overvoltage protection (OVP), and thermal shutdown (TSD).
In addition, the A8651 provides open-circuit, adjacent pin
short-circuit, and short-to-ground protection at every pin to
satisfy the most demanding automotive applications.
Continued on the next page…
DESCRIPTION
Package: 20-pin TSSOP with exposed
thermal pad (suffix LP)
APPLICATIONS:
•
•
•
•
Not to scale
SYNCin
C
SYNC
V
IN
C
IN1
EN1
R
Z1
C
Z1
C
IN2
EN2
R
Z2
C
Z2
C
SS2
R
SET2
C
SS1
R
SET1
11
VIN2
R
FSET
20 VIN1
16 GND
2
PGND1
3
EN1
17
COMP1
19
SS1
4
ISET1
5
GPS/infotainment
Automotive audio
Home audio
Network and telecom
1
L
O1
V
OUT1
C
O1
FSET/SYNC
SW1
FB1
A8651
NPOR1
SW2
FB2
18
R
FB1
R
FB2
R
PU1
NPOR1
15
10
L
O2
C
P1
V
OUT2
C
O2
C
P2
9 PGND2
8
EN2
13
COMP2
12
SS2
7
ISET2
14
R
FB3
R
FB4
R
PU2
NPOR2
6
NPOR2
Typical Application Diagram
A8651-DS, Rev. 8
December 5, 2016
A8651
Low Input Voltage, Adjustable Frequency Dual Synchronous
2 A / 2 A Buck Regulator with Synchronization, 2× EN, and 2× NPOR
DESCRIPTION (CONTINUED)
The A8651 device is available in a 20-pin TSSOP package with
exposed thermal pad for enhanced thermal dissipation (suffix LP).
It is lead (Pb) free, with 100% matte-tin leadframe plating.
Selection Guide
Part Number
A8651KLPTR-T
[2]
A8651KLPTR-T-1
1
2
Operating Ambient
Temperature Range
T
A
, (°C)
–40 to 125
Package
20-pin TSSOP with
exposed
thermal pad
Packing
[1]
Leadframe Plating
4000 pieces per
13-in. reel
100% matte tin
Contact Allegro™ for additional packing options.
Part variant discontinued. Date of status change: September 1, 2016. Suggested replacement: A8651KLPTR-T-1.
Specifications
Table of Contents
2
3
4
5
Functional Description
Absolute Maximum Ratings
Thermal Characteristics
Top-Level Functional Block Diagram
Detailed Functional Block Diagram
Pinout Diagram and Terminal List
Electrical Characteristics
Characteristic Performance
Timing Diagram
Overview
Reference Voltage
Oscillator/Switching Frequency (R
FSET
, f
OSC
)
Transconductance Error Amplifier
Slope Compensation
ENx, VINx, and Sleep Mode
Synchronization (FSET/SYNC)
Power MOSFETs
Pulse Width Modulation (PWM)
Current Sense Amplifier
Soft-Start (Startup) and Inrush Current Control
3
6
7
10
12
13
13
13
13
13
13
14
14
14
14
14
14
Design and Component Selection
Pre-Biased Startup
15
Active Low Power-On Reset (NPORx)
16
Protection Features
16
Undervoltage Lockout (UVLO)
16
16
Thermal Shutdown (TSD)
Overvoltage Protection (OVP)
16
Pulse-by-Pulse Overcurrent Protection (OCP) 16
Output Short Circuit (Hiccup Mode) Protection 17
Setting the Output Voltage (V
OUT1
, R
FBx
)
PWM Switching Frequency (R
FSET
)
Output Inductor (L
O
)
Output Capacitors
Input Capacitors
Soft-Start and Hiccup Mode Timing (C
SS1
)
Compensation Components (RZ, CZ, CP)
A Generalized Tuning Procedure
Power Dissipation and Thermal Calculations
PCB Component Placement and Routing
Package Outline Diagram
20
20
20
21
22
22
23
24
26
28
30
33
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A8651
Low Input Voltage, Adjustable Frequency Dual Synchronous
2 A / 2 A Buck Regulator with Synchronization, 2× EN, and 2× NPOR
SPECIFICATIONS
Absolute Maximum Ratings
1
Characteristic
VIN1 and VIN2 to GND
SW1 and SW2 to GND
2
All Other Pins
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
1
Operation
Symbol
V
IN
V
SW
–
T
A
T
J
(max)
T
stg
K temperature range
Continuous
t < 50 ns
Notes
Rating
–0.3 to 6.0
–0.3 to V
IN
+ 0.3
–1.0 to V
IN
+2.0
–0.3 to 6.0
–40 to 125
150
–55 to 150
Unit
V
V
V
V
ºC
ºC
ºC
at levels beyond the ratings listed in this table may cause permanent damage to the device. The Absolute Maximum ratings are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated in the Electrical Characteristics table is not implied. Exposure to Absolute
Maximum-rated conditions for extended periods may affect device reliability.
2
SW1 and SW2 have internal clamp diodes to GND and V . Applications that forward bias these diodes should take care not to exceed the A8651 package power
IN
dissipation limits.
Thermal Characteristics:
May require derating at maximum conditions; see application information
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
On 4-layer PCB based on JEDEC standard
Value
32
Unit
ºC/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
3
A8651
Low Input Voltage, Adjustable Frequency Dual Synchronous
2 A / 2 A Buck Regulator with Synchronization, 2× EN, and 2× NPOR
VIN1
VIN1 UVLO
ISENSE1
A8651
VIN1
START
VIN1
STOP
GND
EN1
COMP1
SS1
ISET1
SWITCHER #1
(SW1)
ADJUSTABLE
V
OUT
V
REF
&
SYNCHRONOUS
BUCK
CLK0°
TSD
80 mΩ
f
SW1
55 mΩ
SW1
POR &
V
REF
PGND1
FB1
POR
2
FSET/
SYNC
f
OSC
or f
SYNC
with
180° shift
NPOR1
VIN2
VIN2
UVLO
ISENSE2
EN2
COMP2
SS2
ISET2
VIN2
START
VIN2
STOP
SWITCHER #2
(SW2)
ADJUSTABLE
V
OUT
SYNCHRONOUS
BUCK
CLK180°
TSD
80 mΩ
f
SW2
55 mΩ
SW2
PGND2
FB2
2
TSD
NPOR2
Note: VIN1 supplies the bandgap (V
REF
), oscillator, TSD, and other critical circuits
Top-Level Functional Block Diagram
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A8651
Low Input Voltage, Adjustable Frequency Dual Synchronous
2 A / 2 A Buck Regulator with Synchronization, 2× EN, and 2× NPOR
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