EL7562CU-T13 INTERSIL [Intersil Corporation], EL7562CU-T13 Datasheet - Page 7

• Manufacturer Part Number: EL7562CU-T13
• Description: Monolithic 2Amp DC-DC Step-Down Regulator
• Manufacturer: INTERSIL [Intersil Corporation]

Block Diagram
Applications Information
Circuit Description
General
The EL7562 is a fixed frequency, current mode controlled
DC-DC converter with integrated N-channel power
MOSFETs and a high precision reference. The device
incorporates all the active circuitry required to implement a
cost effective, user-programmable 2A synchronous step-
down regulator suitable for use in DSP core power supplies.
Theory of Operation
The EL7562 is composed of 5 major blocks:
PWM Controller
The EL7562 regulates output voltage through the use of
current-mode controlled pulse width modulation. The three
1. PWM Controller
2. NMOS Power FETs and Drive Circuitry
3. Bandgap Reference
4. Oscillator
5. Thermal Shut-down
5V
EN
39Ω
0.1µF
VDD
SGND
7
Controller
Supply
Temperature
Junction
FB
Controlle
Reference
PWM
Voltage
Current
Sense
VREF
0.1µF
Oscillator
Drivers
COSC
main elements in a PWM controller are the feedback loop
and reference, a pulse width modulator whose duty cycle is
controlled by the feedback error signal, and a filter which
averages the logic level modulator output. In a step-down
(buck) converter, the feedback loop forces the time-
averaged output of the modulator to equal the desired output
voltage. Unlike pure voltage-mode control systems, current-
mode control utilizes dual feedback loops to provide both
output voltage and inductor current information to the
controller. The voltage loop minimizes DC and transient
errors in the output voltage by adjusting the PWM duty-cycle
in response to changes in line or load conditions. Since the
output voltage is equal to the time-averaged of the modulator
output, the relatively large LC time constant found in power
supply applications generally results in low bandwidth and
poor transient response. By directly monitoring changes in
inductor current via a series sense resistor the controller's
response time is not entirely limited by the output LC filter
and can react more quickly to changes in line and load
conditions. This feed-forward characteristic also simplifies
AC loop compensation since it adds a zero to the overall
loop response. Through proper selection of the current-
feedback to voltage-feedback ratio the overall loop response
Power
Power
FET
FET
270pF
VDRV
VHI
VIN
PGND
0.1µF
4.7µH
100µF
2370Ω
1kΩ
V
OUT