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PM6675 Datasheet(PDF) 25 Page - STMicroelectronics

Part # PM6675
Description  Very fast load transient response using constant on-time control loop
PDF  47 Pages
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Manufacturer  STMICROELECTRONICS [STMicroelectronics]
Direct Link  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

PM6675 Datasheet(HTML) 25 Page - STMicroelectronics

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6.1.5
Current sensing and current limit
The PM6675 switching controller uses a valley current sensing algorithm to properly handle
the current limit protection and the inductor current zero-crossing information. The current is
detected during the conduction time of the low-side MOSFET. The current sensing element
is the on-resistance of the low-side switch. The sensing scheme is visible in Figure 12.
Figure 12. Current sensing scheme
An internal 100
µA current source is connected to C
SNS pin that is also the non-inverting
input of the positive current limit comparator. When the voltage drop developed across the
sensing parameter equals the voltage drop across the programming resistor RILIM, the
controller skips subsequent cycles until the overcurrent condition is detected or the output
UV protection latches off the device (see Section 6.1.11: Switching section OV and UV
protections on page 28
).
Referring to Figure 12, the RDS(on) sensing technique allows high efficiency performance
without the need for an external sensing resistor. The on-resistance of the MOSFET is
affected by temperature drift and nominal value spread of the parameter itself; this must be
considered during the RILIM setting resistor design.
Table 6. Mode-of-operation settings summary
VSEL
NOSKIP
VOUT
Operating mode
VVSEL > 4.3V
VNOSKIP > 4.2V
1.5V
Forced-PWM
1V <VNOSKIP < 3.5V
Non-audible pulse-skip
< 0.5V
Pulse-skip
VVSEL < 3.7V
VNOSKIP > 4.2V
ADJ
Forced-PWM
1V <VNOSKIP < 3.5V
Non-audible pulse-skip
VNOSKIP < 0.5V
Pulse-skip
HGATE
PHASE
CSNS
LGATE
PGND
PM6675
100µA·
R
ILIM
V
IN
V
OUT
I
VALLEY·RDSon
HGATE
PHASE
CSNS
LGATE
PGND
PM6675
100µA·
R
ILIM
V
IN
V
OUT
I
VALLEY·RDSon



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