LT3750EMS#PBF Linear Technology, LT3750EMS#PBF Datasheet - Page 6

• Manufacturer Part Number: LT3750EMS#PBF
• Description: IC CTLR CAPACITOR CHARGE 10-MSOP
• Manufacturer: Linear Technology
• Type: Flyback, Forward Converterr

Specifications of LT3750EMS#PBF

• Applications: Power Supply Controller
• Mounting Type: Surface Mount
• Package / Case: 10-MSOP, Micro10™, 10-uMAX, 10-uSOP
• Ic Function: Capacitor Charger Controller
• Supply Voltage Range: 3V To 24V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: MSOP
• No. Of Pins: 10
• Msl: MSL 1 - Unlimited
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

OPERATIO
LT3750
The LT3750 is designed to charge capacitors quickly and
efficiently. Operation can be best understood by referring
to Figures 1 and 2. Operation proceeds in four phases:
1. Start-up, 2. Primary-side charging, 3. Secondary en-
ergy transfer, 4. Discontinuous mode sensing.
1. Start-Up
Start-up occurs for approximately 20µs after the charge
pin is raised high. During this phase, a one-shot enables
the master latch and turns on the NMOS. The master latch
will remain in the set state until the target output voltage
is reached or a fault condition resets it.
6
(1c) Equivalent Circuit During Discontinuous Mode Detection
(1b) Equivalent Circuit During Secondary Energy
Transfer and Output Detection
(1a) Equivalent Circuit During Primary-Side Charging
V
V
V
TRANS
TRANS
TRANS
Figure 1. Equivalent Circuits
V
I
V
I
V
LPRI
I
LPRI
DRAIN
U
LPRI
DRAIN
DRAIN
+
–
+
–
+
–
•
•
•
+
–
+
–
+
–
V
S1
S1
V
V
S1
PRI
1:N
PRI
PRI
1:N
1:N
•
I
V
I
•
•
LSEC
V
I
V
LSEC
LSEC
SEC
SEC
+
–
SEC
+
–
+
–
S2
S2
S2
3750 F01c
3750 F01a
3750 F01b
2. Primary Side Charging
When the NMOS on latch is set, the gate driver rapidly
charges the gate pin to V
on forcing V
Consequently, current in the primary coil rises linearly at
V
DRAIN
I
I
V
LSEC
I
V
LPRI
I
PK
PK
N
SEC
PRI
V
–N (V
V
TRANS
PRIMARY-SIDE
TRANS
CHARGING
V
TRANS
DS(ON)
L
Figure 2. Idealized Charging Waveforms
– V
PRI
1.
– V
TRANS
DS(ON)
DS(ON)
– V
DS(ON)
– V
)
ENERGY TRANSFER
DS(ON)
AND OUTPUT
–(V
CC
SECONDARY
V
DETECTION
V
V
TRANS
OUT
OUT
OUT +
– 2V. The external NMOS turns
2.
L
across the primary winding.
+ V
+ V
N
SEC
+
V
V
DIODE
DIODE
DIODE
OUT
+ V
)
N
DISCONTINUOUS
DIODE
DETECTION
MODE
3.
V
TRANS
V
DS(ON)
3750 F02
3750fa