ame5142c AME, Inc., ame5142c Datasheet - Page 8

• Manufacturer Part Number: ame5142c
• Description: High Efficiency 6 White Led Driver With Open Led Protection
• Manufacturer: AME, Inc.

n Detailed Description
verter with an internal switch. The operations of AME5142C
can be understood from block diagram clearly figure.4.
The oscillator triggers the SET input of SR latch to turn
on the power switch MS at the start of each cycle. A
current sense voltage sum with a stabilizing ramp is con-
nected to the positive terminal of the PWM comparator.
When this voltage exceeds the output voltage of the error
amplifier, the SR latch is reset to turn off the power switch
till next cycle starts. The output voltage of the error am-
plifier is amplified from the difference between the refer-
ence voltage 0.15V and the feedback voltage. In this man-
ner, if the error amplifiers voltage increases, more current
is delivered to the output; if it decreases, less current is
delivered. A 28V Zener diode connects from OVP pin to
FB pin internally to provide an optional protection func-
tion which prevents SW pin from over-voltage damage.
Especially when the case of the feedback loop broken
due to component wear-out or improper connection oc-
curs.
Current Limit Protection
vent excessive stress on itself and external components
during overload conditions. The internal current limit com-
parator will disable the NMOS power device at a typical
switch peak current limit of 850mA.
Output Over-Voltage Protection
toring the output voltage. In the event that the primary
LED network is disconnected the output will increase and
be limited to 28V (TYP), which will turn the NMOS off
when the output voltage is at 28V (max.) until the output
voltage reach 28V (TYP.) or lower. The 28V limit allows
the use of 28V 1 F ceramic output capacitors creating an
overall small solution for white LED applications. If the
output ever exceeds OVP, the AME5142C will shut down.
AME5142C will not switch again until the power is re-
cycled.
Under Voltage Protection
NMOS power device off in case the input voltage or bat-
tery voltage is too low preventing an on state of the power
device conducting large amounts of current.
8
AME5142C
The AME5142C is a constant frequency step-up con-
The AME5142C has current limiting protection to pre-
The AME5142C contains dedicated circuitry for moni-
The AME5142C has an UVP comparator to turn the
AME
High Efficiency 6 White LED Driver
n Application Information
Inductor Selection
plications is 10 H. Small size and better efficiency are
the major concerns for portable device, such as
AME5142C used for dual panel mobile phone. The in-
ductor should have low DCR for better efficiency. To avoid
inductor saturation, current rating should be at least 1A.
The input range is 2.8V to 5.5V.
Capacitor Selection
voltage stability, to increase the input capacitor value or
using LC filter is feasible, especially in the Li-ion battery
application. 0.22 F output capacitor is sufficient to re-
duce output voltage ripple. For better voltage filtering,
ceramic capacitors with low ESR are recommended. X5R
and X7R types are suitable because of their wider volt-
age and temperature ranges.
Diode Selection
cause of its lower forward voltage drop and faster reverse
recovery. Using schottky diode can get better efficiency.
The high speed rectification is also a good characteristic
of schottky diode for high switching frequency. Current
rating of the diode must meet the root mean square of
the peak current and output average current multiplica-
tion.
Duty Cycle
determines the maximum boost ratio of output-to-
input voltage that the converter can attain in mode of
operation. The duty cycle for a given boost application is
defined as: This applies for continuous mode operation.
The recommended value of inductor for AME5142C ap-
1 F input capacitor can reduce input ripple. For better
Schottky diode is a good choice for AME5142C be-
The maximum duty cycle of the switching regulator
D =
With Open LED Protection
V
V
OUT
OUT
+ V
+ V
DIODE
DIODE
- V
- V
SW
IN
Rev. B.01