LT1070_1 Datasheet, PDF (6/12 Pages) Linear Technology – 5A and 2.5A High Efficiency Switching Regulators

LT1070/LT1071
TYPICAL PERFORMANCE CHARACTERISTICS
Switch “Off” Characteristics
1000
900
800
700
600
500
V_SUPPLY =
400
300
3V 15V
40V 55V
200
100
0
0 10 20 30 40 50 60 70 80 90 100
SWITCH VOLTAGE (V)
1070/71 G19
V_C Pin Characteristics
300
T_J = 25°C
200
100
V_FB = 1.5V
(CURRENT INTO
V_C PIN)
0
– 100
– 200
V_FB = 0.8V
(CURRENT OUT OF V_C PIN)
– 300
– 400
0
0.5 1.0 1.5 2.0 2.5
V_C PIN VOLTAGE (V)
1070/71 G20
Transconductance of Error
Amplifier
7000
– 30
6000
5000
4000
0
θ
30
g_m
60
3000
90
2000
120
1000
150
0
180
– 1000
1k
10k
100k
1M
FREQUENCY (Hz)
210
10M
1070/71 G21
BLOCK DIAGRAM
V_IN
2.3V
REG
40kHz
OSC
16V
FLYBACK
ERROR
AMP
LOGIC
DRIVER
SWITCH
OUT
5A, 75V
SWITCH
MODE
SELECT
FB
–
ERROR
+ ^AMP
1.24V
REF
COMP
ANTISAT
V_C
SHUTDOWN
CIRCUIT
0.15V
CURRENT
AMP
GAIN ≈ 6
0.02Ω
(0.04Ω LT1071)
U
OPERATION
The LT1070/LT1071 is a current mode switcher. This
means that switch duty cycle is directly controlled by
switch current rather than by output voltage. Referring to
the Block Diagram, the switch is turned “on” at the start
of each oscillator cycle. It is turned “off” when switch
current reaches a predetermined level. Control of output
6
1070/71 BD
voltage is obtained by using the output of a voltage
sensing error amplifier to set current trip level. This
technique has several advantages. First, it has immediate
response to input voltage variations, unlike ordinary
switchers which have notoriously poor line transient
response. Second, it reduces the 90° phase shift at
10701fe