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參數(shù)資料
| 型號(hào)： | LM2796 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | LED驅(qū)動(dòng)器 |
| 英文描述： | Dual-Display White LED Driver with 3/2x Switched Capacitor Boost |
| 中文描述： | 雙顯示器白光LED驅(qū)動(dòng)3/2x開關(guān)電容升壓 |
| 文件頁數(shù)： | 4/8頁 |
| 文件大?。?/td> | 172K |
| 代理商： | LM2796 |
Electrical Characteristics
(Notes 2, 7) (Continued)
Limits in standard typeface and typical values apply for T
= 25
o
C. Limits in
boldface
type apply over the full operating junction
temperature range (-30C
≤
T
≤
+85C) . Unless otherwise specified: V
= 3.6V; V
= 3.6V; V(EN) = 2.0V; Group A and
Group B LEDs not ON simultaneously (ENA = V
IN
and ENB = GND, or ENA = GND and ENB = V
IN
); R
SET
= 8.35k
; C
IN
, C
1
,
C
2
, and C
POUT
= 1μF. (Note 8)
Symbol
Parameter
Condition
f
SW
Switching Frequency
3.0V
≤
V
IN
≤
4.2V
t
START
Start-up Time
I
Dx
= 90% steady state
1.5x/1x
Charge pump gain cross-over:
Gain = 1.5 when V
IN
is below
threshold. Gain = 1 when V
IN
is
above threshold.
Logic Pin Specifications: EN, ENA, ENB
V
IL
Input Logic Low
2.7V
≤
V
IN
≤
5.5V
V
IH
Input Logic High
2.7V
≤
V
IN
≤
5.5V
I
LEAK
Input Leakage Current
V
ENx
= 0V
V
ENx
= 3V (Note 13)
Min
325
Typ
500
100
4.75
Max
675
Units
kHz
μs
V
1.5x to 1x Threshold
1x to 1.5x Threshold
4.55
V
0
0.5
V
IN
V
V
μA
1.1
0.1
10
Note 1:
Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Operating Ratings are conditions under which operation of
the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the
Electrical Characteristics tables.
Note 2:
All voltages are with respect to the potential at the GND pin.
Note 3:
Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at T
J
= 160C (typ.) and disengages at T
J
=
120C (typ.). The thermal shutdown function is guaranteed by design.
Note 4:
The Human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. The machine model is a 200pF capacitor discharged directly
into each pin. MIL-STD-883 3015.7
Note 5:
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be
derated. Maximum ambient temperature (T
A-MAX
) is dependent on the maximum operating junction temperature (T
J-MAX-OP
= 125C), the maximum power
dissipation of the device in the application (P
D-MAX
), and the junction-to ambient thermal resistance of the part/package in the application (
θ
JA
), as given by the
following equation: T
A-MAX
= T
J-MAX-OP
– (
θ
JA
x P
D-MAX
).
Note 6:
Junction-to-ambient thermal resistance is highly dependent on application and board layout. In applications where high maximum power dissipation exists,
special care must be paid to thermal dissipation issues in board design.
Note 7:
Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm.
Note 8:
C
IN
, C
OUT
, C
1
, and C
2
: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used in setting electrical characteristics
Note 9:
If both LED groups are to be ON simultaneously, the maximum V
Dxx
voltage may need to be derated, depending on minimum input voltage conditions. Refer
to the "MAXIMUM OUTPUT CURRENT, MAXIMUM LED VOLTAGE, MINIMUM INPUT VOLTAGE" section.
Note 10:
For the two groups of outputs on a part (Group A and Group B), the following are determined: the maximum output current in the group (MAX), the
minimum output current in the group (MIN), and the average output current of the group (AVG). For each group, two matching numbers are calculated:
(MAX-AVG)/AVG and (AVG-MIN)/AVG. The largest number of the two (worst case) is considered the matching figure for the group. The matching figure for a given
part is considered to be the highest matching figure of the two groups. The typical specification provided is the most likely norm of the matching figure for all parts.
Note 11:
Output resistance (R
OUT
) models all voltage losses in the charge pump. R
OUT
can be used to estimate the voltage at the charge pump output (P
OUT
):
V
Pout
= (1.5 x V
IN
) – (R
OUT
x I
OUT
). In the equation, I
OUT
is the total output current: the sum of all active Dxx output currents and all current drawn from P
OUT
. The
equation applies when the charge pump is operating with a gain of 3/2 (V
IN
≤
4.75V typ.).
Note 12:
Headroom voltage: V
HR
= V
Pout
– V
Dxx
. If headroom voltage requirement is not met, LED current regulation will be compromised.
Note 13:
There is a 300k
(typ.) pull-down resistor connected internally between each enable pin (EN, ENA, ENB) and GND.
L
www.national.com
4
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