Datasheet

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SLVS519A − MAY 2004 − REVISED OCTOBER 2004
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10
Table 3.
SWITCHING FREQUENCY SYNC PIN RT PIN
250 kHz, internally set Generates SYNC output signal AGND
500 kHz, internally set Generates SYNC output signal Float
Externally set to 250 kHz to 700 kHz
Terminate to quiet ground
with 10-kΩ resistor.
R = 215 kΩ to 69 kΩ
Externally synchronized frequency Synchronization Signal
Set RT resistor equal to 90% to 110% of external synchronization
frequency.When using a dual setup (see Figure 27 for example),
if the master 35x device RT pin is left floating, use a 110 kΩ
resistor to tie the slave RT pin to ground. Conversely, if the master
35x device RT pin is grounded, use a 237 kΩ resistor to tie the
slave RT pin to ground.
1805 Out of Phase Synchronization (SYNC)
The SYNC pin is configurable as an input or as an output,
per the description in the previous section. When
operating as an input, the SYNC pin is a falling-edge
triggered signal (see Figures 3, 4, and 19). When operating
as an output, the signal’s falling edge is approximately
180° out of phase with the rising edge of the PH pins. Thus,
two TPS5435x devices operating in a system can share an
input capacitor and draw ripple current at twice the
frequency of a single unit.
When operating the two TPS5435x devices 180° out of
phase, the total RMS input current is reduced. Thus
reducing the amount of input capacitance needed and
increasing efficiency.
When synchronizing a TPS5435x to an external signal, the
timing resistor on the RT pin must be set so that the
oscillator is programmed to run at 90% to 110% of the
synchronization frequency.
V
I(SYNC)
V
O(PH)
Figure 3. SYNC Input Waveform