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PDF AP3421A Data sheet ( Hoja de datos )
| Número de pieza | AP3421A | |
| Descripción | Dual 1.0A Synchronous Step-down Converters | |
| Fabricantes | BCD Semiconductor | |
| Logotipo |  |
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Preliminary Datasheet
1.3MHz, Dual 1.0A Synchronous Step-down Converters AP3421/A/B
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
• 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
• 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
Feb. 2013 Rev. 1. 4
DFN-3×3-10
Figure 1. Package Type of AP3421/A/B
BCD Semiconductor Manufacturing Limited
1
1 page  
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
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
VIN
VFB
VE/S
VSW
θJA
TJ
TSTG
TLEAD
Value
-0.3 to 7
-0.3 to VIN+0.3
-0.3 to VIN+0.3
VPGND-1 to VIN+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
Symbol
VIN
AP3421
AP3421A/B
IO1 (Max)
IO2 (Max)
TA
5
Min
Max
Unit
4.5
3.0
5.5
5.5
V
1A
1A
-40 85 °C
BCD Semiconductor Manufacturing Limited
5 Page 
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
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 without
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.
Feb. 2013 Rev. 1. 4
BCD Semiconductor Manufacturing Limited
11
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet AP3421A.PDF ] | |
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