DCP01B SERIES
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SBVS012C − DECEMBER 2000 − REVISED AUGUST 2005
If synchronized devices are used, it should be noted that
at startup, all devices will draw maximum current
simultaneously. This can cause the input voltage to dip. If
it dips below the minimum input voltage (4.5V), the devices
may not start up. A 2.2µF capacitor should be connected
close to the input pins.
FUNCTIONAL DESCRIPTION
OVERVIEW
The DCP01B offers up to 1W of unregulated output power
with a typical efficiency of up to 85%. This is achieved
through highly integrated packaging technology and the
implementation of a custom power stage and control IC.
The circuit design uses an advanced BiCMOS/DMOS
process. For additional information, refer to the application
notes located in the DCP01B product folder at www.ti.com.
If more than eight devices are to be synchronized, it is
recommended that the SYNCIN pins are driven by an
external device. Details are contained in Application
Report SBAA035, External Synchronization of the
DCP01/02 Series of DC/DC Converters, available for
download at www.ti.com.
POWER STAGE
CONSTRUCTION
This uses a push-pull, center-tapped topology switching at
400kHz (divide-by-2 from 800kHz oscillator).
The DCP01B basic construction is the same as standard
ICs. There is no substrate within the molded package. The
DCP01B is constructed using an IC, rectifier diodes, and
a wound magnetic toroid on a leadframe. Since there is no
solder within the package, the DCP01B does not require
any special PCB assembly processing. This results in an
isolated DC/DC converter with inherently high reliability.
OSCILLATOR AND WATCHDOG
The onboard 800kHz oscillator generates the switching
frequency via a divide-by-2 circuit. The oscillator can be
synchronized to other DCP01B circuits or an external
source, and is used to minimize system noise.
A watchdog circuit checks the operation of the oscillator
circuit. The oscillator can be stopped by pulling the SYNC
pin low. The output pins will be tri-stated. This will occur in
2µs.
ADDITIONAL FUNCTIONS
DISABLE/ENABLE
The DCP01B can be disabled or enabled by driving the
SYNCIN pin using an open drain CMOS gate. If the
SYNCIN pin is pulled low, the DCP01B will be disabled.
The disable time depends upon the external loading; the
internal disable function is implemented in 2µs. Removal
of the pull-down will cause the DCP01B to be enabled.
THERMAL SHUTDOWN
The DCP01B is protected by a thermal shutdown circuit.
If the on-chip temperature exceeds 150°C, the device will
shut down. Once the temperature falls below 150°C,
normal operation will resume. If the thermal condition
continues, operation will randomly cycle on and off. This
will continue until the temperature is reduced.
Capacitive loading on the SYNCIN pin should be
minimized in order to prevent a reduction in the oscillator
frequency.
SYNCHRONIZATION
DECOUPLING
In the event that more than one DC/DC converter is
needed onboard, beat frequencies and other electrical
interference can be generated. This is due to the small
variations in switching frequencies between the DC/DC
converters.
Ripple Reduction
A high switching frequency of 400kHz allows simple
filtering. To reduce ripple, it is recommended that at least
a 1µF capacitor is used on VOUT. Dual outputs should have
both the positive and negative buses decoupled to VOUT
ground (pin 5). The required 2.2µF low equivalent series
resistance (ESR) ceramic capacitor on the input of the 5V
to 15V versions, and the ≥ 0.47µF low-ESR ceramic
capacitor on the 24V versions help reduce ripple and
noise. See Application Bulletin SBVA012, DC-to-DC
Converter Noise Reduction, available for download at
www.ti.com.
The DCP01B overcomes this by allowing devices to be
synchronized to one another. Up to eight devices can be
synchronized by connecting the SYNCIN pins together,
taking care to minimize the stray capacitance. Stray
capacitance (> 3pF) will have the effect of reducing the
switching frequency, or even stopping the oscillator circuit.
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