MAX15569 Datasheet, PDF (19/41 Pages) Maxim Integrated Products – 2-Phase/1-Phase QuickTune-PWM Controller with Serial I2C Interface

MAX15569
2-Phase/1-Phase QuickTune-PWM Controller with
Serial I²C Interface
R_SENSE1
NETWORK
R_SENSE2
NETWORK
MAX15569
IMON REGISTER
8-BIT DAC
CSP1
(VCSP1 - VCSN1)
CSN1
0 TO 2.56V RANGE
Gm(IMON)
IIMON
RIMON = 2.56V/(RSENSE_ x Gm(IMON) x IOUT(MAX))
CIMON x RIMON = 150µs
IIMON
VIMON
R_IMON
CIMON
CSP2
(VCSP2 - VCSN2)
CSN2
3.2V
IMON CLAMP
Figure 5. IMON Network
where R_SENSE is the value of the effective current-sense
resistance. Choose R_IMON so that V_IMON is 2.56V at the
full load current.
C_IMON is the IMON averaging capacitor. IMON is
sampled every 400µs. Choose C_IMON such that R_IMON
x C_IMON gives a time constant of approximately 150µs
(see Figure 5).
The IMON voltage is internally clamped to a maximum
3.2V (typ), preventing the IMON output from exceeding
the IMON voltage rating even under overload or short-
circuit conditions. IMON is high impedance when in
shutdown.
Feedback Adjustment Amplifier
Load-Line Amplifier (Steady State and AC Droop)
The device includes a transconductance amplifier for
controlling the load-line regardless of the sense imped-
ance value. The input signal of the amplifier is the sum of
the current-sense voltages (V_CSP1, V_CSN1, and V_CSP2,
V_CSN2), which differentially sense the current-sense volt-
age. See Figure 6.
The AC-droop amplifier output (FBAC) connects to the
remote-sense point of the output through a resistor network
(R_DROOP) that sets the DC and AC current-loop gain:
V_OUT = V_TARGET - (R_DROOP × I_FBAC)
where the target voltage (V_TARGET) is defined in the
Nominal Output-Voltage Selection section, and FBAC
amplifier’s output current (I_FBAC) is determined by the
current-sense voltage:
I_FBAC = G_m(FBAC) × Σ(V_{CSP_} - V_{CSN_})
where G_m(FBAC) = 1.2µA/mV (typ), as defined in the
Electrical Characteristics section. Since the feedback
voltage (V_FB) is regulated to the SETVOUT voltage, the
output voltage changes in response to the FBAC current
(I_FBAC) to create a load-line with accuracy defined by the
characteristics of the R_DROOP network and G_m(FBAC).
The device supports flexible combinations of AC and DC
load-lines: An AC load-line > DC load-line, an AC load-line
= DC load-line, and an AC load-line < DC load-line.
● The effective impedance (Z_FBAC) between the output
of the load-line transconductance amplifier (FBAC)
and the positive side of the remote-sensed output
voltage sets the transient AC droop.
● The effective impedance (Z_FB) between the feedback-
sense input (FB) and the positive side of the feedback
remote sense sets the static (DC) droop.
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