MIC38300_10 Datasheet, PDF (10/12 Pages) Micrel Semiconductor – HELDO 3A High Efficiency Low Dropout Regulator

Micrel, Inc.
case, inductor selection becomes increasingly critical in
efficiency calculations. As the inductors are reduced in
size, the DC resistance (DCR) can become quite
significant. The DCR losses can be calculated as
follows:
L_P_D = I_OUT2 × DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows;
Efficiency
_
Loss
=
⎡
⎢^{1 −}
⎢⎣
⎜⎜⎝⎛
V_OUT ×
V_OUT × I_OUT
I_OUT
+L
_
P_D
⎟⎟⎠⎞⎥⎥⎦⎤
× 100
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
selection becomes a trade-off between efficiency and
size in this case.
MIC38300
Current Sharing Circuit
The following circuit allows two MIC38300 HELDO
regulators to share the load current equally. HELDO1
senses the output voltage at the load, on the other side
of a current sense resistor. As the load changes, a
voltage equal to the output voltage, plus the load current
times the sense resistor, is developed at the V_OUT
terminal of HELDO1. The Op-Amp (MIC7300) inverting
pin senses this voltage and compares it to the voltage on
the V_OUT terminal of HELDO2.
If the current through the current sense of HELDO2 is
less than the current through the current sense of
HELDO1, the inverting pin will be at a higher voltage
than the non-inverting pin and the Op-Amp will drive the
FB of HELDO2 low. The low voltage sensed on
HELDO2 FB pin will drive the output up until the output
voltage of HELDO2 matches the output voltage of
HELDO1. Since V_OUT will remain constant and both
HELDO V_OUT terminals and sense resistances are
matched, the output currents will be shared equally
June 2010
Current Sharing Circuit for 6A Output
10
M9999-061010-D