Datasheet

MAX1954A
Low-Cost, Current-Mode PWM Buck
Controller with Foldback Current Limit
_______________________________________________________________________________________ 9
Place the high-side MOSFET as close as possible to
the controller and connect HSD and LX to the MOSFET
using Kelvin-sense connections to guarantee current-
sense accuracy and improve stability.
Current-Limit Circuit
The current-limit circuit employs a lossless, foldback,
valley current-limiting algorithm that uses the low-side
MOSFET’s on-resistance as the sensing element. Once
the high-side MOSFET turns off, the voltage across the
low-side MOSFET is monitored. If the voltage across the
low-side MOSFET (R
DS(ON)
x I
INDUCTOR
) does not
exceed the current limit, the high-side MOSFET turns on
normally. In this condition, the output drops smoothly out
of regulation. If the voltage across the low-side MOSFET
exceeds the current-limit threshold at the beginning of a
new oscillator cycle, the low-side MOSFET remains on
and the high-side MOSFET remains off.
Typical Application Circuits
HSD
COMP
N1
L1
C4
D1
C
F
R
C
C1 C2
C5
C
C
C3
C6
R3
R1
R2
GND
BST
DH
LX
DL
PGND
FB
IN
MAX1954A
V
OUT
1.8V
V
IN
3V TO 5.5V
V
HSD
5.5V TO 13.2V
Figure 1. MAX1954A Typical Application Circuit
IN
COMP
N1
L1
0.8µH
C7
0.1µF
D1
C
F
15pF
R
C
270kΩ
C
C
560pF
C1
0.22µF
C15
C14
R3
R1
10kΩ
C8–C13
270µF
C2–C6
10µF
R2
8.06kΩ
GND
BST
DH
LX
DL
PGND
FB
HSD
MAX1954A
V
OUT
+1.8V AT 20A
V
HSD
10.8V TO 13.2V
V
IN
3V TO 5.5V
N2
N3 N4
Figure 2. MAX1954A Circuit Capable of 20A Output