
Date: 5/25/04
SP6121 Low Voltage, Synchronous Step Down PWM Controller Copyright 2004 Sipex Corporation
1
SP6121
■
Optimized for Single Input Voltage - 3V to 5.5V
■
High Efficiency: Greater than 95% possible
■
Accurate, 500kHz Fixed Frequency Operation
■
Fast Transient Response
■
500
μ
A, I
Q
(25
μ
A in Shutdown)
■
Internal, 0.4 V/ms, Soft Start Circuit
■
Precision 1% Reference
■
Resistor Programmable Output Voltage
■
Lossless Adjustable Current Limit with
■
High Side R
DS(ON)
Sensing
■
0% to 100% Duty Cycle Range
■
High Side PMOS Switch Negates Need for
■
External Charge Pump
■
Output Over Voltage Protection
■
Hiccup Mode Current Limit Protection
Low Voltage, Synchronous Step Down PWM Controller
Ideal for 2A to 10A, Small Footprint, DC-DC Power Converters
APPLICATIONS
■
Supply Bias for
- DSP
- Microprocessor Core
- I/O & Logic
■
Video Cards
■
Board Level Supply in
Distributed Power Systems
DESCRIPTION
The SP6121 is a fixed frequency, voltage mode, synchronous PWM controller designed to work
from a single 5V or 3.3V input supply, providing excellent AC and DC regulation for high efficiency
power conversion. The operating frequency is internally set at 500kHz, permitting the use of
small, surface mount inductors and capacitors. Requiring only few external components, the
SP6121 packaged in an 8-pin SOIC, is especially suited for low voltage applications where cost,
small size and high efficiency are critical. With its low voltage capability and inherent 100% duty
cycle operation, the SP6121 allows low dropout operation in the event of a low input supply
voltage condition.
Q1 = FAIRCHILD FDS6375
Q2 = FAIRCHILD FDS6690A
DS = STMICROELECTRONICS STPS2L25BU
L1 = PANASONIC ETQ-P6F1R6SFA
C
OUT
= SANYO 4TPB470M
1
2
3
4
5
6
7
8
COMP
V
FB
GND
PDRV
NDRV
I
SET
I
SENSE
V
CC
SP6121
8 Pin SOIC
V
CC
CB
3.3
μ
F
C
IN
47
F
Ceramic 6.3V
I
SET
3.3V
V
IN
PDRV
GND
COMP
SP6121
U1
V
FB
NDRV
I
SENSE
CP
50pF
RZ
10k
CZ
3.7nF
V
OUT
1.8
μ
H
L1
C
OUT
470
μ
F x 2
RSET
2.3k
1.9V 8A
Q1
Q2
RV
CC
5
DS
R1
R2
10k
FEATURES
TYPICAL APPLICATION CIRCUIT
Now Available in Lead Free Packaging