U2893B Datasheet, PDF (6/14 Pages) TEMIC Semiconductors – Modulation PLL for GSM, DCS and PCS Systems

U2893B
Supply Current of the Charge Pump
i(VSP) vs. Time
Due to the pulsed operation of the charge pump, the cur-
rent into the charge-pump supply pin VSP is not constant.
Depending on I (see figure 6) and the phase difference at
the phase detector inputs, the current i(VSP) over time va-
ries. Basically, the total current is the sum of the quiescent
current, the charge-/discharge current, and – after each
phase comparison cycle – a current spike (see figure 3).
up
down
5I
i(VSP)
3I
Initial Charge Pump Current after
Power-Up
Due to stability reasons, the reference current generator
for the charge pump needs an external capacitor (>500 pF
from CPC to GND). After power-up, only the on-chip
generated current I = I_CPCK is available for charging the
external capacitor. Due to the charge pump’s architecture,
the charge pump current will be 2 I = 2 I_CPCK until
the voltage on CPC has reached the reference voltage
(1.1 V). The following figures illustrate this behavior.
The behavior of I(CPO) after power-up can be very
advantageous for a fast settling of the loop. By using
larger capacitors (>1 nF), an even longer period with
maximum charge pump current is possible.
V(CPC)
I_CPCK R_CPC
I
t
Vref
2I
i(CPO)
t
–2I
tt
t
t
1
0
2
Figure 3. Supply current of the charge pump = f(t)
I(CPC)
Internal current, I, vs. current out of pin CPC
2 I_CPCK
I vs. I(CPC)
ICPC
I
CPC open
0
0.5 mA
2.23 kW to GND
–0.5 mA
1.0 mA
I
743 W to GND
–1.5 mA
2.0 mA
CPC shorted to GND
I_CPCK
>2.0 mA
t
t
1
[ Time t₁ can be calculated as t₁ (1.1 V C_CPC)/I_CPCK
³ [ m e.g., C_CPC = 1 nF, I_max = 3.5 A t₁ 0.3 s.
[ W Time t₂ can be calculated as t₂ (R_CPC/2230 ) C_CPC
W ³ [ m e.g., C_CPC = 1 nF, R_CPC = 2230
t₂ 1.1 s
Figure 4.
6 (14)
TELEFUNKEN Semiconductors
Preliminary Information
Rev. A1, 29-Jan-76