DPA423 Power Integrations, Inc., DPA423 Datasheet - Page 4

• Manufacturer Part Number: DPA423
• Description: Highly Integrated DC-DC Converter Ics For Distributed Power Architecturesthe Dpa-switch ic Family Introduces a Highly Integratedsolution For DC-DC Conversion Applications in The 16-75 Vdcinput Range.dpa-switch Uses The Same Proven Topology as Topswit
• Manufacturer: Power Integrations, Inc.

DPA-Switch Family Functional
Description
DPA-Switch is an integrated switched mode power supply chip
that converts a current at the control input to a duty cycle at the
open drain output of a high voltage power MOSFET. During
normal operation the duty cycle of the power MOSFET decreases
linearly with increasing CONTROL pin current as shown in
Figure 4. A patented high-voltage CMOS technology allows
both the high-voltage power MOSFET and all the low voltage
control circuitry to be cost effectively integrated onto a single
monolithic chip.
In addition to the standard TOPSwitch features, such as the
high-voltage start-up, the cycle-by-cycle current limiting, loop
compensation circuitry, auto-restart and thermal shutdown,
DPA-Switch also offers many advanced features that reduce
system cost and increase power supply performance and design
flexibility. Following is a summary of the advanced features:
1. A fully integrated 5 ms soft-start limits peak currents and
2. A 75% maximum duty cycle (DC
3. High switching frequency (400 kHz/300 kHz, pin selectable)
4.
5.
6.
7. External current limit adjustment allows the setting of the
8. Synchronization function allows the synchronization of
9.
10. Hysteretic over-temperature shutdown provides automatic
11. Tight absolute tolerances and small temperature variations
4
DPA423-426
voltages during start-up and reduces or eliminates output
overshoot in most applications.
line feed forward with DC
DPA-Switch well suited for both flyback and forward
topologies.
allows the use of smaller size transformers and offers high
bandwidth for power supply control loop.
Cycle skipping operation at light load minimizes standby
power consumption (typically <10 mA input current).
Line under-voltage ensures glitch free operations at both
power-up and power-down and is tightly toleranced over
process and temperature to meet system level requirements
common in DC to DC converters (e.g. ETSI).
Line overvoltage protects DPA-Switch against excessive
input voltage and line surge.
current limit externally to a lower level near the operating
peak current and, if desired, further adjusts the level
gradually as line voltage rises. This makes possible an ideal
implementation of overload power limiting.
DPA-Switch operation to an external lower frequency.
Remote ON/OFF feature permits DPA-Switch based power
supplies to be easily switched on/off using logic signals.
Maximum input current consumption is 2 mA in Remote
OFF.
recovery from thermal fault.
on switching frequency, current limit, and under-voltage
lock out threshold (UV).
L
4/04
MAX
reduction feature makes
MAX
) together with the
Figure 4. Relationship of Duty Cycle to CONTROL Pin Current.
Three pins, LINE-SENSE (L), EXTERNAL CURRENT LIMIT
(X) and FREQUENCY (F), are used to implement all the pin
controllable features. A resistor from the LINE-SENSE pin to
DC input bus implements line UV, line OV and line feed
forward with DC
CURRENT LIMIT pin to the SOURCE pin sets current limit
externally. In addition, remote ON/OFF may be implemented
through either the LINE-SENSE pin or the EXTERNAL
CURRENT LIMIT pin depending on the polarity of the logic
signal available as well as other system specific considerations.
Shorting both the LINE-SENSE and the EXTERNAL
CURRENT LIMIT pins to the SOURCE pin disables line OV,
line UV, line feed forward with DC
current limit, remote ON/OFF and synchronization. The
FREQUENCY pin sets the switching frequency to 400 kHz if
connected to the SOURCE pin, or 300 kHz if connected to the
CONTROL pin. This pin should not be left open. Please refer
to “Using Feature Pins” section for detailed information
regarding the proper use of those pins.
CONTROL Pin Operation
The CONTROL pin is a low impedance node that is capable of
receiving a combined supply and feedback current. During
normal operation, a shunt regulator is used to separate the
feedback signal from the supply current. CONTROL pin
voltage V
including the MOSFET gate driver. An external bypass capacitor
closely connected between the CONTROL and SOURCE pins
is required to supply the instantaneous gate drive current. The
total amount of capacitance connected to this pin also sets the
auto-restart timing as well as control loop compensation.
When the DC input voltage is applied to the DRAIN pin during
start-up, the MOSFET is initially off, and the CONTROL pin
capacitor is charged through the switched high voltage current
source connected internally between the DRAIN and
CONTROL pins. When the CONTROL pin voltage V
75
42
4
Auto-restart
C
is the supply voltage for the control circuitry
I
CD1
MAX
reduction. A resistor from the EXTERNAL
I
L
= 115 µA
I
B
I
C
(mA)
Slope = PWM Gain
MAX
reduction, external
I
L
< I
L(DC)
PI-2761-112102
C
I
reaches
C (SKIP)