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UP6204

Compact Three-Phase Synchronous-Rectified Buck Controller

Unspecified 

Preliminary

uP6204

Functional Description

uP6204

5VCC

PHASE1

PHASE2

L

DCR

VOUT

10mV

S/H

PHASE[1:3]

RSEN

ISEN[1:3]

Figure 7. Phase Current Sensing.

The uP6204 fine tunes the duty cycle of each channel for

current balance according to the sensed inductor current

signals. If the current of channel 1 is smaller than the current

of channel 2 and 3, the uP6204 increases the duty cycle of

the corresponding phase to increase its phase current

accordingly, vice versa. The user can adjust RSEN to adjust

current ratio between phases.

The sampled-and-held current ISEN[1:3] are monitored for

phase over current protection. If any one of ISEN[1:3] is higher

than 20uA, phase over current protection is activated and

shuts down the uP6204.

Total Current Sensing

The uP6204 extracts output current by parasitic DCR of the

inductors for over current protection. A RC network is

paralleled to the inductor for current sensing as shown in

Figure 8 where DCR is the parasitic resistance. The V

C

across the capacitor equals to VDCR = IL x DCR across the

DCR of the inductor if the time constants match:

R1C = R2C = R3C = 3xL/DCR

S

S

S

The GM amplifier will source a current source I = V /R

AVG

C CSN

to virtually short its two inputs. Consequently ICSN is

calculated as:

ICSN

=

VC

RCSN

= IL ×DCR

RCSN

=

IOUT × DCR

3 × RCSN

PHASE3

R1 CS

RCSN

CSN

IAVG

R2

VC

R3

CSP

Figure 8. DCR Current Sensing Scheme

The sourcing capability of the GM amplifier is 100uA. It is

recommended to scale ICSN = 40uA at rated inductor current.

Take a 90A converter for example. Assume DCR = 2mΩ,

select the sense resistor according to

RCSN

=

90A × 2mΩ

3 × 40uA

= 1.5kΩ

Output Voltage Droop Tuning

The uP6204 dynamically adjusts the output voltage

according to the output current the droop tuning resistor

RDRP as shown in Figure 4. The sensed current signal

IAVG is mirrored and injected to EAP pin, producing a voltage

drop between SS pin and EAP pin.

VEAP

=

VSS

− 3 × IAVG × RDRP

=

VREF

−

IOUT × DCR

RCSN

×

RDRP

Since the FB voltage is regulated to track VEAP, it shows

a load line with slope = (DCR x RDRP / 3 / RCSN).

Short the RDRP to disable the droop function.

Over Current Protection

The sensed current signal I is mirrored and injected to

AVG

IMAX pin for over current protection. If the IMAX pin voltage

is higher than 3.0V, over current protection is activated and

shuts down the uP6204 as shown in Figure 9. A resistor

connected to IMAX set the over current protection level as:

IMAX

=

3 × 3V × RCSN

RIMAX × DCR

For example, if DCR = 2mΩ, RCSN = 1.5kΩ, and RIMAX =

47kΩ, the over current protection level is calculated as 144A.

uPI Semiconductor Corp., http://www.upi-semi.com

10

Rev. P01, File Name: uP6204-DS-P0100

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