LTC3720_15 Datasheet, PDF (6/24 Pages) Linear Technology – Single Phase VRM8.5 Current Mode Step-Down Controller

LTC3720
TYPICAL PERFOR A CE CHARACTERISTICS
Transient Response
(Forced Continuous Mode)
Transient Response
(Discontinuous Mode)
V_OUT
50mV/DIV
V_OUT
50mV/DIV
I_L
10A/DIV
20µs/DIV
LOAD STEP = 0A TO 15A
V_IN = 15V
V_OUT = 1.5V
FCB = 0V
FIGURE 7 CIRCUIT
3720 G18
I_L
10A/DIV
20µs/DIV
LOAD STEP = 1A TO 15A
V_IN = 15V
V_OUT = 1.5V
FCB = INTV_CC
FIGURE 7 CIRCUIT
3720 G19
PI FU CTIO S
RUN/SS (Pin 1): Run Control and Soft-Start Input. A
capacitor to ground at this pin sets the ramp time to full
output current (approximately 3s/µF) and the time delay
for overcurrent latchoff (see Applications Information).
Forcing this pin below 0.8V shuts down the device.
V_ON (Pin 2): On-Time Voltage Input. Voltage trip point for
the on-time comparator. Tying this pin to the output
voltage makes the on-time proportional to V_OUT. The
comparator input defaults to 0.7V when the pin is grounded,
2.4V when the pin is tied to INTV_CC.
PGOOD (Pin 3): Power Good Output. Open drain logic
output that is pulled to ground when the output voltage is
not within ±7.5% of the regulation point.
V_RNG (Pin 4): Sense Voltage Range Input. The voltage at
this pin is ten times the nominal sense voltage at maxi-
mum output current and can be set from 0.5V to 2V by a
resistive divider from INTV_CC. The nominal sense voltage
defaults to 70mV when this pin is tied to ground, 140mV
when tied to INTV_CC.
FCB (Pin 5): Forced Continuous Input. Tie this pin to
ground to force continuous synchronous operation at low
load or to INTV_CC to enable discontinuous mode operation
at low load.
I_TH (Pin 6): Current Control Threshold and Error Amplifier
Compensation Point. The current comparator threshold
increases with this control voltage. The voltage ranges
from 0V to 2.4V with 0.8V corresponding to zero sense
voltage (zero current).
SGND (Pin 7, 10): Signal Ground. All small-signal compo-
nents and compensation components should connect to
this ground, which in turn connects to PGND at one point.
I_ON (Pin 8): On-Time Current Input. Tie a resistor from V_IN
to this pin to set the one-shot timer current and thereby set
the switching frequency.
V_FB (Pin 9, 11): Error Amplifier Feedback Input. This pin
connects to both the error amplifier input and to the output
of the internal resistive divider. It can be used to attach
additional compensation components if desired.
V_OSENSE (Pin 12): Output Voltage Sense. The output
voltage connects here to the input of the internal resistive
feedback divider.
VID0-VID4 (Pins 13, 14, 15, 16, 17): VID Digital Inputs.
The voltage identification (VID) code sets the internal
feedback resistor divider ratio for different output voltages
as shown in Table 1. If unconnected, the pins are pulled
high by internal 40k pull-up resistors.
3720f
6