1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B
The AP3421/A/B is a fully integrated dual output
voltage regulator. The two converters are current
mode and internally compensated. The converters
include integrated control and synchronous rectifier
switches. The outputs are both rated for up to 1A.
Both outputs are adjustable using external resistors.
The step-down converters operate at 1.3MHz fixed
switching frequency under normal load and in a pulse
skipping mode for light loads. The switching clock is
shifted 180° for SW2. The E/S pin provides an enable
function and allows the converter to be synchronized
to an external clock. With E/S held low, the
AP3421/A/B draws less than 10µA current.
In the start-up sequence, the VO1 output is designed
to precede the VO2 output. The two outputs have
controlled start-up sequence.
Power On Reset (POR) function is provided by
means of an open-drain output present on the POR
pin. The POR function monitors VMON, FB1 and
FB2, and pulls low if any of these begin to drop out.
The POR is internally deglitched and provides a
delayed recovery/reset time.
The AP3421/A/B provides peak over-current
protection, short circuit protection and thermal
shutdown. Discharge-Before-Turn-On discharges the
outputs completely before soft-starting to always
bring them up in the proper sequence at start-up or
after a POR (For AP3421/A only).
The AP3421/A/B is available in DFN-3×3-10
• VO1=1.8 to 3.6V at 1A
• VO2=1.0 to 3.6V at 1A
• Switching Frequency: 1.3MHz
• 180° Phase Shifted Switching
• No Rectifier Diode Required
• Optional External Clocking (2× Clock Required)
• Light Load Pulse Skipping
• Enable/Sleep State
• Internal Soft-start
• Open-drain Power On Reset Monitors Input and
• Discharge-Before-Turn-On (For AP3421/A)
• Pre-bias Function (For AP3421B)
• Peak Over Current Protection
• Short Circuit Protection
• Over Temperature Shutdown
• Hard Disk Drivers
• Set Top Boxes
Feb. 2013 Rev. 1. 4
Figure 1. Package Type of AP3421/A/B
BCD Semiconductor Manufacturing Limited