ISL8200AM INTERSIL [Intersil Corporation], ISL8200AM Datasheet - Page 15

• Manufacturer Part Number: ISL8200AM
• Description: Complete Current Share 10A DC/DC Power Module
• Manufacturer: INTERSIL [Intersil Corporation]

The ISL8200AM has the ability to work under a pre-charged output.
The PWM outputs will not be fed to the drivers until the first PWM
pulse is seen. The low side MOSFET is held low for the first clock
cycle to provide charge for the bootstrap capacitor. If the
pre-charged output voltage is greater than the final target level but
less than the 113% setpoint, switching will not start until the output
voltage is reduced to the target voltage and the first PWM pulse is
generated. The maximum allowable pre-charged level is 113%. If
the pre-charged level is above 113% but below 120%, the output
will hiccup between 113% (LGATE turns on) and 87% (LGATE turns
off) while EN is pulled low. If the pre-charged load voltage is above
120% of the targeted output voltage, then the controller will be
latched off and not be able to power-up.
Δ RAMP
where N is number of EN pins connected together
R
V
V
EN_FTH
V CC_FF
UP
FIGURE 27. SOFT-START WITH V
=
-100mV
-100mV
------------------------------
NxI
V
FIRST PWM PULSE
EN_HYS
=
INIT. VOUT
=
=
EN_HYS
0.0V
V
max(V CC_FF
max(0.8V, V FF )
FIGURE 26. SOFT-START WITH V
EN_RTH
FIRST PWM PULSE
–
V
EN_HYS
×
G RAMP , VCC - 1.4V - V RAMP_OFFSET )
R
SYSTEM DELAY
DOWN
15
=
t
FIGURE 29. SIMPLIFIED ENABLE AND VOLTAGE FEEDFORWARD CIRCUIT
ss_DLY
SS SETTLING AT VREF + 100mV
------------------------------------------------------ -
V
SS SETTLING AT VREF + 100mV
EN_FTH
OUT
R UP V
VOUT TARGET VOLTAGE
≈
< TARGET VOLTAGE
VOUT TARGET VOLTAGE
•
384
--------- -
f
t
SW
–
ss
EN_REF
OUT
V
EN_REF
≈
2560
------------- -
= 0V
f
R
SW
R
DOWN
UP
VIN
ISL8200AM
VCC
EN
FF
Voltage Feedforward
The voltage applied to the FF pin is fed to adjust the sawtooth
amplitude of the channel. The amplitude the sawtooth is set to is
1.25 times the corresponding FF voltage when the module is
enabled. This configuration helps to maintain a constant gain
(G
optimum loop response over a wide input voltage range. The
sawtooth ramp offset voltage is 1V (equal to 0.8V*1.25), and the
peak of the sawtooth is limited to V
ramp has a maximum peak-to-peak amplitude of V
to 3V); so the feed-forward voltage effective range is typically 3x
as the ramp amplitude ranges from 1V to 3V.
A 384 cycle delay is added after the system reaches its rising
POR and prior to the soft-start. The RC timing at the FF pin should
be sufficiently small to ensure that the input bus reaches its
static state and the internal ramp circuitry stabilizes before
soft-start. A large RC could cause the internal ramp amplitude
not to synchronize with the input bus voltage during output
start-up or when recovering from faults. A 1nF capacitor is
recommended as a starting value for typical applications. The
voltage on the FF pin needs to be above 0.8V prior to soft-start
and during PWM switching to ensure reliable regulation. In a
typical application, FF pin can be shorted to the EN pin.
0.8V
FIGURE 28. SOFT-START WITH V
M
= V
OV, OT, OC, AND PLL LOCKING FAULTS
V
IN
G
CC_FF
0.8V
RAMP
• D
I
EN_HYS
MAX
TARGET VOLTAGE
= 1.25
V
FIRST PWM PULSE
/ΔV
= 30µA
RAMP_OFFSET
RAMP
∑
) and input voltage to achieve
VCC - 1.4V
LIMITER
= 1.0V
OUT
EN_POR
CC
VOUT TARGET VOLTAGE
BELOW OV BUT ABOVE FINAL
- 1.4V. With V
SAWTOOTH
AMPLITUDE
(ΔV
RAMP
)
OV = 113%
UPPER LIMIT
LOWER LIMIT
(RAMP OFFSET)
CC
September 13, 2012
CC
- 2.4V (equal
= 5.4V, the
FN8271.2