ISL78220 Datasheet, PDF (15/22 Pages) Intersil Corporation – 6-Phase Interleaved Boost PWM Controller with Light Load Efficiency Enhancement

ISL78220
SOFT-START WAVEFORM (CASE B, LIGHT LOAD)
V
Vfb
Vref
0 t4 t5
V
5V
2.5V
NOTE: t4, t5 PERIOD ARE FROM FIGURE 5
t6
DIODE EMULATION
LOWER FET TURN ON
t7
SYNCHRONOUS
OPERATION WITH
CYCLE-BY-CYCLE
DIODE EMULATION
(PWM_INV = 0)
PWM
0
SYNCHRONOUS
DIODE EMULATION
OPERATION WITH
CYCLE-BY-CYCLE
DIODE EMULATION
5V
(PWM_INV = 1)
PWM
2.5V
0
SOFT-START WAVEFORM (CASE C)
V
Vfb
Vref
0 t4 t5
NOTE: t4, t5 PERIOD ARE FROM FIGURE 5
t6
V
LOWER FET TURN ON
5V
(PWM_INV = 0)
PWM
0
5V
(PWM_INV = 1)
PWM
0
5V
DRIVE_EN
5V
DRIVE_EN
0
FIGURE 16. SOFT-START WAVEFORM (CASE B, LIGHT LOAD)
0
FIGURE 17. SOFT-START WAVEFORM (CASE C, LIGHT LOAD)
Case C (V_{PWM_TRI} = 0)
For applications that the driver cannot identify a tri-state PWM signal,
the V_{PWM_TRI} should be connected to GND (Logic LOW), such that
the PWM signal will only be 2 levels between 0V and 5V. Then
DRIVE_EN pin can be connected to the EN pin of the external drivers.
DRIVE_EN will be asserted when the PWM first toggles such that the
pre-bias start up capability can be achieved. Detailed soft start for
case C is shown in Figure 17.
Time t₄, t₅: Same as the t₄, t₅ in Figure 14, soft-start has not
started yet, see “Operation Initialization Before Soft-Start” on
page 13 for detailed description.
Time t₆: At the beginning of t₆, the PWM signal will start to
switch between 0V and 5V. The driver will turn on the lower and
upper MOSFETs accordingly, and the duty cycle for lower MOSFET
will increase gradually from 0 to steady state. DRIVE_EN will be
pulled high when the first PWM toggles at the beginning of t₆ to
enable the external drivers.
15
FN7688.0
December 15, 2011