A5974D
Up to 2.5 A step-down switching regulator for automotive
applications
Datasheet
-
production data
Application
HSOP8 - exposed pad
Dedicated to automotive applications
Description
Features
Qualified following the AEC-Q100
requirements (see PPAP for more details)
2.5 A DC output current
Operating input voltage from 4 V to 36 V
3.3 V / (± 2%) reference voltage
Output voltage adjustable from 1.235 V to 35 V
Low dropout operation: 100% duty cycle
250 kHz internally fixed frequency
Voltage feed-forward
Zero load current operation
Internal current limiting
Inhibit for zero current consumption
Synchronization
Protection against feedback disconnection
Thermal shutdown
Figure 1. Application schematic
U1
VIN =4V TO 36V
L1
15uH
TP2
VOUT
The A5974D is a step-down monolithic power
switching regulator with a minimum switch current
limit of 3.1 A, so it is able to deliver up to 2.5 A DC
current to the load depending on the application
conditions. The output voltage can be set from
1.235 V to 35 V. The high current level is also
achieved thanks to an HSOP8 package with an
exposed frame, that allows to reduce the R
th(JA)
down to approximately 40 °C/W. The device uses
an internal P-channel DMOS transistor (with
a typical R
DS(on)
of 250 m) as a switching
element to minimize the size of the external
components. An internal oscillator fixes the
switching frequency at 250 kHz. Having
a minimum input voltage of 4 V only it fits the
automotive applications requiring the device
operation even in cold crank conditions. A pulse-
by-pulse current limit with the internal frequency
modulation offers an effective constant current
short-circuit protection.
8
TP1
VCC
VREF
SYNC
COMP
INH
3
VOUT
1
6
2
4
A5974D
EX-PAD
9
FB
GND
7
D1
STPS3L40U
R1
5.6K
5
C1
10uF
50V
C2
68nF
50V
C3
100p
R3
10K
R2
3.3K
C9
C4
33nF
TP3
GND
330uF
small signal
power plane
TP4
GND
June 2014
This is information on a product in full production.
DocID018774 Rev 2
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Contents
A5974D
Contents
1
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1
1.2
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
2.2
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
4
5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Datasheet parameters over the temperature range . . . . . . . . . . . . . . . . 8
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Voltages monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
PWM comparator and power stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6
Additional features and protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1
6.2
6.3
Feedback disconnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Output overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Zero load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
7
Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1
7.2
7.3
Error amplifier and compensation network . . . . . . . . . . . . . . . . . . . . . . . . 16
LC filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
PWM comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
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DocID018774 Rev 2
A5974D
Contents
8
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1
8.2
8.3
Component selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.3.1
8.3.2
Thermal resistance RthJA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Thermal impedance Z
THJ-A
(t) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.4
8.5
8.6
8.7
8.8
8.9
8.10
8.11
8.12
R.M.S. current of the embedded Power MOSFET . . . . . . . . . . . . . . . . . . 30
Short-circuit protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Positive buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Negative buck-boost regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Floating boost current generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Synchronization example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Compensation network with MLCC at the output . . . . . . . . . . . . . . . . . . . 39
External SOFT_START network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
9
10
11
12
Typical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
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46
Pin settings
A5974D
1
1.1
Pin settings
Pin connection
Figure 2. Pin connection (top view)
1.2
Pin description
Table 1. Pin description
No.
1
2
3
4
5
6
7
8
Pin
OUT
SYNCH
INH
COMP
FB
VREF
GND
VCC
Regulator output.
Master/slave synchronization.
A logical signal (active high) disables the device. If INH not used the pin
must be grounded. When it is open an internal pull-up disables the
device.
E/A output for frequency compensation.
Feedback input. Connecting directly to this pin results in an output
voltage of 1.23 V. An external resistive divider is required for higher
output voltages.
3.3 V V
REF
. No cap is requested for stability.
Ground.
Unregulated DC input voltage.
Description
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DocID018774 Rev 2
A5974D
Electrical data
2
2.1
Electrical data
Maximum ratings
Table 2. Absolute maximum ratings
Symbol
V
8
V
1
I
1
V
4
, V
5
V
3
V
2
P
TOT
T
J
T
STG
Input voltage
OUT pin DC voltage
OUT pin peak voltage at
t
= 0.1
s
Maximum output current
Analog pins
INH
SYNCH
Power dissipation at T
A
60 °C
Operating junction temperature range
Storage temperature range
Parameter
Value
40
-1 to 40
-5 to 40
Int. limit.
4
-0.3 to V
CC
-0.3 to 4
2.25
-40 to 150
-55 to 150
V
V
V
W
°C
°C
Unit
V
V
V
2.2
Thermal data
Table 3. Thermal data
Symbol
R
thJA
Parameter
Maximum thermal resistance junction ambient
Value
40
(1)
Unit
°C/W
1. Package mounted on evaluation board.
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