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PDF ADT7351 Data sheet ( Hoja de datos )
| Número de pieza | ADT7351 | |
| Descripción | Step-Down Converter | |
| Fabricantes | ADtech | |
| Logotipo |  |
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ADT7351
ADT7351
Data Sheet
* This specifications are subject to be changed without notice
Oct. 31. 2011 / Rev0.0
1/15 http://www.ad-tech.co.kr
Datasheet pdf - http://www.DataSheet4U.net/
1 page  
www.DataSheet.co.kr
ADT7351
Functional Block Diagram
EN
7
Shutdown
Internal
Regulator
Voltage
Reference
OSC
VIN
2
Current
Sense
Amplifier
+
-
Regulator
Σ
RS
1 BST
FB 5
Current
Limit
Control
LOGIC
+
+
-
Error
Amplifier
-
Comparator
68
COMP SS
Figure 2. Functional Block Diagram
Absolute Maximum Ratings (Note1)
Driver
Driver
3 SW
4
GND
Parameter
Symbol
Min.
Typ.
Max.
Unit
Power supply voltage
SW pin voltage
BST pin voltage
All Other Pins
VIN
VSW
VBST
-
-0.3
-0.5
-0.3
-0.3
- 30 V
-
VIN + 0.3
V
-
VSW + 6
V
- +6 V
Max. power dissipation (Ta=25℃) (Note2)
PD
-
- 2.08 W
Thermal resistance (Note3)
ΘJA - 60 - ℃/W
Storage temperature
TSTG
-65
-
+150
℃
Junction temperature
TJ.MAX
-
-
+150
℃
Note1. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
Note2. Derate 17mW/℃ above +25℃. This is recommended to operate under this power dissipation specification.
Note3. Measured on JESD51-7, 4-layer PCB
Operating Ratings
Parameter
Power supply voltage
Output voltage
Operating temperature
Junction temperature
Symbol
VIN
VOUT
TOPR
TJ
Min.
4.5
0.92
-40
-
Typ.
12.0
-
-
-
* This specifications are subject to be changed without notice
Max.
28.0
21
+85
+125
Unit
V
V
℃
℃
Oct. 31. 2011 / Rev0.0
5/15 http://www.ad-tech.co.kr
Datasheet pdf - http://www.DataSheet4U.net/
5 Page 
www.DataSheet.co.kr
ADT7351
APPLICATION INFORMATION (continued)
Input Capacitor
The input capacitor is used to filter out discontinuous, pulsed input current and to maintain input voltage
stable. Therefore input capacitor should be able to supply the AC current to the step-down converter. Its
input ripple voltage can be estimated by:
ΔVIN
=
IOUT
FSW × CIN
×
VOUT
VIN
× ⎜⎜⎝⎛1−
VOUT
VIN
⎟⎟⎠⎞
where, CIN is input capacitor value.
The voltage rating of input capacitor must be greater than the maximum input voltage plus ripple voltage.
Since the input capacitor absorbs the input switching current, it requires an proper ripple current rating. The
RMS current in the input capacitor can be approximated by:
ICIN_RMS = IOUT ×
VOUT
VIN
× ⎜⎜⎝⎛1−
VOUT
VIN
⎟⎟⎠⎞
The worst-case condition occurs at VIN=2×VOUT (50% duty condition), and its worst RMS current is
approximately half of the IOUT. For reliable operation and best performance, the input capacitors must have
current rating higher than ICIN_RMS at worst operating conditions. Ceramic capacitors are preferred for input
capacitors because of their low ESR and high current rating. When selecting ceramic capacitors, X5R or
X7R type dielectric ceramic capacitors should be used for their better temperature and voltage
characteristics.
Output Capacitor
The output capacitor is required to maintain the DC output voltage. In a step-down converter circuit, output
ripple voltage is determined by the inductor value, switching frequency, output capacitor value and ESR.
That is:
where,
ΔVOUT
=
ΔIL
× ⎜⎜⎝⎛ ESR
+
1
8× FSW
× CO
⎟⎟⎠⎞
CO is output capacitor value,
ESR is the equivalent series resistance of the output capacitor.
Low ESR capacitors are preferred to keep the output voltage ripple low. When low ESR ceramic capacitor is
used as output capacitor, its ESR value can be waived. So, the impedance at the switching frequency is
dominated by the capacitance. Therefore the output voltage ripple is:
ΔVOUT
=
ΔIL
×
⎜⎜⎝⎛
8
×
1
FSW
× CO
⎟⎟⎠⎞
On the other hand, in the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the
switching frequency. In this case, the output voltage ripple is:
ΔVOUT = ΔIL × (ESR )
In a step-down converter, output capacitor current is continuous. Usually, the ripple current rating of the
output capacitor is not concerned because of its low ripple current.
* This specifications are subject to be changed without notice
Oct. 31. 2011 / Rev0.0
11/15
http://www.ad-tech.co.kr
Datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
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| PDF Descargar | [ Datasheet ADT7351.PDF ] | |
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