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AD8240YRMZ-R7

P1-P3P4-P6P7-P9P10-P12P13-P13
AD8240
Rev. 0 | Page 3 of 12
SPECIFICATIONS
T
A
= operating temperature range, V
PLUS
= 13.5 V, unless otherwise noted.
Table 1.
Parameter Conditions Min Typ Max Unit
V
O
5 V Reference = 5 V 12 V
V
O
Regulation
1
at 25°C V
PLUS
= 13 V to 27 V −3 ±1 +3 %
V
O
Regulation
2
-40°C to 125°C V
PLUS
= 13 V to 27 V −6 ±2 +6 %
I
OUT
3
R
SHUNT
= 0.4 Ω 500 mA
V
O
Rise Time I
OUT
= 250 mA, C
M
= 22 nF, CL = 47 nF 12 µs
V
SENSE
Gain 24
V
SENSE
Accuracy −7 ±3 +7 %
V
SENSE
Output Impedance 8 10 12 kΩ
Base Drive 15 mA
PWM Turn-On Threshold 3.5 V
PWM Turn-Off Threshold 1.4 V
V
SENSE
Latch-Off Threshold
4
0 0.1 0.3 V
Latch-Off Delay
5
2 µs
PWM Frequency Range DC 500 Hz
C
M
22 nF
C
LOAD
Range CL = 47 nF −30 +30 %
Operating Current
6
V
PLUS
> 13 V 360 µA
V
PLUS
Operating Range 9 27 V
Shutdown Current PWM low 10 µA
5 V Reference Current 160 200 240 µA
Operating Temperature Range −40 +125 °C
1
V
O
= 12/5 of the applied reference voltage ±1% typical. Minimum V
PLUS
voltage for regulation depends on the external transistor V
be
and the shunt voltage.
2
V
O
= 12/5 of the applied reference voltage ±2% typical. Minimum V
PLUS
voltage for regulation depends on the external transistor V
be
and the shunt voltage.
3
The maximum output current level is set by the selection of the current shunt and power transistor.
4
(V
SENSE
– 5 V Reference) The latch-off level is determined by the output level of the sense amplifier. When the amplifier output approaches 5 V, the output is latched off.
This allows the maximum current output level to be determined by the shunt resistor value. Latch-off can be restored to on by cycling the PWM input off and back on.
5
Internal delay only. The external delay depends on the external capacitor values, LED string impedance, and wiring inductance.
6
This specifies V
PLUS
only—ground current includes external transistor base drive.
AD8240
Rev. 0 | Page 4 of 12
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameters Rating
Supply Voltage, Continuous 27 V
Supply Voltage, Transient 30 V
Reverse Supply Protection −0.3 V
Operating Temperature 125°C
Storage Temperature −65°C to +150°C
Output Short-Circuit Duration
1
Indefinite
1
Output short circuits result in a latch-off condition.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
AD8240
Rev. 0 | Page 5 of 12
PRODUCT DESCRIPTION
The AD8240 consists of four functional blocks labeled A
through D, as shown in Figure 2.
B
GND
V
O
V
SENSE
5V
REFERENCE
PWM
V
PLUS
BASESHUNT
04824-0-002
C
AD8240
D
A
Figure 2. Simplified Functional Block Diagram
Table 3 briefly describes the blocks, while the sections that
follow provide more detailed information.
Table 3.
Block Description
A Linear regulator
B High-side current-sense amplifier
C Comparator
D Driver
LINEAR REGULATOR (BLOCK A)
The simplified architecture of the linear regulator block is an
amplifier and resistor divider. One input to the amplifier is
tied to the 5 V reference. The other input is tied to a resistor
divider that sets the ratio of the 5 V reference to V
O
. As a
result, the accuracy of the voltage output is proportional to
the accuracy of the 5 V reference. For example, if the 5 V
reference is 5% high (5.25 V), the output is 5% high (12.6 V).
HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH
OPEN LED DETECTION (BLOCK B)
This amplifier is used to measure the LED current by ampli-
fying the voltage across a user-selected shunt resistor. It has a
gain of 24 and an overall accuracy of 5%. The output of the
amplifier is typically connected to a microcontroller A/D
converter input so that the condition of the LED lamp can be
determined. This output can also be tied to other devices such
as a latching comparator or output buffer. It is important to note
that the output of this amplifier has a relatively high impedance
of approximately 10 kΩ. As a result, a buffer amplifier should be
used if the load is less than 100 kΩ.
COMPARATOR WITH LATCH-OFF OVERCURRENT
PROTECTION (BLOCK C)
This block is used to shut down the output in the case of a
short circuit or an overcurrent condition. When the output
of the high-side current-sense amplifier approaches 5 V, the
comparator output switches, causing the driver to latch off the
output voltage.
INTELLIGENT DRIVER (BLOCK D)
The intelligent driver provides multiple functions:
• Level shifts and conditions the output of the regulator
amplifier to drive an external user-selected power
transistor.
• Accepts PWM input so that LED brightness can be
controlled by a user-supplied PWM signal.
• The PWM input can also be used as a simple on/off
control for applications that do not require variable
brightness.
• Latch-off input that latches the output off when the
comparator trips during an overcurrent event. The latch
is reset by cycling the PWM input.
P1-P3P4-P6P7-P9P10-P12P13-P13

AD8240YRMZ-R7

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LED Lighting Drivers IC LED Dvr/Monitor
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