MIC2155 datasheet(19/33 Pages) MICREL

19 / 33 page

Micrel, Inc.

MIC2155/2156

May 2009

M9999-052709-A

(408) 944-0800

RL = 0.01Ω (-40dB), C1=0.1µF and R1=1.5k. The time

constants are equal and diverge at the same rate. The

overall impedance, H(s), equals RL for all frequencies.

-10

-20

-30

-40

-50

FREQUENCY (Hz)

L/R

H(s)

100

10k

100k

Figure 17. Current Sense Gain/Phase Plot

Current Sharing

The schematic in Figure 18 illustrates the current sharing

scheme. The error amplifier in Channel 1, E/A 1,

monitors the output voltage and adjusts the duty cycle of

Channel 1 to regulate that voltage. The inputs of

transconductance error amplifier, E/A 2, are connected

to the current sense points of each channel. The error

amplifier regulates Channel 2 current by monitoring the

current sense point of Channel 1 and forcing the current

sense point of Channel 2 to be equal.

Any offset or difference in current between the two

channels is caused by tolerances in the inductance,

DCR, and tolerances of R1, C1, R2 and C2. Additionally,

voltage offset in E/A 2 may cause variations in output

current sharing. At lower currents, these variations may

force the current of Channel 2 to be 0.

A nominal 10mV offset inhibits the Channel 2 low-side

MOSFET until the output current increases to the

magnitude where the voltage across C1 is 10mV. This

prevents the low-side MOSFET of Channel 2 from

sinking current to ground during startup or during low

current operation.

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