MAX1540A Datasheet, PDF (16/49 Pages) Maxim Integrated Products – Dual Step-Down Controllers with Saturation Protection, Dynamic Output, and Linear Regulator

Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
PIN
MAX1540A MAX1541
1
1
2
2
3
3
4
4
5
5
—
6
—
7
Pin Description
NAME
OVP/UVP
SKIP
LSAT
TON
V_CC
GATE
CC1
FUNCTION
Overvoltage/Undervoltage Protection and Discharge-Mode Control Input. This four-
level logic input selects between various output fault-protection options (Table 7) by
selectively enabling OVP protection and UVP protection. When enabled, the OVP limit
defaults at 116% of the nominal output voltage, and the UVP limit defaults at 70% of
the nominal output voltage. Discharge mode is enabled when OVP protection is also
enabled. Connect OVP/UVP to the following pins for the desired function:
V_CC = enable OVP and discharge mode, enable UVP.
Open = enable OVP and discharge mode, disable UVP.
REF = disable OVP and discharge mode, enable UVP.
GND = disable OVP and discharge mode, disable UVP.
See the Fault Protection and (ON_) sections.
Pulse-Skipping Control Input. This four-level logic input enables or disables the light-
load pulse-skipping operation of each output:
V_CC = OUT1 and OUT2 in forced-PWM mode.
Open = OUT1 in forced-PWM mode, OUT2 in pulse-skipping mode.
REF = OUT1 in pulse-skipping mode, OUT2 in forced-PWM mode.
GND = OUT1 and OUT2 in pulse-skipping mode.
Inductor-Saturation Control Input. This four-level logic input sets the inductor-current
saturation limit as a multiple of the valley current-limit threshold set by ILIM, or
disables the function if not required. Connect LSAT to the following pins to set the
saturation current limit:
V_CC = 2 x I_LIM(VAL)
Open = 1.75 x I_LIM(VAL)
REF = 1.5 x I_LIM(VAL)
GND = disable LSAT protection
See the Inductor Saturation Limit and Setting the Current Limit sections.
On-Time Selection Control Input. This four-level logic input sets the K-factor value
used to determine the DH_ on-time (see the On-Time One-Shot (TON) section).
Connect to analog ground (GND), REF, or V_CC; or leave TON unconnected to select
the following nominal switching frequencies:
V_CC = 235kHz (OUT1) / 170kHz (OUT2)
Open = 345kHz (OUT1) / 255kHz (OUT2)
REF = 485kHz (OUT1) / 355kHz (OUT2)
GND = 620kHz (OUT1) / 460kHz (OUT2)
Analog Supply Input. Connect to the system supply voltage (+4.5V to +5.5V) through
a series 20Ω resistor. Bypass V_CC to analog ground with a 1µF or greater ceramic
capacitor.
Buffered N-Channel MOSFET Gate Input. A logic low on GATE turns off the internal
MOSFET so OD appears as high impedance. A logic high on GATE turns on the
internal MOSFET, pulling OD to ground.
Integrator Capacitor Connection for Controller 1. Connect a 47pF to 470pF (47pF typ)
capacitor from CC1 to analog ground (GND) to set the integration time constant for
the main MAX1541 controller (OUT1).
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