Enable pin. Logic input. High = normal operation, Low = shutdown (charge
pump and all current sources OFF).
LED Outputs - Group A
LED Outputs - Group B
Enable for Group-A LEDs (current outputs). Logic input.
High = Group-A LEDs ON. Low = Group A LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.
Enable for Group-B LEDs (current outputs). Logic input.
High = Group-B LEDs ON. Low = Group B LEDs OFF.
Pulsing this pin with a PWM signal (100Hz-1kHz) can be used to dim LEDs.
Placing a resistor (R
SET
) between this pin and GND sets the LED current for
all LEDs. LED Current = 100 x (1.25V ÷ R
SET
).
Pin Descriptions
Input voltage. Input range: 2.7V to 5.5V.
E7
EN-B
C7
I
SET
Ordering Information
Order Information
LM2796TL
LM2796TLX
Package
TLA18 Micro SMD
Supplied As
250 Units, Tape & Reel
3000 Units, Tape & Reel
www.national.com
2
LM2796
Absolute Maximum Ratings
(Notes 1, 2)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
V
IN
pin voltage
EN, ENA, ENB pin voltages
Continuous Power Dissipation
(Note 3)
Junction Temperature (T
J-MAX
)
Storage Temperature Range
Maximum Lead Temperature
(Soldering, 10 sec.)
ESD Rating (Note 4)Human Body
Model:
Machine Model
-0.3V to 7.1V
-0.3V to (V
IN
+0.3V)
w/ 5.6V max
Internally Limited
150 C
-65
o
C to +150
o
C
265
o
C
2.0kV
200V
o
Operating Rating
Input Voltage Range
(Notes 1, 2)
2.7V to 5.5V
-30˚C to +125˚C
-30˚C to +85˚C
Junction Temperature (T
J
) Range
Ambient Temperature (T
A
) Range
(Note 5)
Thermal Properties
Juntion-to-Ambient Thermal
Resistance (θ
JA
), (Note 6)
100˚C/W
Electrical Characteristics
(Notes 2, 7)
Limits in standard typeface and typical values apply for T
J
= 25
o
C. Limits in
boldface
type apply over the full operating junction
temperature range (-30˚C
≤
T
J
≤
+85˚C) . Unless otherwise specified: V
IN
= 3.6V; V
Dxx
= 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
= 8.35kΩ; C
IN
, C
1
,
C
2
, and C
POUT
= 1µF. (Note 8)
Symbol
Parameter
Condition
3.0V
≤
V
IN
≤
4.2V, and V
IN
= 5.5V
2.5V
≤
V
Dxx
≤
3.8V;
R
SET
= 8.35kΩ
3.0V
≤
V
IN
≤
5.5V;
2.5V
≤
V
Dxx
≤
3.6V;
R
SET
= 6.25kΩ
I
Dxx
Output Current Regulation
3.0V
≤
V
IN
≤
5.5V;
2.5V
≤
V
Dxx
≤
3.9V;
R
SET
= 12.5kΩ
2.7V
≤
V
IN
≤
3.0V;
2.5V
≤
V
Dxx
≤
3.3V;
R
SET
= 8.35kΩ
ENA and ENB ON (all 7 I
DX
outputs active),
V
IN
= 3.0V, C
IN
= C
OUT
= 2.2µF
I
Dxx-MATCH
Current Matching Between Any
Two Group A Outputs or Group
B Outputs
I
Q
Quiescent Supply Current
V
IN
= 3.0V (Note 10)
Min
13.8
(-8%)
Typ
15
20
mA
10
mA
15
mA
15
1
Max
16.2
(+8%)
Units
mA
(%)
mA
%
2.7V
≤
V
IN
≤
4.2V;
No Load Current,
EN = ON, ENA = ENB = OFF
2.7V
≤
V
IN
≤
5.5V, EN = OFF
2.7V
≤
V
IN
≤
5.5V
3.5
6
mA
I
SD
V
SET
I
Dxx
/I
SET
R
OUT
V
HR
Shutdown Supply Current
I
SET
Pin Voltage
Output Current to Current Set
Ratio
3
1.25
100
2.7
320
4.5
µA
V
Charge Pump Output Resistance V
IN
= 3.0V
(Note 11)
Current Source Headroom
Voltage Requirement (Note 12)
I
Dxx
= 95% X I
Dxx
(nom)
R
SET
= 8.35kΩ
(I
Dxx
(nom)
≈
15mA)
I
Dxx
= 95%X I
Dxx
(nom)
R
SET
= 12.5kΩ
(I
Dxx
(nom)
≈
10mA)
3
Ω
mV
220
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LM2796
Electrical Characteristics
(Notes 2, 7)
(Continued)
Limits in standard typeface and typical values apply for T
J
= 25
o
C. Limits in
boldface
type apply over the full operating junction
temperature range (-30˚C
≤
T
J
≤
+85˚C) . Unless otherwise specified: V
IN
= 3.6V; V
Dxx
= 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
= 8.35kΩ; C
IN
, C
1
,
C
2
, and C
POUT
= 1µF. (Note 8)
Symbol
f
SW
t
START
1.5x/1x
Parameter
Switching Frequency
Start-up Time
Charge pump gain cross-over:
Gain = 1.5 when V
IN
is below
threshold. Gain = 1 when V
IN
is
above threshold.
Input Logic Low
Input Logic High
Input Leakage Current
3.0V
≤
V
IN
≤
4.2V
I
Dx
= 90% steady state
1.5x to 1x Threshold
1x to 1.5x Threshold
Condition
Min
325
Typ
500
100
4.75
4.55
Max
675
Units
kHz
µs
V
V
Logic Pin Specifications: EN, ENA, ENB
V
IL
V
IH
I
LEAK
2.7V
≤
V
IN
≤
5.5V
2.7V
≤
V
IN
≤
5.5V
V
ENx
= 0V
V
ENx
= 3V (Note 13)
0
1.1
0.1
10
0.5
V
IN
V
V
µA
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
= 160˚C (typ.) and disengages at T
J
=
120˚C (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
= 125˚C), 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 300kΩ(typ.) pull-down resistor connected internally between each enable pin (EN, ENA, ENB) and GND.
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Part 6：条件状态和分支 在探讨CPSR时我们已经接触了条件状态。我们通过跳转（分支）或者一些只有满足特定条件才执行的指令来控制程序在运行时的执行流。通过CPSR寄存器中的特定bit位来表示条件状态。这些位根据指令每次执行的结果而不断变化。例如，比较运算时如果两个数相等，那么就置CPSR中的Zero位（Z=1），实际上是因为：a - b = 0，这种情况下就是相等状态。如果第一个数大，那么就...[详细]
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