A4492
Triple Output Step-Down Switching Regulator
Features and Benefits
▪
Three buck converters
▪
4.5 to 34 V input voltage range
▪
550 kHz fixed frequency
▪
Multiphase switching
▪
Independent control of each converter
▪
Power-on-reset flag
▪
Internal compensation
▪
4 × 4 mm QFN Package, small PCB footprint
▪
RoHS compliant
Description
Designed to provide the power supply requirements for a
wide range of applications, the A4492 provides three high
current, high performance, switching regulator outputs with
independent soft start.
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. A charge pump is used
to provide the supply for driving the power switches, ensuring
operation at very wide operating duty cycles and avoiding the
need for power-draining clamp circuits.
A power-on-reset circuit with user configurable delay indicates
when enabled regulators are in specification. The power-on-
reset 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.
Continued on the next page…
Package: 20-contact QFN (suffix ES)
Approximate size
Typical Application
V
BB
VDD
PORZ
CPOR
Microcontroller or
Controller Logic
CP1 CP2
VCP VBB1
LX1
V
REG1
FB1
VBB2
LX2
FB2
A4492
ENB1
ENB2
ENB3
V
REG2
PGND
VBB3
LX3
V
REG3
FB3
GND
4492-DS, Rev. 1
A4492
Triple Output Step-Down Switching Regulator
Description (continued)
The A4492 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
A4492EESTR-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
36
–1 to 36
–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.
34
34
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, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A4492
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
PWM 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
PWM Control
D2
10
μF
R3
FB2
PORZ
POR Block
C14
470 nF
ENB3
SS
CPOR
VCP
LX3
Switcher #3
PWM 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 X7R.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A4492
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, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A4492
Triple Output Step-Down Switching Regulator
ELECTRICAL CHARACTERISTICS
1
at T
A
= –40°C to 85°C, V
BB
= 6.0 to 34 V, V
DD
supplied externally, unless noted otherwise
Characteristics
General
VBB Quiescent Current
VDD Supply Range
VDD Quiescent Current
REG1, REG2, and REG3
Feedback Input Bias Current
Feedback Voltage
Output Voltage Regulation
2
PWM Frequency
Maximum Duty Cycle
Minimum Duty Cycle
I
BIAS
V
FB
V
OUT
f
SW
D
max
D
min
T
J
= –40°C, I
LOAD
= 1.5 A, V
BB
= 6.0 V
T
J
= 25°C, I
LOAD
= 1.5 A, V
BB
= 6.0 V
Buck Switch On-Resistance
R
DS(on)
T
J
= 125°C, I
LOAD
= 1.5 A, V
BB
= 6.0 V
T
J
= –40°C, I
LOAD
= 1.5 A, V
BB
= 4.5 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
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
V
IL
V
IH
V
I(hys)
I
IL
V
PORZL
I
PORZH
t
POR
V
IH
≤
5 V
I
PORZL
= 1 mA, fault asserted
V
PORZ
= 5 V, fault not asserted
C
POR
= 470 nF
–
2.0
–
–1
–
–1
75
–
–
500
–
–
–
115
0.8
–
–
1
0.4
1
175
V
V
mV
μA
V
μA
ms
I
LIM
t
ss
Peak current through switch with D = 0.9
With respect to 0.8 V target voltage
V
REGx
= 5.0 V, I
OUT
= 0 to 1.5 A, measured in volts
–400
–
–3.5
450
90
–
–
–
–
–
–
–
2.0
0.625
–100
±1.5
–
550
–
5
450
450
700
560
560
870
–
1.25
100
–
3.5
630
–
–
–
–
–
–
–
–
–
2
nA
%
%
kHz
%
%
mΩ
mΩ
mΩ
mΩ
mΩ
mΩ
A
ms
I
BBON
I
BBOFF
V
DD
I
DD
ENBx = high
ENBx = 0 V
ENBx = high, I
LOAD
= 0 mA, V
BB
= 12 V,
current drawn by feedback resistors ignored
ENBx = 0 V
–
–
3.3
–
–
1
1
–
–
1
2
–
5.5
6
–
mA
μA
V
mA
μA
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
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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