参数资料
型号: TPS65040ZQER
厂商: TEXAS INSTRUMENTS INC
元件分类: 电源管理
英文描述: 8-CHANNEL POWER SUPPLY MANAGEMENT CKT, PBGA71
封装: 5 X 5 MM, 0.50 MM PITCH, GREEN, PLASTIC, MICRO, BGA-71
文件页数: 40/73页
文件大小: 1928K
代理商: TPS65040ZQER
Buck-Boost Mode Operation
Current-Limit Protection
SLVS708B – NOVEMBER 2006 – REVISED APRIL 2007
The DC/DC converter is able to regulate the output voltage at all possible input voltages. The buck mode,
buck-boost mode, and boost mode are automatically switched in the analog circuit. It operates as buck mode
when the input voltage of VBDDP is higher than the output voltage of VOUT, and as boost mode when the input
voltage of VBDDP is lower than the output voltage of VOUT. It operates as buck-boost mode when the input
voltage of VBDDP is close to the output voltage of VOUT. In buck mode, MP1 and MN1 on the L1 side, shown
in Figure 70, are switching continuously. MP2 on the L2 side, shown in Figure 70 is always on, and MN2 on the
L2 side is always off. When the voltage difference between input voltage of VBDDP and output voltage of VOUT
is 0.5 V or less, MP2 and MN2 on the L2 side start switching. Therefore, the mode is switched from buck mode
to buck-boost mode. In boost mode, MP2 and MN2 on the L2 side are switching continuously. MP1 on the L1
side is always on, and MN1 on the L1 side is always off. When the voltage difference between the output
voltage of VOUT and the input voltage of VBDDP is 0.5 V or less, MP1 and MN1 on the L1 side start switching.
Therefore the mode is switched from boost mode to buck-boost mode.
Figure 73 and Figure 74 show coil current, VOUT output voltage, PABIAS1 input voltage operations, and
current-limit protection mode. Current-limit protection has a limit value of 4 A and 1.5 A detected peak current.
Figure 73(a) shows PABIAS1 input voltage, VOUT output voltage regulation, and coil current. VOUT output
voltage begins to ramp to target value based on the reducing PABIAS1 input voltage. Then, coil current
increases for fast transient response. Current-limit value in the current-limit protection circuit shifts from 1.5 A to
4 A, after the 1.5 A current limit value is detected twice in normal mode operation. This is the current-limit 4-A
detection mode, which keeps within 50
s (typ) counted internal oscillator. Coil current is decreased when
settling of the output voltage reaches completion in current-limit 4-A detection mode. When 50
s (typ) of
current-limit 4-A detection mode ending, the current-limit protection circuit shifts to current-limit 1.5-A detection
mode automatically, and detects the coil current by 1.5-A current limit value between 5
s (typ) counted by
internal oscillator. When the current limit protection circuit does not detect 1.5-A coil current between 5
s (typ),
it shifts from current-limit 1.5-A detection mode to normal operation mode. Thereafter, while the current limit
protection circuit continuously monitors the peak current of the coil, and a 1.5-A current limit condition is
detected twice continuously, it shifts to current-limit 4-A detection mode again. This describes the operation for
continuous coil current flow.
Figure 73(b) shows the operation when the coil current flows continuously. When the current-limit protection
circuit detects 1.5 A continuously twice, it shifts to the current-limit 4-A detection mode. Even if 4 A keeps
flowing after mode shifting, it shifts from the current-limit 4-A detection mode, to the current-limit 1.5-A detection
mode after 50
s (typ). However, when 1.5 A keeps flowing for a specific cause for more than 5 s (typ), the
current-limit protection circuit keeps operating in the current-limit 1.5-A detection mode. The output voltage
decreases when DC/DC converter can not drive the low impedance load because of current limit conditions. The
short-circuit protection circuit operates when the output voltage falls to 80% or less. See the SHORT-CIRCUIT
PROTECTION Section for details.
While 1.5 A is flowing continuously, the current-limit protection circuit is operating in the current-limit 1.5-A
detection mode. When the coil current falls to 1.5 A or less, 5
s (typ) is counted again.
Figure 74 shows the operation when the coil current is decreasing from current-limit 1.5-A detection mode, and
the mode shifts to normal mode operation. It is waited that Coil current becomes 1.5 A or less continuing after
1.5 A kept flowing between 5
s (typ) by Current-limit 1.5-A detection mode. When the coil current falls to 1.5 A
or less, another 5
s (typ) is counted. Meanwhile, the current-limit protection circuit shifts from current-limit 1.5-A
detection mode to normal operation mode if the current-limit protection circuit does not detect a 1.5 A
current-limit value. But if the current limit value of 1.5 A is detected again within this 5
s (typ) interval, it remains
in the current-limit 1.5-A detection mode, and waits for the coil current to fall to 1.5 A, or less.
Current-limit protection not only detects output transient response by PABIAS1, but it also detects heavy load
conditions during stable output conditions.
Note that the detection time is counted by an internal oscillator which generates the switching frequency (fs) of
the DC/DC converter.
45
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