SGM6132 Datasheet, PDF (9/14 Pages) SG Micro Corp – 1.4MHz Step-Down Converter

SGM6132
3A, 28.5V, 1.4MHz Step-Down Converter
APPLICATION INFORMATION
Since the input capacitor (C_IN) absorbs the input
switching current, it requires an adequate ripple current
rating. The RMS current in the input capacitor can be
estimated by:
I_RMS  I_LOAD 
V_OUT
V_IN
 ^1

V_OUT
V_IN



The worst-case condition occurs at V_IN = 2V_OUT, where:
I_RMS(MAX)

I_LOAD
2
For simplification, choose the input capacitor whose RMS
current rating is greater than half of the maximum load
current.
Where L is the inductor value, C_OUT is the output
capacitance value, and R_ESR is the equivalent series
resistance (ESR) value of the output capacitor.
In the case of ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance.
The output voltage ripple is mainly caused by the
capacitance. For simplification, the output voltage ripple
can be estimated by:
ΔV_OUT

V_OUT
8

f²
OSC

L

C_OUT
 ^1

V_OUT
V_IN



In the case of tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching frequency. For
simplification, the output ripple can be approximated to:
The input capacitor can be electrolytic, tantalum or
ceramic. When using electrolytic or tantalum capacitors,
a small, high quality ceramic capacitor, i.e. 0.1µF, should
be placed as close to the IC as possible. When using
ceramic capacitors, make sure that they have enough
capacitance to provide sufficient charge to prevent
excessive voltage ripple at input. The input voltage ripple
caused by capacitance can be estimated by:
ΔV_IN

I_LOAD
f_OSC  C_IN

V_OUT
V_IN
 ^1

V_OUT
V_IN



C_IN is the input capacitance value.
Output Capacitor
The output capacitor (C_OUT) is required to maintain the
DC output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended.
Low ESR capacitors are preferred to keep the output
voltage ripple low. The output voltage ripple can be
estimated by:
ΔV_OUT

V_OUT
f_OSC 
L

₁


V_OUT
V_IN





R_ESR


1
8  f_OSC  C_OUT



ΔV_OUT

V_OUT
f_OSC  L
 ^1

V_OUT
V_IN



R_ESR

The characteristics of the output capacitor also affect the
stability of the regulation system. The SGM6132 can be
optimized for a wide range of capacitance and ESR
values.
Compensation Components
SGM6132 employs current mode control for easy
compensation and fast transient response. The system
stability and transient response are controlled through the
COMP pin. COMP pin is the output of the internal
transconductance error amplifier. A serial capacitor and
resistor combination sets a pole-zero combination to
control the characteristics of the control system.
The DC gain of the voltage feedback loop is given by:
A _VDC
 R_LOAD
 G_CS
 A_EA

V_FB
V_OUT
Where A_EA is the error amplifier voltage gain, 10000V/V,
G_CS is the current sense transconductance, 6.2A/V, and
R_LOAD is the load resistor value.
SG Micro Corp
9
www.sg-micro.com