go into a current limiting mode.
In this condition the output voltage decreases proportionately as the output
current increases, thereby maintaining a somewhat constant power dissipa-
tion—referred to as Power Limiting (see Figure ꢀ). As the load approaches a
short circuit, the output current will continue to increase until it reaches the
rated Short Circuit Current limit.
BCP-5/15-3.3/15-D24, D48 Current Limiting Characteristics
For optimum thermal performance in a natural convection application, the
low-profile heat sink should be mounted with the fins vertically oriented. Both
models are shipped with 0.009" sellf-adhesive thermal pad and mounting
screws.
(Nominal VIN
)
6.00
5.00
4.00
3.00
2.00
1.00
0
5V Output
6
5
4
HS-CPLP2
3
3.3V Output
HS-CP
2
1
0
Output Current, IOUT (Amps)
0
100
200
300
400
500
600
700
Figure 2. Current Limiting Characteristics
AIR VELOCITY (FT./MIN.)
HS-CP and HS-CPLP2 Heat Sink Performance Vs. Air Flow
(@ 10.5 Watts Power Dissipation)
5
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