Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters
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.
AP3421/A/B
Features
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
V
O1
=1.8 to 3.6V at 1A
V
O2
=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
Outputs
Discharge-Before-Turn-On (For AP3421/A)
Pre-bias Function (For AP3421B)
Peak Over Current Protection
Short Circuit Protection
Over Temperature Shutdown
Applications
•
•
Hard Disk Drivers
Set Top Boxes
DFN-3×3-10
Figure 1. Package Type of AP3421/A/B
Feb. 2013
Rev. 1. 4
1
BCD Semiconductor Manufacturing Limited
Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters
Pin Configuration
DN Package
(DFN-3×3-10)
Pin 1 Mark
AP3421/A/B
1
2
3
4
5
10
9
8
7
6
Figure 2. Pin Configuration of AP3421/A/B (Top View)
Pin Description
Pin Number
1
2
3
4
Pin Name
FB2
AVIN
PVIN
SW2
Function
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 10µF
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
5
PGND
6
SW1
7
E/S
Feb. 2013
Rev. 1. 4
2
BCD Semiconductor Manufacturing Limited
Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters
Pin Description (Continued)
Pin Number
8
AP3421/A/B
Pin Name
POR
Function
Power on reset output pin. Monitors FB1, FB2 output
voltage levels and V
IN
. POR is pulled low if an output
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
9
10
11
VMON
FB1
AGND
Feb. 2013
Rev. 1. 4
3
BCD Semiconductor Manufacturing Limited
Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters
Functional Block Diagram
AP3421/A/B
Figure 3. Functional Block Diagram of AP3421/A/B
Feb. 2013
Rev. 1. 4
4
BCD Semiconductor Manufacturing Limited
Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters
Ordering Information
AP3421
-
AP3421/A/B
Circuit Type
A: AP3421A
B: AP3421B
Blank: AP3421
Package
DN: DFN-3×3-10
Package
DFN-3×3-10
G1: Green
TR: Tape & Reel
Temperature
Range
-40 to 85°C
Part Number
AP3421DNTR-G1
AP3421ADNTR-G1
AP3421BDNTR-G1
Marking ID
BCB
BDD
BDE
Packing Type
Tape & Reel
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
Input Voltage
Feedback Voltage
E/S Pin Voltage
SW1, SW2 Pin Voltage
Thermal Resistance
Operating Junction Temperature
Storage Temperature
Lead Temperature (Soldering, 10sec)
Symbol
V
IN
V
FB
V
E/S
V
SW
θ
JA
T
J
T
STG
T
LEAD
Value
-0.3 to 7
-0.3 to V
IN
+0.3
-0.3 to V
IN
+0.3
V
PGND
-1 to V
IN
+1
33
150
-25 to 150
260
Unit
V
V
V
V
ºC /W
ºC
ºC
ºC
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.
Recommended Operating Conditions
Parameter
Input Voltage
VO1 Maximum Output Current
VO2 Maximum Output Current
Operating Ambient Temperature
Feb. 2013
Rev. 1. 4
5
Symbol
V
IN
AP3421
AP3421A/B
I
O1
(Max)
I
O2
(Max)
T
A
Min
4.5
3.0
1
1
-40
Max
5.5
5.5
Unit
V
A
A
°C
85
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