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SLVS456C − OCTOBER 2003 − REVISED OCTOBER 2004
SWITCHING FREQUENCY
SYNC PIN
RT PIN
AGND
250 kHz, internally set
500 kHz, internally set
Generates SYNC output signal
Generates SYNC output signal
Float
Externally set to 250 kHz to 700 kHz
Terminate to quiet ground
R = 215 kΩ to 69 kΩ
with 10-kΩ resistor.
Externally synchronized frequency
Synchronization Signal
Use 110 kΩ when RT floats and 237 kΩ when RT is grounded and
using the sync out signal of another TPS54350. Set RT resistor
equal to 90% to 110% of external synchronization frequency.
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 TPS54350 devices operating in a system can share an
input capacitor and draw ripple current at twice the
frequency of a single unit.
phase, the total RMS input current is reduced. Thus
reducing the amount of input capacitance needed and
increasing efficiency.
When synchronizing a TPS54350 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.
NOTE:
Do not use synchronization input for designs with
output voltages > 10 V.
When operating the two TPS54350 devices 180° out of
V
I(SYNC)
V
O(PH)
Figure 3. SYNC Input Waveform
Internal Oscillator
V
O(PH)
V
O(SYNC)
Figure 4. SYNC Output Waveform
8
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