Current Mode Control for Excellent Line and
Load Transient Response
■
Overcurrent and Overtemperature Protected
■
Available in 8-Lead MSOP Package
U
APPLICATIO S
■
Cellular Telephones
■
Wireless Modems
■
Personal Information Appliances
■
Portable Instruments
■
Distributed Power Systems
■
Battery-Powered Equipment
U
May 2000
DESCRIPTIO
The LTC®1878 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current
mode architecture. Supply current during operation is
only 10µA and drops to < 1µA in shutdown. The 2.65V to
6V input voltage range makes the LTC1878 ideally suited
for single Li-Ion battery-powered applications. 100% duty
cycle provides low dropout operation, extending battery
life in portable systems.
Switching frequency is internally set at 550kHz, allowing
the use of small surface mount inductors and capacitors.
For noise sensitive applications the LTC1878 can be
externally synchronized from 400kHz to 700kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low, preventing low
frequency ripple from interfering with audio circuitry.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feedback reference voltage. The LTC1878 is available in a
space saving 8-lead MSOP package.
For higher input voltage (12V abs max) applications, refer
to the LTC1877 data sheet.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
V
IN
2.65V
TO 6V
22µF**
CER
220pF
*
TOKO D62CB A920CY-100M
**
TAIYO-YUDEN CERAMIC JMK325BJ226MM
***
SANYO POSCAP 6TPA47M
†
V
CONNECTED TO VIN FOR 2.65V < VIN < 3.3V
OUT
7
SYNC
6
V
IN
1
RUN
2
I
TH
LTC1878
GND
4
SW
U
10µH*
5
20pF
V
OUT
3.3V
†
Efficiency vs Output Load Current
+
47µF***
887k
3
V
FB
280k
1878 TA01
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
1
LTC1878
1
2
3
4
8
7
6
5
TOP VIEW
MS8 PACKAGE
8-LEAD PLASTIC MSOP
PLL LPF
SYNC/MODE
V
IN
SW
RUN
I
TH
V
FB
GND
WWWU
ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
UU
W
(Note 1)
Input Supply Voltage (VIN)...........................– 0.3V to 7V
ITH, PLL LPF Voltage ................................–0.3V to 2.7V
RUN, VFB Voltages ......................................–0.3V to V
SYNC/MODE Voltage ..................................–0.3V to V
IN
IN
ORDER PART
NUMBER
LTC1878EMS8
SW Voltage ................................... –0.3V to (VIN + 0.3V)
P-Channel MOSFET Source Current (DC) ........... 800mA
N-Channel MOSFET Sink Current (DC) ............... 800mA
Peak SW Sink and Source Current ........................ 1.5A
T
= 125°C, θJA = 150°C/W
JMAX
MS8 PART MARKING
LTNX
Operating Ambient Temperature Range
(Note 2) .................................................. – 40°C to 85°C
Consult factory for Industrial and Military grade parts.
Junction Temperature (Note 3)............................ 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3.6V unless otherwise specified.
Output Overvoltage Lockout∆V
Reference Voltage Line RegulationVIN = 2.65V to 6V (Note 4)0.050.2%/V
Output Voltage Load RegulationMeasured in Servo Loop; V
Input Voltage Range●2.656V
Input DC Bias Current(Note 5)
Pulse Skipping Mode2.65V < V
Burst Mode OperationV
ShutdownV
Oscillator FrequencyVFB = 0.8V495550605kHz
SYNC Capture Range400700kHz
Phase Detector Output Current
Sinking Capabilityf
Sourcing Capabilityf
R
of P-Channel MOSFETISW = 100mA0.50.7Ω
DS(ON)
R
of N-Channel MOSFETISW = –100mA0.60.8Ω
DS(ON)
= V
OVL
OVL
Measured in Servo Loop; V
IN
SYNC/MODE
= 0V, VIN = 6V01µA
RUN
V
= 0V80kHz
FB
< f
PLLIN
OSC
> f
PLLIN
OSC
≤ 85°C●0.740.80.84V
A
– V
< 6V, V
= VIN, I
FB
= 0.9V● 0.1 0.5%
ITH
= 1.6V●–0.1–0.5%
ITH
SYNC/MODE
OUT
= 0V, I
= 0A1015µA
= 0A230350µA
OUT
●2050110mV
● 3 10 20µA
●–3–10–20µA
2
LTC1878
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3.6V unless otherwise specified.