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 buck and linear regulators
▪ Enable input
▪ 6 to 50 V supply voltage range
▪ Overcurrent protection
▪ Undervoltage lockout (UVLO)
▪ Thermal shutdown protection
DESCRIPTION
The A4402 is a dual-output regulator, combining in a single
package a constant on-time buck regulator and a linear regulator
(LDO)—each with adjustable output voltages. It is ideal for
applications that require two regulated voltages, such as in
microcontroller- or DSP-based applications requiring core
and I/O voltage rails.
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, allowing the use of small low value inductors
and capacitors while avoiding sensitive EMI frequency bands
such as AM radio in automotive applications.
Protection features include undervoltage lockout and thermal
shutdown. In case of a shorted load, each regulator features
overcurrent protection.
The device has an integrated power-on reset with adjustable
delay to monitor LDO output voltage and provide a signal that
can be used to reset a DSP or microcontroller. It also includes
a watchdog circuit.
The A4402 is provided in a 16-pin eTSSOP, with exposed
pad for enhanced thermal dissipation. It is lead (Pb) free, with
100% matte tin leadframe plating.
APPLICATIONS:
A
utomotive
(“K”
version
)
• Power steering control units
• Transmission control units
• Lighting control units
• Infotainment
• Cluster
• Centerstack
• Other body control
C
ommerCiAl
(“e”
version
)
• Photo and inkjet printers
• Industrial controls
• Distributed power systems
• Networking applications
• Point-of-sale
• Security systems
PACKAGE:
16-pin eTSSOP
with exposed thermal pad
(suffix LP)
Not to scale
Typical Application
TON
C
TSET
TSET
0.15 µF
C
POR
POR
0.33 µF
R
ton
750
kΩ
VIN1
0.1 µF
10 µF
Switching Regulator Output
V
SW
5V
V
BAT
Efficiency vs. Output Current
90
85
5
3.3
V
OUT
(V)
BOOT
LX
ISEN
0.01 µF
L1
33 µH
RSENSE
4.7 µF
R1
31.6
kΩ
R2
9.76
kΩ
A 4402
Efficiency %
Linear Regulator Output
V
LIN
3.3 V
250 mA
1 µF
80
75
70
65
60
0
200
400
GND
GND
V
O2
20
kΩ
NPOR
ENB
WDI
4.7
kΩ
GND
FB2
VIN2
VO2
FB1
R3
10
kΩ
600
800
1000 1200
I
OUT
(mA)
R4
5.62
kΩ
Data is for reference only. Efficiency data from circuit shown in left panel.
4402-DS, Rev. 12
MCO-0000345
November 28, 2017
A4402
Constant On-Time Buck Converter
With Integrated Linear Regulator
SELECTION GUIDE
Part Number
A4402ELPTR-T
A4402KLPTR-T
Ambient Operating
Temperature, T
A
–40°C to 85°C
–40°C to 150°C
Packing
4000 pieces per 13-inch reel
Package
16-pin eTSSOP with exposed thermal pad
ABSOLUTE MAXIMUM RATINGS
Characteristic
VIN1 Pin
VIN2 Pin
LX Pin
ISEN Pin
ENB Pin
VO2 Pin
WDI Pin
TON Pin
FB1 and FB2 Pins
NPOR
TSET Pin
POR Pin
BOOT Pin
Ambient Operating Temperature
Junction Temperature
Storage Temperature Range
Symbol
V
IN1
V
IN2
V
LX
V
ISEN
V
ENB
V
O2
V
WDI
V
TON
V
FBx
V
NPOR
V
TSET
V
POR
V
BOOT
T
A
T
J(max)
T
stg
Range E
Range K
Notes
Rating
–0.3 to 50
–0.3 to 7
–1 to 50
–0.5 to 1
–0.3 to 7
–0.3 to 7
–0.3 to 6
–0.3 to 7
–0.3 to 7
–0.3 to 6.5
–0.3 to 7
–0.3 to 6
V
LX
to V
IN1
+ 7
–40 to 85
–40 to 150
150
–40 to 150
Unit
V
V
V
V
V
V
V
V
V
V
V
V
V
°C
°C
°C
°C
THERMAL CHARACTERISTICS
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
On 4-layer PCB based on JEDEC standard JESD51-7
Value
34
Unit
°C/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4402
Constant On-Time Buck Converter
With Integrated Linear Regulator
FUNCTIONAL BLOCK DIAGRAM
C
TSET
TSET
0.15 µF
WDI
C
POR
POR
0.33 µF
Soft Start
Ramp Generator
Watchdog Timer
V
REF
BOOT
TON
0.01 µF
VIN1
R
ton
750
kΩ
V
BAT
Boot
Charge
0.1 µF
10 µF
LX
ISEN
L1
33 µH
4.7 µF
R
SENSE
V
SW
5V
Switch PWM
Control
ENB
GND
GND
V
FB2
Switch
Disable
V
O2
20
kΩ
NPOR
R1
31.6
kΩ
FB1
R2
9.76
kΩ
FAULT
VIN2
TSD
VO2
V
SW
ENB
WDI
4.7
kΩ
VIN1
VIN2
R3
10
kΩ
1 µF
V
LIN
3.3 V
250 mA
Internal
Regulator
V
REG
V
REF
V
REG
V
REF
FB2
R4
5.62
kΩ
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4402
Constant On-Time Buck Converter
With Integrated Linear Regulator
PINOUT DIAGRAM AND TERMINAL LIST
TON 1
GND 2
FB2 3
VIN2 4
VO2 5
WDI 6
TSET 7
NPOR 8
PAD
16 ENB
15 VIN1
14 GND
13 LX
12 BOOT
11 ISEN
10 POR
9 FB1
LP-16 PINOUT DIAGRAM
TERMINAL LIST TABLE
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
–
Name
TON
GND
FB2
VIN2
VO2
WDI
TSET
NPOR
FB1
POR
ISEN
BOOT
LX
GND
VIN1
ENB
PAD
On time setting terminal
Ground
Feedback for V
LIN
Input voltage 2
Regulator 2 output
Watchdog input
Soft start and watchdog timing capacitor terminal
Fault output
Feedback for V
SW
POR delay
Current sense, limit setting for switching regulator, connect to GND
through series resistor
Boot node for LX
Switching regulator output
Ground
Input voltage 1
Enable input
Exposed thermal pad
Function
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4402
Constant On-Time Buck Converter
With Integrated Linear Regulator
ELECTRICAL CHARACTERISTICS
[1]
:
Valid for Temperature Range E version at T
J
= 25°C and
Characteristics
Supply Quiescent Current
ENB Logic Input Voltage
ENB Hysteresis
ENB Logic Input Current
[2]
LINEAR REGULATOR
Feedback Voltage
V
O2
Undervoltage Lockout Threshold
V
O2
Undervoltage Lockout Hysteresis
Feedback Input Bias Current
[2]
Current Limit
SWITCHING REGULATOR
Feedback Voltage
Feedback Input Bias Current
Switcher On Time
t
on
Low Voltage Threshold
t
on
High Voltage Threshold
Changeover Hysteresis
Minimum On-Time
Minimum Off-Time
Buck Switch On-Resistance
ISEN Voltage
Valley Current Limit Threshold
PROTECTION CIRCUITRY
NPOR Output Voltage
NPOR Leakage Current
NPOR Reset
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
V
NPOR
I
NPOR
V
NPORRESET
T
JTSD
T
JTSDHYS
I
NPOR
= 1 mA
V
NPOR
= 5.5 V
20 kΩ pullup connected to VOUT2
T
J
rising
V
FB1
I
FB1
t
on
V
PL
V
PH
V
HYS
t
onmin
t
offmin
R
DS(on)
V
ISEN
I
lim
R
SENSE
= 0.27 Ω
6 V < V
IN1
< 8 V
T
J
= 25°C, I
LOAD
= 1 A
T
J
= 125°C, I
LOAD
= 1 A
I
OUT
= I
SW
+ I
LIN
= 1 mA to 1.0 A, 8 V < V
IN1
< 18 V
V
IN1
= 6 V
V
IN1
= 19.25 V, R
ton
= 750 kΩ
V
IN1
= 13.5 V, R
ton
= 750 kΩ
V
IN1
= 8 V, R
ton
= 750 kΩ
V
IN1
rising
V
IN1
rising
V
FB2
V
O2UVLO
V
O2UVHYS
I
FB2
I
O2
1 mA < I
O2
< 250 mA, 3.3 V < V
IN2
< 5 V
V
O2
rising based on FB voltage
Symbol
I
IN(Q)
V
ENB
V
ENBHYS
I
ENB
High input level, V
ENB
= 3 V
Low input level, V
ENB
< 0.4 V
Test Conditions
V
ENB
= 5 V, I
OUT
= I
SW
+ I
LIN
= 0 mA, 13.5 V < V
IN1
< 50 V
V
ENB
= 0 V, 13.5 V < V
IN1
< 18 V, I
OUT
= I
SW
+ I
LIN
= 0 mA
V
ENB
rising
for Temperature Range K version at T
J
= –40°C to 150°C, V
IN1
= 6 to 50 V (unless otherwise noted)
Min.
1
–
2.0
–
–
–2
1.156
0.896
30
–100
250
1.139
–400
450
165
1050
8.1
15.75
–
80
130
–
–
–150
–
–
–
–
–
–
–
Typ.
–
–
2.28
100
–
–
1.180
0.944
50
100
–
1.180
–100
640
230
1480
9
17.5
250
–
–
400
650
–250
740
–
–
–
–
170
15
Max.
6
1
2.56
–
100
2
1.204
0.990
70
400
350
1.221
100
830
300
1925
9.9
19.25
–
–
–
–
–
–350
–
550
400
1.5
0.7
–
–
Unit
mA
µA
V
mV
µA
µA
V
V
mV
nA
mA
V
nA
ns
ns
ns
V
V
mV
ns
ns
mΩ
mΩ
mV
mA
mA
mV
µA
V
°C
°C
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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