MAX15569 Datasheet, PDF (17/41 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
MAX15569
BST
CBST
LX
POWER
STAGE
INDUCTOR
L
RDCR
R1
R2
C_EQ
CSP_
CSN_
R2
RCS =
RDCR
R1 + R2
COUT
RDCR
=
L
CEQ
1 ₊₁
R1 R2
FOR THERMAL COMPENSATION:
R2 SHOULD CONSIST OF AN NTC RESISTOR
IN SERIES WITH A STANDARD THIN-FILM RESISTOR
A) LOSSLESS INDUCTOR SENSING
BST
MAX15569
LX
POWER
STAGE
CBST
L
SENSE RESISTOR
LESL
RSENSE
R1
CEQ
CEQREQ = ^LESL
RSENSE
CSP_
CSN_
B) OUTPUT SERIES RESISTOR SENSING
Figure 4. Sense Resistor and DCR Current-Sense Methods
Inductor DCR and Sense Resistor Current Sense
Using the DC resistance (R_DCR) of the output inductor
allows higher efficiency compared to using a current-
sense resistor. The initial tolerance and temperature
coefficient of the inductor’s DCR must be accounted
for in the output-voltage droop-error budget and current
monitor. This current-sense method uses an RC filter
network to extract the current information from the output
inductor (see Figure 4).
The RC network should match the time constant of the
inductor (L/RDCR):
R _CS
=


R2
R1+ R2
_{R DCR}
and:
= R _DCR
C
L
EQ
1
_R1
+
1
R2^
where R_CS is the required current-sense resistance and
R_DCR is the inductor’s series DC resistance. Use the
typical inductance and R_DCR values provided by the
inductor manufacturer. To minimize the current-sense
error, due to the leakage current of the current-sense
inputs (I_{CSP_} and I_{CSN_}), choose R1||R2 to be less than
2kΩ and use the previous equation to determine the
sense capacitance (C_EQ). Choose capacitors with 5%
tolerance and resistors with 1% tolerance specifications.
Temperature compensation is recommended for this cur-
rent-sense method. See the Load-Line Amplifier (Steady
State and AC Droop)section for detailed information.
When using a current-sense resistor for accurate output
load-line control, the circuit requires a differential RC filter
to eliminate the AC voltage step caused by the equivalent
series inductance (L_ESL) of the current-sense resistor
(see Figure 4). The ESL-induced voltage step might affect
the average current-sense voltage. The time constant
of the RC filter should match the L_ESL/R_SENSE time
constant formed by the parasitic inductance of the
current-sense resistor:
L _ESL
R _SENSE
=
C _EQR _EQ
where L_ESL is the equivalent series inductance of the
current-sense resistor, R_SENSE is the current-sense
resistance value, and C_EQ and R_EQ are the time-constant
matching components.
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