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PDF A4402 Data sheet ( Hoja de datos )
| Número de pieza | A4402 | |
| Descripción | Constant On-Time Buck Converter | |
| Fabricantes | Allegro Micro Systems | |
| Logotipo |  |
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A4402
Constant On-Time Buck Converter
with Integrated Linear Regulator
Features and Benefits
▪ 2 MHz switching frequency
▪ Adjustable soft start timer
▪ Watchdog input
▪ Power-on reset output
▪ Adjustable 2% buck regulator
▪ Adjustable 2% linear regulator
▪ Enable input
▪ 6 to 50 V supply voltage range
▪ Overcurrent protection
▪ Undervoltage lockout (UVLO)
▪ Thermal shutdown protection
Applications:
▪ Photo and inkjet printers
▪ Industrial controls
▪ Distributed power systems
▪ Network applications
Package: 16-pin TSSOP with exposed
thermal pad (suffix LP)
Description
The A4402 is a power management IC that combines a 2%
constant on-time buck regulator and a 2% linear regulator.
Ideal for applications that require two regulated voltages. The
buck regulator output supplies the adjustable linear regulator
to reduce power dissipation and increase overall efficiency.
The switching regulator is capable of operating above 2 MHz.A
greater than 2 MHz switching frequency enables the customer
to select low value inductors and capacitors while avoiding
EMI.
Protection features include undervoltage lockout and thermal
shutdown. In case of a shorted load, each regulator features
overcurrent protection. The A4402 also features a power-on
reset with adjustable delay for the microprocessor output.
The A4402 is provided in a 16-pin, ≤1.20 mm nominal
overall height TSSOP, with exposed pad for enhanced thermal
dissipation. It is lead (Pb) free, with 100% matte tin leadframe
plating.
Not to scale
VO2
20 kΩ
4.7 kΩ
CTSET
TSET
0.15 μF
CPOR
POR
0.33 μF
NPOR
ENB
WDI
Typical Application
TON
A 4402
GND
VIN1
BOOT
LX
ISEN
GND
GND
FB1
VIN2
VO2
FB2
Rton
750 kΩ
VBAT
0.1 μF
10 μF
0.01 μF
L1
33 μH
RSENSE
R1
31.6 kΩ
4.7 μF
Switching Regulator Output
VSW
5V
R2
9.76 kΩ
R3
10 kΩ
Linear Regulator Output
VLIN
3.3 V
300 mA
1 μF
R4
5.62 kΩ
4402-DS, Rev. 1
1 page  
A4402www.DataSheet4U.com
Constant On-Time Buck Converter
with Integrated Linear Regulator
ELECTRICAL CHARACTERISTICS1,2 (continued) valid at TJ = 25°C, VIN = 13.5 V (unless otherwise noted)
Characteristics
Symbol
Test Conditions
Min.
Typ.
Protection Circuitry
NPOR Output Voltage
NPOR Leakage Current
NPOR Reset
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
Timing Circuitry
VNPOR
INPOR
VNPORRESET
TJTSD
TJTSDHYS
INPOR = 1 mA
VNPOR = 5 V
20 kΩ pullup connected to VOUT2, VIN <
TJ rising
––
––
––
– 170
– 15
TSET Current, Watchdog Mode
TSET Valley Voltage, Watchdog
Mode
ITSETWDI
VTRIP
NPOR = high
7 10
– 1.2
TSET Reset Voltage, Watchdog
Mode
VRESET
– 0.48
WDI Frequency
WDI Duty Cycle
WDI Logic Input
fWDI
DCWDI
VWDI(0)
–
10
VIN2 ×
0.55
–
–
–
WDI Logic Input Current
IWDI VWDI = 0 to 5 V
–20
WDI Input Hysteresis
VWDIHYS
–
TSET Current, Soft Start Mode
ITSETSS
NPOR = low
14
POR Current
IPOR
3.92
1For input and output current specifications, negative current is defined as coming out of (sourcing) the specified pin.
2Performance in the range –40°C to 85°C guaranteed by design and characterization.
< 1.0
300
20
5.60
Max.
400
1
0.7
–
–
14
–
–
100
90
–
20
–
26
7.28
Units
mV
μA
V
ºC
ºC
μA
V
V
kHz
%
V
μA
mV
μA
μA
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
5 Page 
A4402www.DataSheet4U.com
Constant On-Time Buck Converter
with Integrated Linear Regulator
Application Information
Switcher On-Time and Switching Frequency In order for
the switcher to maintain regulation, the energy that is transferred
to the inductor during the on-time must be transferred to the
capacitor during the off-time. Because of this relationship, the
load current, IR drops, as well as input and output voltages, affect
the on-time of the converter. The equation that governs switcher
on-time is:
ton =
TSW × (VSW+ RLOAD× IPEAK + Vf + RSENSE× IPEAK )
VIN1+ RDS(on)× IPEAK + Vf
. (9)
The effects of the voltage drop on the inductor and trace resis-
tance affect the switching frequency. However, the frequency
variation due to these factors is small and is covered in the varia-
tion of the switcher period, TSW , which is ±25% of the target.
Removing these current dependant terms simplifies the equation:
ton =
VSW+ Vf + (VSENSE× IPEAK )
VIN1+ Vf + (VSENSE× IPEAK )
×
1
fSW
.
(10)
Be sure to use worst-case sense voltage and forward voltage of
the diode, including any effects due to temperature. For example,
given a 1 A converter with a supply voltage of 13.5 V, output
voltage is 5 V, Vf is 0.5 V, VSENSE is 0.15 V and the desired fre-
quency is 2.0 MHz. We can solve for ton as follows:
5 + 0.5 + 0.15
1
ton = 13.5 + 0.5 + 0.15 × 2×106 = 199 ns
.
The formulas above describe how ton changes based on input and
load conditions. Because load changes are minimal, and the out-
put voltage is fixed, the dominant factor that affects the on-time
is the input voltage. The converter is able to maintain a constant
period over a varying supply voltage because the on-time change
is based on the input voltage. The current into the TON terminal
is derived from a resistor tied to VIN1, which sets the on-time
proportional to the supply voltage. Selecting the resistor value,
based on the ton calculated above, is done using the following
formula:
RTON =
VIN1× (ton+ 10 ns)
3.12 × 10–12
.
(11)
After the resistor is selected and a suitable ton is found, it must
be demonstrated that ton does not, under worst-case conditions,
exceed the minimum on-time or minimum off-time of the con-
verter. The minimum on-time occurs at maximum input voltage
and minimum load. The maximum off time is occurs at minimum
supply voltage and maximum load. For supply voltages below
9.5 V and above 7 V, refer to the Low Voltage Operation section.
Low Voltage Operation The converter can run at very low
input voltages. With a 5 V output, the minimum input supply can
be as low as 6 V. When operating at high frequencies, the on-time
of the converter must be very short because the available period
is short. At high input voltages the converter must maintain very
short on-times, while at low input voltages the converter must
maintain long off-times. Rather than limit the supply voltage
range, the converter solves this problem by automatically increas-
ing the period by a factor of 3.5. With the period extended, the
converter will not violate the minimum on-time or off-time. If the
input voltage is between 9.5 V and 17 V, the converter will main-
tain a constant period. When calculating worst-case on-times and
off-times, make sure to use the multiplier if the supply voltage is
between those values.
When operating at voltages below 8 V, additional care must be
taken when selecting the inductor and diode. At low voltages
the maximum current may be limited due to the IR drops in the
current path. When selecting external components for low voltage
operation, the IR drops must be considered when determining
on-time, so the complete formula should be used to make sure the
converter does not violate the timing specification.
Inductor Selection Choosing the right inductor is critical to
the correct operation of the switcher. The converter is capable of
running at frequencies above 2 MHz. This makes it possible to
use small inductor values, which reduces cost and board area.
The inductor value is what determines the ripple current. It is
important to size the inductor so that under worst-case conditions
IVALLEY equals IAV minus half the ripple current plus reasonable
margin. If the ripple current is too large, the converter will be
current limited. Typically peak-to-peak ripple current should be
limited to 20% to 25% of the maximum average load current.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet A4402.PDF ] | |
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