Datasheet

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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
V
OUT
V
PU
R
A
C
A
R
BIAS
10 kΩ
10 kΩ
UDG−05078
R
A
+ R
BIAS
ƪ
ǒ
V
PU
* V
FB
1.3 0.16 V
FB
Ǔ* 1
ƫ
(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
thereby eliminate any PGOOD signal bounce) is to add a small resistor (R
A
) and capacitor (C
A
) between the FB
pin and the PGOOD pin. See Figure 3 for implementation.
Figure 3. Adding Hysteresis to the PGOOD Signal
To select R
A
and C
A
, the following criteria can be used.
V
PU
and the PGOOD pull-up voltage and V
FB
is the TPS40130 internal reference voltage. The factor 1.3 in
Equation 1 provides a margin for robustness.
11
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