SGM6232 Datasheet, PDF (8/14 Pages) SG Micro Corp – 1.4MHz Step-Down Converter

SGM6232
2A, 38V, 1.4MHz Step-Down Converter
APPLICATION INFORMATION
Setting the Output Voltage
The output voltage is set using a resistive voltage divider
from the output voltage to FB pin. The voltage divider
divides the output voltage down to the feedback voltage
by the ratio:
V_FB

V_OUT
R2
R1  R2
Where V_FB is the feedback voltage and V_OUT is the output
voltage. Thus the output voltage is:
V_OUT

0.8

R1 R2
R2
The value for R2 can be as high as 100kΩ, but a typical
value is 10kΩ. Using that value, R1 is determined by:
R1 = 12.5 × (V_OUT - 0.8) (kΩ)
For example, for a 3.3V output voltage, R2 is 10kΩ, and
R1 is 31.25kΩ.
Inductor
The inductor is required to supply constant current to the
output load while being driven by the switched input
voltage. A larger value inductor will result in less ripple
current that will result in lower output ripple voltage.
However, the larger value inductor will have a larger
physical size, higher series resistance, and/or lower
saturation current. A good rule for determining the
inductance to use is to allow the peak-to-peak ripple
current in the inductor to be approximately 30% of the
maximum switch current limit. Also, make sure that the
peak inductor current is below the maximum switch
current limit. The inductance value can be calculated by:
L

V_OUT
f_OSC  ΔI_L
 ^1

V_OUT
V_IN



Where V_IN is the input voltage, f_OSC is the 1.4MHz
switching frequency, and ΔI_L is the peak-to-peak inductor
ripple current.
Choose an inductor that will not saturate under the
maximum inductor peak current. The peak inductor
current can be calculated by:
I_LP
 I_LOAD

V_OUT
2  f_OSC  L
 ^1

V_OUT
V_IN



I_LOAD is the load current.
Output Rectifier Diode
The output rectifier diode supplies the current to the
inductor when the high-side switch is off. To reduce
losses due to the diode forward voltage and recovery
times, use a Schottky diode.
Choose a diode whose maximum reverse voltage rating
is greater than the maximum input voltage, and whose
current rating is greater than the maximum load current.
Table 1 lists example Schottky diodes and manufacturers.
Table 1. Diode Selection Guide
Diode
SK33
SK34
B330
B340
MBRS330
MBRS340
Voltage,
Current Rating
30V, 3A
40V, 3A
30V, 3A
40V, 3A
30V, 3A
40V, 3A
Manufacturer
Diodes Inc.
Diodes Inc.
Diodes Inc.
Diodes Inc.
On Semiconductor
On Semiconductor
Input Capacitor
The input current to the step-down converter is
discontinuous, therefore a capacitor is required to supply
the AC current to the step-down converter while
maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic capacitors
are preferred, but tantalum or low-ESR electrolytic
capacitors may also suffice.
Since the input capacitor absorbs the input switching
current, it requires an adequate ripple current rating.
SG Micro Corp
8
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