ELM604PA 1.4MHz, 800mA dual PWM step-down converter
■Marking
TDFN10-3x3
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lmnop
Mark
a to p
Content
Assembly lot No.:
0 to 9 & A to Z
■Application notes
ELM604PA has dual independent constant frequency current mode PWM step-down converters.
ELM604PA is optimized for low voltage, Li-ion battery powered applications where high efficiency and
small size are critical. ELM604PA uses external resistor dividers to set two output voltages indepe
ndently from 0.6V to 6V. The device integrates both main switches and synchronous rectifiers, which pro-
vides high efficiency and eliminates the need for an external Schottky diode. ELM604PA can achieve 100% du-
ty cycle. The duty cycle D of each step-down converter is defined as:
D = Ton × Fosc × 100% ≈ (Vout/Vin) × 100%
Where Ton is the main switch on time, Fosc is the oscillator frequency (1.4MHz), Vout is the output voltage
and Vin is the input voltage.
1) Current mode PWM Control
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current li-
mit for superior load and line response and protection of the internal main switch and synchronous rec
tifier. Each channel switches at a constant frequency (1.4MHz) and regulates the output voltage. Dur-
ing each cycle the PWM comparator modulates the power transferred to the load by changing the induct
or peak current based on the feedback error voltage. During normal operation, the main switch is tur
ned on for a certain time to ramp the inductor current at each rising edge of the internal oscillato
r, and switched off when the peak inductor current is above the error voltage. When the main switch is off, the syn-
chronous rectifier will be turned on immediately and stay on until the next cycle starts.
2) Dropout operation
Each channel of the ELM604PA allows the main switch to remain on for more than one switching cycle a
nd increases the duty cycle while the input voltage is dropping close to the output voltage. When the duty cy-
cle reaches 100%, the main switch is held on continuously to deliver current to the output up to the P MOSFET cur-
rent limit. The output voltage then is the input voltage minus the voltage drop across the main switch and the in-
ductor.
Rev.1.2
7 - 4
ELM-TECH [ ELM Technology Corporation ]
