LTC1909-8_15 Datasheet, PDF (1/32 Pages) Linear Technology – Wide Operating Range, No RSENSE Step-Down DC/DC Controller with SMBus Programming

LTC1909-8
Wide Operating Range,
No R_SENSE^TM Step-Down DC/DC
Controller with SMBus Programming
FEATURES
s _SMBus/I²_C^TM _{Programmable Output Voltage:}
1.3V to 3.5V
s _{No Sense Resistor Required}
s _{2% to 90% Duty Cycle at 200kHz}
s _{tON(MIN) ≤ 100ns}
s _{True Current Mode Control}
s _{Stable with Ceramic COUT}
s _{Power Good Output Voltage Monitor and 50µs Timer}
s _{Wide VIN Range: 4V to 36V (Abs Max)}
s _{Precision Resistor Divider and Reference Provide}
±1.35% Output Voltage Accuracy Over Temperature
s _{Adjustable Switching Frequency and Current Limit}
s _{Forced Continuous Control Pin}
s _{Programmable Soft-Start}
s _{Output Overvoltage Protection}
s _{Optional Short-Circuit Shutdown Timer}
s _{Available in a 28-Lead SSOP Package}
U
APPLICATIO S
s _{Power Supplies for DSPs, ASICs, FPGAs and CPUs}
s _{Voltage Margining}
DESCRIPTIO
The LTC^®1909-8 is a synchronous step-down switching
regulator controller with a digitally programmable output
voltage. The output voltage is selected from one of two
5-bit settings programmed into internal registers via a
2-wire SMBus/I²C interface. The interface features safe-
guards against invalid output voltages and allows the mi-
croprocessor to turn the regulator on and off. Valley cur-
rent control delivers very low duty cycles without requiring
a sense resistor. Operating frequency is selected by an
external resistor and is compensated for variations in V_IN
and V_OUT.
Discontinuous mode operation provides high efficiency
operation at light loads. A forced continuous control pin
reduces noise and RF interference and can assist second-
ary winding regulation by disabling discontinuous mode
operation when the main output is lightly loaded.
Fault protection is provided by internal foldback current
limiting, an output overvoltage comparator and optional
short-circuit shutdown timer.
The LTC1909-8 is available in the 28-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
No R_SENSE is a trademark of Linear Technology Corporation.
I²C is a trademark of Philips Electronics N.V.
TYPICAL APPLICATIO
100k
100k
100k
0.1µF
11k
39k
100pF
470pF
20k
SEL
SDA
SCL
VRON
LTC1909-8
1
28
RUN/SS BOOST
2
V_ON
3
PGOOD
27
TG
26
SW
4
V_RNG
5
FCB
SENSE^{+ 25}
24
PGND
6
I_TH
7
SGND
8
ION
9
V_FB
10
SEL
11
SDA
BG
INTV_CC
V_IN
EXTV_CC
V_CC
GND
23
22
21
20 5V
19 ^EXT
18
12
SCL
17
FB
13
16
VRON V_OSENSE
14
15
PGTMR CPUON
CMDSH-3
0.22µF
1Ω
+
0.1µF
R_ON
1.4M 1%
M1 _L1
1.8µH
C_IN
10µF
50V
×4
V_IN
5V TO 24V
GND
V_OUT
2.5V OR 2.6V
10A
(V_OUT SET BY SEL)
M2
4.7µF
6.3V
+
C_{OUT1, 2}
180µF
C_OUT3
22µF
4V
6.3V
×2
X7R
D1
GND
19098 F01
C_IN: UNITED CHEMICON THCR60E1H106TZ
C_{OUT1, 2}: CORNELL DUBILIER ESRE181ME04B/
PANASONIC EEFVEOG181R
D1: DIODES INC. B340A
L1: SUMIDA CEP125-1R8MC-H
M1: Si4884
M2: Si4874
Figure 1. High Efficiency Step-Down Converter
19098f
1