ISL6410 Datasheet, PDF (8/13 Pages) Intersil Corporation – Single Synchronous Buck Regulators with Integrated FET

ISL6410, ISL6410A
Power Good
This output is asserted high when the PWM is enabled, and
Vout is within 8.0% typical of its final value, and is active low
outside this range. When disabled, the output turns active
low. It is recommended to leave the PG pin unconnected
when not used.
PWM Overvoltage and Overcurrent Protection
The PWM output current is sampled at the end of each PWM
cycle, exceeding the overcurrent limit, causes a 4 bit
up/down counter to increment by one LSB. A normal current
state causes the counter to decrement by one LSB (the
counter will not however “rollover” or count below 0000).
When the PWM goes into overcurrent, the counter rapidly
reaches count 1111 and the PWM output is shut down and
the soft-start counter is reset. After 16 clocks the PWM
output is enabled and the soft-start cycle is started.
If Vout exceeds the overvoltage limit for 32 consecutive clock
cycles the PWM output is shut off and the soft-start cycle is
initiated.
No Load Operation
If there is no load connected to the output, the converter will
regulate the output voltage by allowing the inductor current
to reverse for a short period of time.
Output Capacitor Selection
For best performance, a low ESR output capacitor is
needed. Output voltages below 1.8V require a larger output
capacitor and ESR value to improve the performance and
stability of the converter. For 1.8V output applications, a
ceramic capacitor of 10µF or higher value with ESR ≤50mΩ
is recommended.
The RMS ripple current is calculated as:
1 – -^V-----^o--
I_RMS(Co)
=
V
o
×
----------^V----ⁱ--ⁿ--
L×f
×
-------¹---------
2× 3
L = the inductor value
f = the switching frequency
The overall output ripple voltage is the sum of the voltage spike
caused by the output capacitor ESR and the voltage ripple
caused by charge and discharge of the output capacitor:
1 – -^V-----^o--
∆V o
=
Vo ×
----------^V----ⁱ--ⁿ--
L×f
×


------------¹-------------
8 × Co × f
+
E S R_
Where the highest output voltage ripple occurs at the highest
input voltage VIN.
TABLE 2. RECOMMENDED OUTPUT CAPACITORS
CAPACITOR ESR
VALUE (mΩ)
COMPONENT
SUPPLIER
COMMENTS
10µF
<50 AVX 08056D106KAT2A
Ceramic
Input Capacitor Selection
The input current to the buck converter is pulsed, and
therefore a low ESR input capacitor is required. This results
in good input voltage filtering and minimizes the interference
it causes to other circuits. The input capacitor should have a
minimum value of 10µF and a higher value can be selected
for improving input voltage filtering. The input capacitor
should be rated for the maximum input ripple current
calculated as:
I_RMS = Io(max) ×
-^V-----^o---
Vin
×


1
–
V^-V----i^-o-n^{--}
The worst case RMS ripple current occurs at D = 0.5 and is
calculated as: Irms = Io/2.
D = Duty Cycle
Ceramic capacitors are preferred because of their low ESR
value. They are also less sensitive to voltage transients
when compared to tantalum capacitors. It is good practice to
place the input capacitor as close as possible to the input pin
of the IC for optimum performance.
Inductor Selection
The ISL6410 is an internally compensated device and hence
a minimum of 8.2µH must be used for the ISL6410 and a
minimum of 12µH for the ISL6410A. The selected inductor
must have a low DC resistance and a saturation current
greater than the maximum inductor current value can be
calculated from the equations below
1 – -^V-----^o--
dIL
=
Vo
×
----------^V----ⁱ--ⁿ--
L×f
IL max = Io max + ^d----^I--^L--
2
where
dIL = the peak to peak inductor current
L = the inductor value
f = the switching frequency
ILmax = the max inductor current
TABLE 3. RECOMMENDED INDUCTORS
INDUCTOR VALUE DCR (mΩ)
COMPONENT
SUPPLIER
8.2µH
75
Coilcraft
MSS6122-822MX
12µH
100
Coilcraft
MSS6122-123MX
8