Datasheet

MAX1858
With dual synchronized out-of-phase operation, the
MAX1858’s high-side MOSFETs turn on 180° out-of-
phase. The instantaneous input current peaks of both
regulators no longer overlap, resulting in reduced RMS
ripple current and input voltage ripple. This reduces the
required input capacitor ripple-current rating, allowing
fewer or less expensive capacitors, and reduces shield-
ing requirements for EMI. The Out-of-Phase Waveforms
in the Typical Operating Characteristics demonstrate
synchronized 180° out-of-phase operation.
Internal 5V Linear Regulator (V
L
)
All MAX1858 functions are internally powered from an
on-chip, low-dropout 5V regulator. The maximum regu-
lator input voltage (V+) is 23V. Bypass the regulator’s
output (V
L
) with a 4.7µF ceramic capacitor to PGND.
The V
L
dropout voltage is typically 500mV, so when V+
is greater than 5.5V, V
L
is typically 5V. The MAX1858
also employs an undervoltage lockout circuit that dis-
ables both regulators when V
L
falls below 4.5V. V
L
should also be bypassed to GND with 0.1µF.
Dual 180° Out-of-Phase PWM Step-Down
Controller with Power Sequencing and POR
8 _______________________________________________________________________________________
V+
BST1
DH1
LX1
DL1
V
L
BST2
DH2
LX2
DL2
FB1
COMP1
*IRF7811W
**OPTIONAL
FB2
COMP2
PGND
REF
GND
OSC
SYNC
CKO
ILIM1
ILIM2EN
OFF
ON
RESET OUTPUT
CLOCK OUTPUT
V
L
RST
MAX1858
C
V+
0.22µF
C
IN1
2
×
10µF
C
OUT1
4
×
220µF
N
H1*
N
L1*
L1
1µH
V
IN
6V - 23V
C
BST1
0.1µF
R1A
8.06kΩ
R1B
10kΩ
C
COMP1B
100pF
C
REF
0.22µF
C
COMP2B
100pF
R2B
10kΩ
118kΩ
140kΩ
R2A
15kΩ
4.7Ω
4.7Ω
R
V+
4.7Ω
N
L2*
**
**
N
H2*
L2
1.2µH
C
OUT2
4
×
220µF
C
IN2
2
×
10µF
OUTPUT2
V
OUT
= 2.5V
C
BST2
0.1µF
C
VL
4.7µF
0.1µF
C
COMP2A
6.8nF
R
COMP2
8.2kΩ
96.5kΩ
D3
CMSSH-3
OUTPUT1
V
OUT
= 1.8V
R
COMP1
5.9kΩ
C
COMP1A
10nF
84.5kΩ
D2
CMSSH-3
Figure 1. Standard Application Circuit