A6986F
Automotive 38 V, 1.5 A synchronous step-down switching regulator
with 30
μA
quiescent current
Datasheet
-
production data
Description
The A6986F automotive grade device is a step-
down monolithic switching regulator able to
deliver up to 1.5 A DC. The output voltage
adjustability ranges from 0.85 V to VIN. The 100%
duty cycle capability and the wide input voltage
range meet the cold crank and load dump
specifications for automotive systems. The “Low
Consumption Mode” (LCM) is designed for
applications active during car parking, so it
maximizes the efficiency at light-load with
controlled output voltage ripple. The “Low Noise
Mode” (LNM) makes the switching frequency
constant and minimizes the output voltage ripple
overload current range, meeting the low noise
application specification like car audio. The output
voltage supervisor manages the reset phase for
any digital load (µC, FPGA). The RST open
collector output can also implement output
voltage sequencing during the power-up phase.
The synchronous rectification, designed for high
efficiency at medium - heavy load, and the high
switching frequency capability make the size of
the application compact. Pulse by pulse current
sensing on both power elements implements an
effective constant current protection.
HTSSOP16 (R
TH
= 40 °C/W)
Features
AEC-Q100 qualified
1.5 A DC output current
4 V to 38 V operating input voltage
Low consumption mode or low noise mode
30 µA I
Q
at light-load (LCM V
OUT
= 3.3 V)
8 µA I
Q-SHTDWN
Adjustable f
SW
(250 kHz - 2 MHz)
Fixed output voltage (3.3 V and 5 V) or
adjustable from 0.85 V to V
IN
Embedded output voltage supervisor
Synchronization
Adjustable soft-start time
Internal current limiting
Overvoltage protection
Output voltage sequencing
Peak current mode architecture
R
DSON HS
= 180 m, R
DSON LS
= 150 m
Thermal shutdown
Applications
Designed for automotive systems
Battery powered applications
Car body applications (LCM)
Car audio and low noise applications (LNM)
February 2017
This is information on a product in full production.
DocID027739 Rev 5
1/78
www.st.com
Contents
A6986F
Contents
1
2
Application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1
2.2
2.3
2.4
2.5
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
ESD protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3
4
5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Datasheet parameters over the temperature range . . . . . . . . . . . . . . . 13
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1
5.2
5.3
Power supply and voltage reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Switchover feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Voltages monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Soft-start and inhibit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.3.1
5.3.2
Ratiometric startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Output voltage sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.4
5.5
5.6
5.7
5.8
Error amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Output voltage line regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Output voltage load regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
High-side switch resistance vs. input voltage . . . . . . . . . . . . . . . . . . . . . . 26
Light-load operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.8.1
5.8.2
5.8.3
Low noise mode (LNM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Low consumption mode (LCM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Quiescent current in LCM with switchover . . . . . . . . . . . . . . . . . . . . . . . 34
5.9
Switchover feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
5.9.1
5.9.2
LCM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
LNM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
5.10
Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
OCP and switchover feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
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Contents
5.11
5.12
Overvoltage protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6
Closing the loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6.1
6.2
6.3
6.4
6.5
G
CO
(s) control to output transfer function . . . . . . . . . . . . . . . . . . . . . . . . 42
Error amplifier compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Voltage divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Total loop gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Compensation network design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
7
Application notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
7.1
7.2
7.3
7.4
7.5
7.6
Output voltage adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Switching frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
MLF pin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Voltage supervisor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Synchronization (LNM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Design of the power components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
7.6.1
7.6.2
7.6.3
Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
8
9
10
11
Application board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Efficiency curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
EMC testing results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
11.1
HTSSOP16 package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
12
13
Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
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Application schematic
A6986F
1
Application schematic
Figure 1. Application schematic
4/78
DocID027739 Rev 5
A6986F
Pin settings
2
2.1
Pin settings
Pin connection
Figure 2. Pin connection (top view)
2.2
No.
1
Pin
RST
Pin description
Table 1. Pin description
Description
The RST open collector output is driven low when the output voltage is out of regulation. The RST
is released after an adjustable time DELAY once the output voltage is over the active delay
threshold.
Connect a ceramic capacitor (≥ 470 nF) to filter internal voltage reference. This pin supplies the
embedded analog circuitry.
An open collector stage can disable the device clamping this pin to GND (INH mode). An internal
current generator (4
A typ.) charges the external capacitor to implement the soft-start.
The pin features Master / Slave synchronization in LNM (see
Section 5.8.1 on page 26)
and skip
current level selection in LCM (see
Section 5.8.2 on page 27).
In LNM, leave this pin floating when
not used.
A pull up resistor (E24 series only) to VCC or pull down to GND selects the switching frequency.
Pinstrapping is active only before the soft-start phase to minimize the IC consumption.
A pull up resistor (E24 series only) to VCC or pull down to GND selects the low noise mode/low
consumption mode and the active RST threshold. Pinstrapping is active only before the soft-start
phase to minimize the IC consumption.
Output of the error amplifier. The designed compensation network is connected at this pin.
An external capacitor connected at this pin sets the time DELAY to assert the rising edge of the
RST o.c. after the output voltage is over the reset threshold. If this pin is left floating, RST is like
a Power Good.
Output voltage sensing
Signal GND
2
3
VCC
SS/INH
SYNCH/
ISKP
FSW
4
5
6
7
8
9
10
MLF
COMP
DELAY
VOUT
SGND
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