MAX1845 Maxim, MAX1845 Datasheet - Page 14

• Manufacturer Part Number: MAX1845
• Description: Dual / High-Efficiency / Step-Down Controller with Accurate Current Limit
• Manufacturer: Maxim

Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
include larger physical size and degraded load-tran-
sient response (especially at low input voltage levels).
DC output accuracy specifications refer to the threshold
of the error comparator. When the inductor is in continu-
ous conduction, the output voltage will have a DC regula-
tion higher than the trip level by 50% of the ripple. In
discontinuous conduction (SKIP = GND, light-load), the
output voltage will have a DC regulation higher than the
trip level by approximately 1.5% due to slope compensa-
tion.
The low-noise, forced-PWM mode (SKIP = high) dis-
ables the zero-crossing comparator, which controls the
14
Figure 3. PWM Controller (One Side Only)
______________________________________________________________________________________
OPPOSITE
OPPOSITE
Forced-PWM Mode ( SKIP = High)
FROM
PWM
PWM
TO
TON
OVP
V
CC
- 1V
FROM ILIM
COMPARATOR
TRIG
0.1V
COMPUTE
ON-TIME
1-SHOT
TON
TON
V+
UVP
1.14V
Q
FROM
REF
OUT
R
R
Q
Q
FROM ZERO-CROSSING
S
S
COMPARATOR
ERROR
AMP
0.7V
TIMER
Q
TOFF 1-SHOT
S
R
low-side switch on-time. This causes the low-side gate-
drive waveform to become the complement of the high-
side gate-drive waveform. This in turn causes the
inductor current to reverse at light loads as the PWM
loop strives to maintain a duty ratio of V
benefit of forced-PWM mode is to keep the switching
frequency fairly constant, but it comes at a cost: The
no-load battery current can be 10mA to 40mA, depend-
ing on the external MOSFETs.
Forced-PWM mode is most useful for reducing audio-
frequency noise, improving load-transient response,
providing sink-current capability for dynamic output
voltage adjustment, and improving the cross-regulation
Q
TRIG
x2
S
R
FAULT
Q
(SEE FIGURE 9)
FEEDBACK
MUX
1.1V
TO PGOOD
OR-GATE
0.9V
OUT_
FB_
TO DH DRIVER
TO DL DRIVER
SHUTDOWN
OUT
/V
IN
. The