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CONTROL
LOGIC
SM1 OUTPUT
VOLTAGESETTING
SM1/SM2 PHASE
CONTROL
I2C
REGISTERS
SM1 OPERATING
MODE :
ON/OFF,
PWM, PFM, STANDBY
SM1 DISCHARGE
SWITCHENABLE ,
LOWPFMRIPPLE
L1
PGND1
VIN_SM1
SM1
SM2 OUTPUT
VOLTAGESETTING
L2
PGND2
VIN_SM2
SM2
SM 1 CONVERTER
3.3 Hµ
10 Fµ
V
O(SM1)
10 Fµ
3.3 Hµ
10 Fµ
V
O(SM2)
10 Fµ
OUT
P1
P2
+
_
+
_
29 Ω
V( V IN_S M 1)
39 Ω
V(VIN_SM1)
SET
RESET
OUT
EN_PFM
POWERSTAGE
CURRENT COMPARATORS
I(L1)
I(L1)
SM1
CONTROL
LOGIC
EN_PFM
EN_PWM
EN_ALL
DCHGON
SM2 OPERATING
MODE :
ON/OFF,
SM1 DISCHARGE
SWITCHENABLE ,
LOWPFMRIPPLE
TPS65810
LSM1
LSM2
C21
C22
C19
C20
PWMCONTROL
PFMCONTROL
PFMON
PWMON
DAC
EN_PWM
SM2CONVERTER
SAMETOPOLOGY ASSM1CONVERTER
PWM, PFM, STANDBY
PWM, PFM, STANDBY
I
PFM(LEAVE)
+
V(VIN_SM3)
29 W
,
I
PFM(ENTER)
+
V(VIN_SM3)
39 W
(6)
Output Voltage Slew Rate
TPS65810
TPS65811
SLVS658B – MARCH 2006 – REVISED FEBRUARY 2007
Figure 41. SM1/SM2 Converter
The TPS65810 SM1 and SM2 buck converters can be set to operate only in PWM mode or to switch
automatically between PFM and PWM modes. The average load current is monitored, and the PFM mode is set
if the average load current is below the threshold IPFM(ENTER). When in PFM mode the load current is also
monitored, and the PWM mode is set when the load current exceeds the threshold I
PFM(LEAVE)
. The thresholds for
automatic PFM/PWM switching are calculated as shown in Equation 6 for the SM1 converter, the same
thresholds apply to the SM2 converter by replacing VIN_SM1 by VIN_SM2:
The automatic switching mode is enabled via the control bits PFM_SM1 and PFM_SM2 on I
2
C registers
SM1_SET1 and SM2_SET1.
I
2
C registers enable setting the output voltage slew rate, when transitioning from one programmed voltage to a
new programmed voltage value. These events can be triggered by a new output voltage selection or by switching
from a low power mode (standby) to a normal operating mode. During a transition, the output voltage is stepped
from the currently programmed voltage to the new target voltage. The slew rate from the initial voltage to the final
voltage can be selected using I
2
C registers, SM1_SET2 and SM2_SET2, ranging from 0.24 mv/ µ s to 15.36
mV/ µ s for the SM1 converter and 0.48 to 30.72 mV/ µ S for the SM2 converter. If the slew rate is set to OFF the
output voltage goes from the current value to the programmed value in a single step.
During the transition to standby mode the Power Good comparators are disabled.
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