LTC1559CGN-3.3 Linear Technology, LTC1559CGN-3.3 Datasheet - Page 10

• Manufacturer Part Number: LTC1559CGN-3.3
• Description: IC BACKUP BATT CNTRLR3.3V 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC1559CGN-3.3

• Function: Back-Up Management
• Battery Type: Nickel Cadmium (NiCd)
• Voltage - Supply: 2.9 V ~ 3.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.150", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS
LTC1559-3.3/LTC1559-5
If V
3.3) after the first boost cycle, the LTC1559 immediately
reconnects SW to ground, repeating the boost cycle. If
after two consecutive pulses, V
boost threshold V
the LTC1559 decides that the load is not so light after all,
and doubles the internal inductor charging current limit to
330mA for subsequent cycles. This is high current mode.
By doubling the peak inductor current, each boost cycle
effectively carries four times more energy compared to
low current mode (E = 1/2 • LI
output power. When V
– 7% (LTC1559-3.3) boost threshold, the LTC1559 stops
the boost converter and resets the internal 2-pulse counter.
The next time V
(LTC1559-3.3), the boost converter restarts in low current
mode for at least two boost cycles. Moderate or changing
loads cause the LTC1559 to shift between the two peak
inductor current limits, keeping the output in tight regula-
tion. Near its maximum load capability, the LTC1559 will
stay in 330mA high current mode and the output voltage
V
(LTC1559-3.3).
V
The type of output capacitor and the rated V
affect the LTC1559’s output ripple and efficiency. In most
applications, the V
the requirements of the main power supply. Such a
capacitor will generally meet the requirements of the
LTC1559. In unusual circumstances or circuits where
the main system V
away from the LTC1559, a local output capacitor may be
necessary.
The ripple on the V
voltage drop due to the boost converter’s output current
pulses. The ripple frequency and output duty cycle is
proportional to the inductor discharge time. Given a fixed
inductor value (22 H) and a known peak current limit, the
booster’s discharge time in each boost cycle is propor-
tional to the difference between V
for the LTC1559-3.3 and 92.5% of the rated V
LTC1559-5) and the battery cell voltage, V
10
CC
BAK
CC
Capacitor ESR
is still less than V
will hover around V
CC
CC
CC
CC
U
CC
falls below V
capacitor is primarily determined by
(rated value) – 7% (LTC1559-3.3),
capacitor is located some distance
pin is equal to the capacitor ESR
CC
CC
INFORMATION
U
exceeds the V
(rated value) – 7% (LTC1559-
CC
2
BAK
CC
), doubling the available
CC
(rated value) – 7%
W
is still not above the
(93% of the rated V
(rated value) – 7%
CC
BAT
(rated value)
CC
(1.2V).
U
CC
value will
for the
CC
Assuming ESR = 0.2 , I
V
Since V
resistor ratio:
Therefore the ripple seen by the V
The discharge time period,
For V
The internal V
response time to filter away this ripple. The V
value) – 5.5% (LTC1559-3.3) and V
comparators have a 6 s rising edge delay and 2 s falling
edge delay. The V
comparator has a similar 6 s rising time delay but a much
longer falling time delay of 20 s. This enables the com-
parator to control the boost converter properly, and avoids
turning off the boost converter prematurely due to false
triggering by the ESR ripple.
Exit from Backup
When a main battery is inserted into the system, the
LTC1559 follows a specific sequence to exit backup mode
and return control to the main supply. The sequence
depends on the type of main power supply used. In
systems where the main supply’s output impedance is
RIPPLE(P-P)
V
RB resistor ratio = 3.3/1.272 = 2.594
Ripple voltage = 25.4mV
t
DISCH
RIPPLE(P-P)
CC
t
DISCH
CC
= 3.3V and I
= 3.9 s
must be scaled down internally, the external
= (I
= (330mA)(0.2 )
= 66mV
= 5V/1.272V
= 3.931
= 66mV/3.931
= 16.79mV
= (L • I
= (22 H • 330mA)/(4.625 – 1.2V)
= 2.12 s
CC
= 66mV
IND(PEAK)
comparators are designed to have a slow
CC
IND(PEAK)
IND(PEAK)
(rated value) – 7% (LTC1559-3.3)
IND(PEAK)
)(R
ESR(CAP)
)/(V
= 330mA,
BAK
= 330mA, V
CC
CC
– V
)
comparators is:
(rated value) – 9%
BAT
)
CC
CC
= 5V,
(rated