TC1221 Datasheet, PDF (6/16 Pages) Microchip Technology – High Frequency Switched Capacitor Voltage Converters with Shutdown in SOT Packages

TC1221/TC1222
Table 4-1 shows various values of C1 and the
corresponding output resistance values @ +25°C. It
assumes a 0.1Ω ESR_C1 and 2Ω R_SWITCH. Table 4-2
shows the output voltage ripple for various values of
C2. The V_RIPPLE values assume 10mA output load
current and 0.1Ω ESR_C2.
TABLE 4-1: OUTPUT RESISTANCE
VS. C1 (ESR = 0.1Ω)
C1 (µF)
0.22
0.33
0.47
1.0
TC1221
R_OUT(Ω)
52.9
40.8
33.5
25
TC1222
R_OUT(Ω)
22.6
20.5
19.4
17.8
TABLE 4-2:
C2 (µF)
0.22
0.33
0.47
1.0
OUTPUT VOLTAGE RIPPLE
VS. C2 (ESR = 0.1Ω)
I_OUT 10mA
TC1221
V_RIPPLE (mV)
184
123
87
42
TC1222
V_RIPPLE (mV)
32
22
16
9
4.4 Input Supply Bypassing
The V_IN input should be capacitively bypassed to
reduce AC impedance and minimize noise effects due
to the internal switching of the device. The recom-
mended capacitor depends on the configuration of the
TC1221/TC1222.
4.5 Shutdown Input
The TC1221/TC1222 is enabled when SHDN is high,
and disabled when SHDN is low. This input cannot be
allowed to float. The SHDN input should be limited to
0.5V above V_IN to avoid significant current flows.
4.6 Voltage Inverter
The most common application for charge pump
devices is the inverter (Figure 4-3). This application
uses two external capacitors: C1 and C2 (plus a power
supply bypass capacitor, if necessary). The output is
equal to -V_IN plus any voltage drops due to loading.
Refer to Table 4-1 and Table 4-2 for capacitor
selection.
FIGURE 4-3:
VOLTAGE INVERTER
TEST CIRCUIT
V_IN
C3 ⁺
1 _OUT
C1+ ⁶
TC1221
+
2 _{IN TC1220}
C1
C2
+
R_L
3
5
C1^–
SHDN
4
GND
V_OUT
Device
TC1221
TC1222
C1
1µF
0.22µF
C2
1µF
0.22µF
C3
1µF
0.22µF
DS21367B-page 6
 2002 Microchip Technology Inc.