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PDF A7986A Data sheet ( Hoja de datos )
| Número de pieza | A7986A | |
| Descripción | 3A step-down switching regulator | |
| Fabricantes | STMicroelectronics | |
| Logotipo |  |
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A7986A
3 A step-down switching regulator for automotive applications
Datasheet - production data
Applications
Dedicated to automotive applications
Automotive LED driving
HSOP8 exposed pad
Features
Qualified following AEC-Q100 requirements
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
Description
The A7986A is a step-down switching regulator
with a 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 HSOP8 package with exposed pad allows
the reduction of Rth(JA) down to 40 °C/W.
Figure 1. Application circuit
March 2014
This is information on a product in full production.
DocID022801 Rev 6
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1 page  
A7986A
2 Maximum ratings
Maximum ratings
Symbol
VCC
OUT
FSW, COMP, SYNCH
EN
FB
PTOT
TJ
Tstg
Table 2. Absolute maximum ratings
Parameter
Input voltage
Output DC voltage
Analog pin
Enable pin
Feedback voltage
Power dissipation at TA < 60 °C
Junction temperature range
Storage temperature range
HSOP8
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
3 Thermal data
Table 3. Thermal data
Symbol
Parameter
Rth(JA) Maximum thermal resistance junction ambient(1)
1. Package mounted on demonstration board.
HSOP8
Value
40
Unit
°C/W
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A7986A
Functional description
5.2 Soft-start
Soft-start is essential to assure a correct and safe startup of the step-down converter. It
avoids inrush current surge and makes the output voltage increase monothonically.
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 7). 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 7. Soft-start scheme
Soft-start time results:
Equation 2
SSTIME = 3----F2----s---w-6---4--
For example, with a switching frequency of 250 kHz, the SSTIME is 8 ms.
DocID022801 Rev 6
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| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet A7986A.PDF ] | |
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