AP1538_09 Datasheet, PDF (1/13 Pages) Diodes Incorporated – 18V 3A 300KHz BUCK CONVERTER

AP1538
18V 3A 300KHz BUCK CONVERTER
Features
• Input voltage : 3.6V to 18V
• Output voltage : 0.8V to VCC
• Output current : up to 3A
• Duty ratio: 0% to 99% PWM control
• Oscillation frequency: 300KHz typical
• Soft-start like, Current limit and Enable function
• Thermal Shutdown function
• Built-in internal SW P-channel MOS
• SOP-8L and SOP-8L-DEP: Available in “Green”
Molding Compound (No Br, Sb)
• Lead Free Finish / RoHS Compliant (Note 1)
Applications
• PC Motherboard
• LCD Monitor
• Graphic Card
• DVD-Video Player
• Telecom Equipment
• ADSL Modem
• Printer and other Peripheral Equipment
• Microprocessor core supply
Typical Application Circuit
General Description
AP1538 consists of step-down switching regulator with
PWM control. These devices include a reference voltage source,
oscillation circuit, error amplifier, internal PMOS.
AP1538 provides low-ripple power, high efficiency, and excellent
transient characteristics. The PWM control circuit is able to vary
the duty ratio linearly from 0 up to 99%. This converter also
contains an error amplifier circuit as well as a soft-start circuit that
prevents overshoot at startup. An enable function, an over
current protect function and a short circuit protect function are built
inside, and when OCP or SCP happens, the operation frequency
will be reduced from 300KHz to 50KHz. Also, an internal
compensation block is built in to minimum external component
count.
With the addition of an internal P-channel Power MOS, a coil,
capacitors, and a diode connected externally, these ICs can
function as step-down switching regulators. They serve as ideal
power supply units for portable devices when coupled with the
SOP-8L and SOP-8L-DEP mini-packages, providing such
outstanding features as low current consumption. Since this
converter can accommodate an input voltage up to 18V, it is also
suitable for the operation via an AC adapter.
V_IN
Vcc
Output
R_OCSET C_OCSET
3K Option
AP 1538
C _IN
OCSET
FB
470uF
EN
V _SS
CVcc
R_EN
100K
0.1uF
C_EN
0.1uF
L1
22uH
Cc
Option*
D1**
V_{OUT = 5V/3A}
R_A
6.8K
+
-
R_B
1.3K
+
C
0.1uF_-
C_OUT
470uF***
Notes:
V_OUT= V _FB x (1+ R_A/RB)
R_B= 0.7K~5K ohm
* Typical feedback compensation (Cc): 5600pF.
** Suggested DIODES Power Schottky P/N: B540 series or PDS540.
*** Suggested C_OUT for V_OUT < 1V; 680uF.
AP1538 Rev. 5
DS31451
1 of 13
www.diodes.com
OCTOBER 2009
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