AIC1577 AIC [Analog Intergrations Corporation], AIC1577 Datasheet - Page 10

• Manufacturer Part Number: AIC1577
• Description: External NMOS Step-Down PWM Controller
• Manufacturer: AIC [Analog Intergrations Corporation]

Output Diode Selection
In order not to exceed the diode ratings, it is impor-
tant to specify the diode peak current and average
power dissipation.
C
To prevent the high voltage spike resulted from high
frequency switching, a low ESR input capacitor for
the maximum RMS current must be used. Usually
capacitors may be paralleled to meet size or height
requirements in the design.
The selection of C
fective series resistance (ESR). In general once the
ESR requirement is met, the capacitance is suitable
for filtering. The output ripple voltage (ΔV
determined by:
where f = operating frequency, C
pacitance and ΔI
Once the ESR requirement for C
the RMS current rating generally far exceeds the
I
Topside MOSFET Driver Supply (C3)
External bootstrap capacitor C3 connecting to
BOOST pin supplies the gate drive voltage for high-
side MOSFET. C3 is charged from INTV
SW pin is low. When the high-side MOSFET turns
on, the driver places the C3 voltage across the gate
to the source of MOSFET. It will enhance the
MOSFET and turn on the high-side switch. Then
the switch node voltage SW rises to V
BOOST pin rises to V
0.1µF is acceptable.
Output Voltage Programming
The typical AIC1577 application circuit is shown in
figure18. A resistive divider, as in the following for-
mula, sets the output voltage.
∆
RIPPLE(P-P)
IN
V
OUT
and C
≈
∆
OUT
I
L
requirement.




ESR
Selection
L
OUT
+
= ripple current of the inductor.
4
fC
depends on the required ef-
1
OUT
IN
+ INTV




OUT
OUT
CC
has been met,
. In general,
= output ca-
CC
OUT
IN
when
and
) is
I
The feedback reference voltage 0.8V allows low
output voltages from 0.8V to input voltage. A small
capacitor at 1nF in parallel to the upper feedback
resistor is required for a stable feedback.
I
The I
vides loop compensation as well as shutdown func-
tion. An internal current source at 2.5µA charges up
the external capacitor C5. When the voltage on
I
operate.
Over Current Protection
Over current protection occurs when the peak in-
ductor current reaches maximum current sense
threshold divided by sense resistor. The maximum
current under over current protection can be calcu-
lated by the following formula.
At the same time, the frequency of oscillator will be
reduced to sixteenth of original value, 500kHz. This
lower frequency allows the inductor current to
safely discharge, thereby preventing current run-
away. The frequency of oscillator will automatically
MAX
V
TH
TH
OUT
/RUN pin reaches 0.8V, the AIC1577 begins to
/RUN Function
TH
=
=
/RUN pin, also as a dual-purpose pin, pro-
0
150mV(Maxi
Fig. 12 I
8 .
V



C7
1µF
1
V
IN
+
4.5V~24V
R
R
TH
2
R4
1.2M
1
/RUN pin interfacing



mum
LL4148
D2
current
R
I
TH
S
/RUN
R3
24k
C5
330pF
sense
AIC1577
threshold)
10