AP1516 데이터 시트보기 (PDF) - Anachip Corporation
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AP1516 Datasheet PDF : 10 Pages
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150KHz, 3A PWM Buck DC/DC Converter + 1A Ultra Low
Drop Regulator
AP1516
Function Description
Pin Functions
+VIN, B
This is the positive input supply for the IC switching
regulator. A suitable input bypass capacitor must be
present at this pin to minimize voltage transients
and to supply the switching currents needed by the
regulator.
Ground
Circuit ground.
VOUT1
Internal switch. The voltage at this pin switches
between (+VIN1 – VSAT) and approximately – 0.5V,
with a duty cycle of approximately VOUT1 / VIN1. To
minimize coupling to sensitive circuitry, the PC
board copper area connected to this pin should be
kept a minimum.
of two external resistors to any voltages within the
range of 1.25V to 15.5V. Another major
requirement of these graphic chips is the need to
switch the load current from zero to several amps in
tens of nanoseconds at the processor pins, which
translates to an approximately 300 to 500ns of
current step at the regulator. In addition, the output
voltage tolerances are also extremely tight and they
include the transient response as part of the
specification.
The channel 2 is specifically designed to meet
the fast current transient needs as well as
providing an accurate initial voltage, reducing
the overall system cost with the need for fewer
number of output capacitors. Another feature of
the device is its true remote sensing capability
that allows accurate voltage setting at the load
rather than at the device.
Feedback
Senses the regulated output voltage to complete
the feedback loop.
SD
Allows the switching regulator circuit to be
shutdown using logic level signals thus dropping
the total input supply current to approximately
150uA. Pulling this pin below a threshold voltage of
approximately 1.3V turns the regulator on, and
pulling this pin above 1.3V (up to a maximum of
18V) shuts the regulator down. If this shutdown
feature is not needed, the SD pin can be wired to
the ground pin.
Introduction
The channel 2 regulator is a extremely low dropout
voltages comparable to the PNP type without the
disadvantage of the extra power dissipation due to
the base current associated with PNP regulators.
This is done by bringing out the control pin of the
regulator that provides the base current to the
power NPN and connecting it to a voltage that is
greater than the voltage present at the VIN2 pin. This
flexibility makes the channel 2 ideal for applications
where dual inputs are available such as a computer
motherboard with an ATX style power supply that
provides 5V and 3.3V to the board. One such
application is the new graphic chip sets that require
anywhere from 2.4V to 2.7V supply. The channel
2-ADJ can easily be programmed with the addition
Output Voltage Setting
The channel 2 can be programmed to any voltages
in the range of 1.25V to 15.5V with the addition of
R1 and R2 external resistors according to the
following formula:
Vout = Vref (1+R2/R1) + IFB2 * R2 where : Vref = 1.25V & IFB2=50uA Typically
Vin3
Vout2
Channel 2-ADJ
Vsense2
Vin2
FB
Vref R1+
IFB2=50uA
R2+
The channel 2 keeps a constant 1.25V between the
VSENSE pin and the FB2 pin. By placing a resistor R1
across these two pins and connecting the VSENSE
and VOUT pin together, a constant current flows
through R1, adding to the IFB2 current and into the
R2 resistor producing a voltage equal to the
(1.25/R1)*R2 + IFB2*R2. This voltage is then added
to the 1.25V to set the output voltage. This is
summarized in the above equation.
Anachip Corp.
www.anachip.com.tw
Rev.1.1 May 23, 2005
8/10
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