ELM611DA 2A 23V
high efficiency synchronous PWM step down DC/DC converter
■Application notes
ELM611DA is 350kHz fixed frequency PWM synchronous step-down regulator, whose input voltage can be
set within the range from 4.75V to 23V and output one is adjustable within the range from 0.923V to 18V;
maximum output current of ELM611DA can reach 2A. ELM611DA adopts current-mode control to regulate
output voltage; error between voltage divided by resistive voltage divider from output voltage is input to FB and
internal standard voltage is controlled by internal transconductance error amplifier. CR circuit, which corrects
the transmission function of error amplifier to ensure stable operation, is connected to COMP. ELM611DA in-
cludes 2 N-channel MOSFETs which works as switches; it is required that gate voltage is higher than the input
one in order to turn the NMOS switch of power side on and this voltage can be generated by internal boost strap
circuit. A boost capacitor between SW and BS to drive the high side gate. The boost capacitor is charged by the
internal 5V line when SW is low. If FB voltage of ELM611DA is higher than 0.923V by 20% or more under
monitoring, the over voltage comparator will activate, COMP and SS are discharged to GND, and forces MOS
switch to be off. In order to activate internal circuit under 5V, ELM does not recommend adding voltage higher
than 5V to FB, COMP, EV and SS.
1. Pin description
BS: High side gate drive boost input
BS supplies the drive for the high-side N-channel MOSFET switch. Connect a capacitor of 0.01μF or greater
between SW and BS to power the high side switch.
VIN: Power input
ELM611DA is powered by VIN and input range is 4.75V to 23V. To absorb switch noise, connect the capacitor
of suitable value between VIN and GND.
SW: Power switch output
SW powers output by switching inductor current. Connect LC filter between SW and output load. A capacitor
between SW and BS is required.
GND: Ground
Connect to PCB wiring which is lower than high frequency impedance.
FB: Control voltage feedback
FB regulates voltage by detecting output voltage. Feedback threshold is 0.923V. FB is connected through resis-
tive voltage divider network between output and GND.
COMP: Compensation node
COMP is used to compensate regulation control loop. Connect series RC between COMP and GND. In some
cases, an additional capacitor from COMP to GND is required.
EN: Enable input
EN is digital input that turns the regulator on/off. The regulator works when it’s high input by high enable and
becomes standby when it’s low input. Automatic startup would activate with pullup by 100kΩ resistor.
EN threshold is 1.6V(typ.). It is possible to adjust automatic startup voltage using register divider (R4, R5) be-
tween Vin and GND.
SS: Soft-start control input
SS controls soft start period. By connecting to a 0.15μF capacitor, soft-start period can be set to 15ms. Soft-
start function would be disabled when SS is open.
Rev.1.2
11 - 4
ELM-TECH [ ELM Technology Corporation ]
