MIC2132 datasheet(22/48 Pages) MICROCHIP

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MIC2132

DS20006654B-page 22

 2022 Microchip Technology Inc. and its subsidiaries

4.5

Detailed Device Description

The MIC2132 always operates in CCM and both

phases support the load current equally at high loads.

4.5.1

CURRENT BALANCING BETWEEN

PHASES

One important benefit of the two-phase operation is the

thermal advantage gained by distributing the heat over

multiple devices and a greater PCB area. By doing this,

the system designer avoids the complexity of driving

parallel MOSFETs and the expense of using expensive

heatsinks.

In order to achieve the thermal advantage, it is import-

ant that each phase carries the same amount of current

at any load level. In the MIC2132, both phase currents

are sensed across the low-side MOSFET, RDS(ON),

during off-time. The low-side MOSFET current is

tracked during off-time and held close to peak value in

the valley point. The average current information is

generated by summing all the phases’ sensed currents

and dividing by the number of phases (two for two

phases). An error current per phase is generated by

making the difference between the average current

information and each phase current, which is used to

modulate TON1 and TON2 in order to cancel the error in

the current sharing.

FIGURE 4-6:

MIC2132 Current Sharing

Circuit.

4.5.2

CURRENT LIMIT

The MIC2132 uses the RDS(ON) of the external low-side

power MOSFET to sense overcurrent conditions, or a

sense resistor inserted with the source of the bottom

FET can be used for more accurate results and not

requiring temperature compensation. The bottom FET

RDS(ON) sensing method will avoid adding cost, use of

additional board space and power losses taken by a

discrete current sense resistor.

The current limit threshold can be programmed by

connecting a resistance from the ILIM pin to AGND.

Both phases use the same current limit threshold.

FIGURE 4-7:

MIC2132 Current-Limiting

Circuit.

The MIC2132 forces a constant 9.6 µA current through

the ILIM setting resistor, tied from the ILIM pin to

AGND, to program VILIM.

In each switching cycle of both phases of the MIC2132

converter, the inductor valley current is sensed by mon-

itoring the VDS voltage across the low-side MOSFET

during the off period. There is a 150 ns (typical) blanking

period before each current sense signal is considered

for protection. The blanking period improves noise

immunity. If the valley low-side MOSFET current is

greater than the current limit threshold current for seven

consecutive cycles in either phase, then the MIC2132

turns off the high-side and low-side MOSFETs of both

phases and a soft start sequence is triggered after the

hiccup timer has expired. This mode of operation is

called Hiccup mode and its purpose is to protect the

downstream load in case of a hard short. Figure 4-8

illustrates the MIC2132 operation during overload condi-

tions. When the load current is increased gradually, the

inductor current also increases, as shown in Figure 4-8.

When the load current is around the current limit thresh-

old, the high-side and low-side MOSFET current can be

higher than the current limit, as highlighted in Figure 4-8

as Case #1. In Case #1, even though the low-side

MOSFET instantaneous current exceeds the current

limit threshold for some duration, the low-side MOSFET

current is lower than the current limit at the end of the

150 ns blanking time. This causes the MIC2132 to not

enter the current limit protection and initiate the next

high-side MOSFET turn-on cycle. After the high-side

MOSFET is turned on, the current ramps up to a value

that is determined by the operating duty cycle and induc-

tor value. When the high-side MOSFET is turned off and

SW1

CSN1

VIN

DL1

DH1

MIC2132

SW2

CSN2

VIN

DL2

DH2

CSP1

CSP2

TON1

GENERATOR

CSH

DROOP

SAMPLE TRACK

& HOLD

SAMPLE TRACK

& HOLD

‒

1.2V

0.5

CONTROL

LOGIC

TON2

GENERATOR

OUTS

ITON1

ITON2

PHASE1

DRIVER

CONTROL

LOGIC

PHASE2

DRIVER

CONTROL

LOGIC

ADAPTABLE

TON

CONTROL

FREQ

VIN

ITON2

‒

VOUT

OUTS

‒

+120mV

‒

SW2

CSN2

VIN

ILIM

DL2

DH2

MIC2132

VILIM

CSP2

PGND

ICL

VDD

1.2V

RILIM

‒

0.25

SW1

CSN1

VIN

DL1

DH1

CSP1

VOUT

CH1 SHORT

COMPARATOR

CH2 SHORT

COMPARATOR

SHORT LIMIT 1

SHORT LIMIT 2

SHORT LIMIT &

HICCP CONTROL

SS CONTROL

DRIVERS

CONTROL LOGIC

DL2

DL1

DH1

DH2

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