AP5004 データシートの表示（PDF） - Diodes Incorporated.
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AP5004 Datasheet PDF : 10 Pages
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AP5004
PWM CONTROL 2.5A STEP-DOWN CONVERTER
Functional Description
PWM Control
The AP5004 consists of DC/DC converters that employ a
pulse-width modulation (PWM) system. The PWM controller is
internally clocked by a fixed 300KHz oscillator.
In converters of the AP5004, the pulse width varies in a range
from 0 to 90%, according to the load current. The ripple voltage
produced by the switching can easily be removed through a filter
because the switching frequency remains constant. Therefore,
these converters provide a low-ripple power over broad ranges of
input voltage and load current.
Enable Control
This allows the output of AP5004 to be turned ON or OFF.
Connecting this pin to GND or any voltage lower than 0.8V turn
off the output OFF. At OFF state current drawn through the VCC
input is approximately 2uA. Note that the slew rate from ON to
OFF must be >0.013v/us to ensure proper operation.
C BOOST
A capacitor must be connected from pin 3 to the switch output,
pin 4. This capacitor boosts the gate drive to the internal
MOSFET above VIN to fully turn it ON. This minimizes conduction
losses in the power switch to maintain high efficiency. The
recommended value for C Boost is 0.1uF.
FEEDBACK
This is the input to a two-stage high gain amplifier, which drivers
the PWM controller. It is necessary to connect pin 2 to the actual
output of the power supply to set the DC output voltage. Two
external resistors are required to set the DC output voltage. For
stable operation of the power supply, it is important to prevent
coupling of any inductor flux to the feedback input.
Current Limit
The current limit threshold is set by the internal circuit that
minimum switching current is 3.5A. The output voltage will be
reduced immediately and switching frequency will be dropped to
50KHz when switching current over limit threshold.
Inductor Selection
For most designs, the operates with inductors of 15µH to 33µH.
The inductor value can be derived from the following equation:
( ) L = VIN − VOUT TON
ΔI L × f osc
Where is inductor Ripple Current. Large value inductors lower
ripple current and small value inductors result in high ripple
currents. Choose inductor ripple current approximately 15% of
the maximum load current 2.5A, ∆IL=0.375A. The DC current
rating of the inductor should be at least equal to the maximum
load current plus half the ripple current to prevent core saturation
(2A+0.19A).
Input Capacitor Selection
The input current to the step-down converter is discontinuous,
and therefore an input capacitor C2 is required to supply the AC
current to the step-down converter while maintaining the DC input
voltage. A low ESR capacitor is required to keep the noise at the
IC to a minimum. Its RMS current rating should be greater than
approximately 1/2 of the DC load current.
Output Capacitor Selection
The output capacitor is required to maintain the DC output
voltage. Low ESR capacitors are preferred to keep the output
voltage ripple low. The characteristics of the output capacitor also
affect the stability of the regulation control system. The
ESR dominates the impedance at the switching frequency, and
so the output ripple is calculated as:
VRIPPLE ≅ ΔI × RESR
Output Rectifier Diode
The output rectifier diode supplies the current to the inductor
when the high-side switch is off. To reduce losses due to the
diode forward voltage and recovery times, use a Schottky
rectifier.
PCB Layout Guide
If you need low TC & TJ or large PD(Power Dissipation), The dual
Output pin(4) and VSS pins(7& 8)on the SOP-8L package are
internally connected to die pad, The PCB layout should allow for
maximum possible copper area at the SW pins.
1. Connect C3 to VCC and VSS pin as closely as possible to get
good power filter effect.
2. Connect ground side of the C2 & D1 as closely as possible.
Typical PC Board Layout
Top Side Layout Guide
Bottom Side Layout Guide
AP5004 Rev. 3
8 of 10
www.diodes.com
JUNE 2008
© Diodes Incorporated
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