Datasheet

3
LT3781
3781f
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
CC
= V
BST
= 12V, V
BSTREF
= 0V, V
VC
= 2V, V
TS
= 0V, V
FB
= V
REF
= 1.25V, C
TG
= C
BG
= C
SG
= 1000pF.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Error Amp
V
FB
Error Amplifier Reference Voltage Measured at Feedback Pin 1.242 1.250 1.258 V
● 1.225 1.265 V
I
FB
Feedback Input Current V
FB
= V
REF
–50 nA
A
V
Error Amplifier Voltage Gain 72 dB
I
VC
Error Amplifier Current Limit Source ● 10 25 mA
Sink
● 0.5 1 mA
V
VC
Zero Current Output Voltage 1.4 V
Maximum Output Voltage 3.2 V
GBW Gain Bandwidth Product (Note 3) 1 MHz
Current Sense
A
V
Amplifier DC Gain 12 V/V
I
SENSE
Input Bias Current –275 µA
V
SENSE
Current Limit Threshold Measured at SENSE Pin 135 150 165 mV
● 130 170 mV
t
D
Current Sense to Switch Delay 175 ns
t
MIN
Switch Minimum On Time Measured at BG Output 250 ns
THERM and OVLO Fault Detectors
V
THERM
/ Threshold (Rising Edge) ● 1.2 1.25 1.3 V
V
OVLO
Threshold Hysteresis ● 20 40 60 mV
t
D
Fault Delay to Output Disable >50mV Overdrive 650 ns
Oscillator and Synchronization Decoder
f
OSC
Oscillator Frequency, Free Run Measured at F
SET
Pin 700 kHz
Frequency Programming Error f
OSC
≤ 500kHz (Note 3) ● –10 5 %
I
FSET
FSET Input Bias Current F
SET
Charging, V
FSET
= 2V 50 nA
V
SYNC
SYNC Logic High Input Threshold Positive-Going Edge ● 1.4 2 V
SYNC Logic Low Input Threshold Negative-Going Edge ● 0.8 1.4 V
f
SYNC
SYNC Frequency ● f
OSC
/2 350 kHz
t
H, L
Maximum SYNC Pulse Width f
OSC
= Oscillator Free-Run Frequency 1/f
OSC
s
(Logic High or Logic Low)
Output Drivers
V
TG
TG On Voltage ● 11 11.5 V
TG Off Voltage
● 0.1 0.5 V
t
TGr/f
TG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
V
BG
BG On Voltage ● 11 11.5 12 V
BG Off Voltage
● 0.1 0.5 V
t
BGr/f
BG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
V
SG
SG On Voltage ● 11 11.5 12 V
SG Off Voltage
● 0.1 0.5 V
t
SGr/f
SG Rise/Fall Time 10% to 90%/90% to 10% 35 ns
t
SG-BG
SG to BG Enable Lag Time 4V On/Off Thresholds ● 80 150 300 ns
t
TG-BG
TG to BG Enable Lag Time 4V On/Off Thresholds 100 ns