Rainbow Electronics MAX1541 - Manual (Page 16)

MAX1540/MAX1541
Dual Step-Down Controllers with Saturation
Protection, Dynamic Output, and Linear Regulator
16 ______________________________________________________________________________________
PIN
MAX1540 MAX1541
NAME FUNCTION
1 1 OVP/UVP
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 Shutdown and Output Discharge sections.
2 2 SKIP
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.
3 3 LSAT
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.
4 4 TON
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 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)
5 5 V CC
Analog Supply Input. Connect to the system supply voltage (+4.5V to +5.5V) through
a series 20
Ω resistor. Bypass V
CC to analog ground with a 1µF or greater ceramic
capacitor.
— 6 GATE
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.
— 7 CC1
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).
Pin Description