ISL97671IRZ-T Intersil, ISL97671IRZ-T Datasheet - Page 25

• Manufacturer Part Number: ISL97671IRZ-T
• Description: IC LED DVR PWM CTRL 6CH 20QFN
• Manufacturer: Intersil

Specifications of ISL97671IRZ-T

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: RGB, White LED
• Frequency: 600kHz ~ 1.2MHz
• Voltage - Supply: 4.5 V ~ 26.5 V
• Mounting Type: Surface Mount
• Package / Case: 20-VFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 40mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

Phase Shift Control Register (0x0A)
The Phase Shift Control register is used to set phase
delay between each channels. When bit 7 is set high, the
phase delay is set by the number of channels enabled
and the PWM frequency. Refer to Figures 4 and 5, the
delay time is defined by Equation 17:
t
where N is the number of channels enabled, and t
the period of the PWM cycle. When bit 7 is set low, the
phase delay is set by bits 6 to 0 and the PWM frequency.
Referencing Figure 24, the programmable delay time is
defined by Equation 18:
t
where PS is an integer from 0 to 127, and t
period of the PWM cycle. By default, all the register bits
are set low, which sets zero delay between each channel.
Note that the user should not program the register to
give more than one period of the PWM cycle delay
between the first and last enabled channels.
Components Selections
According to the inductor Voltage-Second Balance
principle, the change of inductor current during the
switching regulator On time is equal to the change of
inductor current during the switching regulator Off time.
Since the voltage across an inductor is:
V
and ΔI
(
where D is the switching duty cycle defined by the turn-
on time over the switching period. V
forward voltage that can be neglected for approximation.
D1
PD
EQUALPHASE PHASESHIFT6 PHASESHIFT5 PHASESHIFT4 PHASESHIFT3 PHASESHIFT2 PHASESHIFT1 PHASESHIFT0
V
L
REGISTER 0x0A
Bit 7 (R/W)
I
=
–
=
BIT ASSIGNMENT
=
0 ) L ⁄
L
PhaseShift[6..0]
(
(
t
×
L
PS
FPWM
EqualPhase
ΔI
@ On = ΔI
×
<
L
D
6 0
⁄
Δt
,
×
⁄
N
t
S
>
)
=
xt
Bit 6 (R/W)
(
FPWM
V
L
O
@ Off, therefore:
PHASE SHIFT CONTROL REGISTER
–
V
⁄
D
(
FIGURE 37. DESCRIPTIONS OF PHASE SHIFT CONTROL REGISTER
255
–
25
V
)
I
Controls phase shift mode - When 0, phase shift is defined by PhaseShift<6:0>.
)
)
⁄
When 1, phase shift is 360/N (where N is the number of channels enabled).
L
Bit 5 (R/W)
×
1 (
–
D
7-bit Phase shift setting - phase shift between each channel is
D )
is Schottky diode
In direct PWM modes, phase shift between each channel is
×
t
S
FPWM
Bit 4 (R/W)
is the
(EQ. 17)
(EQ. 18)
(EQ. 19)
(EQ. 20)
FPWM
PhaseShift<6:0>/(255*PWMFreq)
ISL97671
BIT FIELD DEFINITIONS
PhaseShift<6:0>/12.8MHz
is
Bit 3 (R/W)
Rearranging the terms without accounting for V
the boost ratio and duty cycle respectively as:
V
D
Input Capacitor
Switching regulators require input capacitors to deliver
peak charging current and to reduce the impedance of
the input supply. This reduces interaction between the
regulator and input supply, thereby improving system
stability. The high switching frequency of the loop causes
almost all ripple current to flow in the input capacitor,
which must be rated accordingly.
A capacitor with low internal series resistance should be
chosen to minimize heating effects and improve system
efficiency, such as X5R or X7R ceramic capacitors, which
offer small size and a lower value of temperature and
voltage coefficient compared to other ceramic capacitors.
In Boost mode, input current flows continuously into the
inductor; AC ripple component is only proportional to the
rate of the inductor charging, thus, smaller value input
capacitors may be used. It is recommended that an input
capacitor of at least 10µF be used. Ensure the voltage
rating of the input capacitor is suitable to handle the full
supply range.
Inductor
The selection of the inductor should be based on its
maximum current (I
dissipation (DCR), EMI susceptibility (shielded vs
unshielded), and size. Inductor type and value influence
many key parameters, including ripple current, current
limit, efficiency, transient performance and stability.
The inductor’s maximum current capability must be
adequate enough to handle the peak current at the worst
case condition. If an inductor core is chosen with too low
a current rating, saturation in the core will cause the
effective inductor value to fall, leading to an increase in
peak to average current level, poor efficiency and
O
=
⁄
V
(
V
I
=
O
1
–
⁄
V
(
1 D
I
) V
–
⁄
Bit 2 (R/W)
O
)
SAT
) characteristics, power
Bit 1 (R/W)
Bit 0 (R/W)
June 24, 2010
D
(EQ. 21)
(EQ. 22)
gives
FN7631.0