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PDF L7986TA Data sheet ( Hoja de datos )
| Número de pieza | L7986TA | |
| Descripción | 3A step-down switching regulator | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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L7986TA
3 A step-down switching regulator
Features
■ 3 A DC output current
■ 4.5 V to 38 V input voltage
■ Output voltage adjustable from 0.6 V
■ 250 kHz switching frequency, programmable
up to 1 MHz
■ Internal soft-start and enable
■ Low dropout operation: 100% duty cycle
■ Voltage feed-forward
■ Zero load current operation
■ Overcurrent and thermal protection
■ HSOP8 package
■ Guarantee overtemperature range (-40 °C to
125 °C)
Applications
■ Automotive:
– Car audio, car infotainment
■ Industrial:
– PLD, PLA, FPGA, chargers
■ Networking: XDSL, modems, DC-DC modules
■ Computer:
– Optical storage, hard disk drive, printers
■ LED driving
Datasheet − production data
HSOP8 exposed pad
Description
The L7986TA is a step-down switching regulator
with 3.7 A (min.) current limited embedded power
MOSFET, so it is able to deliver up to 3 A current
to the load depending on the application
conditions.
The input voltage can range from 4.5 V to 38 V,
while the output voltage can be set starting from
0.6 V to VIN.
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 HSOP package with exposed pad allows the
reduction of RthJA down to 40 °C/W.
October 2012
This is information on a product in full production.
Doc ID 022098 Rev 3
1/43
www.st.com
43
Free Datasheet http://www.datasheet4u.com/
1 page  
L7986TA
2 Maximum ratings
Table 2. Absolute maximum ratings
Symbol
Parameter
Vcc
OUT
FSW, COMP, SYNCH
EN
Input voltage
Output DC voltage
Analog pin
Enable pin
FB
PTOT
TJ
Tstg
Feedback voltage
Power dissipation
at TA < 60 °C
HSOP
Junction temperature range
Storage temperature range
3 Thermal data
Table 3. Thermal data
Symbol
Parameter
RthJA
Maximum thermal resistance
junction-ambient (1)
1. Package mounted on demonstration board.
HSOP8
Maximum ratings
Value
45
-0.3 to VCC
-0.3 to 4
-0.3 to VCC
-0.3 to 1.5
2
-40 to 150
-55 to 150
Unit
V
W
°C
°C
Value
40
Unit
°C/W
Doc ID 022098 Rev 3
5/43
Free Datasheet http://www.datasheet4u.com/
5 Page 
L7986TA
Functional description
5.2 Soft-start
The soft-start is essential to assure correct and safe startup of the step-down converter. It
avoids inrush current surge and makes the output voltage increase monothonically.
The soft-start is performed by a staircase ramp on the non-inverting input (VREF) of the error
amplifier. So the output voltage slew rate is:
Equation 1
SROUT
=
SRVREF ⋅
⎛
⎝
1
+
RR-----12--⎠⎞
where SRVREF is the slew rate of the non-inverting input, while R1and R2 is the resistor
divider to regulate the output voltage (see Figure 6). The soft-start staircase consists of 64
steps of 9.5 mV each, from 0 V to 0.6 V. The time base of one step is of 32 clock cycles. So
the soft-start time and then the output voltage slew rate depend on the switching frequency.
Figure 6. Soft-start scheme.
Soft-start time results:
Equation 2
SSTIME
=
3----2-----⋅-----6----4--
Fsw
For example, with a switching frequency of 250 kHz the SSTIME is 8 ms.
Doc ID 022098 Rev 3
11/43
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
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