PI3740-00 Datasheet, PDF (35/48 Pages) Vicor Corporation – Parallel capable with single wire current sharing

Small Signal Models CV-CC Modes
Small Signal Model – Constant Voltage Mode
The PI3740-00 product is a variable frequency CrCM / DCM ZVS
Buck Boost Regulator. The small signal model for this powertrain
is that of a voltage controlled current source which has a
trans-conductance that varies depending on the operating mode.
When the converter is operating at its programmed frequency,
it is in discontinuous mode. As the load increases to the point
at which the boundary between discontinuous and continuous
modes is reached, the powertrain changes frequency to remain
in critical conduction mode. This mode of operation allows the
PI3740-00 product family to have a very simple compensation
scheme, as the control to output transfer function always has a
slope of -1. In addition, when critical conduction is reached, the
voltage controlled current source becomes more ideal with a
higher output equivalent resistance with less variation.
V_EAO
G_MOD
+
V_OUT
r_EQ
C_OUT
R_LOAD
Figure 57 — PI3740-00 Small Signal Model Control-Output
The Control-Output transfer function (also known as the small
signal modulator gain) has a single pole response determined
by the parallel combination of Rload and r_EQ and the output
capacitor C_OUT. Equation (10) determines the frequency of the
modulator pole:
( ) Fpmod =
2•π•
1
R_LOAD • r_EQ
R_LOAD + r_EQ
• C_OUT
(10)
Error Amplifier
The small signal model of the error amplifier and compensator
is shown in Figure 56. The error amplifier is a wide bandwidth
Trans-Conductance Amplifier (TCA). It is capable of sourcing and
sinking ±400µA. Here it is important to note that the external
components are C_COMP, C_HF, R1 and R2. R_ZI is pre-programmed by
the factory and is internal to the PI3740-00 SiP.
V_OUT
GM_EAO
+
R1
R2
PI3740-00
C_HF
R_ZI
C_COMP
R_OUT
V_EAO
Figure 58 — PI3740-00 Error Amplifier Model
When the amplifier is configured as shown in Figure 58,
it forms a Type II amplifier configuration with poles and
zeros determined by:
Fplf =
1
2 • π • (R_ZI +R_OUT) • (C_COMP + C_HF)
Fzmb =
Fphf =
1
2 • π • (R_ZI //R_OUT) • C_COMP
C_{HF +} C_COMP
2 • π • (R_ZI //R_OUT) • C_COMP • C_HF
(11)
(12)
(13)
Lighting Mode (LGH)
The Lighting (LGH) mode allows the PI3740-00 product 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 PI3740-00 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 PI3740-00 has a separate current
amplifier, called LGH, and built in 100mV lighting reference that
has its output connected to the EAO pin internally. If the current
through an external shunt starts to develop 100mV 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.
Cool-Power^® ZVS Switching Regulators
Page 35 of 48
Rev 1.4
04/2017
vicorpower.com
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