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LT1961EMS8E Datasheet Download

Part No.:
LT1961EMS8E
Download:
Download Datasheet
Description:
[1.5A, 1.25MHz Step-Up Switching Regulator]
File Size:
149 K
Page:
16 Pages
Logo:
Manufacturer:
LINER [ LINEAR TECHNOLOGY ]
PCB Prototype
 LT1961EMS8E Datasheet Page:2LT1961EMS8E Datasheet Page:3LT1961EMS8E Datasheet Page:4LT1961EMS8E Datasheet Page:5LT1961EMS8E Datasheet Page:7LT1961EMS8E Datasheet Page:8LT1961EMS8E Datasheet Page:9LT1961EMS8E Datasheet Page:10 
LT1961
BLOCK DIAGRAM
The LT1961 is a constant frequency, current-mode boost
converter. This means that there is an internal clock and
two feedback loops that control the duty cycle of the power
switch. In addition to the normal error amplifier, there is a
current sense amplifier that monitors switch current on a
cycle-by-cycle basis. A switch cycle starts with an oscilla-
tor pulse which sets the R
S
flip-flop to turn the switch on.
When switch current reaches a level set by the inverting
input of the comparator, the flip-flop is reset and the
switch turns off. Output voltage control is obtained by
using the output of the error amplifier to set the switch
current trip point. This technique means that the error
V
IN
1
2.5V BIAS
REGULATOR
SYNC
8
SHUTDOWN
COMPARATOR
1.35V
3μA
ERROR
AMPLIFIER
g
m
= 850μMho
7 V
C
Figure 1. Block Diagram
6
SHDN
5
+
W
amplifier commands current to be delivered to the output
rather than voltage. A voltage fed system will have low
phase shift up to the resonant frequency of the inductor
and output capacitor, then an abrupt 180° shift will occur.
The current fed system will have 90° phase shift at a much
lower frequency, but will not have the additional 90° shift
until well beyond the LC resonant frequency. This makes
it much easier to frequency compensate the feedback loop
and also gives much quicker transient response.
A comparator connected to the shutdown pin disables the
internal regulator, reducing supply current.
INTERNAL
V
CC
SLOPE COMP
Σ
0.3V
1.25MHz
OSCILLATOR
S
CURRENT
COMPARATOR
R
S
FLIP-FLOP
R
CURRENT SENSE
AMPLIFIER VOLTAGE
GAIN = 40
DRIVER
CIRCUITRY
2
Q1
POWER
SWITCH
SW
+
7μA
+
0.01Ω
+
6
FB
3
1.2V
4
GND
GND
1767 F01
1961fa