A4405
Constant On-Time Buck Regulator
With One External and Two Internal Linear Regulators
Features and Benefits
• AEC Q100 Grade 0 qualified
• Internal buck pre-regulator followed by LDO outputs
• 5.5 to 36 V VIN operating range (50 V maximum);
for start/stop, cold crank, and load dump requirements
• 2.2 MHz constant on-time buck regulator
• Valley current sensing achieves shortest buck on-times
• 50 V absolute maximum input voltage for surges
• 5.5 to 46 V input voltage range
•
−40ºC
to 150ºC junction temperature range
• Power-on reset (NPOR pin) with adjustable rising delay
• 5 V (V5P pin) internal low dropout tracking
linear regulator with both overcurrent foldback and
short-to-battery protection
Continued on the next page…
Description
The A4405 is an automotive power management IC that uses a
high frequency constant on-time 5.45 V pre-regulator to supply
two internal 5 V linear regulators and a 3.3 V linear DMOS
driver. Designed to supply CAN and microprocessor power
supplies in high temperature environments, the A4405 is ideal
for under hood applications. Efficient operation is achieved by
using a buck pre-regulator to efficiently drop the input voltage
before supplying the linear regulators; this reduces power
dissipation and increases overall regulator efficiency.
The switching regulator is capable of operating at a nominal
switching frequency of 2.2 MHz. The high switching frequency
enables the customer to select low value inductors and ceramic
capacitors while avoiding EMI in the AM frequency band.
Protection features include undervoltage lockout and thermal
shutdown. The V5P output is protected from short-to-battery
events. In case of a shorted load, all regulators feature
Continued on the next page…
Package: 20-pin TSSOP with exposed
thermal pad (suffix LP)
Applications:
Automotive Control Modules, such as:
• Electronic power steering (EPS)
• Transmission control (TCU)
• Antilock braking (ABS)
• Emissions control
Not to scale
Typical Application Circuit
0.22
μF
3.3 V
VCP
CP1
0.22
μF
V
BAT
R
TON
412 kΩ
TON
VIN
C
IN1
4.7
μF
C
IN2
4.7
μF
D
IN
B240A
4.7 kΩ
NPOR
LX
CP2
3.3 V
4.7 kΩ
D
BUCK
B240A
R
SENSE
300 mΩ
1
/ W
4
L1
10
μH,
1.3 A
65 mΩ MAX
CPOR
ISEN–
C
CPOR
0.22
μF
ENBATS
A4405
ISEN+
V
IGN
1 kΩ
100 nF
100
Ω
ENBAT
VREG
PAD
CLV33
C
VREG
10
μF
R
CL
390 mΩ
1
/ W
4
R
DROP
1.2
Ω
1
/
2
W
40 °C/W
175°C MAX
3.3 V, 400 mA
(500 mA MAX)
Enable
5V
VIN(Pin1)
D2
5V
B240A
Protected
C
V5P
1 to 2.2
μF
A
ENB
V5
0.47
μF
Q
V33
C
V5
1 to 2.2
μF
V5P
GND
G33
V33
D1
B240A
C
V33
1 to 4.7
μF
A
Protec on diodes D1 and D2 are required when the V5P pin is driving a wiring harness (or excessively long
PCB trace) where parasi c inductance will cause the voltage at the V5P to momentarily transi on above
VIN or below ground during a fault condi on.
A4405-DS, Rev. 1
A4405
Constant On-Time Buck Regulator
With One External and Two Internal Linear Regulators
Description (continued)
overcurrent protection. The A4405 also features power-on-reset
with adjustable delay for the microprocessor output.
The A4405 is supplied in a low profile (1.2 mm max) 20-pin TSSOP
package with exposed thermal pad (suffix LP). The package is lead
(Pb) free with 100% matte-tin leadframe plating
Features and Benefits (continued)
• 5 V (V5 pin) internal low dropout linear regulator with
overcurrent foldback protection
• 3.3 V (V33 pin) external linear regulator DMOS driver with a
programmable current limit (up to 500 mA) and overcurrent
foldback protection
• Logic enable input (ENB pin)
• Ignition enable input (ENBAT pin)
• Ignition status indicator (ENBATS pin)
• Buck pulse-by-pulse overcurrent protection
• Buck LX short circuit protection (latched)
• Missing asynchronous diode protection (latched)
• Switcher (VREG pin), 3.3 V (V33 pin), and charge pump
(VCP pin) undervoltage lockout protection (UVLO)
• Thermal shutdown protection (TSD)
Absolute Maximum Ratings
1
Characteristic
VIN Pin
LX Pin
VCP, CP1, and CP2 Pins
ISEN– Pin
ISEN+ Pin
ENBAT Pin
2
ENBAT Pin Current
VREG Pin
V33 Pin
G33 Pin
3
CLV33 Pin
V5P Pin
V5 Pin
TON Pin
NPOR and CPOR Pins
ENB and ENBATS Pins
Operating Ambient Temperature
Junction Temperature
Storage Temperature Range
1
Absolute
2
The
Selection Guide
Part Number
A4405KLPTR-T
Packing
4000 pieces per 13-in. reel
Symbol
V
IN
V
LX
V
VCP
, V
CPx
V
ISEN–
V
ISEN+
V
ENBAT
I
ENBAT
V
VREG
V
V33
V
G33
V
CLV33
V
V5P
V
V5
V
TON
V
xPOR
V
EN
, V
ENBATS
T
A
T
J
(max)
T
stg
Range K
t < 250 ns
Notes
Rating
–0.3 to 50
–0.3 to 50
–1.5
–0.3 to 60
–0.5 to 1
–0.5 to 0.5
–0.3
–50 to 50
–0.3 to 8
–0.3 to 7
–0.3
–0.3 to 10
–0.3 to V
IN
+0.5
–0.3 to 7
–0.3 to 50
–0.3 to 7
–0.3 to 7
–40 to 135
–40 to 150
–40 to 150
Unit
V
V
V
V
V
V
V
mA
V
V
V
V
V
V
V
V
V
°C
°C
°C
maximum ratings are limiting values that should not be exceeded under worst case operating conditions or damage may occur.
ENBAT pin is internally clamped to approximately 8.5 V due to an ESD protection device.
3
The G33 pin is internally clamped by an ESD protection device. Clamp voltages range from 10 V (min) to 15 V (max).
Thermal Characteristics
may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
Estimated on 4-layer PCB based on JEDEC standard
Value
32
Unit
ºC/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4405
Constant On-Time Buck Regulator
With One External and Two Internal Linear Regulators
Table of Contents
Specifications
Functional Block Diagram
Pin-out Diagram and Terminal List
Electrical Characteristics
2
4
5
6
9
11
11
11
11
11
11
11
12
12
13
13
13
14
14
15
15
15
15
15
16
18
18
18
18
19
19
19
19
20
21
23
26
Characteristic Performance
Functional Description
Basic Operation
Overcurrent Protection
Dropout Mode
Soft Start
Buck Pulse Width ( t
ON
)
ISEN+ and ISEN–
Switcher Overcurrent Protection
LX Short Circuit Protection
Missing Asynchronous Diode Protection
Thermal Shutdown
Power-On Reset (NPOR)
V5 Regulator
V5P Tracking Regulator
3.3 V Linear Regulator
Charge Pump
ENBAT
ENBATS
ENB
Timing Diagrams
Application Information
Switcher On-Time and Switching Frequency
Low Voltage Operation
Inductor Selection
Output Capacitor
Input Capacitor
Rectification Diode
External MOSFET Selection
3.3 V Dropping Resistor (R
DROP
)
PCB Layout
Application Circuit Performance
Package Outline Drawing
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4405
Constant On-Time Buck Regulator
With One External and Two Internal Linear Regulators
Functional Block Diagram
3.3 V
(From V33)
0.22
μF
0.22
μF
V
BAT
R
TON
412 kΩ
C
IN1
4.7
μF
TON
C
IN2
4.7
μF
D
IN
B240A
VCP
Microcontroller
Reset
4.7 kΩ
NPOR
CP1
CP2
VIN
Charge Pump
LX
C
CPOR
0.22
μF
V
IGN
1 kΩ
100
Ω
CPOR
D
BUCK
B240A
PWM Control
–
V
REG
UVLO
Fault
ENBAT
ISEN–
V
33
UVLO
TSD
Switch
Disable
+
ISEN+
R
SENSE
300 mΩ
1
/ W
4
L1
10
μH,
1.3 A
65 mΩ MAX
4.7 kΩ
ENBATS
4.0 V
H
2.2 V
L
Microcontroller
Enable
ENB
5V
B240A
Protected
D2
A
V5P
C
V5P
1 to 2.2
μF
D1
B240A
GND
V
REF
Short to Supply
Protection
PAD
V5
Regulator
A
Protec on diodes D1 and D2 are required when the V5P pin is driving a wiring harness (or excessively long
PCB trace) where parasi c inductance will cause the voltage at the V5P to momentarily transi on above
VIN or below ground during a fault condi on.
–
VIN(Pin1)
+
V5 Control and
V33 to V5P
Tracking Control
–
+
3.3 V
(From V33)
100 nF
8.5 V
Soft Start
Ramp
Generator
V
REF
ENB
0.47
μF
V
REF
V
33
V
REG
V33 FET
Driver
V
REG
V
REF
V33
VREG
Regulator V
REF
CLV33
10
μF
C
VREG
R
CL
390 mΩ
1
/ W
4
R
DROP
1.2
Ω
1
/ W
2
G33
Q
V33
3.3 V, 400 mA
(500 mA MAX)
1 to 4.7
μF
5V
C
V33
V5
1 to 2.2
μF
C
V5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4405
Constant On-Time Buck Regulator
With One External and Two Internal Linear Regulators
Pin-out Diagram
VIN 1
GND 2
TON 3
ENBAT 4
ENB 5
ENBATS 6
NPOR 7
CPOR 8
V5 9
V5P 10
PAD
20 VCP
19 CP2
18 CP1
17 LX
16 ISEN+
15 ISEN–
14 VREG
13 CLV33
12 G33
11 V33
Terminal List Table
Name
CLV33
CP1
CP2
CPOR
ENB
ENBAT
ENBATS
G33
GND
ISEN–
ISEN+
LX
NPOR
PAD
TON
V33
V5
V5P
VCP
VIN
VREG
Number
13
18
19
8
5
4
6
12
2
15
16
17
7
–
3
11
9
10
20
1
14
Function
3.3 V current sense and limit input
Charge pump capacitor terminal 1
Charge pump capacitor terminal 2
NPOR delay programming pin
Logic enable input from the microcontroller
Ignition enable input from the key or switch via a 1 kΩ resistor
Open drain ignition status output
Gate driver to the external MOSFET for 3.3 V regulation
Ground terminal
Buck negative current sense pin, sense resistor and diode node
Buck positive current sense pin, sense resistor and ground node
Buck regulator switching node
Active low, open-drain fault indication output
Exposed pad for enhanced thermal dissipation
Buck regulator on-time programming pin
3.3 V regulator output
5 V regulator output
5 V tracking, protected regulator output
Charge pump reservoir capacitor terminal
Input voltage
Buck regulator DC output, and input to the 3.3 V external regulator
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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