PI3542-00-LGIZ Datasheet, PDF (28/37 Pages) Vicor Corporation – 36 Vin to 60 Vin Cool-Power ZVS Buck Regulator & LED Driver

PI354x-00
Ginctl(s) = GMeao •
R_OUT
+
s
(Rzi
•
Ccomp
•
R)
OUT
R2
•
(5)
1 + s • (Ccomp + Chf) + s² • (Chf • Ccomp • Rzi) _{R1 + R2}
The transfer function of the error amplifier and compensator
(also known as the Input To Control transfer function)
reveals the response of a Type II amplifier with a low
frequency pole determined by Equation (6), a zero which sets
the mid-band gain determined by Equation (7) and a high
frequency pole determined by Equation (8). Figure 58 shows
the calculated Input To Control transfer function. Multiplying
Equation (3) by Equation (5) ; described by Equation (9),
results in the total loop gain (also known as the Output To
Input transfer function). A graph is shown in Figure 58. The
strategy is to set the zero such that the mid-band gain allows
a high crossover frequency while providing maximum phase
boost at crossover, with proper gain and phase margin.
1
Fplf =
= 33 Hz (6)
2 • π • (Rzi + R ) • (Ccomp + Chf)
OUT
1
Fzmb =
= 6.8 kHz
(7)
2 • π • (Rzi // R ) • Ccomp
OUT
Chf + Ccomp
Fphf =
= 580 kHz (8)
2 • π • (Rzi // R ) • Ccomp • Chf
OUT
Goutin(s) = Gco(s) • Ginctl(s)
(9)
100
Gain - dBV
Phase-Degrees
150
50
100
0
50
50
1
0
10
100
1000
10000
100000
1000000
Frequency- Hz
Figure 58 — PI354X Output-Input Gain/Phase
Lighting Mode (LGH)
The Lighting (LGH) mode allows the PI354x-00 product
family to be able to operate in constant current mode (CC) so
that it can support a wide range of applications that require
the ability to regulate current or voltage. Primary
applications are LED lighting, battery / super-capacitor
charging and high peak current pulse transient load
applications. The PI354x-00 product family can operate in
dual modes, either as a constant voltage (CV) regulator or a
constant current (CC) regulator. Both modes can be utilized
in a single system. The PI354x-00 family has a separate
current amplifier, called LGH, and built in 100 mV lighting
reference that has its output connected to the EAO pin
internally. If the current through an external shunt starts to
develop 100 mV at the LGH pin, the LGH amplifier will take
over regulation by pulling down on the EAO output until the
current is in regulation according to the designed shunt
value. The LGH amplifier is a sink only trans-conductance
amplifier (TCA). It does not source current. In the event of an
open LED string or open current signal, the voltage loop can
be set to regulate the output voltage to a safe or desired value
in CV mode.
Vin
Cin
VIN
PGND _PI354X
VDR
SYNCO
SYNCI
PWRGD
EN
TESTx
SGND
VS1
VOUT
VSN
VSP
VDIFF
LGH
EAIN
EAO
COMP
TRK
L1
R1
R2
Cout
RC
Vout
Rlgh _Rshunt
Figure 59 — Lighting Configuration Using CC Mode
When using the CC mode, it is important to set R1 and R2
appropriately to avoid voltage loop interaction with the
current loop. In this case, the voltage setting at the EAIN pin
should be set so that the error between it and the 1 V
reference is sufficient to force the EAO to be open loop and
source current always. When not using the LGH amplifier,
the LGH pin should be connected to SGND.
The LGH amplifier is able to sink more current than the error
amplifier can source, thus avoiding arbitration issues when
transitioning back and forth from LGH mode to voltage
mode. The equation for setting the source current for EAO is
shown in Equation (10).
Ieao = (Veain – Vref) • Gmea > 400 μA
(10)
Cool-Power®
Page 28 of 37
Rev 1.3
2/2016
vicorpower.com
800 927.9474