Datasheet

16 Maxim Integrated
High-Efficiency, 4A, Step-Down DC-DC
Regulators with Internal Power Switches
MAX15066/MAX15166
The average current through the inductor is expressed as:
L MOD COMP
IG V= ×
where IL is the average inductor current and G
MOD
is
the power modulator’s transconductance. For a buck
converter:
OUT LOAD L
VR I= ×
where R
LOAD
is the equivalent load resistor value.
Combining the above two relationships, the power mod-
ulator’s transfer function in terms of V
OUT
with respect
to V
COMP
is:
OUT LOAD L
LOAD MOD
COMP
L
MOD
VRI
RG
V
I
G
×
= = ×




The peak current-mode controller’s modulator gain is
attenuated by the equivalent divider ratio of the load
resistance and the current-loop gain. G
MOD
becomes:
( )
( )
MOD MC
LOAD
S
SW
1
G DC g
R
1 K 1 D 0.5
fL
= ×


+ × ×− −


×

where R
LOAD
= V
OUT/IOUT(MAX)
, f
SW
is the switching
frequency, L is the output inductance, D is the duty cycle
(V
OUT
/V
IN)
, and K
S
is the slope compensation factor
calculated from the following equation:
( )
SLOPE SLOPE SW MC
S
N IN OUT
S V f Lg
K1 1
S VV
× ××
=+=+
−
where:
SLOPE
SLOPE SLOPE SW
SW
V
S Vf
t
= = ×
( )
IN OUT
N
MC
VV
S
Lg
−
=
×
Figure 3. Peak Current-Mode Regulator Transfer Model
L
CONTROL
LOGIC
V
COMP
V
OUT
PWM
COMPARATOR
COMP
V
COMP
R
C
R
OUT
g
MV
V
IN
POWER MODULATOR OUTPUT FILTER
AND LOAD
NOTE: THE G
MOD
STAGE SHOWN ABOVE MODELS THE AVERAGE CURRENT OF THE INDUCTOR, I
L
,
INJECTED INTO THE OUTPUT LOAD, I
OUT
, e.g., I
L
= I
OUT
.
SUCH CAN BE USED TO SIMPLIFY/MODEL THE MODULATION/CONTROL/POWER STAGE
CIRCUITRY SHOWN WITHIN THE BOXED AREA.
ERROR AMPLIFIERFEEDBACK
DIVIDER
COMPENSATION
RAMP
g
MC
DCR
I
L
Q
LS
V
OUT
V
OUT
I
L
ESR
C
OUT
R
LOAD
C
C
REF
*C
FF
IS OPTIONAL, DESIGNED TO EXTEND THE REGULATOR’S
GAIN BANDWIDTH AND INCREASED PHASE MARGIN FOR SOME
LOW-DUTY CYCLE APPLICATIONS.
FB
R1
*C
FF
V
FB
R2
G
MOD
C
Q
HS
R
OUT
=
10
AVEA(dB)/20
g
MV
I
OUT