Datasheet

Current Sharing and TurboTrans™
PTH08T255W
www.ti.com ........................................................................................................................................................................................... SLTS290 – NOVEMBER 2008
Table 7. Required Connections for Current Sharing
(1)
TERMINAL
MASTER SLAVE
NAME NO.
V
I
6,7,14,15 Connect to the Input Bus. Connect to the Input Bus.
V
O
10,11 Connect to the Output Bus. Connect to the Output Bus.
GND 8,9,12,13 Connect to Common Power GND. Connect to Common Power GND.
Inhibit and Use for Inhibit control & UVLO adjustments. If
21 No Connection. Leave open-circuit.
UVLO unused leave open-circuit.
Use to set the output voltage. Connect R
SET
V
o
Adjust 18 No Connection. Leave open-circuit.
resistor between this pin and AGND (pin 4).
Connect to the output voltage either at the load or
+Sense 17 No Connection. Leave open-circuit.
at the module (pin 11).
Connect to the output GND either at the load or at
– Sense 16 No Connection. Leave open-circuit.
the module (pin 13).
Track 20 Connect to Track control or to V
I
(pin 15). No Connection. Leave open-circuit.
Connect TurboTrans resistor, R
TT,
between this pin
TurboTrans™ 19 No Connection. Leave open-circuit.
and +Sense (pin 17).
Connect to an external clock. If unused connect to
SmartSync 22 Connect to Common Power GND.
GND.
CONFIG 1 Connect to GND.
(2)
Connect to the Input Bus.
Share 2 Connect to pin 2 of Slave.
(2)
Connect to pin 2 of Master.
Comp 3 Connect to pin 3 of Slave.
(2)
Connect to pin 3 of Master.
AGND 4 Connect to pin 4 of Slave.
(3)
Connect to pin 4 of Master.
CLKIO 5 Connect to pin 5 of Slave.
(2)
Connect to pin 5 of Master.
(1) For more details on the pin descriptions, please refer to the ' Terminal Functions ' described in Table 1
(2) See Layer A in Figure 22 for recommended layout
(3) See Layer B in Figure 22 for recommended layout
When using TurboTrans while paralleling two modules, the TurboTrans resistor, R
TT
, must be connected from the
TurboTrans pin (pin 19) of the Master module to the +Sense pin (pin 17) of the Master module. When paralleling
modules the procedure to calculate the proper value of output capacitance and R
TT
is similar to that explained in
the TurboTrans Selection section, however the values must be calculated for a single module. Therefore, the
total output current load step must be halved before determining the required output capacitance and the R
TT
value as explained in the TurboTrans Selection section. The value of output capacitance calculated is the
minimum required output capacitance per module and the value of R
TT
must be calculated using this value of
output capacitance. The TurboTrans pin of the Slave module must be left open.
As an example, let's look at a 12-V application requiring a 40 mV deviation during a 20 A load transient. A
majority of 470 µ F, 10 m Ω output capacitors are used. Use the 12 V, Type B capacitor chart, Figure 7 . First,
halving the load transient gives 10 A. Dividing 40 mV by 10 A gives 4 mV/A transient voltage deviation per amp
of transient load step. Select 4 mV/A on the Y-axis and read across to the 'With TurboTrans' plot. Following this
point down to the X-axis gives us a minimum required output capacitance of approximately 1800 µ F. This is the
minimum required output capacitance per module. Hence, the total minimum output capacitance would be 2 ×
1800 µ F = 3600 µ F. The required R
TT
resistor value for 1800 µ F can then be calculated or selected from Table 4 .
The required R
TT
resistor is approximately 26.7 k Ω .
Copyright © 2008, Texas Instruments Incorporated 25
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