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Current Sensing and Balancing (U1, U9 and U18)

PowerGood

15

18

+

+

TPS40130DBT

0.616 V

0.784 V

FB

PGOOD

PGOOD window

comparator

Optional components for

hysteresis

10 k

Ω

10 k

Ω

UDG−05078

R

V

1.3

0.16

V

FB

* 1

(1)

TPS40130

SLUS602B – JUNE 2004 – REVISED SEPTEMBER 2005

FUNCTIONAL DESCRIPTION (continued)

The controller employs peak current mode control scheme, thus naturally provides certain degree of current

balancing. With current mode, the level of current feedback should comply with certain guidelines depending on

duty factor known as “slope compensation” to avoid the sub-harmonic instability. This requirement can prohibit

achieving a higher degree of phase current balance. To avoid the controversy, a separate current loop that

forces phase currents to match is added to the proprietary control scheme. This effectively provides high degree

of current sharing independent of the controller’s small signal response and is implemented in U9, ICTLR.

High bandwidth current amplifiers, U1 and U18 can accept as an input voltage either the voltage drop across

dedicated precise current sense resistors, or inductor’s DCR voltage derived by an RC network, or thermally

compensated voltage derived from the inductor’s DCR. The wide range of current sense arrangements ease the

cost/complexity constrains and provides superior performance compared to controllers utilizing the low-side

MOSFET current sensing. The current sense amplifier inputs must not exceed 4 V. See the Inductor DCR

Current Sense section for more information on selecting component values for the R-C network.

The PGOOD pin indicates when the inputs and output are within their specified ranges of operation. Also

monitored are the EN/SYNC and SS pins. PGOOD has high impedance when indicating inputs and outputs are

within specified limits and is pulled low to indicate an out-of-limits condition. Some applications may require

hysteresis on the PGOOD signal to avoid a PGOOD signal bounce. A simple method to achieve this (and

pin and the PGOOD pin. See Figure 3 for implementation.

Figure 3. Adding Hysteresis to the PGOOD Signal

Equation 1 provides a margin for robustness.

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