SP7656EN2-L Exar Corporation, SP7656EN2-L Datasheet - Page 4

• Manufacturer Part Number: SP7656EN2-L
• Description: IC CONV BUCK NON-SYNC 8HNSOIC
• Manufacturer: Exar Corporation
• Series: Power Blox™r
• Type: Step-Down (Buck)r

Specifications of SP7656EN2-L

• Package / Case: 8-SOIC (0.154", 3.90mm Width) Exposed Pad
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 V ~ 28 V
• Current - Output: 3A
• Frequency - Switching: 600kHz
• Voltage - Input: 4.5 V ~ 29 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: *
• Output Current: 3 Amps
• Input Voltage: 4.5 V
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

SP7656 General Overview:
The SP7656 PowerBlox is a fixed frequency,
voltage
controller co-packaged with a P-Channel FET.
SP7656 is optimized for minimum component,
small form factor and cost effectiveness. It has
been designed for single-supply operation
ranging from 4.5V to 29V. SP7656 has Type-2
internal
Electrolytic/Tantalum output capacitors. For
ceramic capacitors Type-3 compensation can
be implemented by simply adding an R and C
between output and Feedback.
A precision 0.6V reference, present on the
positive terminal of the internal error amplifier,
permits programming of the output voltage
down to 0.6V via the FB pin. The output of the
Error Amplifier is internally compared to a
feed-forward (V
generates the PWM control.
Timing is governed by an internal oscillator
that sets the PWM frequency at 600kHz.
SP7656 contains useful protection features.
Over-current protection is based on the
internal
programmable via a resistor placed between
I
(UVLO) ensures that the controller starts
functioning only when sufficient voltage exists
for powering IC’s internal circuitry.
SP7656 Loop Compensation
The
compensation
compensation.
components are not required for systems with
tantalum
capacitors with sufficiently high ESR. Use the
condition below as a guideline to determine
whether or not the internal compensation is
sufficient for your design. Type-2 internal
compensation is sufficient if the following
condition is met:
where:
11/07/08 SP7656 PowerBlox
SET
and LX node. Under-Voltage Lock-Out
SP7656
mode,
f
or aluminum
compensation
MOSFET
ESRZERO
f
ESRZERO
IN
/5 peak-to-peak) ramp and
includes
components
External

non-synchronous
2


Rds(on)
f
R
DBPOLE
electrolytic output
ESR
1
for
Type-2
C
compensation
OUT
use
for
and
internal
PWM
loop
with
is
4
Creating a Type-3 compensation Network
The above condition requires the ESR zero to
be at a lower frequency than the double-pole
from the LC filter. If this condition is not met,
Type-3 compensation should be used and can
be accomplished by placing a series RC
combination in parallel with R1 as shown
below. The value of CZ can be calculated as
follows and RZ selected from table 1.
Figure 1- RZ and CZ in conjunction with internal
compensation components form a Type-3
CZ2
f
f
1X
2X
3X
5X
>= 10X
DBPOLE
ESRZERO
SP7656
130pF
Table1- RZ Selection
CP1
Error Amplif ier
compensation
CZ 
2pF
-
+

RZ2
/f
2

DBPOLE
200k
Vref =0.6V
Copyright 2008 EXAR Corporation
L
R
1
L
C
1
C
OUT
RZ
50K
40K
30K
10K
2K
FB
RZ
CZ
Vout
R1
200k, 1%
R2