SP6651AEU-L Exar Corporation, SP6651AEU-L Datasheet - Page 7

• Manufacturer Part Number: SP6651AEU-L
• Description: IC CONV SYNC BUCK 800MA 10MSOP
• Manufacturer: Exar Corporation
• Type: Step-Down (Buck)r
• Series: -r

Specifications of SP6651AEU-L

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1 V ~ 5.5 V
• Current - Output: 800mA
• Voltage - Input: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 10-TFSOP, 10-MSOP (0.118", 3.00mm Width)
• Primary Input Voltage: 5.5V
• No. Of Outputs: 1
• Output Voltage: 5V
• Output Current: 800mA
• No. Of Pins: 10
• Operating Temperature Range: -40°C To +85°C
• Supply Voltage Range: 2.7V To 5.5V
• Mounting Style: SMD/SMT
• Frequency - Switching: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

Date: 5/25/04
The SP6651A is a high efficiency synchronous
buck regulator with an input voltage range of
+2.7V to +5.5Vand an output that is adjustable
between +1.0V and V
a unique on-time control loop that runs in dis-
continuous conduction mode (DCM) or con-
tinuous conduction mode (CCM) using syn-
chronous rectification. Other features include
over-temperature shutdown, over-current pro-
tection, digitally controlled enable and under-
voltage lockout, a battery low indicator, and an
external feedback pin.
The SP6651A operates with a light load quies-
cent current of 20µA using a 0.3Ω PMOS main
switch and a 0.3Ω NMOS synchronous switch.
It operates with excellent efficiency across the
entire load range, making it an ideal solution for
battery powered applications and low current
step-down conversions. The part smoothly tran-
sitions into a 100% duty cycle under heavy load/
low input voltage conditions.
On-Time Control - Charge Phase
The SP6651A uses a precision comparator and
a minimum on-time to regulate the output volt-
age and control the inductor current under nor-
mal load conditions. As the feedback pin drops
below the regulation point, the loop comparator
output goes high and closes the main switch.
The minimum on-timer is triggered, setting a
logic high for the duration defined by:
T
where:
K
V
V
To accommodate the use of ceramic and other
low ESR capacitors, an open loop ramp is added
to the feedback signal to mimic the inductor
current ripple. The following waveforms de-
scribe the ideal ramp operation in both CCM and
DCM operation.
In either CCM or DCM, the negative going
ON
ON
IN
OUT
= V
=
= 2.25V*µsec constant
= V
IN
V
OUT
pin voltage
IN
K
- V
ON
pin voltage
OUT
IN
. The SP6651A features
SP6651A High Efficiency 800mA Synchronous Buck Regulator
7
DRVON
I(L1)
FB’
ramp voltage (V
is added to FB and this creates the FB's signal.
This FB signal is applied to the negative termi-
nal of the loop comparator. To the positive
terminal of the loop comparator is applied the
REF voltage of 0.8V plus an offset voltage Vos
to compensate for the DC level of V
plied to the negative terminal. The result is an
internal ramp with enough negative going offset
(approximately 50mV) to trip the loop com-
parator whenever FB falls below regulation.
The output of the loop comparator, a rising
VOLOW, causes a SET if BLANK = 0 and
OVR_I = 0. This starts inductor charging
(DRVON = 1) and starts the minimum on-timer.
The minimum on-timer times out and indicates
DRVON can be reset if the voltage loop is
satisfied. If V
DRVON
I(L1)
FB’
REF’
RAMP: CCM OPERATION
RAMP: DCM OPERATION
OUT
RAMP
THEORY OF OPERATION
is still below the regulation
in the functional diagram)
© Copyright 2004 Sipex Corporation
V
OS
V
OS
REF, FB
REF’
RAMP
REF, FB
ap-