MAX16814ATP+ Maxim Integrated Products, MAX16814ATP+ Datasheet - Page 19

• Manufacturer Part Number: MAX16814ATP+
• Description: LED Drivers Integrated 4-Channel High-Brightness LED
• Manufacturer: Maxim Integrated Products

Specifications of MAX16814ATP+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

During normal operation, the feedback control loop reg-
ulates the minimum OUT_ voltage to 1V when LED string
currents are enabled during PWM dimming. When LED
currents are off during PWM dimming, the control loop
turns off the converter and stores the steady-state condi-
tion in the form of capacitor voltages, mainly the output
filter capacitor voltage and compensation capacitor
voltage. For the MAX16814A_ _ and the MAX16814U_
_, when the PWM dimming pulses are less than five
switching clock cycles, the feedback loop regulates the
converter output voltage to 95% of the OVP threshold.
The worst-case condition for the feedback loop is when
the LED driver is in normal mode regulating the minimum
OUT_ voltage to 1V. The switching converter small-signal
transfer function has a right-half plane (RHP) zero for
boost configuration if the inductor current is in continuous
conduction mode. The RHP zero adds a 20dB/decade
gain together with a 90N-phase lag, which is difficult to
compensate.
The worst-case RHP zero frequency (f
lated as follows:
For boost configuration:
For SEPIC and coupled-inductor boost-buck configura-
tions:
where f
tance value of L1 in henries, and I
simple way to avoid this zero is to roll off the loop gain
to 0dB at a frequency less than one fifth of the RHP zero
frequency with a -20dB/decade slope.
The switching converter small-signal transfer function
also has an output pole. The effective output impedance
together with the output filter capacitance determines the
output pole frequency f
For boost configuration:
ZRHP
Integrated, 4-Channel, High-Brightness LED
f
is in hertz, V
ZRHP
f
Driver with High-Voltage DC-DC Controller
ZRHP
f
P1
______________________________________________________________________________________
=
=
2
=
2
× π ×
P1
π × ×
V
V
LED
LED
LED
that is calculated as follows:
L I
2
V
π × ×
I
LED
(1 D
LED
(1 D
Feedback Compensation
LED
is in volts, L is the induc-
−
L I
−
×
MAX
×
C
MAX
LED
LED
D
OUT
MAX
)
)
2
is in amperes. A
2
ZRHP
) is calcu-
For SEPIC and coupled-inductor boost-buck configurations:
where f
and C
Compensation components, R
form two functions. C
pole that presents a -20dB/decade slope to the loop
gain. R
frequencies above the zero formed by R
C
output pole frequency f
decade slope for frequencies above f
modulator and compensator response.
The value of R
f
decade slope at 1/5 the RHP zero frequency is calcu-
lated as follows:
For boost configuration:
For SEPIC and coupled-inductor boost-buck configura-
tions:
where R
f
sense resistor in ohms, and GM
ductance of the error amplifier (600FS).
The value of C
If the output capacitors do not have low ESR, the ESR
zero frequency may fall within the 0dB crossover fre-
quency. An additional pole may be required to cancel
out this pole placed at the same frequency. This is usu-
ally implemented by connecting a capacitor in parallel
with C
configuration and Figure 6 shows the coupled-inductor
boost-buck configuration.
P1
ZRHP
COMP
so that the total loop gain crosses 0dB with -20dB/
R
R
COMP
OUT
COMP
COMP
and f
P1
COMP
. For compensation, this zero is placed at the
COMP
is in hertz, V
is in farads.
P2
=
=
C
and R
flattens the gain of the error amplifier for
5 f
COMP
COMP
5 f
f
COMP
are in hertz, R
P1
is the compensation resistor in ohms,
×
×
P1
=
P1
f
ZRHP
COMP
2
×
×
is calculated as follows:
needed to fix the total loop gain at
COMP
× π ×
=
GM
LED
GM
I
f
P1
LED
ZRHP
2
COMP
×
π ×
. Figure 5 shows the SEPIC
COMP
is in volts, I
V
so that it provides a -20dB/
R
LED
introduces a low-frequency
×
R
CS
D
×
CS
COMP
COMP
R
MAX
×
×
×
1
×
COMP
CS
I
V
C
is the switch current-
V
LED
LED
LED
OUT
×
P1
×
LED
and C
I
×
f
LED
P1
× −
to the combined
× −
is the transcon-
D
(1 D
(1 D
MAX
is in amperes,
COMP
COMP
MAX
MAX
, per-
)
)
and
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