LT1931IS5#PBF Switching Voltage Regulators 1.2MHz/2.2MHz Inverting DC/DC Converters
LT1931IS5#PBF Switching Voltage Regulators 1.2MHz/2.2MHz Inverting DC/DC Converters
| Linear Technology | |
| Product Category: | Switching Voltage Regulators |
| RoHS: | Details |
| 34 V | |
| 1 A | |
| 16 V | |
| 1 Output | |
| Inverting | |
| SOT-23-5 | |
| SMD/SMT | |
| 1.2 MHz | |
| - 40 C | |
| + 85 C | |
| LT1931 | |
| 2.6 V | |
| Brand: | Linear Technology |
| Height: | 1 mm |
| Operating Supply Current: | 4.2 mA |
| Product Type: | Switching Voltage Regulators |
| Subcategory: | PMIC - Power Management ICs |
DESCRIPTION
The LT1931/LT1931A are the industry's highest power
inverting SOT- 23 current mode DC/DC converters. Both
parts include a 1A integrated switch allowing high current
outputs to be generated in a small footprint. The LT1931
switchesat 1.2MHzwhile theLT1931Aswitches at2.2MHz.
These high speeds enable the use of tiny, low cost
capacitors and inductors 2mm or less in height. The
LT1931 is capable of generating - 5V at 350mA or -12V
at 150mA from a 5V supply, while the LT1931A can
generate - 5V at 300mA using significantly smaller induc-
tors. Both parts are easy pin-for-pin upgrades for higher
power LT1611 applications.
The LT1931/LT1931A operate in a dual inductor inverting
topology that filters both the input side and output side
curent. Verylow outputvoltage ripple approaching 1mVp_p
can be achieved when ceramic output capacitors are used.
Fixed frequency switching ensures a clean output free
from low frequency noise typically present with charge
pump solutions. The low impedance output remains within
1% of nominal during large load steps. The 36V switch
allows VIN to Vout differential of up to 34V.
FEATURES
■Fixed Frequency 1.2MHz/2.2MHz Operation
■Very Low Noise: 1mVp.p Output Ripple
■- 5V at 350mA from 5V Input
■-12V at 150mA from 5V Input
■1 Uses Small Surface Mount Components
■Wide Input Range: 2.6V to 16V
■Low Shutdown Current: < 1μA
■Low VCESAT Switch: 400mV at 1A
■Pin-for-Pin Compatible with the LT1611
■Low Profile (1mm) ThinSOTIM Package
APPLICATIONS
■1 Disk Drive MR Head Bias
■Digital Camera CCD Bias .
■LCD Bias
■GaAs FET Bias
■Local Low Noise/Low Impedance Negative Supply
OPERATION
The LT1931 uses a constant frequency, current mode control scheme to provide ecellent line and load regula-
tion. Operation can be best understood by rferring to the Block Diagram in Figure 2. At the start of each oscillator
cycle, the SR latch is set, turning on the power switch Q3. A voltage proportional to the switch current is added to a
stabilizing ramp and the resulting sum is fed into thepositive terminal of the PWM comparator A2. When this
voltage exceeds the level at the negative inputof A2, the SRlatch is reset, turning off the power switch. The level at the
negative input of A2 is set by the error amplifier (9m) and is simply an amplified version of the difference between
the feedbackvoltage and the reference voltage of-1.255V.
In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error
amplifier's output increases, more current is taken fromthe output; if it decreases, less current is taken. One
function not shown in Figure 2 is the current limit. The switch current is constantly monitored and not allowed to
exceed the nominal value of 1.2A. If the switch current reaches 1.2A, the SR latch is reset regardless of the state
of comparator A2. This current limit protects the power switch as well as various external components connected
to the LT1931.
The Block Diagram for theLT1931A is identical except that the oscillator is 2.2MHz and resistors R3 to R6 are one-half
the LT1931 values.
