AME, Inc.
AME5134
n
Detailed Description
The AME5134 features a minimum off-time, current-
limited control scheme. Operation can be best under-
stood by referring to Figure 2. When the voltage at the
FB pin is less than regulation threshold, NMOS switch is
turned on and the inductor current ramps up to the cur-
rent limit. Once the current in the inductor reaches peak
current limit the NMOS switch will be turned off for 250nS,
at mean time the SW voltage will rise to a voltage that
equals output voltage plus a diode drop and the inductor
current will begin to decrease as shown in Figure 2. Dur-
ing this time the energy stored in the inductor is trans-
ferred to C
OUT
and the load. After 250ns, if the voltage at
FB is above the regulation threshold, the NMOS switch
stays off. If the voltage at FB is below the regulation thresh-
old, the NMOS switch turns back on and the cycle re-
peats.
Shutdown
The AME5134 features a low-current shutdown fea-
ture. When EN is low, the IC turns off, reducing its sup-
ply current to approximately 0.1µA. For normal opera-
tion, drive EN high or connect to V
IN
.
Soft-Start
Soft-start provided on the AME5134 to minimize in-
rush current. The soft-start time is set with an external
capacitor, C3. Use the following equation to solve for C3:
C3 =
tss
2 x 10
5
High-Efficiency, 30V Boost
Converters for 2 to 6 White LEDs
Dimming Control
A. Use a DC Signal to CTRL pin
At CTRL, applying a DC signal in the range of 0V to
1.8V control the LED current. CTRL can be overdriven;
however, applying a CTRL greater than 1.8V does not in-
crease the LED current above the level at 1.8V. ( See the
LED Current vs. CTRL Voltage graph.)
B. Use a PWM Signal to CTRL pin
The CTRL input is used as a digital input allowing LED
brightness control with a logic-level PWM signal applied
directly to CTRL. The frequency range is from 100Hz to
10kHz, while 0% duty cycle corresponds to minimum
current, and 100% duty cycle corresponds to full current.
(See the LED Current vs. CTRL Duty Cycle graph). The
CTRL resistor and SS capacitor from a low pass filter, so
PWM dimming results in DC current to the LEDs without
the need for additional RC filters.
Capacitor Selection
A 0.47µF ceramic output capacitor (C2) is recom-
mended for most applications. For circuits driving six or
fewer LEDs, use a 4.7µF ceramic input capacitor (C1).
For best stability over a wide temperature range, use
capacitors with an X5R, X7R, or better dielectric.
Inductor Selection
The AME5134 has a 220mA inductor current limit and
can drive up to six LEDs at 20mA. The selected induc-
tor must have a saturation current that meets the maxi-
mum peak current of the converter. For best efficiency,
the inductor's DC resistance should also be as low as
possible.
Diode Selection
The AME5134 high switching frequency demands a
high-speed rectification diode (D1) for optimum efficiency.
A Schottky diode is recommended due to its fast recov-
ery time and low forward-voltage drop.
Where t
ss
is the soft-start time.
Overvoltage Protection
OVP is designed to prevent the output voltage from
exceeding the maximum internal NMOS switch voltage
rating of 30V. The peak output voltage in an overvoltage-
protection event is set with a resistor-divider from the
output connected to 0V (R1 and R2). Select a value for
R2(10kΩ is recommended), then solve for R1 using the
following equation:
R1 = R2 x (
V
OUT
V
OV
1)
Where V
OV
is the overvoltage threshold, and V
OUT
is the
desired peak output voltage.
Rev.C.01
7
AME [ ANALOG MICROELECTRONICS ]
