XRP7665EVB Exar Corporation, XRP7665EVB Datasheet - Page 7

• Manufacturer Part Number: XRP7665EVB
• Description: Power Management Modules & Development Tools Eval Board for XRP7665 Series
• Manufacturer: Exar Corporation
• Type: PMIC Solutionsr

Specifications of XRP7665EVB

• Maximum Operating Temperature: + 85 C
• Operating Supply Voltage: 4.75 V to 18 V
• Product: Power Management Development Tools
• For Use With/related Products: XRP7665
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

THEORY OF OPERATION
F
The XRP7665 is a synchronous, current-mode,
step-down
voltages from 4.75V to 18V and supplies up to
3A of load current. The XRP7665 uses current-
mode control to regulate the output voltage.
The output voltage is measured at FB through
a resistive voltage divider and input to a
transconductance error amplifier. The high-
side switch current is compared to the output
of the error amplifier to control the output
voltage. The regulator utilizes internal N-
channel MOSFETs to step-down the input
voltage. A bootstrapping capacitor connected
between BS and SW acts as a supply for high-
side MOSFET. This capacitor is charged from
the internal 5V supply when SW node is low.
The XRP7665 has several powerful protection
features including OCP, OVP, OTP, UVLO and
output short-circuit.
PROGRAMMABLE SOFT
The soft-start time is fully programmable via
CSS capacitor, placed between the SS and
GND pin. The CSS is charged by a 6µA
constant-current source, generating a ramp
signal fed into non-inverting input of the error
amplifier. This ramp regulates the voltage on
comp pin during the regulator startup, thus
realizing soft-start. Calculate the required CSS
from:
Where:
tss is the required soft-start time
V
OVER CURRENT PROTECTION OCP
The OCP protects against accidental increase
in load current that can cause the regulator to
fail. The current of internal switch M1 is
monitored. If this current reaches 5.6A then
M1 is turned off until next switching cycle.
© 2011 Exar Corporation
FB
UNCTIONAL
is the feedback voltage (0.925V nominal)
regulator.
D
ESCRIPTION
-
START
It
6μ
regulates
input
3
3
A
A
1
1
7/12
8
8
V
V
SHORT
If there is short-circuit across the output, the
feedback voltage V
below 0.3V the XRP7665 will detect a short-
circuit condition and reduce the switching
frequency to 90kHz for system protection. The
regulator will restart once the short-circuit has
been removed.
OVERVOLTAGE PROTECTION OVP
The XRP7665 has internal OVP. When V
exceeds the OVP threshold (when V
1.1V) the power switching will be turned off.
The XRP7665 will restart when overvoltage
condition is removed.
OVER
If the junction temperature exceeds 160°C the
OTP circuit is triggered, turning off the internal
control circuit and switched M1 and M2. When
junction temperature drops below 140°C the
XRP7665 will restart.
APPLICATION INFORMATION
SETTING THE OUTPUT VOLTAGE
Use an external resistor divider to set the
output voltage. Program the output voltage
from:
Where:
R1 is the resistor between V
R2 is the resistor between FB and GND
(nominally 10kΩ)
0.925V is the nominal feedback voltage.
OUTPUT INDUCTOR
Select the output inductor for inductance L, DC
current rating I
I
current. I
50% higher than the regulator output current.
Since the regulator is rated at 3A then I
and I
S
S
SAT
y
y
n
. I
n
c
c
SAT
-
DC
h
TEMPERATURE PROTECTION OTP
h
-
≥4.5A. Calculate the inductance from:
CIRCUIT PROTECTION
r
r
should be larger than regulator output
o
o
SAT
n
n
, as a rule of thumb, should be
o
o
1
u
u
DC
s
s
and saturation current rating
S
S
2
FB
t
t
e
e
p
p
will droop. If V
0.925
-
-
D
D
o
o
OUT
w
w
n
n
and FB
1
X
X
C
C
R
R
o
o
FB
P
n
P
n
Rev. 1.0.0
FB
v
v
exceeds
7
7
e
e
DC
6
6
drops
r
r
≥3A
6
t
6
t
e
OUT
e
5
5
r
r