Datasheet

V
CC
PGND
CNTRL
OUT
OUT_A
OUT_B
OUT_A
OUT_B
K1 * R
SET
N-Channel Active Clamp
(R
SET
to REF)
P-Channel Active Clamp
(R
SET
to GND)
K2 * R
SET
K1 * R
SET
K2 * R
SET
LM5025C
www.ti.com SNVS568C –SEPTEMBER 2008–REVISED MARCH 2013
PWM Outputs
The relative phase of the main (OUT_A) and active clamp outputs (OUT_B) can be configured for the specific
application. For active clamp configurations utilizing a ground referenced P-Channel clamp switch, the two
outputs should be in phase with the active clamp output overlapping the main output. For active clamp
configurations utilizing a high side N-Channel switch, the active clamp output should be out of phase with main
output and there should be a dead time between the two gate drive pulses. A distinguishing feature of the
LM5025C is the ability to accurately configure either dead time (both off) or overlap time (both on) of the gate
driver outputs. The overlap / deadtime magnitude is controlled by the resistor value connected to the TIME pin of
the controller. The opposite end of the resistor can be connected to either REF for deadtime control or GND for
overlap control. The internal configuration detector senses the connection and configures the phase relationship
of the main and active clamp outputs. The magnitude of the overlap/dead time can be calculated as follows:
• Overlap Time (ns) = 2.8 x R
SET
- 1.2
• Dead Time (ns) = 2.9 x R
SET
+20
• R
SET
in kΩ, Time in ns
Figure 12. Active Clamp Configurations
Compound Gate Drivers
The LM5025C contains two unique compound gate drivers, which parallel both MOS and Bipolar devices to
provide high drive current throughout the entire switching event. The Bipolar device provides most of the drive
current capability and provides a relatively constant sink current which is ideal for driving large power MOSFETs.
As the switching event nears conclusion and the Bipolar device saturates, the internal MOS device continues to
provide a low impedance to compete the switching event.
During turn-off at the Miller plateau region, typically around 2V - 3V, is where gate driver current capability is
needed most. The resistive characteristics of all MOS gate drivers are adequate for turn-on since the supply to
output voltage differential is fairly large at the Miller region. During turn-off however, the voltage differential is
small and the current source characteristic of the Bipolar gate driver is beneficial to provide fast drive capability.
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