Diodes AP3421, AP3421A, AP3421B User Manual

1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B

Preliminary Datasheet

General Description

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 package.

Features

• V

• Switching Frequency: 1.3MHz

• 180° Phase Shifted Switching

• No Rectifier Diode Required

• Optional Exter nal Cl ocking (2× Clock Required)

• Light Load Pulse Skipping

• Enable/Sleep State

• Internal Soft-start

• Open-drain Power On Reset Monitors Input and

• Outputs

• Discharge-Before-Turn-On (For AP3421/A)

• Pre-bias Function (For AP3421B)

• Peak Over Current Protection

• Short Circuit Protection

• Over Temperature Shutdown

=1.8 to 3.6V at 1A

O1

=1.0 to 3.6V at 1A

O2

Applications

• Hard Disk Drivers

• Set Top Boxes

DFN-3×3-10

Figure 1. Package Type of AP3421/A/B

Feb. 2013 Rev. 1. 4 BCD Semiconductor Manufacturing Limited

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µ

Preliminary Datasheet

1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B

Pin Configuration

DN Package

(DFN-3×3-10)

Pin 1 Mark

1

2

3

4

56

10

9

8

7

Figure 2. Pin Configuration of AP3421/A/B (Top View)

Pin Description

Pin Number Pin Name Function

1 FB2

2 AVIN

3 PVIN

4 SW2

5 PGND

6 SW1

7 E/S

Feedback from VO2. Connect voltage divider to the load side of VO2 output inductor-capacitor filter

Analog power input. Connect a 1µF ceramic capacitor between this pin and AGND

Control MOSFET switch power input. Connect a 10 ceramic capacitor between this pin and PGND, as close to the IC as possible VO2 synchronous buck switching output. Connect to VO2 inductor Power ground connection. Synchronous rectifier MOSFET source. Provide a star connection between this pin, VO1, VO2 filter capacitor returns, VIN input capacitor return, and AGND. Keep the star connection as close to the IC as possible VO1 synchronous buck switching output. Connect to VO1 inductor Enable/Synchronization. Pulling this pin high statically enables the IC and pulling the pin low statically will shut down the IC. Applying a pulse to this pin will synchronize SW1 and SW2 switching frequency to ½ the external clock frequency

F

Feb. 2013 Rev. 1. 4 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B

Pin Description (Continued)

Pin Number Pin Name Function

Power on reset output pin. Monitors FB1, FB2 output

8 POR

9 VMON

10 FB1

11 AGND

voltage levels and V voltage drop is detected on FB1 or FB2 or VIN, and is Hi-Z during normal operation Voltage monitor–supervisor for one external voltage (could be input voltage). The POR output is triggered if this output falls below the VMON threshold Feedback from VO1. Connect voltage divider to the load side of VO1 output inductor-capacitor filter Signal ground connection. Provide a star connection between this pin and PGND pin

. POR is pulled low if an output

IN

Feb. 2013 Rev. 1. 4 BCD Semiconductor Manufacturing Limited

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Preliminary Datasheet

1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B

Functional Block Diagram

Figure 3. Functional Block Diagram of AP3421/A/B

Feb. 2013 Rev. 1. 4 BCD Semiconductor Manufacturing Limited

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θ

Preliminary Datasheet

1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B

Ordering Information

AP3421 -

Circuit Type

A: AP3421A B: AP3421B Blank: AP3421

Package DN: DFN-3×3-10

G1: Green

TR: Tape & Reel

Package

DFN-3×3-10 -40 to 85°C

Temperature

Range

Part Number Marking ID Packing Type

AP3421DNTR-G1 BCB

Tape & Reel AP3421ADNTR-G1 BDD

AP3421BDNTR-G1 BDE

BCD Semiconductor's Pb-free products, as designated with "G1" suffix in the part number, are RoHS compliant and green.

Absolute Maximum Ratings (Note 1)

Parameter Symbol Value Unit

Input Voltage VIN -0.3 to 7 V Feedback Voltage VFB -0.3 to VIN+0.3 V E/S Pin Voltage V SW1, SW2 Pin Voltage VSW V Thermal Resistance

-0.3 to VIN+0.3 V

E/S

-1 to VIN+1 V

PGND

JA

33 ºC /W Operating Junction Temperature TJ 150 ºC Storage Temperature T Lead Temperature (Soldering, 10sec) T

Note 1: Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under “Recommended Operating Conditions” is not implied. Exposure to “Absolute Maximum Ratings” for extended periods may affect device reliability.

-25 to 150 ºC

STG

260 ºC

LEAD

Recommended Operating Conditions

Parameter Symbol Min Max Unit

Input Voltage V

IN

VO1 Maximum Output Current IO1(Max) 1 A VO2 Maximum Output Current IO2(Max) 1 A Operating Ambient Temperature TA -40 85

Feb. 2013 Rev. 1. 4 BCD Semiconductor Manufacturing Limited

AP3421 4.5 5.5

AP3421A/B 3.0 5.5

V

°C

5