L5986
2.5 A step-down switching regulator
Datasheet
-
production data
Industrial: chargers, PLD, PLA, FPGA
Networking: XDSL, modems, DC-DC modules
Computer: optical storage, hard disk drive,
printers, audio/graphic cards
VFQFPN8 3 x 3 mm
HSOP8 exposed pad
LED driving
Features
2.5 A DC output current
2.9 V to 18 V input voltage
Output voltage adjustable from 0.6 V
250 kHz switching frequency, programmable
up to 1 MHz
Internal soft-start and inhibit
Low dropout operation: 100% duty cycle
Voltage feedforward
Zero load current operation
Overcurrent and thermal protection
VFQFPN 3 x 3 mm -8L and HSOP8 package
Description
The L5986 is a step-down switching regulator
with a 3.0 A (min.) current limited embedded
Power MOSFET, so it is able to deliver up to 2.5 A
current to the load depending on the application
conditions.
The input voltage can range from 2.9 V to 18 V,
while the output voltage can be set starting from
0.6 V to V
IN
. Having a minimum input voltage of
2.9 V, the device is suitable also for a 3.3 V bus.
Requiring a minimum set of external components,
the device includes an internal 250 kHz switching
frequency oscillator that can be externally
adjusted up to 1 MHz.
The QFN and the HSOP packages with an
exposed pad allow reducing the R
thJA
down to
60 °C/W and 40 °C/W respectively.
Applications
Consumer: STB, DVD, DVD recorder, car
audio, LCD TV and monitors
Figure 1. Application circuit
May 2014
This is information on a product in full production.
DocID14971 Rev 5
1/42
www.st.com
Contents
L5986
Contents
1
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1
1.2
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2
3
4
5
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Functional description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1
5.2
5.3
5.4
5.5
5.6
Oscillator and synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Error amplifier and compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Overcurrent protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Inhibit function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Hysteretic thermal shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6
Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1
6.2
6.3
6.4
Input capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Inductor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Output capacitor selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.4.1
6.4.2
Type III compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Type II compensation network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
6.5
6.6
6.7
Thermal considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Layout considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7
Application ideas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7.1
7.2
Positive buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Inverting buck-boost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
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DocID14971 Rev 5
L5986
Contents
8
9
10
Package information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Order codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
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Pin settings
L5986
1
1.1
Pin settings
Pin connection
Figure 2. Pin connection (top view)
OUT
SYNCH
INH
COMP
V
CC
GND
FSW
FB
1.2
Pin description
Table 1. Pin description
No.
1
Type
OUT
Regulator output
Master/slave synchronization. When it is left floating, a signal with
a phase shift of half a period with respect to the power turn-on is present
at the pin. When connected to an external signal at a frequency higher
than the internal one, then the device is synchronized by the external
signal, with zero phase shift.
Connecting together the SYNCH pin of two devices, the one with the
higher frequency works as a master and the other as a slave; so the two
turn-on powers have a phase shift of half a period.
A logical signal (active high) disables the device. With INH higher than
1.9 V the device is OFF and with INH lower than 0.6 V the device is ON.
Error amplifier output to be used for loop frequency compensation
Feedback input. Connecting the output voltage directly to this pin the
output voltage is regulated at 0.6 V. To have higher regulated voltages an
external resistor divider is required from the Vout to the FB pin.
The switching frequency can be increased connecting an external
resistor from the FSW pin and ground. If this pin is left floating, the device
works at its free-running frequency of 250 kHz.
Ground
Unregulated DC input voltage
Description
2
SYNCH
3
4
5
INH
COMP
FB
6
7
8
F
SW
GND
V
CC
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DocID14971 Rev 5
L5986
Maximum ratings
2
Maximum ratings
Table 2. Absolute maximum ratings
Symbol
V
CC
OUT
Input voltage
Output DC voltage
Parameter
Value
20
-0.3 to V
CC
-0.3 to 4
-0.3 to V
CC
-0.3 to 1.5
VFQFPN
HSOP
1.5.
2
-40 to 150
-55 to 150
°C
°C
W
V
Unit
F
SW
, COMP, SYNCH Analog pin
INH
FB
P
TOT
T
J
T
stg
Inhibit pin
Feedback voltage
Power dissipation at T
A
< 60 °C
Junction temperature range
Storage temperature range
3
Thermal data
Table 3. Thermal data
Symbol
R
thJA
Parameter
Maximum thermal resistance junction ambient
(1)
VFQFPN
HSOP
Value
60
40
Unit
°C/W
1. Package mounted on demonstration board.
DocID14971 Rev 5
5/42
42
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