AP6714 Datasheet, PDF (13/15 Pages) Diodes Incorporated – 1.8MHz SYNCHRONOUS BOOST CONVERTER

AP6714
1.8MHz SYNCHRONOUS BOOST CONVERTER
Application Information (Continued)
„ Inductor Selection
The high frequency operation of the AP6714 allows the use of small surface mount inductors. The minimum
inductance value is limited by the following constraints:
L > ^{VIN (MIN ) × (VOUT (MAX ) − VIN (MIN ) )} H
f × I _{SW (Ripple)} × V_{OUT (MAX )}
Where
f= Operating frequency (Hz)
I = SW(Ripple) Allowable Inductor Current Ripple (A)
VIN(MIN)= Minimum Input Voltage (V)
VOUT(MAX)= Maximum Output Voltage (V)
„ Over Current Protection (OCP)
A resistor is required to connect PGND pin and OCP pin to prevent an overload occurs at the output. The
output voltage will drop and duty cycle will be reduced if the OCP exceeds 0.16V. When ROCP is 0.1Ω, the
maximum switching current to operate normally is 1.6A (0.16V/0.1Ω). However, the actual switching current is
related to duty ratio. By the way, larger ROCP is recommended when VOUT − VIN ≤ 0.5V since the dropped output
voltage is smaller then regular case while an overload condition exists.
Internal circuit of OCP function
„ Thermal Information
The maximum recommended junction temperature (TJ) of AP6714 is 125°C. The thermal resistance of the
10-pin MSOP10 package is RθJA = 161°C/W, if the Power PAD is soldered. Specified regulator operation is
assured to an ambient temperature TA of 45°C. Therefore, the maximum power dissipation is about 500mW.
More power can be dissipated if the maximum ambient temperature of the application is lower.
P_{D(MAX )}
=
T_{J (MAX )} − T_A
R_θJA
„ Designing a PC Board
Good PC board layout is important to achieve optimal performance from AP6714. Poor design can cause
excessive conducted and/or radiated noise. Conductors carrying discontinuous currents and any high-current
path should be made as short and wide as possible. A separate low-noise ground plane contain-ing the
reference and signal grounds should connect to the power-ground plane at only one point to minimize the
effects of power-ground currents. Typically, the ground planes are best joined right at the IC. Keep the
voltage-feedback network very close to the IC, preferably within 0.2in (5mm) of the FB pin. Nodes with high
dV/dt (switching nodes) should be kept as small as possible and should be routed away from high-impedance
nodes such as FB.
AP6714 Rev. 4
13 of 15
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FEBRUARY 2009
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