EL7556DCM Просмотр технического описания (PDF) - Renesas Electronics
Номер в каталоге
Компоненты Описание
производитель
EL7556DCM Datasheet PDF : 11 Pages
| |||
EL7556D
Block Diagram
FB1, Pin 1
FB2, Pin 28
VCCDET, Pin 13
CSLOPE, Pin 3
CREF, Pin 27
1.26V
2-1 MUX
OUTEN, Pin 14
VDD
COSC, Pin 4
4V
UVLO
-
+
S
-
+
R
-
+
-
+
-
+
Current Sense
-
+
S Current Limit
-
+
-
+ PWM
VDD
RSS
CSS
V2X
LEB TDELAY
Q
R
Q
S
RFF
S
Zero Cross Detect
Over Temp
Sensor
PWRGD, Pin 16
CP, Pin 27
C2V, Pin 26
VHI, Pin 24
VDD and VIN,
Pin 5,6,8
LX, Pin 20-23
VSSP, Pin 9-
12, 18-19
OT, Pin 15
VSS, Pin 25
Applications Information
Circuit Description
General
The EL7556D 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 of
the active circuitry required to implement a cost effective, user-
programmable 6A synchronous buck converter suitable for use
in CPU power supplies. By combining fused-lead packaging
technology with an efficient synchronous switching
architecture, high power outputs (21W) can be realized without
the use of discrete external heat sinks.
Theory of Operation
The EL7556D is composed of 7 major blocks:
1. PWM Controller
2. Output Voltage Mode Select
3. NMOS Power FETS and Drive Circuitry
4. Bandgap Reference
5. Oscillator
6. Temperature Sensor
7. Power Good and Power On Reset
PWM Controller
The EL7556D regulates output voltage through the use of
current-mode controlled pulse width modulation. The three
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-average of the modulator output the relatively
large LC time constants 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 or 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 will approach a one pole system. The
resulting system offers several advantages over traditional
voltage control systems, including simpler loop compensation,
FN7339 Rev 1.00
August 1, 2005
Page 9 of 11
Share Link: 