Datasheet

5
6
7
14
13
15
0.7 1.1 1.9 2.31.5 2.5
V
O
- Output Voltage - V
V
I
- Input Voltage - V
8
9
10
0.9 1.71.3 2.1
12
11
f
SW
(kHz)
240
300
350
400
350
400
300
240
80
82
84
98
96
100
240 260 340 380300 400
f
SS
- SmartSync Frequency - kHz
Maximum Load Current - %
86
88
90
320280 360
94
92
PTH08T250W
SLTS278G –NOVEMBER 2010–REVISED MARCH 2009 www.ti.com
Operating the PTH08T250W with a low duty cycle may increase the output voltage ripple. When operating at the
nominal switching frequency, input voltages greater than (V
O
× 12) may cause the output voltage ripple to
increase (up to 2×).
When using Smart Sync, the minimum duty cycle varies as a function of output voltage and switching frequency.
Synchronizing to a higher frequency causes greater restrictions on the duty cycle range. For a given switching
frequency, Figure 22 shows the operating region where the output voltage ripple meets the electrical
specifications. Operation above a given curve may cause the output voltage ripple to increase (up to 2×). For
example, a module operating at 400 kHz and an output voltage of 1.2 V, the maximum input voltage that meets
the output voltage ripple specification is 11 V. Exceeding 11 V may cause in an increase in output voltage ripple.
As shown in Figure 22, operating below 6 V allows operation down to the minimum output voltage over the entire
synchronization frequency range without affecting the output voltage ripple. See the Electrical Characteristics
table for the synchronization frequency range limits.
The maximum output current that a single module can deliver may also be affected by the sychronization
frequency. See Figure 23 below for load current derating when sychronizing at frequencies greater than 330 kHz.
First consult the temperature derating graphs in the Typical Characteristics section to determine the maximum
output current based on operating conditions. Any derating due to the SmartSync frequency is in addition to the
temperature derating.
MAXIMUM LOAD CURRENT
vs
OUTPUT VOLTAGE RIPPLE LIMITS SMARTSYNC FREQUENCY
Figure 22. Figure 23.
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