DPA423-426
DPA-Switch Family Functional
Description
Auto-restart
ICD1
IB
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
normaloperationthedutycycleofthepowerMOSFETdecreases
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.
75
Slope = PWM Gain
42
4
I
< I
L(DC)
L
I
C (SKIP)
I
= 115 µA
L
IC (mA)
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:
PI-2761-112102
Figure 4. Relationship of Duty Cycle to CONTROL Pin Current.
Threepins,LINE-SENSE(L),EXTERNALCURRENTLIMIT
(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
forwardwithDCMAX reduction.AresistorfromtheEXTERNAL
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 DCMAX reduction, external
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.
1. A fully integrated 5 ms soft-start limits peak currents and
voltages during start-up and reduces or eliminates output
overshoot in most applications.
2. A 75% maximum duty cycle (DCMAX) together with the
line feed forward with DCMAX reduction feature makes
DPA-Switch well suited for both flyback and forward
topologies.
3. Highswitchingfrequency(400kHz/300kHz,pinselectable)
allows the use of smaller size transformers and offers high
bandwidth for power supply control loop.
4. Cycle skipping operation at light load minimizes standby
power consumption (typically <10 mA input current).
5. Line under-voltage ensures glitch free operations at both
power-up and power-down and is tightly toleranced over
processandtemperaturetomeetsystemlevelrequirements
common in DC to DC converters (e.g. ETSI).
6. Line overvoltage protects DPA-Switch against excessive
input voltage and line surge.
7. External current limit adjustment allows the setting of the
current limit externally to a lower level near the operating
peak current and, if desired, further adjusts the level
graduallyaslinevoltagerises.Thismakespossibleanideal
implementation of overload power limiting.
8. Synchronization function allows the synchronization of
DPA-Switch operation to an external lower frequency.
9. RemoteON/OFFfeaturepermitsDPA-Switchbasedpower
supplies to be easily switched on/off using logic signals.
Maximum input current consumption is 2 mA in Remote
OFF.
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 VC is the supply voltage for the control circuitry
includingtheMOSFETgatedriver. Anexternalbypasscapacitor
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.
10. Hystereticover-temperatureshutdownprovidesautomatic
recovery from thermal fault.
11. Tight absolute tolerances and small temperature variations
on switching frequency, current limit, and under-voltage
lock out threshold (UV).
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
CONTROLpins. WhentheCONTROLpinvoltageVC reaches
K
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