ltc3730 Linear Technology Corporation, ltc3730 Datasheet - Page 17

• Manufacturer Part Number: ltc3730
• Description: 3-phase, 5-bit Intel Mobile Vid, 600khz, Synchronous Buck Controller
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
30 to 100 times that of the total gate charge capacitance of
the topside MOSFET(s) as specified on the manufacturer’s
data sheet. The reverse breakdown of D
than V
Operational Amplifier
The amplifier has a 0 to V
range and an output swing range of 0 to V
output uses an NPN emitter follower without any internal
pull-down current. A DC resistive load to ground is re-
quired in order to sink current.
Output Voltage
The IC includes a digitally controlled 5-bit attenuator
between the AMPOUT pin and the EAIN pin resulting in
output voltages as defined in Table 1. Output voltages with
25mV increments are produced from 0.6V to 1V and 50mV
increments from 1V to 1.75V.
Each VID digital input is pulled up to a logical high with an
internal 3µA. The input logic threshold is approximately
1.2V but the input circuit can withstand an input voltage of
up to 7V.
Table 1. VID Output Voltage Programming
B4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
B3 B2 B1 B0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
IN(MAX).
CODE
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
U
0.600V
0.625V
0.650V
0.675V
0.700V
0.725V
0.750V
0.775V
0.800V
0.825V
0.850V
0.875V
0.900V
0.925V
0.950V
0.975V
V
OUT
U
CC
– 1.4V common mode input
B4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
B3 B2 B1 B0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
W
CODE
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
B
must be greater
CC
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
– 1.2V. The
U
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1.000V
1.050V
1.100V
1.150V
1.200V
1.250V
1.300V
1.350V
1.400V
1.450V
1.500V
1.550V
1.600V
1.650V
1.700V
1.750V
V
OUT
Soft-Start/Run Function
The RUN/SS pin provides three functions: 1) ON/OFF, 2)
soft-start and 3) a defeatable short-circuit latch off timer.
Soft-start reduces the input power sources’ surge cur-
rents by gradually increasing the controller’s current limit
(proportional to an internal buffered and clamped V
The latchoff timer prevents very short, extreme load
transients from tripping the overcurrent latch. A small
pull-up current (>5µA) supplied to the RUN/SS pin will
prevent the overcurrent latch from operating. A maximum
pull-up current of 200µA is allowed into the RUN/SS pin
even though the voltage at the pin may exceed the absolute
maximum rating for the pin. This is a result of the limited
current and the internal protection circuit on the pin. The
following explanation describes how this function oper-
ates.
An internal 1.5µA current source charges up the C
capacitor. When the voltage on RUN/SS reaches 1.5V, the
controller is permitted to start operating. As the voltage on
RUN/SS increases from 1.5V to 3V, the internal current
limit is increased from 0V/R
output current limit ramps up slowly, taking an additional
1s/µF to reach full current. The output current thus ramps
up slowly, eliminating the starting surge current required
from the input power supply. If RUN/SS has been pulled all
the way to ground, there is a delay before starting of
approximately:
By pulling the RUN/SS controller pin below 0.4V the IC is
put into low current shutdown (I
pin can be driven directly from logic as shown in Figure 7.
Diode D1 reduces the start delay but allows C
slowly, providing the soft-start function. The RUN/SS
pin has an internal 6V zener clamp (see the Functional
Diagram).
t
t
DELAY
IRAMP
=
=
1 5
3
1 5
.
V
1 5
.
µ
.
−
V
A
µ
1 5
A
C
.
SS
V
C
=
SS
(
1
s F C
=
SENSE
/
µ
(
1
s F C
)
Q
/
µ
< 50µA). The RUN/SS
to 75mV/R
SS
)
SS
LTC3730
SS
SENSE
to ramp up
17
. The
ITH
3730fa
SS
).