A4491
Triple Output Step-Down Switching Regulator
Features and Benefits
▪
Three buck converters in a single package
▪
4.5 to 23 V input voltage range
▪
550 kHz fixed frequency
▪
Multiphase switching for smaller components and
lower EMI
▪
Independent control of each converter for sequencing and
shutdown control
▪
Power-on-reset flag with adjustable delay
▪
Internal compensation to minimize components and
simply design
▪
4 × 4 mm QFN Package, small PCB footprint
Description
Designed to provide the power supply requirements of printers,
office automation, industrial, and portable equipment, the
A4491 provides three high current, high performance, switching
regulator outputs in a single package, saving space, cost and
component count.
High frequency switching allows selection of inexpensive
inductors and small ceramic output capacitors. The turn-on
cycles of the regulators are interleaved to minimize stresses on
the input capacitors and to reduce EMI. Independent Enable
pins simplify power sequencing and shutdown capabilities,
and a power-on-reset (POR) circuit with user configurable
delay indicates when enabled regulators are in specification.
Continued on the next page…
Package: 20-contact QFN (suffix ES)
Applications:
▪
Photo, inkjet, and portable printers
• Set-top boxes
• Tablet computing
• Other Consumer Electronics applications
• Point-of-sale applications
• Security systems
• Gaming machines
• Other Industrial applications
Approximate size
Typical Application
V
BB
VDD
PORZ
CPOR
Microcontroller or
Controller Logic
CP1 CP2
VCP VBB1
LX1
V
REG1
FB1
VBB2
LX2
FB2
A4491
ENB1
ENB2
ENB3
V
REG2
PGND
VBB3
LX3
V
REG3
FB3
GND
4491-DS, Rev. 1
A4491
Description (continued)
Triple Output Step-Down Switching Regulator
The POR flag also indicates when the input voltage drops below
specification, giving the system controller advance warning while
the switchers continue to operate down to the shutdown level.
Internal diagnostics provide comprehensive protection against
overloads, input undervoltages, and overtemperatures.
Output current capability is
≈
4.5A total for all 3 outputs, depending
on the combinations of V
IN
and each V
OUT
level.
The A4491 is provided in a 20-contact, 4 mm × 4 mm, 0.75 mm
nominal overall height QFN, with exposed pad for enhanced
thermal dissipation. It is lead (Pb) free, with 100% matte tin
leadframe plating.
Selection Guide
Part Number
A4491EESTR-T
Packing
1500 pieces per 7-in. reel
Operating Temperature Range
(°C)
–40 to 85
Absolute Maximum Ratings (reference
to GND)
Characteristic
Load Supply Voltage
LX1, LX2, and LX3 Pins
PORZ and VDD Pins
ENBx Pin Input Current
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
Symbol
V
BB
V
LXn
V
IN
I
ENBx
T
A
T
J
(max)
T
stg
Driven by a current-limited voltage source
Range E
Notes
Rating
24
–1 to 24
–0.3 to 7
1
–40 to 85
150
–55 to 150
Units
V
V
V
mA
ºC
ºC
ºC
Recommended Operating Conditions
Characteristic
Load Supply Voltage
LX1, LX2, and LX3 Pins
Operating Ambient Temperature
Junction Temperature
Symbol
V
BB
V
LXn
T
A
T
J
Conditions
To operate at V
BB
< 6 V, connect V
DD
supply to the V
BB
supply. See Powering
Configurations section.
Min.
4.5
–0.7
–40
–40
Typ.
–
–
–
–
Max.
23
23
85
125
Units
V
V
ºC
ºC
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 Units
37
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
A4491
Triple Output Step-Down Switching Regulator
Functional Block Diagram
C2
47 nF
CP2
CP1
V
BB
C1
100 nF
V
BB
VDD
Regulator
Charge Pump
VCP
C3
Switch
47 nF
VBB1
C4
VCP
10
μF
L1
LX1
Switcher #1
Switcher Control
D1
R1
FB1
R2
10
μF
15
μH
C5
V
REG1
5 V / 1.5 A
V
BB
Bias Supply
100 kΩ
ENB1
SS
VBB2
C6
VCP
LX2
ENB2
V
DD
SS
Switcher #2
Switcher Control
D2
10
μF
R3
FB2
PORZ
POR Block
C14
470 nF
ENB3
SS
CPOR
VCP
LX3
Switcher #3
Switcher Control
FB3
PGND
GND
R6
D3
10
μF
R5
10
μF
10
μF
10
μF
L3
4.7
μH
C10
C11
C12
VBB3
C9
10
μF
V
REG3
1.0 V / 1.5 A
C13
R4
10
μF
10
μF
C7
V
REG2
3.3 V / 1.5 A
C8
L2
10
μH
Note: All capacitors ceramic X5R.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4491
Triple Output Step-Down Switching Regulator
Pin-out Diagram
20 ENB1
18 VBB1
17 VBB3
19 LX1
16 LX3
FB1
VDD
GND
FB2
ENB2
1
2
3
4
5
VCP 10
6
7
8
9
PAD
15
14
13
12
11
ENB3
FB3
PGND
CP1
CP2
CPOR
VBB2
Terminal List
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
–
1
GND
2
The
Name
FB1
VDD
GND
1
FB2
ENB2
LX2
VBB2
2
CPOR
PORZ
VCP
CP2
CP1
PGND
1
FB3
ENB3
LX3
VBB3
2
VBB1
2
LX1
ENB1
PAD
3
Feedback REG1
Bias supply
Ground
Feedback REG2
PORZ
LX2
Function
Enable REG2, logic input, active high
Switch node REG2
Input supply for REG2
POR delay adjustment
Power on reset output, active low
Charge pump reservoir
Charge pump capacitor terminal
Charge pump capacitor terminal
Ground for charge pump circuitry
Feedback REG3
Enable REG3, logic input, active high
Switch node REG3
Input supply for REG3
Input supply for REG1
Switch node REG1
Enable REG1, logic input, active high
Exposed pad for enhanced thermal dissipation
and PGND should be connected externally.
three VBBx pins should be connected together externally.
3
Thermal pad should be connected to the ground (0 V) plane using thermal vias.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4491
Characteristics
General
VBB Quiescent Current
VDD Supply Range
VDD Quiescent Current
REG1, REG2, and REG3
Feedback Input Bias Current
Feedback Voltage
Fixed Frequency
Maximum Duty Cycle
Minimum Duty Cycle
Triple Output Step-Down Switching Regulator
Symbol
Test Conditions
ENBx = high, I
LOAD
= 0 mA, V
BB
= 12 V,
current drawn by feedback resistors ignored
ENBx = 0 V
ENBx = high
ENBx = 0 V
Min.
Typ.
Max.
Units
ELECTRICAL CHARACTERISTICS
*
at T
A
= 25°C, V
BB
= 12 V, V
DD
supplied externally, unless noted otherwise
I
BBON
I
BBOFF
V
DD
I
DD
–
–
3.3
–
–
–400
1
1
–
–
1
–100
±1
550
–
5
450
700
560
870
1.25
–
–
500
–
–
–
115
85
80
5
4.3
4.2
4.1
3.5
500
600
3.6
165
15
2
–
5.5
6
–
100
–
630
–
–
–
–
–
–
1.875
0.8
–
–
1
0.4
1
155
–
–
–
4.7
4.6
4.7
4.3
–
–
–
–
–
mA
μA
V
mA
μA
nA
%
kHz
%
%
mΩ
mΩ
mΩ
mΩ
A
ms
V
V
mV
μA
V
μA
ms
%V
FB
%V
FB
%
V
V
V
V
mV
mV
V
°C
°C
I
BIAS
V
FB
f
SW
DC
max
DC
min
T
J
= 25°C, I
LOAD
= 1.5 A, V
BB
= 6.0 V
T
J
= 125°C, I
LOAD
= 1.5 A, V
BB
= 6.0 V
T
J
= 25°C, I
LOAD
= 1.5 A, V
BB
= 4.5 V
T
J
= 125°C, I
LOAD
= 1.5 A, V
BB
= 4.5 V
Peak current through switch with D = 0.9
With respect to 0.8 V target voltage; V
BB
= 6 to 23 V
–
470
90
–
–
–
–
–
2.0
0.625
–
2.0
300
Buck Switch On-Resistance
R
DS(on)
Current Limit Threshold
Soft Start Duration
Logic Inputs and Outputs
ENBx Input Voltage
ENBx Input Hysteresis
ENBx Input Current
PORZ Output (Open Drain)
PORZ Output Leakage Current
Power-On Reset Duration
Protection
VREGx Undervoltage Lockout Startup
VREGx Undervoltage Lockout Shutdown
VREGx Undervoltage Lockout
Startup Hysteresis
VBB Undervoltage Lockout Startup
VBB Undervoltage Lockout Shutdown
VBB Undervoltage Lockout
Shutdown Hysteresis
VBB Undervoltage Warning Threshold
Junction Overtemperature Shutdown
Junction Overtemperature Shutdown
Hysteresis
*
For
I
LIM
t
ss
V
IL
V
IH
V
I(hys)
I
IL
V
PORZL
I
PORZH
t
POR
V
REGUV(su)
V
REGUV(sd)
V
REGUV(suhys)
V
BBUV(su)
V
BBCPUV(su)
V
BBUV(sd)
V
BBCPUV(sd)
V
BBUV(sdhys)
V
IH
≤
5 V
I
PORZL
= 1 mA, fault asserted
V
PORZ
= 5 V, fault not asserted
C
POR
= 470 nF
FB1, FB2, and FB3 rising
FB1, FB2, and FB3 falling
–1
–
–1
75
–
–
–
No external VDD supply, V
BB
rising
External VDD supply, V
BB
rising
No external VDD supply, V
BB
falling
External VDD supply, V
BB
falling
No external VDD supply
V
BB
falling (forces PORZ low); switchers continue
to operate
Temperature rising
Recovery = T
JTSD
–T
JTSD(hys)
3.7
3.8
3.6
3.0
–
–
–
–
–
V
BBCPUV(sdhys)
External VDD supply
V
BBUV(por)
T
JTSD
T
JTSD(hys)
input and output current specifications, negative current is defined as coming out of (sourcing) the specified pin.
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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