EL7564CREZ-T13 Intersil, EL7564CREZ-T13 Datasheet - Page 10

• Manufacturer Part Number: EL7564CREZ-T13
• Description: IC REG DC/DC STEP-DN 4A 28HTSSOP
• Manufacturer: Intersil
• Type: Step-Down (Buck)r

Specifications of EL7564CREZ-T13

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1 ~ 3.8 V
• Current - Output: 4A
• Frequency - Switching: 1MHz
• Voltage - Input: 4.5 ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-TSSOP Exposed Pad, 28-eTSSOP, 28-HTSSOP
• Power - Output: 13W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Applications Information
Circuit Description
General
The EL7564 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 4A synchronous step-
down regulator suitable for use in DSP core power supplies.
By combining fused-lead packaging technology with an
efficient synchronous switching architecture, high power
output (13W) can be realized without the use of discrete
external heat sinks.
Theory of Operation
The EL7564 is composed of seven major blocks:
PWM Controller
The EL7564 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-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
will approach a one-pole system. The resulting system offers
several advantages over traditional voltage control systems,
1. PWM Controller
2. NMOS Power FETs and Drive Circuitry
3. Bandgap Reference
4. Oscillator
5. Temperature Sensor
6. Power Good and Power On Reset
7. Auxiliary Supply Tracking
10
EL7564
including simpler loop compensation, pulse by pulse current
limiting, rapid response to line variation and good load step
response.
The heart of the controller is an input direct summing
comparator which sum voltage feedback, current feedback,
slope compensation ramp and power tracking signals
together. Slope compensation is required to prevent system
instability that occurs in current-mode topologies operating
at duty-cycles greater than 50% and is also used to define
the open-loop gain of the overall system. The slope
compensation is fixed internally and optimized for 500mA
inductor ripple current. The power tracking will not contribute
any input to the comparator steady-state operation. Current
feedback is measured by the patented sensing scheme that
senses the inductor current flowing through the high-side
switch whenever it is conducting. At the beginning of each
oscillator period the high-side NMOS switch is turned on.
The comparator inputs are gated off for a minimum period of
time of about 150ns (LEB) after the high-side switch is
turned on to allow the system to settle. The Leading Edge
Blanking (LEB) period prevents the detection of erroneous
voltages at the comparator inputs due to switching noise. If
the inductor current exceeds the maximum current limit
(I
the high-side switch on time. If I
the feedback voltage FB derived from the regulator output
voltage V
reference voltage. The resultant error voltage is summed
with the current feedback and slope compensation ramp.
The high-side switch remains on until all four comparator
inputs have summed to zero, at which time the high-side
switch is turned off and the low-side switch is turned on.
However, the maximum on-duty ratio of the high-side switch
is limited to 95%. In order to eliminate cross-conduction of
the high-side and low-side switches a 15ns break-before-
make delay is incorporated in the switch drive circuitry. The
output enable (EN) input allows the regulator output to be
disabled by an external logic control signal.
Output Voltage Setting
In general, EL7564CM:
and EL7564CRE:
A 100nA pull-up current from FB to V
GND in the event that FB is floating.
V
V
LMAX
OUT
OUT
=
=
) a secondary over-current comparator will terminate
0.975V
0.992V
OUT
is then compared to the internal feedback
×
×






1
1
+
+
R
------ -
R
R
------ -
R
2
1
2
1






LMAX
DD
has not been reached,
forces V
OUT
May 9, 2005
FN7297.3
to