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

• 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

1

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

2

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

3

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

4

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

µ

Preliminary Datasheet

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

Electrical Characteristics

V

IN =VE/S

Parameter Symbol Conditions Min Typ Max Unit

Operating Input Voltage VIN
Supply Current ICC V

Shutdown Supply Current I
Under Voltage Lockout Threshold
Under Voltage Lockout Hysteresis V

POR Threshold VMON V
Feedback Voltage V

Switch Current Limit
Oscillator Frequency f

Soft-start Time t
POR Threshold FB1 V
POR Threshold FB2 V

Discharge Complete Threshold
(AP3421/A )

E/S Pin Threshold

Frequency Lock-in Range

POR Assert Delay Time t

POR Release Delay Time t
POR Low Voltage V

VO2 Start Threshold (AP3421/A ) V

SW1, SW2 Discharge Resistance R

Internal
MOSFET on
Resistance

Thermal Shutdown Threshold T
Thermal Shutdown Hysteresis T

=5V, TA=25℃, unless otherwise specified.

AP3421,
AP3421A/B

AP3421A/B

AP3421 4.5 5.0 5.5

AP3421A/B 3.0 3.3 5.5

FB1=VFB2

V

SHDN

AP3421

AP3421A/B 2.4 2.7 3.0

HUVLO

VMON_POR

FB1, VFB2

OSC1

V

I

1.2 1.6

LIM1

I

1.2 1.6

LIM2

, f

1.0 1.30 1.60 MHz

OSC2

0.5 1.0 2.0 ms

SS_FB1

FB11Falling1 86 89 92 %V

FB1_POR

FB21Falling1 86 89 92 %V

FB2_POR

E/S

Rising Edge
300 mV

VMON

0.975 1.0 1.025 V

=1.2V 1.0 mA

=0V, VIN=5.0V 10

3.0 3.5 4.0

Falling 0.97 1.00 1.03 V

FB1 Level Where

V

FB1_DCT

Discharge Cycle Is

50 75 100 mV

Terminated

V

EN_L

V

1.5

EN_H

f

E/S_MIN

f

SWITCHING

=50%×f

E/S

0.6 V

1.5

When Externally

f

3.0

E/S_MAX

POR_DELAY

POR_HOLD

POR_LOW

Clocked
Fault Flag Set to

POR Pull Low
Fault Flag Reset to
POR Hi-Z State

10 25 40

10 20 30 ms

POR Sinking 4mA 300 mV

FB1 Rising Voltage

FB1_ST

for FB2 to Initiate

86 89 92 %V
Soft-start
Discharge1Resistan-

STOP_SW1,2

R

DS_SW1_U

R

DS_SW2_U

R

DS_SW1_L

R

DS_SW2_L

R

DS_SW1_U

R

DS_SW2_U

R

DS_SW1_L

R

DS_SW2_L

ce for SW1, SW2
V

=5.0V

IN

ISW=100mA

260

160

280

180

160 ºC

OTSD

10 20 30 ºC

HYS

=5.0V

V

IN

ISW=-100mA

=3.3V

V

IN

ISW=100mA

=3.3V

V

IN

=-100mA

I

SW

15 30 45

277

249

300

260

MHz

V

A

V

A

FB1
FB2

µs

FB1

Ω

mΩ

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

6

Preliminary Datasheet

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

Typical Performance Characteristics

VIN=V

=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3µH, C1=C3=10µF, C2=C2’=10µF, TA=25°C, unless

E/S

otherwise specified.

1200

1000

800

600

400

SW1, SW2 Frequency (kHz)

200

3.43.63.84.04.24.44.64.85.05.25.45.65.8

Input Voltage (V)

0.66

0.64

0.62

0.60

0.58

0.56

0.54

Supply Current (mA)

0.52

0.50

0.48

-60 -40 -20 0 20 40 60 80 100 120 140

Figure 4. SW1, SW2 Frequency vs. Input Voltage Figure 5. Supply Current vs. Temperature

2.0

1.8

2.0

1.8

1.6

1.4

1.2

1.0

Current Limit 1 (A)

0.8

1.6

1.4

1.2

1.0

Current Limit 2 (A)

0.8

0.6

-60 -40 -20 0 20 40 60 80 100 120 140

Temperature (OC)

0.6

-60 -40 -20 0 20 40 60 80 100 120 140

Figure 6. Current Limit 1 vs. Temperature

Figure 7. Current Limit 2 vs. Temperature

Temperature (oC)

Temperature (OC)

V

FB1=VFB2

=1.2V

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

7

Preliminary Datasheet

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

Typical Performance Characteristics (Continued)

VIN=V

=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3µH, C1=C3=10µF, C2=C2’=10µF, TA=25°C, unless

E/S

otherwise specified.

2.60

2.58

2.56

2.54

2.52

2.50

2.48

2.46

VO1 Voltage (V)

2.44

2.42

2.40
200 400 600 800 1000 1200

Output Current (mA)

VO2=1.2V, IO2=1A

1.300

1.275

1.250

1.225

1.200

1.175

VO2 Voltage (V)

1.150

1.125

1.100

1.075

1.050

1.025

1.000
200 400 600 800 1000 1200 1400

VO1=2.5V, IO1=1A

Output Current (mA)

Figure 8. VO1 Voltage vs. Output Current Figure 9. VO2 Voltage vs. Output Current

100

95
90
85
80
75
70
65
60

VO1 Efficiency (%)

55
50
45
40

200 400 600 800 1000 1200

Output Current (mA)

VO1=2.5V

100

95
90
85
80
75
70
65
60
55
50
45

VO2 Efficiency (%)

40
35
30
25
20

200 400 600 800 1000 1200 1400

VO2=1.2V

Output Current (mA)

Figure 10. VO1 Efficiency vs. Output Current Figure 11. VO2 Efficiency vs. Output Current

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

8

Preliminary Datasheet

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

Typical Performance Characteristics (Continued)

VIN=V

=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3µH, C1=C3=10µF, C2=C2’=10µF, TA=25°C, unless

E/S

otherwise specified.

V

IN

2V/div

V

O1

2V/div

V

O2

1V/div
V

POR

2V/div

V
2V/div

V
1V/div

V

5V/div

V

POR

5V/div

01

O2

IN

Time 4ms/div Time 400µs/div

Figure 12. Start-up from VIN Figure 13. Power-down from VIN

I

O1

500mA/div

(AC)

V

O1

100mV/div

I

O2

500mA/div

(AC)

V

O2

50mV/div

Time 100µs/div Time 100µs/div

Figure 14. Load Transient Figure 15. Load Transient

(VO=2.5V IO=0.5A to 1.0A) (VO=1.2V IO=0.5A to 1.0A)

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

9

Preliminary Datasheet

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

Typical Performance Characteristics (Continued)

VIN=V

=5V, VO1=2.5V, VO2=1.2V, L1=L2=3.3µH, C1=C3=10µF, C2=C2’=10µF, TA=25°C, unless

E/S

otherwise specified.

Output 1
Induction

Current
1A/div

V
5V/div

Output 2
Induction

Current
20mA/div

IN

Output 1
Induction

Current
1A/div

V
5V/div

Output 2
Induction
Current
1A/div

IN

Time 40µs/div Time 40µs/div

Figure 16. Short Protection for Output 1 Figure 17. Short Protection for Output 2

V
2V/div

V
2V/div
V
2V/div

Output 1
Induction

Current
1A/div

IN

O1

O2

Output 2
Induction

Current
1A/div

V
2V/div
V
2V/div

V
2V/div

IN

O1

O2

Time 10ms/div Time 10ms/div

Figure 18. Output 1 Short Recovery Figure 19. Output 2 Short Recovery

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

10

Preliminary Datasheet

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

Application Information

1. Operation

The DC-DC converters are current-mode buck
converters with a synchronous rectifier and internal
compensation. They are designed to be stable with a

1.5µH to 6.8µH inductor value and 10µF to 22µF
output capacitor. Both output voltages are resistor
programmable. The switching frequency of the
converter is fixed and the switches turn on at
alternating 180° phase intervals.

The converter operates in 2 possible modes:
Continuous Mode (CM), and Pulse Skipping Mode
(PSM). CM is the default mode under normal loading.
Under light loads, PSM mode occurs, where
switching cycles are skipped if the current demand is
low.

2. Soft-start

The DC-DC converter contains a soft-start function
that brings the output voltages up in a slowly
increasing ramp with any resistive load from open
circuit to 1A (resistive) and any capacitor from 10µF
to 22µF. During soft-start, the peak inductor current
shall not exceed 750mA until the output voltage
reaches 25% of its final value. Current limit shall be
active but not trip during soft-start into a rated
resistive load. Overshoot voltage during soft-start is
limited to 1%.

3. Power Sequencing and Enable

When power is applied and if E/S input is asserted
(High) or is toggling, the DC-DC converters will
enter RUN mode after a short settling period. If the
E/S pin is a static low, the IC will enter a SLEEP
state where it draws very little input current.

When in RUN mode, if there is no fault condition, the
VO1 output (SW1) will be the first output to begin
soft-start. When the reference voltage for FB1
reaches approximately 90% of the final value, the
VO2 output (SW2) will begin soft-start.

4. POR

Under voltage comparators are provided to monitor
the output voltages and VMON which could be the
input voltage. If any of these voltages falls below its
POR threshold, a POR open drain output will turn on
which pulls the POR pin low. After the POR
condition is cleared, there is a delay of 20ms before

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

th

the POR output transistor is turned off; when off the
POR pin is high-Z and may be pulled up high with a
resistor. The POR function has built-in deglitching.
Once the POR is detected, the power supply outputs
will be discharged prior to restart using the
soft-start/sequencing routine.

5.1Over Current and Short Circuit
Protection

The DC-DC converters shall have over current and
short circuit protection. Under any load condition , at
any time, any value of load resistor (including 0Ω)
can be applied to the DC-DC outputs instantaneously
and held in place indefinitely without the switch
current exceeding the peak current limit and withou t
the IC suffering any permanent damage or loss of
performance. The output voltage is allowed to drop
under over current or short circuit conditions.
Recovery to output voltage regulation is required
within 10ms of the instant the loading is reduced to
maximum allowable rated load; the output voltage
shall not exceed the dynamic load excursion limits
(±5% excursion) upon recovery. Over current shall
not be triggered by a sudden rate of load current
change provided the loading does not exceed the
output load rating of 1A.

6. E/S Function

Enable/Synchronization function. Pulling this pin
high statically enables the AP3421/A/B while pulling
the pin low statically for longer than 4µs will shut
down the AP3421/A/B. Applying a pulse to this pin
will synchronize SW1 and SW2 switching frequency
to ½ the external clock frequency. The external
frequency lock-in ranges from 1.5MHz to 3.0MHz.

11

Preliminary Datasheet

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

Typical Application

VIN=5V

C1'

1

POR

SW2

FB2

F

84.5k

24.9k

L2 3.3

4.7k

C2
10

=1.2VVO1=2.5V

V

O2

C2'

F

10

F

4.02k

20k

OFF ON

30.1k

20k

C3
10

C1
10

F

F

PVIN AVIN VMON

E/S

L1 3.3

SW1

AGND

FB1

PGND

Figure 20. Typical Application Circuit of AP3421 (Note 2)

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

12

Preliminary Datasheet

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

Typical Application (Continued)

VIN=3.3 to 5V

C1'

1

POR

SW2

FB2

F

36k

18k

L2 3.3

4.7k

C2

10

=1.2VVO1=2.5V

V

O2

C2'

F

10

F

4.02k

20k

OFF ON

30.1k

20k

C3
10

C1

10

F

F

PVIN AVIN VMON

E/S

L1 3.3

SW1

FB1

AGND

PGND

Figure 21. Typical Application Circuit of AP3421A /B (Note 2)

Note 2: AVIN and PVIN pin should not be connected together directly to avoid disturbance between them in
PCB layout:

1) Place a 1.0µF capacitor between AVIN pin and AGND for power filtering.

2) Place a 10µF capacitor between PVIN pin and PGND for power filtering.

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

13

Preliminary Datasheet

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

Mechanical Dimensions

DFN-3×3-10 Unit: mm(inch)

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

14

BCD Semiconductor Manufacturing Limited

IMPORTANT NOTICE

IMPORTANT NOTICE

BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi-

BCD Semiconductor Manufacturing Limited reserves the right to make changes without further notice to any products or specifi-

cations herein. BCD Semiconductor Manufacturing Limited does not assume any responsibility for use of any its products for any

cations herein. BCD Semiconductor Manufacturing Limited does not assume any responsibility for use of any its products for any

particular purpose, nor does BCD Semiconductor Manufacturing Limited assume any liability arising out of the application or use

particular purpose, nor does BCD Semiconductor Manufacturing Limited assume any liability arising out of the application or use

of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or

of any its products or circuits. BCD Semiconductor Manufacturing Limited does not convey any license under its patent rights or

other rights nor the rights of others.

other rights nor the rights of others.

http://www.bcdsemi.com

MAIN SITE

MAIN SITE

- Headquarters

BCD Semiconductor Manufacturing Limited

BCD Semiconductor Manufactur ing Limited

- Wafer Fab

No. 1600, Zi Xing Road, Shanghai ZiZhu Science-based Industrial Park, 200241, China

Shanghai SIM-BCD Semiconductor Manufacturing Limited

Tel: [phone], Fax: [phone]

800, Yi Shan Road, Shanghai 200233, China
Tel: [phone], Fax: [phone]

REGIONAL SALES OFFICE

Shenzhen Office

REGIONAL SALES OFFICE

Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd., Shenzhen Office

Shenzhen Office

Unit A Room 1203, Skyworth Bldg., Gaoxin Ave.1.S., Nanshan District, Shenzhen,

Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd. Shenzhen Office

China

Advanced Analog Circuits (Shanghai) Corporation Shenzhen Office

Tel: [phone]

Room E, 5F, Noble Center, No.1006, 3rd Fuzhong Road, Futian District, Shenzhen 518026, China

Fax: [phone]

Tel: [phone]
Fax: [phone]

- Wafer Fab

BCD Semiconductor Manufacturing Limited

Shanghai SIM-BCD Semiconductor Manufacturing Co., Ltd.

- IC Design Group

800 Yi Shan Road, Shanghai 200233, China

Advanced Analog Circuits (Shanghai) Corporation

Tel: [phone], Fax: [phone]

8F, Zone B, 900, Yi Shan Road, Shanghai 200233, China
Tel: [phone], Fax: [phone]

Taiwan Office
BCD Semiconductor (Taiwan) Company Limited

Taiwan Office

4F, 298-1, Rui Guang Road, Nei-Hu District, Taipei,

BCD Semiconductor (Taiwan) Company Limited

Tai wan

4F, 298-1, Rui Guang Road, Nei-Hu District, Taipei,

Tel: [phone]

Taiwan

Fax: [phone]

Tel: [phone]
Fax: [phone]

USA Office
BCD Semiconductor Corp.

USA Office

30920 Huntwood Ave. Hayward,

BCD Semiconductor Corporation

CA 94544, USA

30920 Huntwood Ave. Hayward,

Tel : [phone]

CA 94544, U.S.A

Fax: [phone]

Tel : [phone]
Fax: [phone]