|Description||PWM CONTROL 3A STEP-DOWN CONVERTER|
|AP1510SG-13_17 Datasheet PDF : 9 Pages |
The AP1510 is a DC/DC converter that employs pulse width modulation (PWM) scheme. Its pulse width varies in the range of 0% to 99%, based
on the output current loading. The output ripple voltage caused by the PWM high frequency switching can easily be reduced through an output
filter. Therefore, this converter provides a low ripple output supply over a broad range of input voltage & output current loading.
Under Voltage Lockout
The under voltage lockout circuit of the AP1510 assures that the high-side MOSFET driver remains in the off state whenever the supply voltage
drops below 3.3V. Normal operation resumes once VCC rises above 3.5V.
Current Limit Protection
The current limit threshold is set by external resistor ROCSET connected from VCC supply to OCSET pin. The internal sink current IOCSET (90μA
typical) across this resistor sets the voltage at OCSET pin. When the PWM voltage is less than the voltage at OCSET, an over-current condition is
The current limit threshold is given by the following equation:
IPEAKRDS(ON) IOCSET ROCSET
IPEAK IOUT(MAX) 2
I VIN VOUT VOUT
IPEAK is the output peak current; RDS(ON) is the MOSFET ON resistance; fS is the PWM frequency (300kHz typical). Also, the inductor value will
affect the ripple current ΔI.
The above equation is recommended for input voltage range of 5V to 18V. For input voltage lower than 5V or ambient temperature over +100°C,
higher ROCSET is recommended.
For most designs, the operation range with inductors is from 22µH to 33µH. The inductor value can be derived from the following equation:
L VIN VOUT VOUT
Where IL is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high ripple current. Choose
inductor ripple current approximately 15% of the maximum load current 3A, ∆IL=0.45A. 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 (3A+0.225A).
Input Capacitor Selection
This capacitor should be located close to the IC using short leads and the voltage rating should be approximately 1.5 times the maximum input
voltage. The RMS current rating requirement for the input capacitor of a buck regulator is approximately 1⁄2 the DC load current. A low ESR input
capacitor sized for maximum RMS current must be used. A 470µF low ESR capacitor for most applications is sufficient.
Output Capacitor Selection
The output capacitor is required to filter the output voltage and provides regulator loop stability. The important capacitor parameters are the
100kHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating and capacitance value. For the output capacitor, the
ESR value is the most important parameter. The output ripple can be calculated from the following formula.
Document number: DS31018 Rev. 8 - 2
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