A7525
AiT Semiconductor Inc.
www.ait-ic.com
DC-DC CONVERTER BOOST(STEP-UP)
1.2MHz, MICROPOWER SYNCHRONOUS
Pulse Skipping Mode
At very light load, the A7525 automatically switches into Pulse Skipping Mode to improve efficiency. During
this mode, the PWM control will skip some pulses to maintain regulation. If the load increases and the output
voltage drops, the device will automatically switch back to normal PWM mode and maintain regulation.
Device Shutdown
When CE is set logic high, the A7525 is put into operation. If CE is set logic low, the device is put into
shutdown mode and consumes lower than 1μA current.
Application
Setting the Output Voltage: An external resistor divider is used to set the output voltage. The output voltage of
the switching regulator (VOUT) is determined by the following equation:
VOUT = 1.23V x [1 + (R1/R2)]
Table 1 list the resistor selection for output voltage setting.
Table 1 Resistor selection for output voltage setting
VOUT
3.3V
5.0V
R1(Ω)
1.02M
1.02M
R2(Ω)
604k
332k
Inductor Selection: The high switching frequency of 1.2MHz allows for small surface mount inductors. For
most designs, the A7525 operates with inductors of 4.7μH to 10μH.The equation below can help to select the
inductor, the maximum output current can be get by this equation; where η is the efficiency, IPEAK is the peak
current limit, f is the switching frequency, L is the inductance value and D is the duty cycle.
VIN x D
IOUT= η x
IPEAK
-
x (1-D)
[
]
2 x f x L
Larger inductors mean less inductor current ripple and usually less output voltage ripple. Larger inductors also
mean more load power can be delivered. But large inductors are also with large profile and costly. The
inductor ripple current is typically set for 20% to 40% of the maximum inductor current. When selecting an
inductor, the DC current rating must be high enough to avoid saturation at peak current. For optimum load
transient and efficiency, the low DCR should be selected. Table 2 lists some typical surface mount inductors
that meet target applications for the A7525:
REV1.1
- JAN 2012 RELEASED, SEP 2017 UPDATED -
- 9 -
AITSEMI [ AiT Semiconductor ]
