ISL95870AHRUZ-T Intersil, ISL95870AHRUZ-T Datasheet - Page 22

• Manufacturer Part Number: ISL95870AHRUZ-T
• Description: IC CTRLR PWM 1PHASE GPU 20UTQFN
• Manufacturer: Intersil

Specifications of ISL95870AHRUZ-T

• Applications: Controller, GPU Core Power
• Voltage - Input: 3.3 V ~ 25 V
• Number Of Outputs: 1
• Voltage - Output: 0.5 V ~ 5 V
• Operating Temperature: -10°C ~ 100°C
• Mounting Type: *
• Package / Case: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PGOOD Monitor
The PGOOD pin indicates when the converter is capable
of supplying regulated voltage. The PGOOD pin is an
undefined impedance if the VCC pin has not reached the
rising POR threshold V
below the falling POR threshold V
fault condition of output overcurrent, overvoltage or
undervoltage, PGOOD is asserted low. The PGOOD
pull-down impedance is 50Ω.
Integrated MOSFET Gate-Drivers
The LGATE pin and UGATE pins are MOSFET driver
outputs. The LGATE pin drives the low-side MOSFET of
the converter while the UGATE pin drives the high-side
MOSFET of the converter.
The LGATE driver is optimized for low duty-cycle
applications where the low-side MOSFET experiences
long conduction times. In this environment, the low-side
MOSFETs require exceptionally low r
have large parasitic charges that conduct transient
currents within the devices in response to high dv/dt
switching present at the phase node. The drain-gate
charge in particular can conduct sufficient current
through the driver pull-down resistance that the V
of the device can be exceeded and turned on. For this
reason, the LGATE driver has been designed with low
pull-down resistance and high sink current capability to
ensure clamping the MOSFETs gate voltage below
V
Adaptive Shoot-Through Protection
Adaptive shoot-through protection prevents a gate-driver
output from turning on until the opposite gate-driver
output has fallen below approximately 1V. The dead-time
shown in Figure 18 is extended by the additional period
that the falling gate voltage remains above the 1V
threshold. The high-side gate-driver output voltage is
measured across the UGATE and PHASE pins while the
low-side gate-driver output voltage is measured across
the LGATE and PGND pins. The power for the LGATE
gate-driver is sourced directly from the PVCC pin.
The-power for the UGATE gate-driver is supplied by a
boot-strap capacitor connected across the BOOT and
PHASE pins. The capacitor is charged each time the
phase node voltage falls a diode drop below PVCC such
as when the low-side MOSFET is turned on.
GS(th)
.
VCC_THR
22
, or if
ISL95870, ISL95870A, ISL95870B
VCC_THF
DS(ON)
the
VCC pin is
. If there is a
and tend to
GS(th)
A typical step-down DC/DC converter will have an I
FIGURE 18. GATE DRIVE ADAPTIVE SHOOT-THROUGH
General Application Design
Guide
This design guide is intended to provide a high-level
explanation of the steps necessary to design a single-
phase buck converter. It is assumed that the reader is
familiar with many of the basic skills and techniques
referenced in the following. In addition to this guide,
Intersil provides complete reference designs that
include schematics, bills of materials, and example
board layouts.
Selecting the LC Output Filter
The duty cycle of an ideal buck converter is a function of
the input and the output voltage. This relationship is
expressed in Equation 36:
The output inductor peak-to-peak ripple current is
expressed in Equation 37:
20% to 40% of the maximum DC output load current.
The value of I
such as MOSFET switching loss, inductor core loss, and
the resistive loss of the inductor winding. The DC copper
loss of the inductor can be estimated using Equation 38:
Where, I
The copper loss can be significant so attention has to be
given to the DCR of the inductor. Another factor to
consider when choosing the inductor is its saturation
characteristics at elevated temperature. A saturated
inductor could cause destruction of circuit components,
as well as nuisance OCP faults.
I
P
D
P-P
COPPER
=
=
---------
V
V
IN
O
V
------------------------------ -
O
F
LOAD
SW
⋅
=
(
1 D
I
⋅
–
LOAD
PROTECTION
L
P-P
1V
1V
is the converter output DC current.
)
2
is selected based upon several criteria
⋅
DCR
UGATE
LGATE
1V
1V
December 22, 2009
(EQ. 36)
(EQ. 37)
(EQ. 38)
FN6899.0
PP
of