TC1219 Datasheet, PDF (6/16 Pages) Microchip Technology – Switched Capacitor Voltage Converters with Shutdown in SOT Packages

TC1219/TC1220
4.3 Capacitor Selection
In order to maintain the lowest output resistance and
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C1
will lower the output resistance and larger values of
C2 will reduce output ripple. (Equation 4-1(b) and
Equation 4-3).
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)
1
3.3
10
30
TC1219
R_OUT(Ω)
100
42
25
19.3
TC1220
R_OUT(Ω)
45
25
19.4
17.5
TABLE 4-2:
C2 (µF)
1
3.3
10
30
OUTPUT VOLTAGE RIPPLE
VS. C2 (ESR = 0.1Ω)
I_OUT 10mA
TC1219
V_RIPPLE (mV)
419
128
44
16
TC1220
V_RIPPLE (mV)
145
45
16
7
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
recommended capacitor depends on the configuration
of the TC1219/TC1220.
4.5 Shutdown Input
The TC1219/TC1220 is enabled when SHDN is high,
and disabled when SHDN is low. This input cannot be
allowed to float. (If SHDN is not required, see the
TCM828/829 data sheet.) The SHDN input can be only
driven 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
TC1219
+
2 _{IN TC1220}
C1
C2
+
R_L
3
5
C1^–
SHDN
4
GND
V_OUT
Device
TC1219
TC1220
C1
10µF
3.3µF
C2
10µF
3.3µF
C3
10µF
3.3µF
DS21366B-page 6
 2002 Microchip Technology Inc.