DPA422-426
DPA-Switch Family Functional Description
Auto-restart
ICD1
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.
IB
75
Slope = PWM Gain
42
4
I
< I
L(DC)
L
I
C (SKIP)
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:
I
= 115 µA
L
IC (mA)
PI-2761-112102
Figure 4. Relationship of Duty Cycle to CONTROL Pin Current.
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. High switching frequency (400 kHz/300 kHz, pin selectable)
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 undervoltage 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).
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.
CONTROL (C) 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 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.
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 gradu-
ally as line voltage rises. This makes possible an ideal
implementation of overload power limiting.
8. Synchronization function allows the synchronization of
DPA-Switch operation to an external lower frequency.
9. 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.
10. Hysteretic over-temperature shutdown provides automatic
recovery from thermal fault.
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 VC reaches
approximately 5.8 V, the control circuitry is activated and the
soft-start begins. The soft-start circuit gradually increases the
duty cycle of the MOSFET from zero to the maximum value
over approximately 5 ms. The high-voltage current source is
turned off at the end of the soft-start. If no external feedback/
supply current is fed into the CONTROL pin by the end of the
soft-start, the CONTROL pin will start discharging in response
to the supply current drawn by the control circuitry and the gate
current of the switching MOSFET driver. If the power supply is
designed properly, and no fault condition such as open loop or
11. Tight absolute tolerances and small temperature variations
on switching frequency, current limit, and undervoltage lock
out threshold (UV).
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
DCMAX reduction. A resistor from the EXTERNAL CURRENT
LIMIT pin to the SOURCE pin sets current limit externally. In
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Rev. T 12/12
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