MAX8741EAI+T Maxim Integrated, MAX8741EAI+T Datasheet - Page 18

• Manufacturer Part Number: MAX8741EAI+T
• Description: Current & Power Monitors & Regulators 500kHz Multi-Out Pwr Supply Controller
• Manufacturer: Maxim Integrated

Specifications of MAX8741EAI+T

• Rohs: yes
• Product: Power Monitors
• Supply Voltage - Max: 30 V
• Supply Voltage - Min: 4.2 V
• Input Voltage Range: 4.2 V to 30 V

500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
DL_ is kept low whenever the corresponding SMPS is
disabled, and in shutdown. Since the outputs are not
actively discharged by the SMPS controller, the negative
output voltage caused by quickly discharging the output
through the inductor and low-side MOSFET is eliminated.
The output voltage discharges at a rate determined only
by the output capacitance and load current.
The power-good monitor generates a system RESET
signal. At first power-up, RESET is held low until both
the 3.3V and 5V SMPS outputs are in regulation. At this
point, an internal timer begins counting oscillator puls-
es, and RESET continues to be held low until 32,000
cycles have elapsed. After this timeout period (64ms at
500kHz or 96ms at 333kHz), RESET is actively pulled
up to V
ON3/ON5 controls), only the 3.3V SMPS is monitored—
the 5V SMPS is ignored.
The output undervoltage-lockout circuit is similar to
foldback current limiting, but employs a timer rather
than a variable current limit. Each SMPS has an under-
voltage protection circuit that is activated 4096 clock
cycles after the SMPS is enabled. If either SMPS output
is under 70% of the nominal value, both SMPSs are
latched off with DH_ and DL_ driven low. They won’t
restart until SHDN or RUN/ON3 is toggled, or until V+
power is cycled below 1V.
Both SMPS outputs are monitored for overvoltage. If
either output is more than 7% above the nominal regu-
lation point, both SMPS outputs are latched off and the
low-side gate driver (DL_) of the faulted side is latched
Table 4. Operating Modes
18
Output Undervoltage Shutdown Protection
SHDN
High
High
High
High
High
High
High
High
Low
______________________________________________________________________________________
L
RESET Power-Good Voltage Monitor
. If SEQ is connected to REF (for separate
GND
GND
SEQ
REF
REF
REF
REF
V
V
X
L
L
Output Overvoltage Protection
RUN/ON3
High
High
High
High
Low
Low
Low
Low
X
Timing capacitor
Timing capacitor
Timing capacitor
Timing capacitor
TIME/ON5
High
High
Low
Low
X
Shutdown
Standby
Standby
Standby
MODE
high. The SMPS does not restart until SHDN is brought
low and V
To ensure overvoltage protection on initial power-up,
connect signal diodes from both output voltages to V
(cathodes to V
This circuitry protects the load from accidental overvolt-
age caused by a short circuit across the high-side
power MOSFETs. This scheme relies on the presence
of a fuse, in series with the battery, which is blown by
the resulting crowbar current.
PWM mode (SKIP = high) minimizes RF and audio inter-
ference in noise-sensitive applications (such as hi-fi multi-
media-equipped systems), cellular phones, RF
communicating computers, and electromagnetic pen
entry systems. See the summary of operating modes in
Table 3. SKIP can be driven from an external logic signal.
Interference due to switching noise is reduced in PWM
mode by ensuring a constant switching frequency, thus
concentrating the emissions at a known frequency out-
side the system audio or IF bands. Choose an oscillator
frequency for which switching frequency harmonics do
not overlap a sensitive frequency band. If necessary,
synchronize the oscillator to a tight-tolerance external
clock generator. To extend the output-voltage regula-
tion range, constant operating frequency is not main-
tained under overload or dropout conditions (see the
Dropout Operation section).
PWM mode (SKIP = high) forces two changes upon the
PWM controllers. First, it disables the minimum-current
comparator, ensuring fixed-frequency operation.
Second, it changes the detection threshold for reverse
current limit from 0 to -100mV, allowing the inductor
Run
Run
Run
Run
Run
L
falls below its 2V (typ) POR level.
All circuit blocks turned off.
Supply current = 4µA.
Both SMPSs off. Supply current = 30µA.
3.3V SMPS enabled/5V off.
5V SMPS enabled/3.3V off.
Both SMPSs enabled.
Both SMPSs off. Supply current = 30µA.
Both SMPSs enabled. 5V enabled before 3.3V.
Both SMPSs off. Supply current = 30µA.
Both SMPSs enabled. 3.3V enabled before 5V.
Low-Noise Operation (PWM Mode)
L
) to eliminate the V
DESCRIPTION
L
power-up delay.
L