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ZHCSHG7C January 2018 – July 2018 TPSM84209

PRODUCTION DATA.

7.3.5 Feed-Forward Capacitor

The TPSM84209 is internally compensated to be stable over the operating range of the device. However, depending on the output voltage and amount of output capacitance, an additional feed-forward capacitor, C_FF, may be added for optimum performance. Adding additional output capacitance above the minimum reduces the output voltage ripple of the device. However, adding additional output capacitance also reduces the cross-over frequency of the device, slowing the response to load transients. Adding a feed-forward capacitor when adding more output capacitance helps to restore cross-over frequency of the device, restoring the transient response.

The external feed-forward capacitor must be placed in parallel with the top resistor divider, R_FBT. The placement of C_FF is shown in Figure 19. Table 6 lists the required C_FF values for different amounts of output capacitance. For output voltages < 2.5 V, it is not recommended to add a C_FF capacitor.

Figure 19. Feed-Forward Capacitor

Table 6. C_FF Values⁽¹⁾

V_OUT RANGE (V)		Amount of C_OUT
MIN	MAX	47 µF (1 x 47 µF)	94 µF (2 x 47 µF)	141 µF (3 x 47 µF)	≥ 188 µF (4 x 47 µF)
2.5	< 3.3	Not applicable	C_FF = 100 pF	C_FF = 220 pF	C_FF = 330 pF
3.3	< 5	Not applicable	C_FF = 100 pF	C_FF = 330 pF	C_FF = 330 pF
5	6	C_FF = 100 pF	C_FF = 330 pF	C_FF = 330 pF	C_FF = 330 pF

(1) The C_FF values listed in this table apply when R_FBT = 10 kΩ. To calculate the value of C_FF when using another R_FBT value, multiply the C_FF value listed in the table by 10 kΩ / R_FBT.

7.3.5 Feed-Forward Capacitor

Table 6. CFF Values(1)

Table 6. C_FF Values⁽¹⁾