MAX15112 Datasheet, PDF (17/23 Pages) Maxim Integrated Products – High-Efficiency, 12A, Current-Mode Synchronous Step-Down Regulator with Integrated Switches

MAX15112
High-Efficiency, 12A, Current-Mode Synchronous
Step-Down Regulator with Integrated Switches
Compensation Design Guidelines
The MAX15112 uses a fixed-frequency, peak current-
mode control scheme to provide easy compensation
and fast transient response. The inductor peak current
is monitored on a cycle-by-cycle basis and compared to
the COMP voltage (output of the voltage error amplifier).
The regulator’s duty cycle is modulated based on the
inductor’s peak current value. This cycle-by-cycle con-
trol of the inductor current emulates a controlled current
source. As a result, the inductor’s pole frequency is shift-
ed beyond the gain bandwidth of the regulator. System
stability is provided with the addition of a simple series
capacitor-resistor from COMP to GND. This pole-zero
combination serves to tailor the desired response of the
closed-loop system. The basic regulator loop consists of
a power modulator (composed of the regulator’s pulse-
width modulator, compensation ramp, control circuitry,
MOSFETs, and inductor), the capacitive output filter and
load, an output feedback divider, and a voltage-loop
error amplifier with its associated compensation circuitry.
See Figure 2 for a graphical representation. The power
modulator’s transfer function with respect to V_COMP is:
V_OUT
V_COMP
=
R_LOAD


I_L
×I_L


= R_LOAD × G_MOD
 G_MOD 
where IL is the average inductor current, G_MOD is the
power modulator’s transconductance, and R_LOAD is the
equivalent load resistance value.
FEEDBACK
DIVIDER
V_OUT
ERROR AMPLIFIER
POWER MODULATOR
COMPENSATION
RAMP
V_IN
OUTPUT FILTER
AND LOAD
*CFF FB
R1
VFB
C
g_MC
COMP
VCOMP
CONTROL
LOGIC
PWM
COMPARATOR
R2
g_M
R_OUT
R_C
Q_HS
I_L
V_OUT
L
DCR
I_OUT
Q_LS
ESR
R_LOAD
C_OUT
C_C
REF
R_OUT
=
10 ^AVEA(dB)/20
g_M
*C_FF IS OPTIONAL, DESIGNED TO EXTEND THE REGULATOR’S
GAIN BANDWIDTH AND INCREASED PHASE MARGIN FOR SOME
LOW-DUTY CYCLE APPLICATIONS.
V_{COMP GMOD}
V_OUT
I_L
NOTE: THE G_MOD STAGE SHOWN ABOVE MODELS THE AVERAGE CURRENT OF THE INDUCTOR, I_L,
INJECTED INTO THE OUTPUT LOAD, IOUT, e.g., IL = IOUT.
SUCH CAN BE USED TO SIMPLIFY/MODEL THE MODULATION/CONTROL/POWER STAGE
CIRCUITRY SHOWN WITHIN THE BOXED AREA.
Figure 2. Peak Current-Mode Regulator Transfer Model
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