Datasheet

f
OSC
S
S
G
1
G
2
Q
1
Q
2
Vcc
GND
GND
D2
SN6501
D1
S
S
G
2
G
1
f
OSC
Freq.
Divider
OSC
BBM
Logic
Q
1
Q
2
Q
1
on Q
2
on
Q
2
off
t
BBM
Q
1
off
SN6501
www.ti.com SLLSEA0F –FEBRUARY 2012–REVISED AUGUST 2013
APPLICATION INFORMATION
The SN6501 is a transformer driver designed for low-cost, small form-factor, isolated DC-DC converters utilizing
the push-pull topology. The device includes an oscillator that feeds a gate-drive circuit. The gate-drive,
comprising a frequency divider and a break-before-make (BBM) logic, provides two complementary output
signals which alternately turn the two output transistors on and off.
Figure 61. SN6501 Block Diagram and Output Timing with Break-Before-Make Action
The output frequency of the oscillator is divided down by an asynchronous divider that provides two
complementary output signals, S and S, with a 50% duty cycle. A subsequent break-before-make logic inserts a
dead-time between the high-pulses of the two signals. The resulting output signals, G
1
and G
2
, present the gate-
drive signals for the output transistors Q
1
and Q
2
. As shown in Figure 62, before either one of the gates can
assume logic high, there must be a short time period during which both signals are low and both transistors are
high-impedance. This short period, known as break-before-make time, is required to avoid shorting out both ends
of the primary.
Figure 62. Detailed Output Signal Waveforms
PUSH-PULL CONVERTER
Push-pull converters require transformers with center-taps to transfer power from the primary to the secondary
(see Figure 63).
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