TFS757 Datasheet, PDF (11/36 Pages) Power Integrations, Inc. – Combined Two-Switch Forward and Flyback Power Supply Controllers with Integrated High Voltage MOSFETs

TFS757-764HG
V_IN
385 V
315 V
100 V
30 V
Supply Start-Up Sequence
Standby Power General Introduction
The standby is a wide range power supply, typically a flyback
converter, operating over a wide input range (85-265 VAC) and
delivering up to 20 W continuous output power. The standby
power supply provides two functions in most high-power
applications. It provides a direct secondary output but also
provide bias power to other primary-side devices (in particular
typically a PFC boost converter).
The HiperTFS standby retains most features of the TinySwitch-III,
such as auto-restart, thermal shutdown, multi-level current limit
ON/OFF control, etc. The HiperTFS standby controller has a
few differences versus TinySwitch-III:
Standby
Output
Main
Output
12 ms 2-20 ms
V_BP
5.7 V
4.7 V
6.0 V
PI-5611a-062710
Figure 10. Main and Standby Start-Up.
Main Reset Overvoltage Detection
There is also an overvoltage threshold for the RESET pin. When
triggered, the RESET overvoltage will shutdown only the Main,
leaving the Standby in operation.
V_IN
385 V
300 V
240 V
40 V
Standby
Output
To V_IN
To Clamp
Reset Circuit
R_L
R_R
R
L
1. There are 4 current limits that are selected via the ENABLE
pin (rather than by using different BYPASS pin capacitors as
in TinySwitch-III). There are 4 user selectable current limits
500, 550, 650, 750 mA design for secondary standby
output power of 10, 12.5, 15 and 20 W.
2. Secondary OVP latching shutdown. This is triggered via a
current in excess of the BYPASS pin latching shutdown
threshold (I_BP(SD) = 15 mA).
3. Dedicated LINE-SENSE pin for line-voltage detection providing
absolute UV and OV ON/OFF thresholds (unlike TinySwitch-III
which detects input voltage only during restart).
4. Current limit is compensated as a function of input voltage
to maintain a flat overload characteristic versus input voltage.
In a high-power system, the standby power supply is the first
power supply to begin operating. The main converter cannot
begin working until the standby is in operation. Likewise the
main converter will shutdown at a higher-voltage than the standby
and thus the standby is always the last power supply to
shutdown.
Standby On-Chip Current Limit with External Selection
During start-up, the FEEDBACK pin and ENABLE pin are both
used to select internal current limits for the Main and Standby
converters respectively. The detection period occurs at the
initial start-up of the device (just after BYPASS pin voltage of
4.7 V is achieved), and before the main or standby MOSFETs
start switching. This is done to minimize noise interference.
I EN
(Threshold)
0.0-8.5 mA
L1
8.5-17.7 mA
L2
17.7-33.0 mA
L3
33.0-66.0 mA
L4
I_LIMIT
500
R EN (Select)
(1%)
mA
Open kW
650
mA
280.0 kW
750
mA
137.0 KW
550
mA
63.4 kW
Main
Output
t_HOLDUP
≥ 20 ms
t₁ t₂
Typically turned off by
secondary supervisor
circuit, once regulation
below limit
t₃
t₄
PI-5612a-060910
Figure 11. L and R Pin Duty Limit Mode.
Table 4. ENABLE Pin Standby Current Limit Selection.
The ENABLE pin works in a similar way to the FEEDBACK pin
selection. The only difference being that the ENABLE pin is not
clamped to 1 V during selection, instead remaining at 2.35 V
during the detection period. Thus the selection resistor values
www.powerint.com
11
Rev. C 02/11