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參數資料
| 型號： | AAT3171 |
| 廠商： | Advanced Analog Technology,lnc. |
| 英文描述： | High Current, High Efficiency Charge Pump with Auto-Timer |
| 中文描述： | 大電流，高效率電荷泵與自動定時器 |
| 文件頁數： | 12/19頁 |
| 文件大小： | 382K |
| 代理商： | AAT3171 |
AAT3171
High Current, High Efficiency
Charge Pump with Auto-Timer
12
3171.2007.03.1.1
For examples of standard 1% values where the
LED flash current level is targeted for 700mA, see
Table 3.
Table 3: Open-Drain I/O Example
Resistor Values.
If the I/O port must be configured as an open-drain
PMOS type output, the appropriate equations can
be generated from these same concepts. As done
in the previous example, the necessary values can
then be calculated.
As a reference, the equations applicable to the
PMOS case are:
The value to use for V
IO
must come from the I/O
supply voltage used in the system. 0.7V is the typ-
ical value of the V
RSET
parameter found in the
Electrical Characteristics.
For a push-pull I/O port output configuration, first
calculate the overall R
SET
value needed for the
desired flash level LED current:
Next, choose a reasonable value for R
1
. A value
that is slightly larger than R
SET
, calculated from
above, is appropriate. Calculate R
2
and then calcu-
late the torch mode current level that results:
Once again, the current and resistance values used
in the equations come from the conditions placed on
the I
DX
parameter of the Electrical Characteristics
table. 0.7V is the typical value for the V
RSET
param-
eter. The value to use for V
IO
must come from the
I/O supply voltage used in the system.
Example standard 1% values are provided in Table 4.
Table 4: Push-Pull I/O Example
Resistor Values.
In all of the approaches mentioned, the open-drain
NMOS or PMOS type configurations offer the most
flexibility for current level selection.
When configured as an output, if the I/O port is only
push-pull type, then the equivalent open-drain
NMOS can also be realized. To realize this, acti-
vate the port as output only when driving the line
low. Otherwise, to release the line, set the port to
be tri-stated.
Device Power Efficiency
The AAT3171 power conversion efficiency
depends on the charge pump mode. By definition,
device efficiency is expressed as the output power
delivered to the LED divided by the total input
power consumed.
η
= P
OUT
P
IN
R1
(k
Ω
)
169
165
162
160
R2
(k
Ω
)
1000
1000
1000
1000
I
LED
I
LED
Torch (mA)
Flash (mA)
95
111
124
132
776
792
805
813
I
LED
(torch) = 600mA · 187k
Ω
·
-
R
2
- R
1
R
1
· R
2
V
IO
0.7V · R
2
R
SET
· R
1
R
1
- R
SET
R
2
=
600mA · 187k
Ω
I
LED
(flash)
R
SET
=
V
IO
0.7
I
LED
(torch)
600mA · 187k
Ω
1
R
1
R
2
=
- 1
-
600mA · 187k
Ω
I
LED
(flash)
R
1
=
R1
(k
Ω
)
920
732
649
562
R2
(k
Ω
)
193
205
210
223
I
LED
I
LED
Torch (mA)
Flash (mA)
122
153
173
200
703
701
707
703
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